Use extconf to build external GC modules

Co-Authored-By: Peter Zhu <peter@peterzhu.ca>

8 files changed, 9523 insertions, 14 deletions

diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 7587762d8c..2b15b182c0 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -97,14 +97,14 @@ jobs:
       - run: $SETARCH make prepare-gems
         if: ${{ matrix.test_task == 'test-bundled-gems' }}
 
+      - run: $SETARCH make
+
       - name: Build shared GC
         run: |
           echo "RUBY_GC_LIBRARY=default" >> $GITHUB_ENV
           make shared-gc SHARED_GC=default
         if: ${{ matrix.shared_gc }}
 
-      - run: $SETARCH make
-
       - run: |
           $SETARCH make golf
           case "${{ matrix.configure }}" in
diff --git a/common.mk b/common.mk
index 28035b2aee..72e58ddb3e 100644
--- a/common.mk
+++ b/common.mk
@@ -721,7 +721,7 @@ install-prereq: $(CLEAR_INSTALLED_LIST) yes-fake sudo-precheck PHONY
 clear-installed-list: PHONY
 	@> $(INSTALLED_LIST) set MAKE="$(MAKE)"
 
-clean: clean-ext clean-enc clean-golf clean-docs clean-extout clean-local clean-platform clean-spec
+clean: clean-ext clean-enc clean-golf clean-docs clean-extout clean-gc clean-local clean-platform clean-spec
 clean-local:: clean-runnable
 	$(Q)$(RM) $(ALLOBJS) $(LIBRUBY_A) $(LIBRUBY_SO) $(LIBRUBY) $(LIBRUBY_ALIASES)
 	$(Q)$(RM) $(PROGRAM) $(WPROGRAM) miniruby$(EXEEXT) dmyext.$(OBJEXT) dmyenc.$(OBJEXT) $(ARCHFILE) .*.time
@@ -751,11 +751,13 @@ clean-capi: PHONY
 clean-platform: PHONY
 clean-extout: PHONY
 	-$(Q)$(RMDIR) $(EXTOUT)/$(arch) $(RUBYCOMMONDIR) $(EXTOUT) 2> $(NULL) || $(NULLCMD)
+clean-gc: PHONY
+	$(Q) $(RMALL) .gc
 clean-docs: clean-rdoc clean-html clean-capi
 clean-spec: PHONY
 clean-rubyspec: clean-spec
 
-distclean: distclean-ext distclean-enc distclean-golf distclean-docs distclean-extout distclean-local distclean-platform distclean-spec
+distclean: distclean-ext distclean-enc distclean-golf distclean-docs distclean-extout distclean-gc distclean-local distclean-platform distclean-spec
 distclean-local:: clean-local
 	$(Q)$(RM) $(MKFILES) yasmdata.rb *.inc $(PRELUDES) *.rbinc *.rbbin
 	$(Q)$(RM) config.cache config.status config.status.lineno
@@ -768,6 +770,7 @@ distclean-html: clean-html
 distclean-capi: clean-capi
 distclean-docs: clean-docs
 distclean-extout: clean-extout
+distclean-gc: clean-gc
 distclean-platform: clean-platform
 distclean-spec: clean-spec
 distclean-rubyspec: distclean-spec
@@ -1948,9 +1951,11 @@ shared-gc: probes.h
 		echo "You must specify SHARED_GC with the GC to build"; \
 		exit 1; \
 	fi
-	$(ECHO) generating $(shared_gc_dir)librubygc.$(SHARED_GC).$(SOEXT)
-	$(Q) $(MAKEDIRS) $(shared_gc_dir)
-	$(Q) $(LDSHARED) -I$(srcdir)/include -I$(srcdir) -I$(arch_hdrdir) $(XDLDFLAGS) $(CFLAGS) $(CPPFLAGS) -DBUILDING_SHARED_GC -fPIC -o $(shared_gc_dir)librubygc.$(SHARED_GC).$(SOEXT) $(srcdir)/gc/$(SHARED_GC).c
+	$(Q) $(MAKEDIRS) $(shared_gc_dir) .gc/$(arch)/$(SHARED_GC)
+	$(Q) $(RUNRUBY) -C .gc/$(arch)/$(SHARED_GC) $(CURDIR)/$(srcdir)/gc/$(SHARED_GC)/$(EXTCONF)
+	$(Q) $(CHDIR) .gc/$(arch)/$(SHARED_GC) && \
+		$(MAKE) extout=../../../$(EXTOUT) BUILTRUBY=../../../miniruby$(EXEEXT) && \
+		$(CP) librubygc.$(SHARED_GC).$(DLEXT) $(shared_gc_dir)
 
 help: PHONY
 	$(MESSAGE_BEGIN) \
@@ -7272,7 +7277,7 @@ gc.$(OBJEXT): $(CCAN_DIR)/str/str.h
 gc.$(OBJEXT): $(hdrdir)/ruby.h
 gc.$(OBJEXT): $(hdrdir)/ruby/ruby.h
 gc.$(OBJEXT): $(hdrdir)/ruby/version.h
-gc.$(OBJEXT): $(top_srcdir)/gc/default.c
+gc.$(OBJEXT): $(top_srcdir)/gc/default/default.c
 gc.$(OBJEXT): $(top_srcdir)/gc/gc.h
 gc.$(OBJEXT): $(top_srcdir)/gc/gc_impl.h
 gc.$(OBJEXT): $(top_srcdir)/internal/array.h
diff --git a/gc.c b/gc.c
index 4ea4692a8f..efd19cce71 100644
--- a/gc.c
+++ b/gc.c
@@ -566,7 +566,7 @@ rb_gc_guarded_ptr_val(volatile VALUE *ptr, VALUE val)
 
 static const char *obj_type_name(VALUE obj);
 #define RB_AMALGAMATED_DEFAULT_GC
-#include "gc/default.c"
+#include "gc/default/default.c"
 static int external_gc_loaded = FALSE;
 
 
@@ -580,7 +580,7 @@ typedef struct gc_function_map {
     void *(*objspace_alloc)(void);
     void (*objspace_init)(void *objspace_ptr);
     void (*objspace_free)(void *objspace_ptr);
-    void *(*ractor_cache_alloc)(void *objspace_ptr);
+    void *(*ractor_cache_alloc)(void *objspace_ptr, void *ractor);
     void (*ractor_cache_free)(void *objspace_ptr, void *cache);
     void (*set_params)(void *objspace_ptr);
     void (*init)(void);
@@ -635,6 +635,9 @@ typedef struct gc_function_map {
     // Object ID
     VALUE (*object_id)(void *objspace_ptr, VALUE obj);
     VALUE (*object_id_to_ref)(void *objspace_ptr, VALUE object_id);
+    // Forking
+    void (*before_fork)(void *objspace_ptr);
+    void (*after_fork)(void *objspace_ptr, rb_pid_t pid);
     // Statistics
     void (*set_measure_total_time)(void *objspace_ptr, VALUE flag);
     bool (*get_measure_total_time)(void *objspace_ptr);
@@ -683,7 +686,7 @@ ruby_external_gc_init(void)
             }
         }
 
-        size_t gc_so_path_size = strlen(SHARED_GC_DIR "librubygc." SOEXT) + strlen(gc_so_file) + 1;
+        size_t gc_so_path_size = strlen(SHARED_GC_DIR "librubygc." DLEXT) + strlen(gc_so_file) + 1;
         gc_so_path = alloca(gc_so_path_size);
         {
             size_t gc_so_path_idx = 0;
@@ -693,7 +696,7 @@ ruby_external_gc_init(void)
             GC_SO_PATH_APPEND(SHARED_GC_DIR);
             GC_SO_PATH_APPEND("librubygc.");
             GC_SO_PATH_APPEND(gc_so_file);
-            GC_SO_PATH_APPEND(SOEXT);
+            GC_SO_PATH_APPEND(DLEXT);
             GC_ASSERT(gc_so_path_idx == gc_so_path_size - 1);
 #undef GC_SO_PATH_APPEND
         }
@@ -781,6 +784,9 @@ ruby_external_gc_init(void)
     // Object ID
     load_external_gc_func(object_id);
     load_external_gc_func(object_id_to_ref);
+    // Forking
+    load_external_gc_func(before_fork);
+    load_external_gc_func(after_fork);
     // Statistics
     load_external_gc_func(set_measure_total_time);
     load_external_gc_func(get_measure_total_time);
@@ -862,6 +868,9 @@ ruby_external_gc_init(void)
 // Object ID
 # define rb_gc_impl_object_id rb_gc_functions.object_id
 # define rb_gc_impl_object_id_to_ref rb_gc_functions.object_id_to_ref
+// Forking
+# define rb_gc_impl_before_fork rb_gc_functions.before_fork
+# define rb_gc_impl_after_fork rb_gc_functions.after_fork
 // Statistics
 # define rb_gc_impl_set_measure_total_time rb_gc_functions.set_measure_total_time
 # define rb_gc_impl_get_measure_total_time rb_gc_functions.get_measure_total_time
@@ -915,7 +924,7 @@ newobj_of(rb_ractor_t *cr, VALUE klass, VALUE flags, VALUE v1, VALUE v2, VALUE v
 {
     VALUE obj = rb_gc_impl_new_obj(rb_gc_get_objspace(), cr->newobj_cache, klass, flags, v1, v2, v3, wb_protected, size);
 
-    if (UNLIKELY(ruby_vm_event_flags & RUBY_INTERNAL_EVENT_NEWOBJ)) {
+    if (UNLIKELY(rb_gc_event_hook_required_p(RUBY_INTERNAL_EVENT_NEWOBJ))) {
         unsigned int lev;
         RB_VM_LOCK_ENTER_CR_LEV(cr, &lev);
         {
@@ -1104,6 +1113,44 @@ rb_data_free(void *objspace, VALUE obj)
     return true;
 }
 
+void
+rb_gc_obj_free_vm_weak_references(VALUE obj)
+{
+    if (FL_TEST(obj, FL_EXIVAR)) {
+        rb_free_generic_ivar((VALUE)obj);
+        FL_UNSET(obj, FL_EXIVAR);
+    }
+
+    switch (BUILTIN_TYPE(obj)) {
+      case T_STRING:
+        if (FL_TEST(obj, RSTRING_FSTR)) {
+            st_data_t fstr = (st_data_t)obj;
+            st_delete(rb_vm_fstring_table(), &fstr, NULL);
+            RB_DEBUG_COUNTER_INC(obj_str_fstr);
+
+            FL_UNSET(obj, RSTRING_FSTR);
+        }
+        break;
+      case T_SYMBOL:
+        rb_gc_free_dsymbol(obj);
+        break;
+      case T_IMEMO:
+        switch (imemo_type(obj)) {
+          case imemo_callinfo:
+            rb_vm_ci_free((const struct rb_callinfo *)obj);
+            break;
+          case imemo_ment:
+            rb_free_method_entry_vm_weak_references((const rb_method_entry_t *)obj);
+            break;
+          default:
+            break;
+        }
+        break;
+      default:
+        break;
+    }
+}
+
 bool
 rb_gc_obj_free(void *objspace, VALUE obj)
 {
diff --git a/gc/default/default.c b/gc/default/default.c
new file mode 100644
index 0000000000..004595b30c
--- /dev/null
+++ b/gc/default/default.c
@@ -0,0 +1,9438 @@
+#include "ruby/internal/config.h"
+
+#include <signal.h>
+
+#ifndef _WIN32
+# include <sys/mman.h>
+# include <unistd.h>
+# ifdef HAVE_SYS_PRCTL_H
+#  include <sys/prctl.h>
+# endif
+#endif
+
+#if !defined(PAGE_SIZE) && defined(HAVE_SYS_USER_H)
+/* LIST_HEAD conflicts with sys/queue.h on macOS */
+# include <sys/user.h>
+#endif
+
+#include "internal/hash.h"
+
+#include "ruby/ruby.h"
+#include "ruby/atomic.h"
+#include "ruby/debug.h"
+#include "ruby/thread.h"
+#include "ruby/util.h"
+#include "ruby/vm.h"
+#include "ruby/internal/encoding/string.h"
+#include "ccan/list/list.h"
+#include "darray.h"
+#include "gc/gc.h"
+#include "gc/gc_impl.h"
+
+#ifndef BUILDING_SHARED_GC
+# include "probes.h"
+#endif
+
+#include "debug_counter.h"
+#include "internal/sanitizers.h"
+
+/* MALLOC_HEADERS_BEGIN */
+#ifndef HAVE_MALLOC_USABLE_SIZE
+# ifdef _WIN32
+#  define HAVE_MALLOC_USABLE_SIZE
+#  define malloc_usable_size(a) _msize(a)
+# elif defined HAVE_MALLOC_SIZE
+#  define HAVE_MALLOC_USABLE_SIZE
+#  define malloc_usable_size(a) malloc_size(a)
+# endif
+#endif
+
+#ifdef HAVE_MALLOC_USABLE_SIZE
+# ifdef RUBY_ALTERNATIVE_MALLOC_HEADER
+/* Alternative malloc header is included in ruby/missing.h */
+# elif defined(HAVE_MALLOC_H)
+#  include <malloc.h>
+# elif defined(HAVE_MALLOC_NP_H)
+#  include <malloc_np.h>
+# elif defined(HAVE_MALLOC_MALLOC_H)
+#  include <malloc/malloc.h>
+# endif
+#endif
+
+#ifdef HAVE_MALLOC_TRIM
+# include <malloc.h>
+
+# ifdef __EMSCRIPTEN__
+/* malloc_trim is defined in emscripten/emmalloc.h on emscripten. */
+#  include <emscripten/emmalloc.h>
+# endif
+#endif
+
+#ifdef HAVE_MACH_TASK_EXCEPTION_PORTS
+# include <mach/task.h>
+# include <mach/mach_init.h>
+# include <mach/mach_port.h>
+#endif
+
+#ifndef VM_CHECK_MODE
+# define VM_CHECK_MODE RUBY_DEBUG
+#endif
+
+// From ractor_core.h
+#ifndef RACTOR_CHECK_MODE
+# define RACTOR_CHECK_MODE (VM_CHECK_MODE || RUBY_DEBUG) && (SIZEOF_UINT64_T == SIZEOF_VALUE)
+#endif
+
+#ifndef RUBY_DEBUG_LOG
+# define RUBY_DEBUG_LOG(...)
+#endif
+
+#ifndef GC_HEAP_INIT_SLOTS
+#define GC_HEAP_INIT_SLOTS 10000
+#endif
+#ifndef GC_HEAP_FREE_SLOTS
+#define GC_HEAP_FREE_SLOTS  4096
+#endif
+#ifndef GC_HEAP_GROWTH_FACTOR
+#define GC_HEAP_GROWTH_FACTOR 1.8
+#endif
+#ifndef GC_HEAP_GROWTH_MAX_SLOTS
+#define GC_HEAP_GROWTH_MAX_SLOTS 0 /* 0 is disable */
+#endif
+#ifndef GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO
+# define GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO 0.01
+#endif
+#ifndef GC_HEAP_OLDOBJECT_LIMIT_FACTOR
+#define GC_HEAP_OLDOBJECT_LIMIT_FACTOR 2.0
+#endif
+
+#ifndef GC_HEAP_FREE_SLOTS_MIN_RATIO
+#define GC_HEAP_FREE_SLOTS_MIN_RATIO  0.20
+#endif
+#ifndef GC_HEAP_FREE_SLOTS_GOAL_RATIO
+#define GC_HEAP_FREE_SLOTS_GOAL_RATIO 0.40
+#endif
+#ifndef GC_HEAP_FREE_SLOTS_MAX_RATIO
+#define GC_HEAP_FREE_SLOTS_MAX_RATIO  0.65
+#endif
+
+#ifndef GC_MALLOC_LIMIT_MIN
+#define GC_MALLOC_LIMIT_MIN (16 * 1024 * 1024 /* 16MB */)
+#endif
+#ifndef GC_MALLOC_LIMIT_MAX
+#define GC_MALLOC_LIMIT_MAX (32 * 1024 * 1024 /* 32MB */)
+#endif
+#ifndef GC_MALLOC_LIMIT_GROWTH_FACTOR
+#define GC_MALLOC_LIMIT_GROWTH_FACTOR 1.4
+#endif
+
+#ifndef GC_OLDMALLOC_LIMIT_MIN
+#define GC_OLDMALLOC_LIMIT_MIN (16 * 1024 * 1024 /* 16MB */)
+#endif
+#ifndef GC_OLDMALLOC_LIMIT_GROWTH_FACTOR
+#define GC_OLDMALLOC_LIMIT_GROWTH_FACTOR 1.2
+#endif
+#ifndef GC_OLDMALLOC_LIMIT_MAX
+#define GC_OLDMALLOC_LIMIT_MAX (128 * 1024 * 1024 /* 128MB */)
+#endif
+
+#ifndef GC_CAN_COMPILE_COMPACTION
+#if defined(__wasi__) /* WebAssembly doesn't support signals */
+# define GC_CAN_COMPILE_COMPACTION 0
+#else
+# define GC_CAN_COMPILE_COMPACTION 1
+#endif
+#endif
+
+#ifndef PRINT_ENTER_EXIT_TICK
+# define PRINT_ENTER_EXIT_TICK 0
+#endif
+#ifndef PRINT_ROOT_TICKS
+#define PRINT_ROOT_TICKS 0
+#endif
+
+#define USE_TICK_T                 (PRINT_ENTER_EXIT_TICK || PRINT_ROOT_TICKS)
+
+#ifndef HEAP_COUNT
+# define HEAP_COUNT 5
+#endif
+
+typedef struct ractor_newobj_heap_cache {
+    struct free_slot *freelist;
+    struct heap_page *using_page;
+} rb_ractor_newobj_heap_cache_t;
+
+typedef struct ractor_newobj_cache {
+    size_t incremental_mark_step_allocated_slots;
+    rb_ractor_newobj_heap_cache_t heap_caches[HEAP_COUNT];
+} rb_ractor_newobj_cache_t;
+
+typedef struct {
+    size_t heap_init_slots[HEAP_COUNT];
+    size_t heap_free_slots;
+    double growth_factor;
+    size_t growth_max_slots;
+
+    double heap_free_slots_min_ratio;
+    double heap_free_slots_goal_ratio;
+    double heap_free_slots_max_ratio;
+    double uncollectible_wb_unprotected_objects_limit_ratio;
+    double oldobject_limit_factor;
+
+    size_t malloc_limit_min;
+    size_t malloc_limit_max;
+    double malloc_limit_growth_factor;
+
+    size_t oldmalloc_limit_min;
+    size_t oldmalloc_limit_max;
+    double oldmalloc_limit_growth_factor;
+} ruby_gc_params_t;
+
+static ruby_gc_params_t gc_params = {
+    { GC_HEAP_INIT_SLOTS },
+    GC_HEAP_FREE_SLOTS,
+    GC_HEAP_GROWTH_FACTOR,
+    GC_HEAP_GROWTH_MAX_SLOTS,
+
+    GC_HEAP_FREE_SLOTS_MIN_RATIO,
+    GC_HEAP_FREE_SLOTS_GOAL_RATIO,
+    GC_HEAP_FREE_SLOTS_MAX_RATIO,
+    GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO,
+    GC_HEAP_OLDOBJECT_LIMIT_FACTOR,
+
+    GC_MALLOC_LIMIT_MIN,
+    GC_MALLOC_LIMIT_MAX,
+    GC_MALLOC_LIMIT_GROWTH_FACTOR,
+
+    GC_OLDMALLOC_LIMIT_MIN,
+    GC_OLDMALLOC_LIMIT_MAX,
+    GC_OLDMALLOC_LIMIT_GROWTH_FACTOR,
+};
+
+/* GC_DEBUG:
+ *  enable to embed GC debugging information.
+ */
+#ifndef GC_DEBUG
+#define GC_DEBUG 0
+#endif
+
+/* RGENGC_DEBUG:
+ * 1: basic information
+ * 2: remember set operation
+ * 3: mark
+ * 4:
+ * 5: sweep
+ */
+#ifndef RGENGC_DEBUG
+#ifdef RUBY_DEVEL
+#define RGENGC_DEBUG       -1
+#else
+#define RGENGC_DEBUG       0
+#endif
+#endif
+#if RGENGC_DEBUG < 0 && !defined(_MSC_VER)
+# define RGENGC_DEBUG_ENABLED(level) (-(RGENGC_DEBUG) >= (level) && ruby_rgengc_debug >= (level))
+#elif defined(HAVE_VA_ARGS_MACRO)
+# define RGENGC_DEBUG_ENABLED(level) ((RGENGC_DEBUG) >= (level))
+#else
+# define RGENGC_DEBUG_ENABLED(level) 0
+#endif
+int ruby_rgengc_debug;
+
+/* RGENGC_PROFILE
+ * 0: disable RGenGC profiling
+ * 1: enable profiling for basic information
+ * 2: enable profiling for each types
+ */
+#ifndef RGENGC_PROFILE
+# define RGENGC_PROFILE     0
+#endif
+
+/* RGENGC_ESTIMATE_OLDMALLOC
+ * Enable/disable to estimate increase size of malloc'ed size by old objects.
+ * If estimation exceeds threshold, then will invoke full GC.
+ * 0: disable estimation.
+ * 1: enable estimation.
+ */
+#ifndef RGENGC_ESTIMATE_OLDMALLOC
+# define RGENGC_ESTIMATE_OLDMALLOC 1
+#endif
+
+#ifndef GC_PROFILE_MORE_DETAIL
+# define GC_PROFILE_MORE_DETAIL 0
+#endif
+#ifndef GC_PROFILE_DETAIL_MEMORY
+# define GC_PROFILE_DETAIL_MEMORY 0
+#endif
+#ifndef GC_ENABLE_LAZY_SWEEP
+# define GC_ENABLE_LAZY_SWEEP   1
+#endif
+#ifndef CALC_EXACT_MALLOC_SIZE
+# define CALC_EXACT_MALLOC_SIZE 0
+#endif
+#if defined(HAVE_MALLOC_USABLE_SIZE) || CALC_EXACT_MALLOC_SIZE > 0
+# ifndef MALLOC_ALLOCATED_SIZE
+#  define MALLOC_ALLOCATED_SIZE 0
+# endif
+#else
+# define MALLOC_ALLOCATED_SIZE 0
+#endif
+#ifndef MALLOC_ALLOCATED_SIZE_CHECK
+# define MALLOC_ALLOCATED_SIZE_CHECK 0
+#endif
+
+#ifndef GC_DEBUG_STRESS_TO_CLASS
+# define GC_DEBUG_STRESS_TO_CLASS RUBY_DEBUG
+#endif
+
+typedef enum {
+    GPR_FLAG_NONE               = 0x000,
+    /* major reason */
+    GPR_FLAG_MAJOR_BY_NOFREE    = 0x001,
+    GPR_FLAG_MAJOR_BY_OLDGEN    = 0x002,
+    GPR_FLAG_MAJOR_BY_SHADY     = 0x004,
+    GPR_FLAG_MAJOR_BY_FORCE     = 0x008,
+#if RGENGC_ESTIMATE_OLDMALLOC
+    GPR_FLAG_MAJOR_BY_OLDMALLOC = 0x020,
+#endif
+    GPR_FLAG_MAJOR_MASK         = 0x0ff,
+
+    /* gc reason */
+    GPR_FLAG_NEWOBJ             = 0x100,
+    GPR_FLAG_MALLOC             = 0x200,
+    GPR_FLAG_METHOD             = 0x400,
+    GPR_FLAG_CAPI               = 0x800,
+    GPR_FLAG_STRESS            = 0x1000,
+
+    /* others */
+    GPR_FLAG_IMMEDIATE_SWEEP   = 0x2000,
+    GPR_FLAG_HAVE_FINALIZE     = 0x4000,
+    GPR_FLAG_IMMEDIATE_MARK    = 0x8000,
+    GPR_FLAG_FULL_MARK        = 0x10000,
+    GPR_FLAG_COMPACT          = 0x20000,
+
+    GPR_DEFAULT_REASON =
+        (GPR_FLAG_FULL_MARK | GPR_FLAG_IMMEDIATE_MARK |
+         GPR_FLAG_IMMEDIATE_SWEEP | GPR_FLAG_CAPI),
+} gc_profile_record_flag;
+
+typedef struct gc_profile_record {
+    unsigned int flags;
+
+    double gc_time;
+    double gc_invoke_time;
+
+    size_t heap_total_objects;
+    size_t heap_use_size;
+    size_t heap_total_size;
+    size_t moved_objects;
+
+#if GC_PROFILE_MORE_DETAIL
+    double gc_mark_time;
+    double gc_sweep_time;
+
+    size_t heap_use_pages;
+    size_t heap_live_objects;
+    size_t heap_free_objects;
+
+    size_t allocate_increase;
+    size_t allocate_limit;
+
+    double prepare_time;
+    size_t removing_objects;
+    size_t empty_objects;
+#if GC_PROFILE_DETAIL_MEMORY
+    long maxrss;
+    long minflt;
+    long majflt;
+#endif
+#endif
+#if MALLOC_ALLOCATED_SIZE
+    size_t allocated_size;
+#endif
+
+#if RGENGC_PROFILE > 0
+    size_t old_objects;
+    size_t remembered_normal_objects;
+    size_t remembered_shady_objects;
+#endif
+} gc_profile_record;
+
+struct RMoved {
+    VALUE flags;
+    VALUE dummy;
+    VALUE destination;
+    uint32_t original_shape_id;
+};
+
+#define RMOVED(obj) ((struct RMoved *)(obj))
+
+typedef uintptr_t bits_t;
+enum {
+    BITS_SIZE = sizeof(bits_t),
+    BITS_BITLENGTH = ( BITS_SIZE * CHAR_BIT )
+};
+
+struct heap_page_header {
+    struct heap_page *page;
+};
+
+struct heap_page_body {
+    struct heap_page_header header;
+    /* char gap[];      */
+    /* RVALUE values[]; */
+};
+
+#define STACK_CHUNK_SIZE 500
+
+typedef struct stack_chunk {
+    VALUE data[STACK_CHUNK_SIZE];
+    struct stack_chunk *next;
+} stack_chunk_t;
+
+typedef struct mark_stack {
+    stack_chunk_t *chunk;
+    stack_chunk_t *cache;
+    int index;
+    int limit;
+    size_t cache_size;
+    size_t unused_cache_size;
+} mark_stack_t;
+
+typedef int (*gc_compact_compare_func)(const void *l, const void *r, void *d);
+
+typedef struct rb_heap_struct {
+    short slot_size;
+
+    /* Basic statistics */
+    size_t total_allocated_pages;
+    size_t force_major_gc_count;
+    size_t force_incremental_marking_finish_count;
+    size_t total_allocated_objects;
+    size_t total_freed_objects;
+    size_t final_slots_count;
+
+    /* Sweeping statistics */
+    size_t freed_slots;
+    size_t empty_slots;
+
+    struct heap_page *free_pages;
+    struct ccan_list_head pages;
+    struct heap_page *sweeping_page; /* iterator for .pages */
+    struct heap_page *compact_cursor;
+    uintptr_t compact_cursor_index;
+    struct heap_page *pooled_pages;
+    size_t total_pages;      /* total page count in a heap */
+    size_t total_slots;      /* total slot count (about total_pages * HEAP_PAGE_OBJ_LIMIT) */
+
+} rb_heap_t;
+
+enum {
+    gc_stress_no_major,
+    gc_stress_no_immediate_sweep,
+    gc_stress_full_mark_after_malloc,
+    gc_stress_max
+};
+
+enum gc_mode {
+    gc_mode_none,
+    gc_mode_marking,
+    gc_mode_sweeping,
+    gc_mode_compacting,
+};
+
+typedef struct rb_objspace {
+    struct {
+        size_t limit;
+        size_t increase;
+#if MALLOC_ALLOCATED_SIZE
+        size_t allocated_size;
+        size_t allocations;
+#endif
+    } malloc_params;
+
+    struct rb_gc_config {
+        bool full_mark;
+    } gc_config;
+
+    struct {
+        unsigned int mode : 2;
+        unsigned int immediate_sweep : 1;
+        unsigned int dont_gc : 1;
+        unsigned int dont_incremental : 1;
+        unsigned int during_gc : 1;
+        unsigned int during_compacting : 1;
+        unsigned int during_reference_updating : 1;
+        unsigned int gc_stressful: 1;
+        unsigned int has_newobj_hook: 1;
+        unsigned int during_minor_gc : 1;
+        unsigned int during_incremental_marking : 1;
+        unsigned int measure_gc : 1;
+    } flags;
+
+    rb_event_flag_t hook_events;
+    unsigned long long next_object_id;
+
+    rb_heap_t heaps[HEAP_COUNT];
+    size_t empty_pages_count;
+    struct heap_page *empty_pages;
+
+    struct {
+        rb_atomic_t finalizing;
+    } atomic_flags;
+
+    mark_stack_t mark_stack;
+    size_t marked_slots;
+
+    struct {
+        rb_darray(struct heap_page *) sorted;
+
+        size_t allocated_pages;
+        size_t freed_pages;
+        uintptr_t range[2];
+        size_t freeable_pages;
+
+        size_t allocatable_slots;
+
+        /* final */
+        VALUE deferred_final;
+    } heap_pages;
+
+    st_table *finalizer_table;
+
+    struct {
+        int run;
+        unsigned int latest_gc_info;
+        gc_profile_record *records;
+        gc_profile_record *current_record;
+        size_t next_index;
+        size_t size;
+
+#if GC_PROFILE_MORE_DETAIL
+        double prepare_time;
+#endif
+        double invoke_time;
+
+        size_t minor_gc_count;
+        size_t major_gc_count;
+        size_t compact_count;
+        size_t read_barrier_faults;
+#if RGENGC_PROFILE > 0
+        size_t total_generated_normal_object_count;
+        size_t total_generated_shady_object_count;
+        size_t total_shade_operation_count;
+        size_t total_promoted_count;
+        size_t total_remembered_normal_object_count;
+        size_t total_remembered_shady_object_count;
+
+#if RGENGC_PROFILE >= 2
+        size_t generated_normal_object_count_types[RUBY_T_MASK];
+        size_t generated_shady_object_count_types[RUBY_T_MASK];
+        size_t shade_operation_count_types[RUBY_T_MASK];
+        size_t promoted_types[RUBY_T_MASK];
+        size_t remembered_normal_object_count_types[RUBY_T_MASK];
+        size_t remembered_shady_object_count_types[RUBY_T_MASK];
+#endif
+#endif /* RGENGC_PROFILE */
+
+        /* temporary profiling space */
+        double gc_sweep_start_time;
+        size_t total_allocated_objects_at_gc_start;
+        size_t heap_used_at_gc_start;
+
+        /* basic statistics */
+        size_t count;
+        unsigned long long marking_time_ns;
+        struct timespec marking_start_time;
+        unsigned long long sweeping_time_ns;
+        struct timespec sweeping_start_time;
+
+        /* Weak references */
+        size_t weak_references_count;
+        size_t retained_weak_references_count;
+    } profile;
+
+    VALUE gc_stress_mode;
+
+    struct {
+        VALUE parent_object;
+        int need_major_gc;
+        size_t last_major_gc;
+        size_t uncollectible_wb_unprotected_objects;
+        size_t uncollectible_wb_unprotected_objects_limit;
+        size_t old_objects;
+        size_t old_objects_limit;
+
+#if RGENGC_ESTIMATE_OLDMALLOC
+        size_t oldmalloc_increase;
+        size_t oldmalloc_increase_limit;
+#endif
+
+#if RGENGC_CHECK_MODE >= 2
+        struct st_table *allrefs_table;
+        size_t error_count;
+#endif
+    } rgengc;
+
+    struct {
+        size_t considered_count_table[T_MASK];
+        size_t moved_count_table[T_MASK];
+        size_t moved_up_count_table[T_MASK];
+        size_t moved_down_count_table[T_MASK];
+        size_t total_moved;
+
+        /* This function will be used, if set, to sort the heap prior to compaction */
+        gc_compact_compare_func compare_func;
+    } rcompactor;
+
+    struct {
+        size_t pooled_slots;
+        size_t step_slots;
+    } rincgc;
+
+    st_table *id_to_obj_tbl;
+    st_table *obj_to_id_tbl;
+
+#if GC_DEBUG_STRESS_TO_CLASS
+    VALUE stress_to_class;
+#endif
+
+    rb_darray(VALUE *) weak_references;
+    rb_postponed_job_handle_t finalize_deferred_pjob;
+
+    unsigned long live_ractor_cache_count;
+} rb_objspace_t;
+
+#ifndef HEAP_PAGE_ALIGN_LOG
+/* default tiny heap size: 64KiB */
+#define HEAP_PAGE_ALIGN_LOG 16
+#endif
+
+#if RACTOR_CHECK_MODE || GC_DEBUG
+struct rvalue_overhead {
+# if RACTOR_CHECK_MODE
+    uint32_t _ractor_belonging_id;
+# endif
+# if GC_DEBUG
+    const char *file;
+    int line;
+# endif
+};
+
+// Make sure that RVALUE_OVERHEAD aligns to sizeof(VALUE)
+# define RVALUE_OVERHEAD (sizeof(struct { \
+    union { \
+        struct rvalue_overhead overhead; \
+        VALUE value; \
+    }; \
+}))
+size_t rb_gc_impl_obj_slot_size(VALUE obj);
+# define GET_RVALUE_OVERHEAD(obj) ((struct rvalue_overhead *)((uintptr_t)obj + rb_gc_impl_obj_slot_size(obj)))
+#else
+# define RVALUE_OVERHEAD 0
+#endif
+
+#define BASE_SLOT_SIZE (sizeof(struct RBasic) + sizeof(VALUE[RBIMPL_RVALUE_EMBED_LEN_MAX]) + RVALUE_OVERHEAD)
+
+#ifndef MAX
+# define MAX(a, b) (((a) > (b)) ? (a) : (b))
+#endif
+#ifndef MIN
+# define MIN(a, b) (((a) < (b)) ? (a) : (b))
+#endif
+#define roomof(x, y) (((x) + (y) - 1) / (y))
+#define CEILDIV(i, mod) roomof(i, mod)
+enum {
+    HEAP_PAGE_ALIGN = (1UL << HEAP_PAGE_ALIGN_LOG),
+    HEAP_PAGE_ALIGN_MASK = (~(~0UL << HEAP_PAGE_ALIGN_LOG)),
+    HEAP_PAGE_SIZE = HEAP_PAGE_ALIGN,
+    HEAP_PAGE_OBJ_LIMIT = (unsigned int)((HEAP_PAGE_SIZE - sizeof(struct heap_page_header)) / BASE_SLOT_SIZE),
+    HEAP_PAGE_BITMAP_LIMIT = CEILDIV(CEILDIV(HEAP_PAGE_SIZE, BASE_SLOT_SIZE), BITS_BITLENGTH),
+    HEAP_PAGE_BITMAP_SIZE = (BITS_SIZE * HEAP_PAGE_BITMAP_LIMIT),
+};
+#define HEAP_PAGE_ALIGN (1 << HEAP_PAGE_ALIGN_LOG)
+#define HEAP_PAGE_SIZE HEAP_PAGE_ALIGN
+
+#if !defined(INCREMENTAL_MARK_STEP_ALLOCATIONS)
+# define INCREMENTAL_MARK_STEP_ALLOCATIONS 500
+#endif
+
+#undef INIT_HEAP_PAGE_ALLOC_USE_MMAP
+/* Must define either HEAP_PAGE_ALLOC_USE_MMAP or
+ * INIT_HEAP_PAGE_ALLOC_USE_MMAP. */
+
+#ifndef HAVE_MMAP
+/* We can't use mmap of course, if it is not available. */
+static const bool HEAP_PAGE_ALLOC_USE_MMAP = false;
+
+#elif defined(__wasm__)
+/* wasmtime does not have proper support for mmap.
+ * See https://github.com/bytecodealliance/wasmtime/blob/main/docs/WASI-rationale.md#why-no-mmap-and-friends
+ */
+static const bool HEAP_PAGE_ALLOC_USE_MMAP = false;
+
+#elif HAVE_CONST_PAGE_SIZE
+/* If we have the PAGE_SIZE and it is a constant, then we can directly use it. */
+static const bool HEAP_PAGE_ALLOC_USE_MMAP = (PAGE_SIZE <= HEAP_PAGE_SIZE);
+
+#elif defined(PAGE_MAX_SIZE) && (PAGE_MAX_SIZE <= HEAP_PAGE_SIZE)
+/* If we can use the maximum page size. */
+static const bool HEAP_PAGE_ALLOC_USE_MMAP = true;
+
+#elif defined(PAGE_SIZE)
+/* If the PAGE_SIZE macro can be used dynamically. */
+# define INIT_HEAP_PAGE_ALLOC_USE_MMAP (PAGE_SIZE <= HEAP_PAGE_SIZE)
+
+#elif defined(HAVE_SYSCONF) && defined(_SC_PAGE_SIZE)
+/* If we can use sysconf to determine the page size. */
+# define INIT_HEAP_PAGE_ALLOC_USE_MMAP (sysconf(_SC_PAGE_SIZE) <= HEAP_PAGE_SIZE)
+
+#else
+/* Otherwise we can't determine the system page size, so don't use mmap. */
+static const bool HEAP_PAGE_ALLOC_USE_MMAP = false;
+#endif
+
+#ifdef INIT_HEAP_PAGE_ALLOC_USE_MMAP
+/* We can determine the system page size at runtime. */
+# define HEAP_PAGE_ALLOC_USE_MMAP (heap_page_alloc_use_mmap != false)
+
+static bool heap_page_alloc_use_mmap;
+#endif
+
+#define RVALUE_AGE_BIT_COUNT 2
+#define RVALUE_AGE_BIT_MASK (((bits_t)1 << RVALUE_AGE_BIT_COUNT) - 1)
+#define RVALUE_OLD_AGE   3
+
+struct free_slot {
+    VALUE flags;		/* always 0 for freed obj */
+    struct free_slot *next;
+};
+
+struct heap_page {
+    unsigned short slot_size;
+    unsigned short total_slots;
+    unsigned short free_slots;
+    unsigned short final_slots;
+    unsigned short pinned_slots;
+    struct {
+        unsigned int before_sweep : 1;
+        unsigned int has_remembered_objects : 1;
+        unsigned int has_uncollectible_wb_unprotected_objects : 1;
+    } flags;
+
+    rb_heap_t *heap;
+
+    struct heap_page *free_next;
+    struct heap_page_body *body;
+    uintptr_t start;
+    struct free_slot *freelist;
+    struct ccan_list_node page_node;
+
+    bits_t wb_unprotected_bits[HEAP_PAGE_BITMAP_LIMIT];
+    /* the following three bitmaps are cleared at the beginning of full GC */
+    bits_t mark_bits[HEAP_PAGE_BITMAP_LIMIT];
+    bits_t uncollectible_bits[HEAP_PAGE_BITMAP_LIMIT];
+    bits_t marking_bits[HEAP_PAGE_BITMAP_LIMIT];
+
+    bits_t remembered_bits[HEAP_PAGE_BITMAP_LIMIT];
+
+    /* If set, the object is not movable */
+    bits_t pinned_bits[HEAP_PAGE_BITMAP_LIMIT];
+    bits_t age_bits[HEAP_PAGE_BITMAP_LIMIT * RVALUE_AGE_BIT_COUNT];
+};
+
+/*
+ * When asan is enabled, this will prohibit writing to the freelist until it is unlocked
+ */
+static void
+asan_lock_freelist(struct heap_page *page)
+{
+    asan_poison_memory_region(&page->freelist, sizeof(struct free_list *));
+}
+
+/*
+ * When asan is enabled, this will enable the ability to write to the freelist
+ */
+static void
+asan_unlock_freelist(struct heap_page *page)
+{
+    asan_unpoison_memory_region(&page->freelist, sizeof(struct free_list *), false);
+}
+
+static inline bool
+heap_page_in_global_empty_pages_pool(rb_objspace_t *objspace, struct heap_page *page)
+{
+    if (page->total_slots == 0) {
+        GC_ASSERT(page->start == 0);
+        GC_ASSERT(page->slot_size == 0);
+        GC_ASSERT(page->heap == NULL);
+        GC_ASSERT(page->free_slots == 0);
+        asan_unpoisoning_memory_region(&page->freelist, sizeof(&page->freelist)) {
+            GC_ASSERT(page->freelist == NULL);
+        }
+
+        return true;
+    }
+    else {
+        GC_ASSERT(page->start != 0);
+        GC_ASSERT(page->slot_size != 0);
+        GC_ASSERT(page->heap != NULL);
+
+        return false;
+    }
+}
+
+#define GET_PAGE_BODY(x)   ((struct heap_page_body *)((bits_t)(x) & ~(HEAP_PAGE_ALIGN_MASK)))
+#define GET_PAGE_HEADER(x) (&GET_PAGE_BODY(x)->header)
+#define GET_HEAP_PAGE(x)   (GET_PAGE_HEADER(x)->page)
+
+#define NUM_IN_PAGE(p)   (((bits_t)(p) & HEAP_PAGE_ALIGN_MASK) / BASE_SLOT_SIZE)
+#define BITMAP_INDEX(p)  (NUM_IN_PAGE(p) / BITS_BITLENGTH )
+#define BITMAP_OFFSET(p) (NUM_IN_PAGE(p) & (BITS_BITLENGTH-1))
+#define BITMAP_BIT(p)    ((bits_t)1 << BITMAP_OFFSET(p))
+
+/* Bitmap Operations */
+#define MARKED_IN_BITMAP(bits, p)    ((bits)[BITMAP_INDEX(p)] & BITMAP_BIT(p))
+#define MARK_IN_BITMAP(bits, p)      ((bits)[BITMAP_INDEX(p)] = (bits)[BITMAP_INDEX(p)] | BITMAP_BIT(p))
+#define CLEAR_IN_BITMAP(bits, p)     ((bits)[BITMAP_INDEX(p)] = (bits)[BITMAP_INDEX(p)] & ~BITMAP_BIT(p))
+
+/* getting bitmap */
+#define GET_HEAP_MARK_BITS(x)           (&GET_HEAP_PAGE(x)->mark_bits[0])
+#define GET_HEAP_PINNED_BITS(x)         (&GET_HEAP_PAGE(x)->pinned_bits[0])
+#define GET_HEAP_UNCOLLECTIBLE_BITS(x)  (&GET_HEAP_PAGE(x)->uncollectible_bits[0])
+#define GET_HEAP_WB_UNPROTECTED_BITS(x) (&GET_HEAP_PAGE(x)->wb_unprotected_bits[0])
+#define GET_HEAP_MARKING_BITS(x)        (&GET_HEAP_PAGE(x)->marking_bits[0])
+
+#define GC_SWEEP_PAGES_FREEABLE_PER_STEP 3
+
+#define RVALUE_AGE_BITMAP_INDEX(n)  (NUM_IN_PAGE(n) / (BITS_BITLENGTH / RVALUE_AGE_BIT_COUNT))
+#define RVALUE_AGE_BITMAP_OFFSET(n) ((NUM_IN_PAGE(n) % (BITS_BITLENGTH / RVALUE_AGE_BIT_COUNT)) * RVALUE_AGE_BIT_COUNT)
+
+static int
+RVALUE_AGE_GET(VALUE obj)
+{
+    bits_t *age_bits = GET_HEAP_PAGE(obj)->age_bits;
+    return (int)(age_bits[RVALUE_AGE_BITMAP_INDEX(obj)] >> RVALUE_AGE_BITMAP_OFFSET(obj)) & RVALUE_AGE_BIT_MASK;
+}
+
+static void
+RVALUE_AGE_SET(VALUE obj, int age)
+{
+    RUBY_ASSERT(age <= RVALUE_OLD_AGE);
+    bits_t *age_bits = GET_HEAP_PAGE(obj)->age_bits;
+    // clear the bits
+    age_bits[RVALUE_AGE_BITMAP_INDEX(obj)] &= ~(RVALUE_AGE_BIT_MASK << (RVALUE_AGE_BITMAP_OFFSET(obj)));
+    // shift the correct value in
+    age_bits[RVALUE_AGE_BITMAP_INDEX(obj)] |= ((bits_t)age << RVALUE_AGE_BITMAP_OFFSET(obj));
+    if (age == RVALUE_OLD_AGE) {
+        RB_FL_SET_RAW(obj, RUBY_FL_PROMOTED);
+    }
+    else {
+        RB_FL_UNSET_RAW(obj, RUBY_FL_PROMOTED);
+    }
+}
+
+#define malloc_limit		objspace->malloc_params.limit
+#define malloc_increase 	objspace->malloc_params.increase
+#define malloc_allocated_size 	objspace->malloc_params.allocated_size
+#define heap_pages_lomem	objspace->heap_pages.range[0]
+#define heap_pages_himem	objspace->heap_pages.range[1]
+#define heap_pages_freeable_pages	objspace->heap_pages.freeable_pages
+#define heap_pages_deferred_final	objspace->heap_pages.deferred_final
+#define heaps              objspace->heaps
+#define during_gc		objspace->flags.during_gc
+#define finalizing		objspace->atomic_flags.finalizing
+#define finalizer_table 	objspace->finalizer_table
+#define ruby_gc_stressful	objspace->flags.gc_stressful
+#define ruby_gc_stress_mode     objspace->gc_stress_mode
+#if GC_DEBUG_STRESS_TO_CLASS
+#define stress_to_class         objspace->stress_to_class
+#define set_stress_to_class(c)  (stress_to_class = (c))
+#else
+#define stress_to_class         (objspace, 0)
+#define set_stress_to_class(c)  (objspace, (c))
+#endif
+
+#if 0
+#define dont_gc_on()          (fprintf(stderr, "dont_gc_on@%s:%d\n",      __FILE__, __LINE__), objspace->flags.dont_gc = 1)
+#define dont_gc_off()         (fprintf(stderr, "dont_gc_off@%s:%d\n",     __FILE__, __LINE__), objspace->flags.dont_gc = 0)
+#define dont_gc_set(b)        (fprintf(stderr, "dont_gc_set(%d)@%s:%d\n", __FILE__, __LINE__), objspace->flags.dont_gc = (int)(b))
+#define dont_gc_val()         (objspace->flags.dont_gc)
+#else
+#define dont_gc_on()          (objspace->flags.dont_gc = 1)
+#define dont_gc_off()         (objspace->flags.dont_gc = 0)
+#define dont_gc_set(b)        (objspace->flags.dont_gc = (int)(b))
+#define dont_gc_val()         (objspace->flags.dont_gc)
+#endif
+
+#define gc_config_full_mark_set(b) (objspace->gc_config.full_mark = (int)(b))
+#define gc_config_full_mark_val    (objspace->gc_config.full_mark)
+
+#ifndef DURING_GC_COULD_MALLOC_REGION_START
+# define DURING_GC_COULD_MALLOC_REGION_START() \
+    assert(rb_during_gc()); \
+    bool _prev_enabled = rb_gc_impl_gc_enabled_p(objspace); \
+    rb_gc_impl_gc_disable(objspace, false)
+#endif
+
+#ifndef DURING_GC_COULD_MALLOC_REGION_END
+# define DURING_GC_COULD_MALLOC_REGION_END() \
+    if (_prev_enabled) rb_gc_impl_gc_enable(objspace)
+#endif
+
+static inline enum gc_mode
+gc_mode_verify(enum gc_mode mode)
+{
+#if RGENGC_CHECK_MODE > 0
+    switch (mode) {
+      case gc_mode_none:
+      case gc_mode_marking:
+      case gc_mode_sweeping:
+      case gc_mode_compacting:
+        break;
+      default:
+        rb_bug("gc_mode_verify: unreachable (%d)", (int)mode);
+    }
+#endif
+    return mode;
+}
+
+static inline bool
+has_sweeping_pages(rb_objspace_t *objspace)
+{
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        if ((&heaps[i])->sweeping_page) {
+            return TRUE;
+        }
+    }
+    return FALSE;
+}
+
+static inline size_t
+heap_eden_total_pages(rb_objspace_t *objspace)
+{
+    size_t count = 0;
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        count += (&heaps[i])->total_pages;
+    }
+    return count;
+}
+
+static inline size_t
+total_allocated_objects(rb_objspace_t *objspace)
+{
+    size_t count = 0;
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        count += heap->total_allocated_objects;
+    }
+    return count;
+}
+
+static inline size_t
+total_freed_objects(rb_objspace_t *objspace)
+{
+    size_t count = 0;
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        count += heap->total_freed_objects;
+    }
+    return count;
+}
+
+static inline size_t
+total_final_slots_count(rb_objspace_t *objspace)
+{
+    size_t count = 0;
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        count += heap->final_slots_count;
+    }
+    return count;
+}
+
+#define gc_mode(objspace)                gc_mode_verify((enum gc_mode)(objspace)->flags.mode)
+#define gc_mode_set(objspace, m)         ((objspace)->flags.mode = (unsigned int)gc_mode_verify(m))
+#define gc_needs_major_flags objspace->rgengc.need_major_gc
+
+#define is_marking(objspace)             (gc_mode(objspace) == gc_mode_marking)
+#define is_sweeping(objspace)            (gc_mode(objspace) == gc_mode_sweeping)
+#define is_full_marking(objspace)        ((objspace)->flags.during_minor_gc == FALSE)
+#define is_incremental_marking(objspace) ((objspace)->flags.during_incremental_marking != FALSE)
+#define will_be_incremental_marking(objspace) ((objspace)->rgengc.need_major_gc != GPR_FLAG_NONE)
+#define GC_INCREMENTAL_SWEEP_SLOT_COUNT 2048
+#define GC_INCREMENTAL_SWEEP_POOL_SLOT_COUNT 1024
+#define is_lazy_sweeping(objspace)           (GC_ENABLE_LAZY_SWEEP && has_sweeping_pages(objspace))
+
+#if SIZEOF_LONG == SIZEOF_VOIDP
+# define obj_id_to_ref(objid) ((objid) ^ FIXNUM_FLAG) /* unset FIXNUM_FLAG */
+#elif SIZEOF_LONG_LONG == SIZEOF_VOIDP
+# define obj_id_to_ref(objid) (FIXNUM_P(objid) ? \
+   ((objid) ^ FIXNUM_FLAG) : (NUM2PTR(objid) << 1))
+#else
+# error not supported
+#endif
+
+struct RZombie {
+    struct RBasic basic;
+    VALUE next;
+    void (*dfree)(void *);
+    void *data;
+};
+
+#define RZOMBIE(o) ((struct RZombie *)(o))
+
+int ruby_disable_gc = 0;
+int ruby_enable_autocompact = 0;
+#if RGENGC_CHECK_MODE
+gc_compact_compare_func ruby_autocompact_compare_func;
+#endif
+
+static void init_mark_stack(mark_stack_t *stack);
+static int garbage_collect(rb_objspace_t *, unsigned int reason);
+
+static int  gc_start(rb_objspace_t *objspace, unsigned int reason);
+static void gc_rest(rb_objspace_t *objspace);
+
+enum gc_enter_event {
+    gc_enter_event_start,
+    gc_enter_event_continue,
+    gc_enter_event_rest,
+    gc_enter_event_finalizer,
+};
+
+static inline void gc_enter(rb_objspace_t *objspace, enum gc_enter_event event, unsigned int *lock_lev);
+static inline void gc_exit(rb_objspace_t *objspace, enum gc_enter_event event, unsigned int *lock_lev);
+static void gc_marking_enter(rb_objspace_t *objspace);
+static void gc_marking_exit(rb_objspace_t *objspace);
+static void gc_sweeping_enter(rb_objspace_t *objspace);
+static void gc_sweeping_exit(rb_objspace_t *objspace);
+static bool gc_marks_continue(rb_objspace_t *objspace, rb_heap_t *heap);
+
+static void gc_sweep(rb_objspace_t *objspace);
+static void gc_sweep_finish_heap(rb_objspace_t *objspace, rb_heap_t *heap);
+static void gc_sweep_continue(rb_objspace_t *objspace, rb_heap_t *heap);
+
+static inline void gc_mark(rb_objspace_t *objspace, VALUE ptr);
+static inline void gc_pin(rb_objspace_t *objspace, VALUE ptr);
+static inline void gc_mark_and_pin(rb_objspace_t *objspace, VALUE ptr);
+
+static int gc_mark_stacked_objects_incremental(rb_objspace_t *, size_t count);
+NO_SANITIZE("memory", static inline bool is_pointer_to_heap(rb_objspace_t *objspace, const void *ptr));
+
+static void gc_verify_internal_consistency(void *objspace_ptr);
+
+static double getrusage_time(void);
+static inline void gc_prof_setup_new_record(rb_objspace_t *objspace, unsigned int reason);
+static inline void gc_prof_timer_start(rb_objspace_t *);
+static inline void gc_prof_timer_stop(rb_objspace_t *);
+static inline void gc_prof_mark_timer_start(rb_objspace_t *);
+static inline void gc_prof_mark_timer_stop(rb_objspace_t *);
+static inline void gc_prof_sweep_timer_start(rb_objspace_t *);
+static inline void gc_prof_sweep_timer_stop(rb_objspace_t *);
+static inline void gc_prof_set_malloc_info(rb_objspace_t *);
+static inline void gc_prof_set_heap_info(rb_objspace_t *);
+
+#define gc_prof_record(objspace) (objspace)->profile.current_record
+#define gc_prof_enabled(objspace) ((objspace)->profile.run && (objspace)->profile.current_record)
+
+#ifdef HAVE_VA_ARGS_MACRO
+# define gc_report(level, objspace, ...) \
+    if (!RGENGC_DEBUG_ENABLED(level)) {} else gc_report_body(level, objspace, __VA_ARGS__)
+#else
+# define gc_report if (!RGENGC_DEBUG_ENABLED(0)) {} else gc_report_body
+#endif
+PRINTF_ARGS(static void gc_report_body(int level, rb_objspace_t *objspace, const char *fmt, ...), 3, 4);
+
+static void gc_finalize_deferred(void *dmy);
+
+#if USE_TICK_T
+
+/* the following code is only for internal tuning. */
+
+/* Source code to use RDTSC is quoted and modified from
+ * https://www.mcs.anl.gov/~kazutomo/rdtsc.html
+ * written by Kazutomo Yoshii <kazutomo@mcs.anl.gov>
+ */
+
+#if defined(__GNUC__) && defined(__i386__)
+typedef unsigned long long tick_t;
+#define PRItick "llu"
+static inline tick_t
+tick(void)
+{
+    unsigned long long int x;
+    __asm__ __volatile__ ("rdtsc" : "=A" (x));
+    return x;
+}
+
+#elif defined(__GNUC__) && defined(__x86_64__)
+typedef unsigned long long tick_t;
+#define PRItick "llu"
+
+static __inline__ tick_t
+tick(void)
+{
+    unsigned long hi, lo;
+    __asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi));
+    return ((unsigned long long)lo)|( ((unsigned long long)hi)<<32);
+}
+
+#elif defined(__powerpc64__) && (GCC_VERSION_SINCE(4,8,0) || defined(__clang__))
+typedef unsigned long long tick_t;
+#define PRItick "llu"
+
+static __inline__ tick_t
+tick(void)
+{
+    unsigned long long val = __builtin_ppc_get_timebase();
+    return val;
+}
+
+/* Implementation for macOS PPC by @nobu
+ * See: https://github.com/ruby/ruby/pull/5975#discussion_r890045558
+ */
+#elif defined(__POWERPC__) && defined(__APPLE__)
+typedef unsigned long long tick_t;
+#define PRItick "llu"
+
+static __inline__ tick_t
+tick(void)
+{
+    unsigned long int upper, lower, tmp;
+    # define mftbu(r) __asm__ volatile("mftbu   %0" : "=r"(r))
+    # define mftb(r)  __asm__ volatile("mftb    %0" : "=r"(r))
+        do {
+            mftbu(upper);
+            mftb(lower);
+            mftbu(tmp);
+        } while (tmp != upper);
+    return ((tick_t)upper << 32) | lower;
+}
+
+#elif defined(__aarch64__) &&  defined(__GNUC__)
+typedef unsigned long tick_t;
+#define PRItick "lu"
+
+static __inline__ tick_t
+tick(void)
+{
+    unsigned long val;
+    __asm__ __volatile__ ("mrs %0, cntvct_el0" : "=r" (val));
+    return val;
+}
+
+
+#elif defined(_WIN32) && defined(_MSC_VER)
+#include <intrin.h>
+typedef unsigned __int64 tick_t;
+#define PRItick "llu"
+
+static inline tick_t
+tick(void)
+{
+    return __rdtsc();
+}
+
+#else /* use clock */
+typedef clock_t tick_t;
+#define PRItick "llu"
+
+static inline tick_t
+tick(void)
+{
+    return clock();
+}
+#endif /* TSC */
+#else /* USE_TICK_T */
+#define MEASURE_LINE(expr) expr
+#endif /* USE_TICK_T */
+
+static inline VALUE check_rvalue_consistency(rb_objspace_t *objspace, const VALUE obj);
+
+#define RVALUE_MARKED_BITMAP(obj)         MARKED_IN_BITMAP(GET_HEAP_MARK_BITS(obj), (obj))
+#define RVALUE_WB_UNPROTECTED_BITMAP(obj) MARKED_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(obj), (obj))
+#define RVALUE_MARKING_BITMAP(obj)        MARKED_IN_BITMAP(GET_HEAP_MARKING_BITS(obj), (obj))
+#define RVALUE_UNCOLLECTIBLE_BITMAP(obj)  MARKED_IN_BITMAP(GET_HEAP_UNCOLLECTIBLE_BITS(obj), (obj))
+#define RVALUE_PINNED_BITMAP(obj)         MARKED_IN_BITMAP(GET_HEAP_PINNED_BITS(obj), (obj))
+
+static inline int
+RVALUE_MARKED(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    return RVALUE_MARKED_BITMAP(obj) != 0;
+}
+
+static inline int
+RVALUE_PINNED(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    return RVALUE_PINNED_BITMAP(obj) != 0;
+}
+
+static inline int
+RVALUE_WB_UNPROTECTED(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    return RVALUE_WB_UNPROTECTED_BITMAP(obj) != 0;
+}
+
+static inline int
+RVALUE_MARKING(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    return RVALUE_MARKING_BITMAP(obj) != 0;
+}
+
+static inline int
+RVALUE_REMEMBERED(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    return MARKED_IN_BITMAP(GET_HEAP_PAGE(obj)->remembered_bits, obj) != 0;
+}
+
+static inline int
+RVALUE_UNCOLLECTIBLE(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    return RVALUE_UNCOLLECTIBLE_BITMAP(obj) != 0;
+}
+
+#define RVALUE_PAGE_WB_UNPROTECTED(page, obj) MARKED_IN_BITMAP((page)->wb_unprotected_bits, (obj))
+#define RVALUE_PAGE_UNCOLLECTIBLE(page, obj)  MARKED_IN_BITMAP((page)->uncollectible_bits, (obj))
+#define RVALUE_PAGE_MARKING(page, obj)        MARKED_IN_BITMAP((page)->marking_bits, (obj))
+
+static int rgengc_remember(rb_objspace_t *objspace, VALUE obj);
+static void rgengc_mark_and_rememberset_clear(rb_objspace_t *objspace, rb_heap_t *heap);
+static void rgengc_rememberset_mark(rb_objspace_t *objspace, rb_heap_t *heap);
+
+static int
+check_rvalue_consistency_force(rb_objspace_t *objspace, const VALUE obj, int terminate)
+{
+    int err = 0;
+
+    int lev = rb_gc_vm_lock_no_barrier();
+    {
+        if (SPECIAL_CONST_P(obj)) {
+            fprintf(stderr, "check_rvalue_consistency: %p is a special const.\n", (void *)obj);
+            err++;
+        }
+        else if (!is_pointer_to_heap(objspace, (void *)obj)) {
+            struct heap_page *empty_page = objspace->empty_pages;
+            while (empty_page) {
+                if ((uintptr_t)empty_page->body <= (uintptr_t)obj &&
+                        (uintptr_t)obj < (uintptr_t)empty_page->body + HEAP_PAGE_SIZE) {
+                    GC_ASSERT(heap_page_in_global_empty_pages_pool(objspace, empty_page));
+                    fprintf(stderr, "check_rvalue_consistency: %p is in an empty page (%p).\n",
+                            (void *)obj, (void *)empty_page);
+                    err++;
+                    goto skip;
+                }
+            }
+            fprintf(stderr, "check_rvalue_consistency: %p is not a Ruby object.\n", (void *)obj);
+            err++;
+          skip:
+            ;
+        }
+        else {
+            const int wb_unprotected_bit = RVALUE_WB_UNPROTECTED_BITMAP(obj) != 0;
+            const int uncollectible_bit = RVALUE_UNCOLLECTIBLE_BITMAP(obj) != 0;
+            const int mark_bit = RVALUE_MARKED_BITMAP(obj) != 0;
+            const int marking_bit = RVALUE_MARKING_BITMAP(obj) != 0;
+            const int remembered_bit = MARKED_IN_BITMAP(GET_HEAP_PAGE(obj)->remembered_bits, obj) != 0;
+            const int age = RVALUE_AGE_GET((VALUE)obj);
+
+            if (heap_page_in_global_empty_pages_pool(objspace, GET_HEAP_PAGE(obj))) {
+                fprintf(stderr, "check_rvalue_consistency: %s is in tomb page.\n", rb_obj_info(obj));
+                err++;
+            }
+            if (BUILTIN_TYPE(obj) == T_NONE) {
+                fprintf(stderr, "check_rvalue_consistency: %s is T_NONE.\n", rb_obj_info(obj));
+                err++;
+            }
+            if (BUILTIN_TYPE(obj) == T_ZOMBIE) {
+                fprintf(stderr, "check_rvalue_consistency: %s is T_ZOMBIE.\n", rb_obj_info(obj));
+                err++;
+            }
+
+            if (BUILTIN_TYPE(obj) != T_DATA) {
+                rb_obj_memsize_of((VALUE)obj);
+            }
+
+            /* check generation
+             *
+             * OLD == age == 3 && old-bitmap && mark-bit (except incremental marking)
+             */
+            if (age > 0 && wb_unprotected_bit) {
+                fprintf(stderr, "check_rvalue_consistency: %s is not WB protected, but age is %d > 0.\n", rb_obj_info(obj), age);
+                err++;
+            }
+
+            if (!is_marking(objspace) && uncollectible_bit && !mark_bit) {
+                fprintf(stderr, "check_rvalue_consistency: %s is uncollectible, but is not marked while !gc.\n", rb_obj_info(obj));
+                err++;
+            }
+
+            if (!is_full_marking(objspace)) {
+                if (uncollectible_bit && age != RVALUE_OLD_AGE && !wb_unprotected_bit) {
+                    fprintf(stderr, "check_rvalue_consistency: %s is uncollectible, but not old (age: %d) and not WB unprotected.\n",
+                            rb_obj_info(obj), age);
+                    err++;
+                }
+                if (remembered_bit && age != RVALUE_OLD_AGE) {
+                    fprintf(stderr, "check_rvalue_consistency: %s is remembered, but not old (age: %d).\n",
+                            rb_obj_info(obj), age);
+                    err++;
+                }
+            }
+
+            /*
+             * check coloring
+             *
+             *               marking:false marking:true
+             * marked:false  white         *invalid*
+             * marked:true   black         grey
+             */
+            if (is_incremental_marking(objspace) && marking_bit) {
+                if (!is_marking(objspace) && !mark_bit) {
+                    fprintf(stderr, "check_rvalue_consistency: %s is marking, but not marked.\n", rb_obj_info(obj));
+                    err++;
+                }
+            }
+        }
+    }
+    rb_gc_vm_unlock_no_barrier(lev);
+
+    if (err > 0 && terminate) {
+        rb_bug("check_rvalue_consistency_force: there is %d errors.", err);
+    }
+    return err;
+}
+
+#if RGENGC_CHECK_MODE == 0
+static inline VALUE
+check_rvalue_consistency(rb_objspace_t *objspace, const VALUE obj)
+{
+    return obj;
+}
+#else
+static VALUE
+check_rvalue_consistency(rb_objspace_t *objspace, const VALUE obj)
+{
+    check_rvalue_consistency_force(objspace, obj, TRUE);
+    return obj;
+}
+#endif
+
+static inline bool
+gc_object_moved_p(rb_objspace_t *objspace, VALUE obj)
+{
+    if (RB_SPECIAL_CONST_P(obj)) {
+        return FALSE;
+    }
+    else {
+        int ret;
+        asan_unpoisoning_object(obj) {
+            ret = BUILTIN_TYPE(obj) == T_MOVED;
+        }
+        return ret;
+    }
+}
+
+static inline int
+RVALUE_OLD_P(rb_objspace_t *objspace, VALUE obj)
+{
+    GC_ASSERT(!RB_SPECIAL_CONST_P(obj));
+    check_rvalue_consistency(objspace, obj);
+    // Because this will only ever be called on GC controlled objects,
+    // we can use the faster _RAW function here
+    return RB_OBJ_PROMOTED_RAW(obj);
+}
+
+static inline void
+RVALUE_PAGE_OLD_UNCOLLECTIBLE_SET(rb_objspace_t *objspace, struct heap_page *page, VALUE obj)
+{
+    MARK_IN_BITMAP(&page->uncollectible_bits[0], obj);
+    objspace->rgengc.old_objects++;
+
+#if RGENGC_PROFILE >= 2
+    objspace->profile.total_promoted_count++;
+    objspace->profile.promoted_types[BUILTIN_TYPE(obj)]++;
+#endif
+}
+
+static inline void
+RVALUE_OLD_UNCOLLECTIBLE_SET(rb_objspace_t *objspace, VALUE obj)
+{
+    RB_DEBUG_COUNTER_INC(obj_promote);
+    RVALUE_PAGE_OLD_UNCOLLECTIBLE_SET(objspace, GET_HEAP_PAGE(obj), obj);
+}
+
+/* set age to age+1 */
+static inline void
+RVALUE_AGE_INC(rb_objspace_t *objspace, VALUE obj)
+{
+    int age = RVALUE_AGE_GET((VALUE)obj);
+
+    if (RGENGC_CHECK_MODE && age == RVALUE_OLD_AGE) {
+        rb_bug("RVALUE_AGE_INC: can not increment age of OLD object %s.", rb_obj_info(obj));
+    }
+
+    age++;
+    RVALUE_AGE_SET(obj, age);
+
+    if (age == RVALUE_OLD_AGE) {
+        RVALUE_OLD_UNCOLLECTIBLE_SET(objspace, obj);
+    }
+
+    check_rvalue_consistency(objspace, obj);
+}
+
+static inline void
+RVALUE_AGE_SET_CANDIDATE(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    GC_ASSERT(!RVALUE_OLD_P(objspace, obj));
+    RVALUE_AGE_SET(obj, RVALUE_OLD_AGE - 1);
+    check_rvalue_consistency(objspace, obj);
+}
+
+static inline void
+RVALUE_AGE_RESET(VALUE obj)
+{
+    RVALUE_AGE_SET(obj, 0);
+}
+
+static inline void
+RVALUE_DEMOTE(rb_objspace_t *objspace, VALUE obj)
+{
+    check_rvalue_consistency(objspace, obj);
+    GC_ASSERT(RVALUE_OLD_P(objspace, obj));
+
+    if (!is_incremental_marking(objspace) && RVALUE_REMEMBERED(objspace, obj)) {
+        CLEAR_IN_BITMAP(GET_HEAP_PAGE(obj)->remembered_bits, obj);
+    }
+
+    CLEAR_IN_BITMAP(GET_HEAP_UNCOLLECTIBLE_BITS(obj), obj);
+    RVALUE_AGE_RESET(obj);
+
+    if (RVALUE_MARKED(objspace, obj)) {
+        objspace->rgengc.old_objects--;
+    }
+
+    check_rvalue_consistency(objspace, obj);
+}
+
+static inline int
+RVALUE_BLACK_P(rb_objspace_t *objspace, VALUE obj)
+{
+    return RVALUE_MARKED(objspace, obj) && !RVALUE_MARKING(objspace, obj);
+}
+
+static inline int
+RVALUE_WHITE_P(rb_objspace_t *objspace, VALUE obj)
+{
+    return !RVALUE_MARKED(objspace, obj);
+}
+
+bool
+rb_gc_impl_gc_enabled_p(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    return !dont_gc_val();
+}
+
+void
+rb_gc_impl_gc_enable(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    dont_gc_off();
+}
+
+void
+rb_gc_impl_gc_disable(void *objspace_ptr, bool finish_current_gc)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (finish_current_gc) {
+        gc_rest(objspace);
+    }
+
+    dont_gc_on();
+}
+
+/*
+  --------------------------- ObjectSpace -----------------------------
+*/
+
+static inline void *
+calloc1(size_t n)
+{
+    return calloc(1, n);
+}
+
+void
+rb_gc_impl_set_event_hook(void *objspace_ptr, const rb_event_flag_t event)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    objspace->hook_events = event & RUBY_INTERNAL_EVENT_OBJSPACE_MASK;
+    objspace->flags.has_newobj_hook = !!(objspace->hook_events & RUBY_INTERNAL_EVENT_NEWOBJ);
+}
+
+unsigned long long
+rb_gc_impl_get_total_time(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    unsigned long long marking_time = objspace->profile.marking_time_ns;
+    unsigned long long sweeping_time = objspace->profile.sweeping_time_ns;
+
+    return marking_time + sweeping_time;
+}
+
+void
+rb_gc_impl_set_measure_total_time(void *objspace_ptr, VALUE flag)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    objspace->flags.measure_gc = RTEST(flag) ? TRUE : FALSE;
+}
+
+bool
+rb_gc_impl_get_measure_total_time(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    return objspace->flags.measure_gc;
+}
+
+static size_t
+minimum_slots_for_heap(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    size_t heap_idx = heap - heaps;
+    return gc_params.heap_init_slots[heap_idx];
+}
+
+static int
+object_id_cmp(st_data_t x, st_data_t y)
+{
+    if (RB_TYPE_P(x, T_BIGNUM)) {
+        return !rb_big_eql(x, y);
+    }
+    else {
+        return x != y;
+    }
+}
+
+static st_index_t
+object_id_hash(st_data_t n)
+{
+    return FIX2LONG(rb_hash((VALUE)n));
+}
+
+#define OBJ_ID_INCREMENT (RUBY_IMMEDIATE_MASK + 1)
+#define OBJ_ID_INITIAL (OBJ_ID_INCREMENT)
+
+static const struct st_hash_type object_id_hash_type = {
+    object_id_cmp,
+    object_id_hash,
+};
+
+/* garbage objects will be collected soon. */
+bool
+rb_gc_impl_garbage_object_p(void *objspace_ptr, VALUE ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    bool dead = false;
+
+    asan_unpoisoning_object(ptr) {
+        switch (BUILTIN_TYPE(ptr)) {
+          case T_NONE:
+          case T_MOVED:
+          case T_ZOMBIE:
+            dead = true;
+            break;
+          default:
+            break;
+        }
+    }
+
+    if (dead) return true;
+    return is_lazy_sweeping(objspace) && GET_HEAP_PAGE(ptr)->flags.before_sweep &&
+        !RVALUE_MARKED(objspace, ptr);
+}
+
+VALUE
+rb_gc_impl_object_id_to_ref(void *objspace_ptr, VALUE object_id)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    VALUE obj;
+    if (st_lookup(objspace->id_to_obj_tbl, object_id, &obj) &&
+            !rb_gc_impl_garbage_object_p(objspace, obj)) {
+        return obj;
+    }
+
+    if (rb_funcall(object_id, rb_intern(">="), 1, ULL2NUM(objspace->next_object_id))) {
+        rb_raise(rb_eRangeError, "%+"PRIsVALUE" is not id value", rb_funcall(object_id, rb_intern("to_s"), 1, INT2FIX(10)));
+    }
+    else {
+        rb_raise(rb_eRangeError, "%+"PRIsVALUE" is recycled object", rb_funcall(object_id, rb_intern("to_s"), 1, INT2FIX(10)));
+    }
+}
+
+VALUE
+rb_gc_impl_object_id(void *objspace_ptr, VALUE obj)
+{
+    VALUE id;
+    rb_objspace_t *objspace = objspace_ptr;
+
+    unsigned int lev = rb_gc_vm_lock();
+    if (FL_TEST(obj, FL_SEEN_OBJ_ID)) {
+        st_data_t val;
+        if (st_lookup(objspace->obj_to_id_tbl, (st_data_t)obj, &val)) {
+            id = (VALUE)val;
+        }
+        else {
+            rb_bug("rb_gc_impl_object_id: FL_SEEN_OBJ_ID flag set but not found in table");
+        }
+    }
+    else {
+        GC_ASSERT(!st_lookup(objspace->obj_to_id_tbl, (st_data_t)obj, NULL));
+
+        id = ULL2NUM(objspace->next_object_id);
+        objspace->next_object_id += OBJ_ID_INCREMENT;
+
+        st_insert(objspace->obj_to_id_tbl, (st_data_t)obj, (st_data_t)id);
+        st_insert(objspace->id_to_obj_tbl, (st_data_t)id, (st_data_t)obj);
+        FL_SET(obj, FL_SEEN_OBJ_ID);
+    }
+    rb_gc_vm_unlock(lev);
+
+    return id;
+}
+
+static void free_stack_chunks(mark_stack_t *);
+static void mark_stack_free_cache(mark_stack_t *);
+static void heap_page_free(rb_objspace_t *objspace, struct heap_page *page);
+
+static inline void
+heap_page_add_freeobj(rb_objspace_t *objspace, struct heap_page *page, VALUE obj)
+{
+    asan_unpoison_object(obj, false);
+
+    asan_unlock_freelist(page);
+
+    struct free_slot *slot = (struct free_slot *)obj;
+    slot->flags = 0;
+    slot->next = page->freelist;
+    page->freelist = slot;
+    asan_lock_freelist(page);
+
+    RVALUE_AGE_RESET(obj);
+
+    if (RGENGC_CHECK_MODE &&
+        /* obj should belong to page */
+        !(page->start <= (uintptr_t)obj &&
+          (uintptr_t)obj   <  ((uintptr_t)page->start + (page->total_slots * page->slot_size)) &&
+          obj % BASE_SLOT_SIZE == 0)) {
+        rb_bug("heap_page_add_freeobj: %p is not rvalue.", (void *)obj);
+    }
+
+    asan_poison_object(obj);
+    gc_report(3, objspace, "heap_page_add_freeobj: add %p to freelist\n", (void *)obj);
+}
+
+static void
+heap_allocatable_slots_expand(rb_objspace_t *objspace,
+        rb_heap_t *heap, size_t free_slots, size_t total_slots)
+{
+    double goal_ratio = gc_params.heap_free_slots_goal_ratio;
+    size_t target_total_slots;
+
+    if (goal_ratio == 0.0) {
+        target_total_slots = (size_t)(total_slots * gc_params.growth_factor);
+    }
+    else if (total_slots == 0) {
+        target_total_slots = minimum_slots_for_heap(objspace, heap);
+    }
+    else {
+        /* Find `f' where free_slots = f * total_slots * goal_ratio
+         * => f = (total_slots - free_slots) / ((1 - goal_ratio) * total_slots)
+         */
+        double f = (double)(total_slots - free_slots) / ((1 - goal_ratio) * total_slots);
+
+        if (f > gc_params.growth_factor) f = gc_params.growth_factor;
+        if (f < 1.0) f = 1.1;
+
+        target_total_slots = (size_t)(f * total_slots);
+
+        if (0) {
+            fprintf(stderr,
+                    "free_slots(%8"PRIuSIZE")/total_slots(%8"PRIuSIZE")=%1.2f,"
+                    " G(%1.2f), f(%1.2f),"
+                    " total_slots(%8"PRIuSIZE") => target_total_slots(%8"PRIuSIZE")\n",
+                    free_slots, total_slots, free_slots/(double)total_slots,
+                    goal_ratio, f, total_slots, target_total_slots);
+        }
+    }
+
+    if (gc_params.growth_max_slots > 0) {
+        size_t max_total_slots = (size_t)(total_slots + gc_params.growth_max_slots);
+        if (target_total_slots > max_total_slots) target_total_slots = max_total_slots;
+    }
+
+    size_t extend_slot_count = target_total_slots - total_slots;
+    /* Extend by at least 1 page. */
+    if (extend_slot_count == 0) extend_slot_count = 1;
+
+    objspace->heap_pages.allocatable_slots += extend_slot_count;
+}
+
+static inline void
+heap_add_freepage(rb_heap_t *heap, struct heap_page *page)
+{
+    asan_unlock_freelist(page);
+    GC_ASSERT(page->free_slots != 0);
+    GC_ASSERT(page->freelist != NULL);
+
+    page->free_next = heap->free_pages;
+    heap->free_pages = page;
+
+    RUBY_DEBUG_LOG("page:%p freelist:%p", (void *)page, (void *)page->freelist);
+
+    asan_lock_freelist(page);
+}
+
+static inline void
+heap_add_poolpage(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *page)
+{
+    asan_unlock_freelist(page);
+    GC_ASSERT(page->free_slots != 0);
+    GC_ASSERT(page->freelist != NULL);
+
+    page->free_next = heap->pooled_pages;
+    heap->pooled_pages = page;
+    objspace->rincgc.pooled_slots += page->free_slots;
+
+    asan_lock_freelist(page);
+}
+
+static void
+heap_unlink_page(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *page)
+{
+    ccan_list_del(&page->page_node);
+    heap->total_pages--;
+    heap->total_slots -= page->total_slots;
+}
+
+static void
+gc_aligned_free(void *ptr, size_t size)
+{
+#if defined __MINGW32__
+    __mingw_aligned_free(ptr);
+#elif defined _WIN32
+    _aligned_free(ptr);
+#elif defined(HAVE_POSIX_MEMALIGN) || defined(HAVE_MEMALIGN)
+    free(ptr);
+#else
+    free(((void**)ptr)[-1]);
+#endif
+}
+
+static void
+heap_page_body_free(struct heap_page_body *page_body)
+{
+    GC_ASSERT((uintptr_t)page_body % HEAP_PAGE_ALIGN == 0);
+
+    if (HEAP_PAGE_ALLOC_USE_MMAP) {
+#ifdef HAVE_MMAP
+        GC_ASSERT(HEAP_PAGE_SIZE % sysconf(_SC_PAGE_SIZE) == 0);
+        if (munmap(page_body, HEAP_PAGE_SIZE)) {
+            rb_bug("heap_page_body_free: munmap failed");
+        }
+#endif
+    }
+    else {
+        gc_aligned_free(page_body, HEAP_PAGE_SIZE);
+    }
+}
+
+static void
+heap_page_free(rb_objspace_t *objspace, struct heap_page *page)
+{
+    objspace->heap_pages.freed_pages++;
+    heap_page_body_free(page->body);
+    free(page);
+}
+
+static void
+heap_pages_free_unused_pages(rb_objspace_t *objspace)
+{
+    size_t pages_to_keep_count =
+        // Get number of pages estimated for the smallest size pool
+        CEILDIV(objspace->heap_pages.allocatable_slots, HEAP_PAGE_OBJ_LIMIT) *
+            // Estimate the average slot size multiple
+            (1 << (HEAP_COUNT / 2));
+
+    if (objspace->empty_pages != NULL && objspace->empty_pages_count > pages_to_keep_count) {
+        GC_ASSERT(objspace->empty_pages_count > 0);
+        objspace->empty_pages = NULL;
+        objspace->empty_pages_count = 0;
+
+        size_t i, j;
+        for (i = j = 0; i < rb_darray_size(objspace->heap_pages.sorted); i++) {
+            struct heap_page *page = rb_darray_get(objspace->heap_pages.sorted, i);
+
+            if (heap_page_in_global_empty_pages_pool(objspace, page) && pages_to_keep_count == 0) {
+                heap_page_free(objspace, page);
+            }
+            else {
+                if (heap_page_in_global_empty_pages_pool(objspace, page) && pages_to_keep_count > 0) {
+                    page->free_next = objspace->empty_pages;
+                    objspace->empty_pages = page;
+                    objspace->empty_pages_count++;
+                    pages_to_keep_count--;
+                }
+
+                if (i != j) {
+                    rb_darray_set(objspace->heap_pages.sorted, j, page);
+                }
+                j++;
+            }
+        }
+
+        rb_darray_pop(objspace->heap_pages.sorted, i - j);
+        GC_ASSERT(rb_darray_size(objspace->heap_pages.sorted) == j);
+
+        struct heap_page *hipage = rb_darray_get(objspace->heap_pages.sorted, rb_darray_size(objspace->heap_pages.sorted) - 1);
+        uintptr_t himem = (uintptr_t)hipage->body + HEAP_PAGE_SIZE;
+        GC_ASSERT(himem <= heap_pages_himem);
+        heap_pages_himem = himem;
+
+        struct heap_page *lopage = rb_darray_get(objspace->heap_pages.sorted, 0);
+        uintptr_t lomem = (uintptr_t)lopage->body + sizeof(struct heap_page_header);
+        GC_ASSERT(lomem >= heap_pages_lomem);
+        heap_pages_lomem = lomem;
+    }
+}
+
+static void *
+gc_aligned_malloc(size_t alignment, size_t size)
+{
+    /* alignment must be a power of 2 */
+    GC_ASSERT(((alignment - 1) & alignment) == 0);
+    GC_ASSERT(alignment % sizeof(void*) == 0);
+
+    void *res;
+
+#if defined __MINGW32__
+    res = __mingw_aligned_malloc(size, alignment);
+#elif defined _WIN32
+    void *_aligned_malloc(size_t, size_t);
+    res = _aligned_malloc(size, alignment);
+#elif defined(HAVE_POSIX_MEMALIGN)
+    if (posix_memalign(&res, alignment, size) != 0) {
+        return NULL;
+    }
+#elif defined(HAVE_MEMALIGN)
+    res = memalign(alignment, size);
+#else
+    char* aligned;
+    res = malloc(alignment + size + sizeof(void*));
+    aligned = (char*)res + alignment + sizeof(void*);
+    aligned -= ((VALUE)aligned & (alignment - 1));
+    ((void**)aligned)[-1] = res;
+    res = (void*)aligned;
+#endif
+
+    GC_ASSERT((uintptr_t)res % alignment == 0);
+
+    return res;
+}
+
+static struct heap_page_body *
+heap_page_body_allocate(void)
+{
+    struct heap_page_body *page_body;
+
+    if (HEAP_PAGE_ALLOC_USE_MMAP) {
+#ifdef HAVE_MMAP
+        GC_ASSERT(HEAP_PAGE_ALIGN % sysconf(_SC_PAGE_SIZE) == 0);
+
+        size_t mmap_size = HEAP_PAGE_ALIGN + HEAP_PAGE_SIZE;
+        char *ptr = mmap(NULL, mmap_size,
+                         PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+        if (ptr == MAP_FAILED) {
+            return NULL;
+        }
+
+        // If we are building `default.c` as part of the ruby executable, we
+        // may just call `ruby_annotate_mmap`.  But if we are building
+        // `default.c` as a shared library, we will not have access to private
+        // symbols, and we have to either call prctl directly or make our own
+        // wrapper.
+#if defined(HAVE_SYS_PRCTL_H) && defined(PR_SET_VMA) && defined(PR_SET_VMA_ANON_NAME)
+        prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, ptr, mmap_size, "Ruby:GC:default:heap_page_body_allocate");
+        errno = 0;
+#endif
+
+        char *aligned = ptr + HEAP_PAGE_ALIGN;
+        aligned -= ((VALUE)aligned & (HEAP_PAGE_ALIGN - 1));
+        GC_ASSERT(aligned > ptr);
+        GC_ASSERT(aligned <= ptr + HEAP_PAGE_ALIGN);
+
+        size_t start_out_of_range_size = aligned - ptr;
+        GC_ASSERT(start_out_of_range_size % sysconf(_SC_PAGE_SIZE) == 0);
+        if (start_out_of_range_size > 0) {
+            if (munmap(ptr, start_out_of_range_size)) {
+                rb_bug("heap_page_body_allocate: munmap failed for start");
+            }
+        }
+
+        size_t end_out_of_range_size = HEAP_PAGE_ALIGN - start_out_of_range_size;
+        GC_ASSERT(end_out_of_range_size % sysconf(_SC_PAGE_SIZE) == 0);
+        if (end_out_of_range_size > 0) {
+            if (munmap(aligned + HEAP_PAGE_SIZE, end_out_of_range_size)) {
+                rb_bug("heap_page_body_allocate: munmap failed for end");
+            }
+        }
+
+        page_body = (struct heap_page_body *)aligned;
+#endif
+    }
+    else {
+        page_body = gc_aligned_malloc(HEAP_PAGE_ALIGN, HEAP_PAGE_SIZE);
+    }
+
+    GC_ASSERT((uintptr_t)page_body % HEAP_PAGE_ALIGN == 0);
+
+    return page_body;
+}
+
+static struct heap_page *
+heap_page_resurrect(rb_objspace_t *objspace)
+{
+    struct heap_page *page = NULL;
+    if (objspace->empty_pages != NULL) {
+        GC_ASSERT(objspace->empty_pages_count > 0);
+        objspace->empty_pages_count--;
+        page = objspace->empty_pages;
+        objspace->empty_pages = page->free_next;
+    }
+
+    return page;
+}
+
+static struct heap_page *
+heap_page_allocate(rb_objspace_t *objspace)
+{
+    struct heap_page_body *page_body = heap_page_body_allocate();
+    if (page_body == 0) {
+        rb_memerror();
+    }
+
+    struct heap_page *page = calloc1(sizeof(struct heap_page));
+    if (page == 0) {
+        heap_page_body_free(page_body);
+        rb_memerror();
+    }
+
+    uintptr_t start = (uintptr_t)page_body + sizeof(struct heap_page_header);
+    uintptr_t end = (uintptr_t)page_body + HEAP_PAGE_SIZE;
+
+    size_t lo = 0;
+    size_t hi = rb_darray_size(objspace->heap_pages.sorted);
+    while (lo < hi) {
+        struct heap_page *mid_page;
+
+        size_t mid = (lo + hi) / 2;
+        mid_page = rb_darray_get(objspace->heap_pages.sorted, mid);
+        if ((uintptr_t)mid_page->start < start) {
+            lo = mid + 1;
+        }
+        else if ((uintptr_t)mid_page->start > start) {
+            hi = mid;
+        }
+        else {
+            rb_bug("same heap page is allocated: %p at %"PRIuVALUE, (void *)page_body, (VALUE)mid);
+        }
+    }
+
+    rb_darray_insert(&objspace->heap_pages.sorted, hi, page);
+
+    if (heap_pages_lomem == 0 || heap_pages_lomem > start) heap_pages_lomem = start;
+    if (heap_pages_himem < end) heap_pages_himem = end;
+
+    page->body = page_body;
+    page_body->header.page = page;
+
+    objspace->heap_pages.allocated_pages++;
+
+    return page;
+}
+
+static void
+heap_add_page(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *page)
+{
+    /* Adding to eden heap during incremental sweeping is forbidden */
+    GC_ASSERT(!heap->sweeping_page);
+    GC_ASSERT(heap_page_in_global_empty_pages_pool(objspace, page));
+
+    /* adjust obj_limit (object number available in this page) */
+    uintptr_t start = (uintptr_t)page->body + sizeof(struct heap_page_header);
+    if (start % BASE_SLOT_SIZE != 0) {
+        int delta = BASE_SLOT_SIZE - (start % BASE_SLOT_SIZE);
+        start = start + delta;
+        GC_ASSERT(NUM_IN_PAGE(start) == 0 || NUM_IN_PAGE(start) == 1);
+
+        /* Find a num in page that is evenly divisible by `stride`.
+         * This is to ensure that objects are aligned with bit planes.
+         * In other words, ensure there are an even number of objects
+         * per bit plane. */
+        if (NUM_IN_PAGE(start) == 1) {
+            start += heap->slot_size - BASE_SLOT_SIZE;
+        }
+
+        GC_ASSERT(NUM_IN_PAGE(start) * BASE_SLOT_SIZE % heap->slot_size == 0);
+    }
+
+    int slot_count = (int)((HEAP_PAGE_SIZE - (start - (uintptr_t)page->body))/heap->slot_size);
+
+    page->start = start;
+    page->total_slots = slot_count;
+    page->slot_size = heap->slot_size;
+    page->heap = heap;
+
+    asan_unlock_freelist(page);
+    page->freelist = NULL;
+    asan_unpoison_memory_region(page->body, HEAP_PAGE_SIZE, false);
+    for (VALUE p = (VALUE)start; p < start + (slot_count * heap->slot_size); p += heap->slot_size) {
+        heap_page_add_freeobj(objspace, page, p);
+    }
+    asan_lock_freelist(page);
+
+    page->free_slots = slot_count;
+
+    heap->total_allocated_pages++;
+
+    ccan_list_add_tail(&heap->pages, &page->page_node);
+    heap->total_pages++;
+    heap->total_slots += page->total_slots;
+}
+
+static int
+heap_page_allocate_and_initialize(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    if (objspace->heap_pages.allocatable_slots > 0) {
+        gc_report(1, objspace, "heap_page_allocate_and_initialize: rb_darray_size(objspace->heap_pages.sorted): %"PRIdSIZE", "
+                  "allocatable_slots: %"PRIdSIZE", heap->total_pages: %"PRIdSIZE"\n",
+                  rb_darray_size(objspace->heap_pages.sorted), objspace->heap_pages.allocatable_slots, heap->total_pages);
+
+        struct heap_page *page = heap_page_resurrect(objspace);
+        if (page == NULL) {
+            page = heap_page_allocate(objspace);
+        }
+        heap_add_page(objspace, heap, page);
+        heap_add_freepage(heap, page);
+
+        if (objspace->heap_pages.allocatable_slots > (size_t)page->total_slots) {
+            objspace->heap_pages.allocatable_slots -= page->total_slots;
+        }
+        else {
+            objspace->heap_pages.allocatable_slots = 0;
+        }
+
+        return true;
+    }
+
+    return false;
+}
+
+static void
+heap_page_allocate_and_initialize_force(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    size_t prev_allocatable_slots = objspace->heap_pages.allocatable_slots;
+    // Set allocatable slots to 1 to force a page to be created.
+    objspace->heap_pages.allocatable_slots = 1;
+    heap_page_allocate_and_initialize(objspace, heap);
+    GC_ASSERT(heap->free_pages != NULL);
+    objspace->heap_pages.allocatable_slots = prev_allocatable_slots;
+}
+
+static void
+gc_continue(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    unsigned int lock_lev;
+    gc_enter(objspace, gc_enter_event_continue, &lock_lev);
+
+    /* Continue marking if in incremental marking. */
+    if (is_incremental_marking(objspace)) {
+        if (gc_marks_continue(objspace, heap)) {
+            gc_sweep(objspace);
+        }
+    }
+
+    /* Continue sweeping if in lazy sweeping or the previous incremental
+     * marking finished and did not yield a free page. */
+    if (heap->free_pages == NULL && is_lazy_sweeping(objspace)) {
+        gc_sweep_continue(objspace, heap);
+    }
+
+    gc_exit(objspace, gc_enter_event_continue, &lock_lev);
+}
+
+static void
+heap_prepare(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    GC_ASSERT(heap->free_pages == NULL);
+
+    if (heap->total_slots < gc_params.heap_init_slots[heap - heaps] &&
+            heap->sweeping_page == NULL) {
+        heap_page_allocate_and_initialize_force(objspace, heap);
+        GC_ASSERT(heap->free_pages != NULL);
+        return;
+    }
+
+    /* Continue incremental marking or lazy sweeping, if in any of those steps. */
+    gc_continue(objspace, heap);
+
+    if (heap->free_pages == NULL) {
+        heap_page_allocate_and_initialize(objspace, heap);
+    }
+
+    /* If we still don't have a free page and not allowed to create a new page,
+     * we should start a new GC cycle. */
+    if (heap->free_pages == NULL) {
+        if (gc_start(objspace, GPR_FLAG_NEWOBJ) == FALSE) {
+            rb_memerror();
+        }
+        else {
+            if (objspace->heap_pages.allocatable_slots == 0 && !gc_config_full_mark_val) {
+                heap_allocatable_slots_expand(objspace, heap,
+                        heap->freed_slots + heap->empty_slots,
+                        heap->total_slots);
+                GC_ASSERT(objspace->heap_pages.allocatable_slots > 0);
+            }
+            /* Do steps of incremental marking or lazy sweeping if the GC run permits. */
+            gc_continue(objspace, heap);
+
+            /* If we're not incremental marking (e.g. a minor GC) or finished
+             * sweeping and still don't have a free page, then
+             * gc_sweep_finish_heap should allow us to create a new page. */
+            if (heap->free_pages == NULL && !heap_page_allocate_and_initialize(objspace, heap)) {
+                if (gc_needs_major_flags == GPR_FLAG_NONE) {
+                    rb_bug("cannot create a new page after GC");
+                }
+                else { // Major GC is required, which will allow us to create new page
+                    if (gc_start(objspace, GPR_FLAG_NEWOBJ) == FALSE) {
+                        rb_memerror();
+                    }
+                    else {
+                        /* Do steps of incremental marking or lazy sweeping. */
+                        gc_continue(objspace, heap);
+
+                        if (heap->free_pages == NULL &&
+                                !heap_page_allocate_and_initialize(objspace, heap)) {
+                            rb_bug("cannot create a new page after major GC");
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    GC_ASSERT(heap->free_pages != NULL);
+}
+
+static inline VALUE
+newobj_fill(VALUE obj, VALUE v1, VALUE v2, VALUE v3)
+{
+    VALUE *p = (VALUE *)obj;
+    p[2] = v1;
+    p[3] = v2;
+    p[4] = v3;
+    return obj;
+}
+
+#if GC_DEBUG
+static inline const char*
+rb_gc_impl_source_location_cstr(int *ptr)
+{
+    /* We could directly refer `rb_source_location_cstr()` before, but not any
+     * longer.  We have to heavy lift using our debugging API. */
+    if (! ptr) {
+        return NULL;
+    }
+    else if (! (*ptr = rb_sourceline())) {
+        return NULL;
+    }
+    else {
+        return rb_sourcefile();
+    }
+}
+#endif
+
+static inline VALUE
+newobj_init(VALUE klass, VALUE flags, int wb_protected, rb_objspace_t *objspace, VALUE obj)
+{
+#if !__has_feature(memory_sanitizer)
+    GC_ASSERT(BUILTIN_TYPE(obj) == T_NONE);
+    GC_ASSERT((flags & FL_WB_PROTECTED) == 0);
+#endif
+    RBASIC(obj)->flags = flags;
+    *((VALUE *)&RBASIC(obj)->klass) = klass;
+
+    int t = flags & RUBY_T_MASK;
+    if (t == T_CLASS || t == T_MODULE || t == T_ICLASS) {
+        RVALUE_AGE_SET_CANDIDATE(objspace, obj);
+    }
+
+#if RACTOR_CHECK_MODE
+    void rb_ractor_setup_belonging(VALUE obj);
+    rb_ractor_setup_belonging(obj);
+#endif
+
+#if RGENGC_CHECK_MODE
+    newobj_fill(obj, 0, 0, 0);
+
+    int lev = rb_gc_vm_lock_no_barrier();
+    {
+        check_rvalue_consistency(objspace, obj);
+
+        GC_ASSERT(RVALUE_MARKED(objspace, obj) == FALSE);
+        GC_ASSERT(RVALUE_MARKING(objspace, obj) == FALSE);
+        GC_ASSERT(RVALUE_OLD_P(objspace, obj) == FALSE);
+        GC_ASSERT(RVALUE_WB_UNPROTECTED(objspace, obj) == FALSE);
+
+        if (RVALUE_REMEMBERED(objspace, obj)) rb_bug("newobj: %s is remembered.", rb_obj_info(obj));
+    }
+    rb_gc_vm_unlock_no_barrier(lev);
+#endif
+
+    if (RB_UNLIKELY(wb_protected == FALSE)) {
+        MARK_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(obj), obj);
+    }
+
+#if RGENGC_PROFILE
+    if (wb_protected) {
+        objspace->profile.total_generated_normal_object_count++;
+#if RGENGC_PROFILE >= 2
+        objspace->profile.generated_normal_object_count_types[BUILTIN_TYPE(obj)]++;
+#endif
+    }
+    else {
+        objspace->profile.total_generated_shady_object_count++;
+#if RGENGC_PROFILE >= 2
+        objspace->profile.generated_shady_object_count_types[BUILTIN_TYPE(obj)]++;
+#endif
+    }
+#endif
+
+#if GC_DEBUG
+    GET_RVALUE_OVERHEAD(obj)->file = rb_gc_impl_source_location_cstr(&GET_RVALUE_OVERHEAD(obj)->line);
+    GC_ASSERT(!SPECIAL_CONST_P(obj)); /* check alignment */
+#endif
+
+    gc_report(5, objspace, "newobj: %s\n", rb_obj_info(obj));
+
+    RUBY_DEBUG_LOG("obj:%p (%s)", (void *)obj, rb_obj_info(obj));
+    return obj;
+}
+
+size_t
+rb_gc_impl_obj_slot_size(VALUE obj)
+{
+    return GET_HEAP_PAGE(obj)->slot_size - RVALUE_OVERHEAD;
+}
+
+static inline size_t
+heap_slot_size(unsigned char pool_id)
+{
+    GC_ASSERT(pool_id < HEAP_COUNT);
+
+    size_t slot_size = (1 << pool_id) * BASE_SLOT_SIZE;
+
+#if RGENGC_CHECK_MODE
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    GC_ASSERT(heaps[pool_id].slot_size == (short)slot_size);
+#endif
+
+    slot_size -= RVALUE_OVERHEAD;
+
+    return slot_size;
+}
+
+bool
+rb_gc_impl_size_allocatable_p(size_t size)
+{
+    return size <= heap_slot_size(HEAP_COUNT - 1);
+}
+
+static inline VALUE
+ractor_cache_allocate_slot(rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache,
+                           size_t heap_idx)
+{
+    rb_ractor_newobj_heap_cache_t *heap_cache = &cache->heap_caches[heap_idx];
+    struct free_slot *p = heap_cache->freelist;
+
+    if (RB_UNLIKELY(is_incremental_marking(objspace))) {
+        // Not allowed to allocate without running an incremental marking step
+        if (cache->incremental_mark_step_allocated_slots >= INCREMENTAL_MARK_STEP_ALLOCATIONS) {
+            return Qfalse;
+        }
+
+        if (p) {
+            cache->incremental_mark_step_allocated_slots++;
+        }
+    }
+
+    if (RB_LIKELY(p)) {
+        VALUE obj = (VALUE)p;
+        MAYBE_UNUSED(const size_t) stride = heap_slot_size(heap_idx);
+        heap_cache->freelist = p->next;
+        asan_unpoison_memory_region(p, stride, true);
+#if RGENGC_CHECK_MODE
+        GC_ASSERT(rb_gc_impl_obj_slot_size(obj) == stride);
+        // zero clear
+        MEMZERO((char *)obj, char, stride);
+#endif
+        return obj;
+    }
+    else {
+        return Qfalse;
+    }
+}
+
+static struct heap_page *
+heap_next_free_page(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    struct heap_page *page;
+
+    if (heap->free_pages == NULL) {
+        heap_prepare(objspace, heap);
+    }
+
+    page = heap->free_pages;
+    heap->free_pages = page->free_next;
+
+    GC_ASSERT(page->free_slots != 0);
+
+    asan_unlock_freelist(page);
+
+    return page;
+}
+
+static inline void
+ractor_cache_set_page(rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx,
+                      struct heap_page *page)
+{
+    gc_report(3, objspace, "ractor_set_cache: Using page %p\n", (void *)page->body);
+
+    rb_ractor_newobj_heap_cache_t *heap_cache = &cache->heap_caches[heap_idx];
+
+    GC_ASSERT(heap_cache->freelist == NULL);
+    GC_ASSERT(page->free_slots != 0);
+    GC_ASSERT(page->freelist != NULL);
+
+    heap_cache->using_page = page;
+    heap_cache->freelist = page->freelist;
+    page->free_slots = 0;
+    page->freelist = NULL;
+
+    asan_unpoison_object((VALUE)heap_cache->freelist, false);
+    GC_ASSERT(RB_TYPE_P((VALUE)heap_cache->freelist, T_NONE));
+    asan_poison_object((VALUE)heap_cache->freelist);
+}
+
+static inline size_t
+heap_idx_for_size(size_t size)
+{
+    size += RVALUE_OVERHEAD;
+
+    size_t slot_count = CEILDIV(size, BASE_SLOT_SIZE);
+
+    /* heap_idx is ceil(log2(slot_count)) */
+    size_t heap_idx = 64 - nlz_int64(slot_count - 1);
+
+    if (heap_idx >= HEAP_COUNT) {
+        rb_bug("heap_idx_for_size: allocation size too large "
+               "(size=%"PRIuSIZE"u, heap_idx=%"PRIuSIZE"u)", size, heap_idx);
+    }
+
+#if RGENGC_CHECK_MODE
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    GC_ASSERT(size <= (size_t)heaps[heap_idx].slot_size);
+    if (heap_idx > 0) GC_ASSERT(size > (size_t)heaps[heap_idx - 1].slot_size);
+#endif
+
+    return heap_idx;
+}
+
+size_t
+rb_gc_impl_heap_id_for_size(void *objspace_ptr, size_t size)
+{
+    return heap_idx_for_size(size);
+}
+
+
+static size_t heap_sizes[HEAP_COUNT + 1] = { 0 };
+
+size_t *
+rb_gc_impl_heap_sizes(void *objspace_ptr)
+{
+    if (heap_sizes[0] == 0) {
+        for (unsigned char i = 0; i < HEAP_COUNT; i++) {
+            heap_sizes[i] = heap_slot_size(i);
+        }
+    }
+
+    return heap_sizes;
+}
+
+NOINLINE(static VALUE newobj_cache_miss(rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx, bool vm_locked));
+
+static VALUE
+newobj_cache_miss(rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx, bool vm_locked)
+{
+    rb_heap_t *heap = &heaps[heap_idx];
+    VALUE obj = Qfalse;
+
+    unsigned int lev = 0;
+    bool unlock_vm = false;
+
+    if (!vm_locked) {
+        lev = rb_gc_cr_lock();
+        vm_locked = true;
+        unlock_vm = true;
+    }
+
+    {
+        if (is_incremental_marking(objspace)) {
+            gc_continue(objspace, heap);
+            cache->incremental_mark_step_allocated_slots = 0;
+
+            // Retry allocation after resetting incremental_mark_step_allocated_slots
+            obj = ractor_cache_allocate_slot(objspace, cache, heap_idx);
+        }
+
+        if (obj == Qfalse) {
+            // Get next free page (possibly running GC)
+            struct heap_page *page = heap_next_free_page(objspace, heap);
+            ractor_cache_set_page(objspace, cache, heap_idx, page);
+
+            // Retry allocation after moving to new page
+            obj = ractor_cache_allocate_slot(objspace, cache, heap_idx);
+        }
+    }
+
+    if (unlock_vm) {
+        rb_gc_cr_unlock(lev);
+    }
+
+    if (RB_UNLIKELY(obj == Qfalse)) {
+        rb_memerror();
+    }
+    return obj;
+}
+
+static VALUE
+newobj_alloc(rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx, bool vm_locked)
+{
+    VALUE obj = ractor_cache_allocate_slot(objspace, cache, heap_idx);
+
+    if (RB_UNLIKELY(obj == Qfalse)) {
+        obj = newobj_cache_miss(objspace, cache, heap_idx, vm_locked);
+    }
+
+    rb_heap_t *heap = &heaps[heap_idx];
+    heap->total_allocated_objects++;
+    GC_ASSERT(rb_gc_multi_ractor_p() ||
+        heap->total_slots >=
+            (heap->total_allocated_objects - heap->total_freed_objects - heap->final_slots_count));
+
+    return obj;
+}
+
+ALWAYS_INLINE(static VALUE newobj_slowpath(VALUE klass, VALUE flags, rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, int wb_protected, size_t heap_idx));
+
+static inline VALUE
+newobj_slowpath(VALUE klass, VALUE flags, rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, int wb_protected, size_t heap_idx)
+{
+    VALUE obj;
+    unsigned int lev;
+
+    lev = rb_gc_cr_lock();
+    {
+        if (RB_UNLIKELY(during_gc || ruby_gc_stressful)) {
+            if (during_gc) {
+                dont_gc_on();
+                during_gc = 0;
+                rb_bug("object allocation during garbage collection phase");
+            }
+
+            if (ruby_gc_stressful) {
+                if (!garbage_collect(objspace, GPR_FLAG_NEWOBJ)) {
+                    rb_memerror();
+                }
+            }
+        }
+
+        obj = newobj_alloc(objspace, cache, heap_idx, true);
+        newobj_init(klass, flags, wb_protected, objspace, obj);
+    }
+    rb_gc_cr_unlock(lev);
+
+    return obj;
+}
+
+NOINLINE(static VALUE newobj_slowpath_wb_protected(VALUE klass, VALUE flags,
+                                                   rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx));
+NOINLINE(static VALUE newobj_slowpath_wb_unprotected(VALUE klass, VALUE flags,
+                                                     rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx));
+
+static VALUE
+newobj_slowpath_wb_protected(VALUE klass, VALUE flags, rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx)
+{
+    return newobj_slowpath(klass, flags, objspace, cache, TRUE, heap_idx);
+}
+
+static VALUE
+newobj_slowpath_wb_unprotected(VALUE klass, VALUE flags, rb_objspace_t *objspace, rb_ractor_newobj_cache_t *cache, size_t heap_idx)
+{
+    return newobj_slowpath(klass, flags, objspace, cache, FALSE, heap_idx);
+}
+
+VALUE
+rb_gc_impl_new_obj(void *objspace_ptr, void *cache_ptr, VALUE klass, VALUE flags, VALUE v1, VALUE v2, VALUE v3, bool wb_protected, size_t alloc_size)
+{
+    VALUE obj;
+    rb_objspace_t *objspace = objspace_ptr;
+
+    RB_DEBUG_COUNTER_INC(obj_newobj);
+    (void)RB_DEBUG_COUNTER_INC_IF(obj_newobj_wb_unprotected, !wb_protected);
+
+    if (RB_UNLIKELY(stress_to_class)) {
+        long cnt = RARRAY_LEN(stress_to_class);
+        for (long i = 0; i < cnt; i++) {
+            if (klass == RARRAY_AREF(stress_to_class, i)) rb_memerror();
+        }
+    }
+
+    size_t heap_idx = heap_idx_for_size(alloc_size);
+
+    rb_ractor_newobj_cache_t *cache = (rb_ractor_newobj_cache_t *)cache_ptr;
+
+    if (!RB_UNLIKELY(during_gc || ruby_gc_stressful) &&
+            wb_protected) {
+        obj = newobj_alloc(objspace, cache, heap_idx, false);
+        newobj_init(klass, flags, wb_protected, objspace, obj);
+    }
+    else {
+        RB_DEBUG_COUNTER_INC(obj_newobj_slowpath);
+
+        obj = wb_protected ?
+          newobj_slowpath_wb_protected(klass, flags, objspace, cache, heap_idx) :
+          newobj_slowpath_wb_unprotected(klass, flags, objspace, cache, heap_idx);
+    }
+
+    return newobj_fill(obj, v1, v2, v3);
+}
+
+static int
+ptr_in_page_body_p(const void *ptr, const void *memb)
+{
+    struct heap_page *page = *(struct heap_page **)memb;
+    uintptr_t p_body = (uintptr_t)page->body;
+
+    if ((uintptr_t)ptr >= p_body) {
+        return (uintptr_t)ptr < (p_body + HEAP_PAGE_SIZE) ? 0 : 1;
+    }
+    else {
+        return -1;
+    }
+}
+
+PUREFUNC(static inline struct heap_page *heap_page_for_ptr(rb_objspace_t *objspace, uintptr_t ptr);)
+static inline struct heap_page *
+heap_page_for_ptr(rb_objspace_t *objspace, uintptr_t ptr)
+{
+    struct heap_page **res;
+
+    if (ptr < (uintptr_t)heap_pages_lomem ||
+            ptr > (uintptr_t)heap_pages_himem) {
+        return NULL;
+    }
+
+    res = bsearch((void *)ptr, rb_darray_ref(objspace->heap_pages.sorted, 0),
+                  rb_darray_size(objspace->heap_pages.sorted), sizeof(struct heap_page *),
+                  ptr_in_page_body_p);
+
+    if (res) {
+        return *res;
+    }
+    else {
+        return NULL;
+    }
+}
+
+PUREFUNC(static inline bool is_pointer_to_heap(rb_objspace_t *objspace, const void *ptr);)
+static inline bool
+is_pointer_to_heap(rb_objspace_t *objspace, const void *ptr)
+{
+    register uintptr_t p = (uintptr_t)ptr;
+    register struct heap_page *page;
+
+    RB_DEBUG_COUNTER_INC(gc_isptr_trial);
+
+    if (p < heap_pages_lomem || p > heap_pages_himem) return FALSE;
+    RB_DEBUG_COUNTER_INC(gc_isptr_range);
+
+    if (p % BASE_SLOT_SIZE != 0) return FALSE;
+    RB_DEBUG_COUNTER_INC(gc_isptr_align);
+
+    page = heap_page_for_ptr(objspace, (uintptr_t)ptr);
+    if (page) {
+        RB_DEBUG_COUNTER_INC(gc_isptr_maybe);
+        if (heap_page_in_global_empty_pages_pool(objspace, page)) {
+            return FALSE;
+        }
+        else {
+            if (p < page->start) return FALSE;
+            if (p >= page->start + (page->total_slots * page->slot_size)) return FALSE;
+            if ((NUM_IN_PAGE(p) * BASE_SLOT_SIZE) % page->slot_size != 0) return FALSE;
+
+            return TRUE;
+        }
+    }
+    return FALSE;
+}
+
+bool
+rb_gc_impl_pointer_to_heap_p(void *objspace_ptr, const void *ptr)
+{
+    return is_pointer_to_heap(objspace_ptr, ptr);
+}
+
+#define ZOMBIE_OBJ_KEPT_FLAGS (FL_SEEN_OBJ_ID | FL_FINALIZE)
+
+void
+rb_gc_impl_make_zombie(void *objspace_ptr, VALUE obj, void (*dfree)(void *), void *data)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    struct RZombie *zombie = RZOMBIE(obj);
+    zombie->basic.flags = T_ZOMBIE | (zombie->basic.flags & ZOMBIE_OBJ_KEPT_FLAGS);
+    zombie->dfree = dfree;
+    zombie->data = data;
+    VALUE prev, next = heap_pages_deferred_final;
+    do {
+        zombie->next = prev = next;
+        next = RUBY_ATOMIC_VALUE_CAS(heap_pages_deferred_final, prev, obj);
+    } while (next != prev);
+
+    struct heap_page *page = GET_HEAP_PAGE(obj);
+    page->final_slots++;
+    page->heap->final_slots_count++;
+}
+
+static void
+obj_free_object_id(rb_objspace_t *objspace, VALUE obj)
+{
+    st_data_t o = (st_data_t)obj, id;
+
+    GC_ASSERT(BUILTIN_TYPE(obj) == T_NONE || FL_TEST(obj, FL_SEEN_OBJ_ID));
+    FL_UNSET(obj, FL_SEEN_OBJ_ID);
+
+    if (st_delete(objspace->obj_to_id_tbl, &o, &id)) {
+        GC_ASSERT(id);
+        st_delete(objspace->id_to_obj_tbl, &id, NULL);
+    }
+    else {
+        rb_bug("Object ID seen, but not in mapping table: %s", rb_obj_info(obj));
+    }
+}
+
+typedef int each_obj_callback(void *, void *, size_t, void *);
+typedef int each_page_callback(struct heap_page *, void *);
+
+struct each_obj_data {
+    rb_objspace_t *objspace;
+    bool reenable_incremental;
+
+    each_obj_callback *each_obj_callback;
+    each_page_callback *each_page_callback;
+    void *data;
+
+    struct heap_page **pages[HEAP_COUNT];
+    size_t pages_counts[HEAP_COUNT];
+};
+
+static VALUE
+objspace_each_objects_ensure(VALUE arg)
+{
+    struct each_obj_data *data = (struct each_obj_data *)arg;
+    rb_objspace_t *objspace = data->objspace;
+
+    /* Reenable incremental GC */
+    if (data->reenable_incremental) {
+        objspace->flags.dont_incremental = FALSE;
+    }
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        struct heap_page **pages = data->pages[i];
+        free(pages);
+    }
+
+    return Qnil;
+}
+
+static VALUE
+objspace_each_objects_try(VALUE arg)
+{
+    struct each_obj_data *data = (struct each_obj_data *)arg;
+    rb_objspace_t *objspace = data->objspace;
+
+    /* Copy pages from all heaps to their respective buffers. */
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        size_t size = heap->total_pages * sizeof(struct heap_page *);
+
+        struct heap_page **pages = malloc(size);
+        if (!pages) rb_memerror();
+
+        /* Set up pages buffer by iterating over all pages in the current eden
+         * heap. This will be a snapshot of the state of the heap before we
+         * call the callback over each page that exists in this buffer. Thus it
+         * is safe for the callback to allocate objects without possibly entering
+         * an infinite loop. */
+        struct heap_page *page = 0;
+        size_t pages_count = 0;
+        ccan_list_for_each(&heap->pages, page, page_node) {
+            pages[pages_count] = page;
+            pages_count++;
+        }
+        data->pages[i] = pages;
+        data->pages_counts[i] = pages_count;
+        GC_ASSERT(pages_count == heap->total_pages);
+    }
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        size_t pages_count = data->pages_counts[i];
+        struct heap_page **pages = data->pages[i];
+
+        struct heap_page *page = ccan_list_top(&heap->pages, struct heap_page, page_node);
+        for (size_t i = 0; i < pages_count; i++) {
+            /* If we have reached the end of the linked list then there are no
+             * more pages, so break. */
+            if (page == NULL) break;
+
+            /* If this page does not match the one in the buffer, then move to
+             * the next page in the buffer. */
+            if (pages[i] != page) continue;
+
+            uintptr_t pstart = (uintptr_t)page->start;
+            uintptr_t pend = pstart + (page->total_slots * heap->slot_size);
+
+            if (data->each_obj_callback &&
+                (*data->each_obj_callback)((void *)pstart, (void *)pend, heap->slot_size, data->data)) {
+                break;
+            }
+            if (data->each_page_callback &&
+                (*data->each_page_callback)(page, data->data)) {
+                break;
+            }
+
+            page = ccan_list_next(&heap->pages, page, page_node);
+        }
+    }
+
+    return Qnil;
+}
+
+static void
+objspace_each_exec(bool protected, struct each_obj_data *each_obj_data)
+{
+    /* Disable incremental GC */
+    rb_objspace_t *objspace = each_obj_data->objspace;
+    bool reenable_incremental = FALSE;
+    if (protected) {
+        reenable_incremental = !objspace->flags.dont_incremental;
+
+        gc_rest(objspace);
+        objspace->flags.dont_incremental = TRUE;
+    }
+
+    each_obj_data->reenable_incremental = reenable_incremental;
+    memset(&each_obj_data->pages, 0, sizeof(each_obj_data->pages));
+    memset(&each_obj_data->pages_counts, 0, sizeof(each_obj_data->pages_counts));
+    rb_ensure(objspace_each_objects_try, (VALUE)each_obj_data,
+              objspace_each_objects_ensure, (VALUE)each_obj_data);
+}
+
+static void
+objspace_each_objects(rb_objspace_t *objspace, each_obj_callback *callback, void *data, bool protected)
+{
+    struct each_obj_data each_obj_data = {
+        .objspace = objspace,
+        .each_obj_callback = callback,
+        .each_page_callback = NULL,
+        .data = data,
+    };
+    objspace_each_exec(protected, &each_obj_data);
+}
+
+void
+rb_gc_impl_each_objects(void *objspace_ptr, each_obj_callback *callback, void *data)
+{
+    objspace_each_objects(objspace_ptr, callback, data, TRUE);
+}
+
+#if GC_CAN_COMPILE_COMPACTION
+static void
+objspace_each_pages(rb_objspace_t *objspace, each_page_callback *callback, void *data, bool protected)
+{
+    struct each_obj_data each_obj_data = {
+        .objspace = objspace,
+        .each_obj_callback = NULL,
+        .each_page_callback = callback,
+        .data = data,
+    };
+    objspace_each_exec(protected, &each_obj_data);
+}
+#endif
+
+VALUE
+rb_gc_impl_define_finalizer(void *objspace_ptr, VALUE obj, VALUE block)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    VALUE table;
+    st_data_t data;
+
+    GC_ASSERT(!OBJ_FROZEN(obj));
+
+    RBASIC(obj)->flags |= FL_FINALIZE;
+
+    if (st_lookup(finalizer_table, obj, &data)) {
+        table = (VALUE)data;
+
+        /* avoid duplicate block, table is usually small */
+        {
+            long len = RARRAY_LEN(table);
+            long i;
+
+            for (i = 0; i < len; i++) {
+                VALUE recv = RARRAY_AREF(table, i);
+                if (rb_equal(recv, block)) {
+                    return recv;
+                }
+            }
+        }
+
+        rb_ary_push(table, block);
+    }
+    else {
+        table = rb_ary_new3(1, block);
+        rb_obj_hide(table);
+        st_add_direct(finalizer_table, obj, table);
+    }
+
+    return block;
+}
+
+void
+rb_gc_impl_undefine_finalizer(void *objspace_ptr, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    GC_ASSERT(!OBJ_FROZEN(obj));
+
+    st_data_t data = obj;
+    st_delete(finalizer_table, &data, 0);
+    FL_UNSET(obj, FL_FINALIZE);
+}
+
+void
+rb_gc_impl_copy_finalizer(void *objspace_ptr, VALUE dest, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    VALUE table;
+    st_data_t data;
+
+    if (!FL_TEST(obj, FL_FINALIZE)) return;
+
+    if (RB_LIKELY(st_lookup(finalizer_table, obj, &data))) {
+        table = (VALUE)data;
+        st_insert(finalizer_table, dest, table);
+        FL_SET(dest, FL_FINALIZE);
+    }
+    else {
+        rb_bug("rb_gc_copy_finalizer: FL_FINALIZE set but not found in finalizer_table: %s", rb_obj_info(obj));
+    }
+}
+
+static VALUE
+get_object_id_in_finalizer(rb_objspace_t *objspace, VALUE obj)
+{
+    if (FL_TEST(obj, FL_SEEN_OBJ_ID)) {
+        return rb_gc_impl_object_id(objspace, obj);
+    }
+    else {
+        VALUE id = ULL2NUM(objspace->next_object_id);
+        objspace->next_object_id += OBJ_ID_INCREMENT;
+        return id;
+    }
+}
+
+static VALUE
+get_final(long i, void *data)
+{
+    VALUE table = (VALUE)data;
+
+    return RARRAY_AREF(table, i);
+}
+
+static void
+run_final(rb_objspace_t *objspace, VALUE zombie)
+{
+    if (RZOMBIE(zombie)->dfree) {
+        RZOMBIE(zombie)->dfree(RZOMBIE(zombie)->data);
+    }
+
+    st_data_t key = (st_data_t)zombie;
+    if (FL_TEST_RAW(zombie, FL_FINALIZE)) {
+        FL_UNSET(zombie, FL_FINALIZE);
+        st_data_t table;
+        if (st_delete(finalizer_table, &key, &table)) {
+            rb_gc_run_obj_finalizer(get_object_id_in_finalizer(objspace, zombie), RARRAY_LEN(table), get_final, (void *)table);
+        }
+        else {
+            rb_bug("FL_FINALIZE flag is set, but finalizers are not found");
+        }
+    }
+    else {
+        GC_ASSERT(!st_lookup(finalizer_table, key, NULL));
+    }
+}
+
+static void
+finalize_list(rb_objspace_t *objspace, VALUE zombie)
+{
+    while (zombie) {
+        VALUE next_zombie;
+        struct heap_page *page;
+        asan_unpoison_object(zombie, false);
+        next_zombie = RZOMBIE(zombie)->next;
+        page = GET_HEAP_PAGE(zombie);
+
+        run_final(objspace, zombie);
+
+        int lev = rb_gc_vm_lock();
+        {
+            GC_ASSERT(BUILTIN_TYPE(zombie) == T_ZOMBIE);
+            if (FL_TEST(zombie, FL_SEEN_OBJ_ID)) {
+                obj_free_object_id(objspace, zombie);
+            }
+
+            GC_ASSERT(page->heap->final_slots_count > 0);
+            GC_ASSERT(page->final_slots > 0);
+
+            page->heap->final_slots_count--;
+            page->final_slots--;
+            page->free_slots++;
+            heap_page_add_freeobj(objspace, page, zombie);
+            page->heap->total_freed_objects++;
+        }
+        rb_gc_vm_unlock(lev);
+
+        zombie = next_zombie;
+    }
+}
+
+static void
+finalize_deferred_heap_pages(rb_objspace_t *objspace)
+{
+    VALUE zombie;
+    while ((zombie = RUBY_ATOMIC_VALUE_EXCHANGE(heap_pages_deferred_final, 0)) != 0) {
+        finalize_list(objspace, zombie);
+    }
+}
+
+static void
+finalize_deferred(rb_objspace_t *objspace)
+{
+    rb_gc_set_pending_interrupt();
+    finalize_deferred_heap_pages(objspace);
+    rb_gc_unset_pending_interrupt();
+}
+
+static void
+gc_finalize_deferred(void *dmy)
+{
+    rb_objspace_t *objspace = dmy;
+    if (RUBY_ATOMIC_EXCHANGE(finalizing, 1)) return;
+
+    finalize_deferred(objspace);
+    RUBY_ATOMIC_SET(finalizing, 0);
+}
+
+static void
+gc_finalize_deferred_register(rb_objspace_t *objspace)
+{
+    /* will enqueue a call to gc_finalize_deferred */
+    rb_postponed_job_trigger(objspace->finalize_deferred_pjob);
+}
+
+static int pop_mark_stack(mark_stack_t *stack, VALUE *data);
+
+static void
+gc_abort(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (is_incremental_marking(objspace)) {
+        /* Remove all objects from the mark stack. */
+        VALUE obj;
+        while (pop_mark_stack(&objspace->mark_stack, &obj));
+
+        objspace->flags.during_incremental_marking = FALSE;
+    }
+
+    if (is_lazy_sweeping(objspace)) {
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            rb_heap_t *heap = &heaps[i];
+
+            heap->sweeping_page = NULL;
+            struct heap_page *page = NULL;
+
+            ccan_list_for_each(&heap->pages, page, page_node) {
+                page->flags.before_sweep = false;
+            }
+        }
+    }
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        rgengc_mark_and_rememberset_clear(objspace, heap);
+    }
+
+    gc_mode_set(objspace, gc_mode_none);
+}
+
+void
+rb_gc_impl_shutdown_free_objects(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    for (size_t i = 0; i < rb_darray_size(objspace->heap_pages.sorted); i++) {
+        struct heap_page *page = rb_darray_get(objspace->heap_pages.sorted, i);
+        short stride = page->slot_size;
+
+        uintptr_t p = (uintptr_t)page->start;
+        uintptr_t pend = p + page->total_slots * stride;
+        for (; p < pend; p += stride) {
+            VALUE vp = (VALUE)p;
+            asan_unpoisoning_object(vp) {
+                if (RB_BUILTIN_TYPE(vp) != T_NONE) {
+                    rb_gc_obj_free_vm_weak_references(vp);
+                    if (rb_gc_obj_free(objspace, vp)) {
+                        RBASIC(vp)->flags = 0;
+                    }
+                }
+            }
+        }
+    }
+}
+
+static int
+rb_gc_impl_shutdown_call_finalizer_i(st_data_t key, st_data_t val, st_data_t data)
+{
+    rb_objspace_t *objspace = (rb_objspace_t *)data;
+    VALUE obj = (VALUE)key;
+    VALUE table = (VALUE)val;
+
+    GC_ASSERT(RB_FL_TEST(obj, FL_FINALIZE));
+    GC_ASSERT(RB_BUILTIN_TYPE(val) == T_ARRAY);
+
+    rb_gc_run_obj_finalizer(rb_gc_impl_object_id(objspace, obj), RARRAY_LEN(table), get_final, (void *)table);
+
+    FL_UNSET(obj, FL_FINALIZE);
+
+    return ST_DELETE;
+}
+
+void
+rb_gc_impl_shutdown_call_finalizer(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+#if RGENGC_CHECK_MODE >= 2
+    gc_verify_internal_consistency(objspace);
+#endif
+
+    /* prohibit incremental GC */
+    objspace->flags.dont_incremental = 1;
+
+    if (RUBY_ATOMIC_EXCHANGE(finalizing, 1)) {
+        /* Abort incremental marking and lazy sweeping to speed up shutdown. */
+        gc_abort(objspace);
+        dont_gc_on();
+        return;
+    }
+
+    while (finalizer_table->num_entries) {
+        st_foreach(finalizer_table, rb_gc_impl_shutdown_call_finalizer_i, (st_data_t)objspace);
+    }
+
+    /* run finalizers */
+    finalize_deferred(objspace);
+    GC_ASSERT(heap_pages_deferred_final == 0);
+
+    /* Abort incremental marking and lazy sweeping to speed up shutdown. */
+    gc_abort(objspace);
+
+    /* prohibit GC because force T_DATA finalizers can break an object graph consistency */
+    dont_gc_on();
+
+    /* running data/file finalizers are part of garbage collection */
+    unsigned int lock_lev;
+    gc_enter(objspace, gc_enter_event_finalizer, &lock_lev);
+
+    /* run data/file object's finalizers */
+    for (size_t i = 0; i < rb_darray_size(objspace->heap_pages.sorted); i++) {
+        struct heap_page *page = rb_darray_get(objspace->heap_pages.sorted, i);
+        short stride = page->slot_size;
+
+        uintptr_t p = (uintptr_t)page->start;
+        uintptr_t pend = p + page->total_slots * stride;
+        for (; p < pend; p += stride) {
+            VALUE vp = (VALUE)p;
+            asan_unpoisoning_object(vp) {
+                if (rb_gc_shutdown_call_finalizer_p(vp)) {
+                    rb_gc_obj_free_vm_weak_references(vp);
+                    if (rb_gc_obj_free(objspace, vp)) {
+                        RBASIC(vp)->flags = 0;
+                    }
+                }
+            }
+        }
+    }
+
+    gc_exit(objspace, gc_enter_event_finalizer, &lock_lev);
+
+    finalize_deferred_heap_pages(objspace);
+
+    st_free_table(finalizer_table);
+    finalizer_table = 0;
+    RUBY_ATOMIC_SET(finalizing, 0);
+}
+
+void
+rb_gc_impl_each_object(void *objspace_ptr, void (*func)(VALUE obj, void *data), void *data)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    for (size_t i = 0; i < rb_darray_size(objspace->heap_pages.sorted); i++) {
+        struct heap_page *page = rb_darray_get(objspace->heap_pages.sorted, i);
+        short stride = page->slot_size;
+
+        uintptr_t p = (uintptr_t)page->start;
+        uintptr_t pend = p + page->total_slots * stride;
+        for (; p < pend; p += stride) {
+            VALUE obj = (VALUE)p;
+
+            asan_unpoisoning_object(obj) {
+                func(obj, data);
+            }
+        }
+    }
+}
+
+/*
+  ------------------------ Garbage Collection ------------------------
+*/
+
+/* Sweeping */
+
+static size_t
+objspace_available_slots(rb_objspace_t *objspace)
+{
+    size_t total_slots = 0;
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        total_slots += heap->total_slots;
+    }
+    return total_slots;
+}
+
+static size_t
+objspace_live_slots(rb_objspace_t *objspace)
+{
+    return total_allocated_objects(objspace) - total_freed_objects(objspace) - total_final_slots_count(objspace);
+}
+
+static size_t
+objspace_free_slots(rb_objspace_t *objspace)
+{
+    return objspace_available_slots(objspace) - objspace_live_slots(objspace) - total_final_slots_count(objspace);
+}
+
+static void
+gc_setup_mark_bits(struct heap_page *page)
+{
+    /* copy oldgen bitmap to mark bitmap */
+    memcpy(&page->mark_bits[0], &page->uncollectible_bits[0], HEAP_PAGE_BITMAP_SIZE);
+}
+
+static int gc_is_moveable_obj(rb_objspace_t *objspace, VALUE obj);
+static VALUE gc_move(rb_objspace_t *objspace, VALUE scan, VALUE free, size_t src_slot_size, size_t slot_size);
+
+#if defined(_WIN32)
+enum {HEAP_PAGE_LOCK = PAGE_NOACCESS, HEAP_PAGE_UNLOCK = PAGE_READWRITE};
+
+static BOOL
+protect_page_body(struct heap_page_body *body, DWORD protect)
+{
+    DWORD old_protect;
+    return VirtualProtect(body, HEAP_PAGE_SIZE, protect, &old_protect) != 0;
+}
+#else
+enum {HEAP_PAGE_LOCK = PROT_NONE, HEAP_PAGE_UNLOCK = PROT_READ | PROT_WRITE};
+#define protect_page_body(body, protect) !mprotect((body), HEAP_PAGE_SIZE, (protect))
+#endif
+
+static void
+lock_page_body(rb_objspace_t *objspace, struct heap_page_body *body)
+{
+    if (!protect_page_body(body, HEAP_PAGE_LOCK)) {
+        rb_bug("Couldn't protect page %p, errno: %s", (void *)body, strerror(errno));
+    }
+    else {
+        gc_report(5, objspace, "Protecting page in move %p\n", (void *)body);
+    }
+}
+
+static void
+unlock_page_body(rb_objspace_t *objspace, struct heap_page_body *body)
+{
+    if (!protect_page_body(body, HEAP_PAGE_UNLOCK)) {
+        rb_bug("Couldn't unprotect page %p, errno: %s", (void *)body, strerror(errno));
+    }
+    else {
+        gc_report(5, objspace, "Unprotecting page in move %p\n", (void *)body);
+    }
+}
+
+static bool
+try_move(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *free_page, VALUE src)
+{
+    GC_ASSERT(gc_is_moveable_obj(objspace, src));
+
+    struct heap_page *src_page = GET_HEAP_PAGE(src);
+    if (!free_page) {
+        return false;
+    }
+
+    /* We should return true if either src is successfully moved, or src is
+     * unmoveable. A false return will cause the sweeping cursor to be
+     * incremented to the next page, and src will attempt to move again */
+    GC_ASSERT(RVALUE_MARKED(objspace, src));
+
+    asan_unlock_freelist(free_page);
+    VALUE dest = (VALUE)free_page->freelist;
+    asan_lock_freelist(free_page);
+    asan_unpoison_object(dest, false);
+    if (!dest) {
+        /* if we can't get something from the freelist then the page must be
+         * full */
+        return false;
+    }
+    asan_unlock_freelist(free_page);
+    free_page->freelist = ((struct free_slot *)dest)->next;
+    asan_lock_freelist(free_page);
+
+    GC_ASSERT(RB_BUILTIN_TYPE(dest) == T_NONE);
+
+    if (src_page->slot_size > free_page->slot_size) {
+        objspace->rcompactor.moved_down_count_table[BUILTIN_TYPE(src)]++;
+    }
+    else if (free_page->slot_size > src_page->slot_size) {
+        objspace->rcompactor.moved_up_count_table[BUILTIN_TYPE(src)]++;
+    }
+    objspace->rcompactor.moved_count_table[BUILTIN_TYPE(src)]++;
+    objspace->rcompactor.total_moved++;
+
+    gc_move(objspace, src, dest, src_page->slot_size, free_page->slot_size);
+    gc_pin(objspace, src);
+    free_page->free_slots--;
+
+    return true;
+}
+
+static void
+gc_unprotect_pages(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    struct heap_page *cursor = heap->compact_cursor;
+
+    while (cursor) {
+        unlock_page_body(objspace, cursor->body);
+        cursor = ccan_list_next(&heap->pages, cursor, page_node);
+    }
+}
+
+static void gc_update_references(rb_objspace_t *objspace);
+#if GC_CAN_COMPILE_COMPACTION
+static void invalidate_moved_page(rb_objspace_t *objspace, struct heap_page *page);
+#endif
+
+#if defined(__MINGW32__) || defined(_WIN32)
+# define GC_COMPACTION_SUPPORTED 1
+#else
+/* If not MinGW, Windows, or does not have mmap, we cannot use mprotect for
+ * the read barrier, so we must disable compaction. */
+# define GC_COMPACTION_SUPPORTED (GC_CAN_COMPILE_COMPACTION && HEAP_PAGE_ALLOC_USE_MMAP)
+#endif
+
+#if GC_CAN_COMPILE_COMPACTION
+static void
+read_barrier_handler(uintptr_t original_address)
+{
+    VALUE obj;
+    rb_objspace_t *objspace = (rb_objspace_t *)rb_gc_get_objspace();
+
+    /* Calculate address aligned to slots. */
+    uintptr_t address = original_address - (original_address % BASE_SLOT_SIZE);
+
+    obj = (VALUE)address;
+
+    struct heap_page_body *page_body = GET_PAGE_BODY(obj);
+
+    /* If the page_body is NULL, then mprotect cannot handle it and will crash
+     * with "Cannot allocate memory". */
+    if (page_body == NULL) {
+        rb_bug("read_barrier_handler: segmentation fault at %p", (void *)original_address);
+    }
+
+    int lev = rb_gc_vm_lock();
+    {
+        unlock_page_body(objspace, page_body);
+
+        objspace->profile.read_barrier_faults++;
+
+        invalidate_moved_page(objspace, GET_HEAP_PAGE(obj));
+    }
+    rb_gc_vm_unlock(lev);
+}
+#endif
+
+#if !GC_CAN_COMPILE_COMPACTION
+static void
+uninstall_handlers(void)
+{
+    /* no-op */
+}
+
+static void
+install_handlers(void)
+{
+    /* no-op */
+}
+#elif defined(_WIN32)
+static LPTOP_LEVEL_EXCEPTION_FILTER old_handler;
+typedef void (*signal_handler)(int);
+static signal_handler old_sigsegv_handler;
+
+static LONG WINAPI
+read_barrier_signal(EXCEPTION_POINTERS *info)
+{
+    /* EXCEPTION_ACCESS_VIOLATION is what's raised by access to protected pages */
+    if (info->ExceptionRecord->ExceptionCode == EXCEPTION_ACCESS_VIOLATION) {
+        /* > The second array element specifies the virtual address of the inaccessible data.
+         * https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-exception_record
+         *
+         * Use this address to invalidate the page */
+        read_barrier_handler((uintptr_t)info->ExceptionRecord->ExceptionInformation[1]);
+        return EXCEPTION_CONTINUE_EXECUTION;
+    }
+    else {
+        return EXCEPTION_CONTINUE_SEARCH;
+    }
+}
+
+static void
+uninstall_handlers(void)
+{
+    signal(SIGSEGV, old_sigsegv_handler);
+    SetUnhandledExceptionFilter(old_handler);
+}
+
+static void
+install_handlers(void)
+{
+    /* Remove SEGV handler so that the Unhandled Exception Filter handles it */
+    old_sigsegv_handler = signal(SIGSEGV, NULL);
+    /* Unhandled Exception Filter has access to the violation address similar
+     * to si_addr from sigaction */
+    old_handler = SetUnhandledExceptionFilter(read_barrier_signal);
+}
+#else
+static struct sigaction old_sigbus_handler;
+static struct sigaction old_sigsegv_handler;
+
+#ifdef HAVE_MACH_TASK_EXCEPTION_PORTS
+static exception_mask_t old_exception_masks[32];
+static mach_port_t old_exception_ports[32];
+static exception_behavior_t old_exception_behaviors[32];
+static thread_state_flavor_t old_exception_flavors[32];
+static mach_msg_type_number_t old_exception_count;
+
+static void
+disable_mach_bad_access_exc(void)
+{
+    old_exception_count = sizeof(old_exception_masks) / sizeof(old_exception_masks[0]);
+    task_swap_exception_ports(
+        mach_task_self(), EXC_MASK_BAD_ACCESS,
+        MACH_PORT_NULL, EXCEPTION_DEFAULT, 0,
+        old_exception_masks, &old_exception_count,
+        old_exception_ports, old_exception_behaviors, old_exception_flavors
+    );
+}
+
+static void
+restore_mach_bad_access_exc(void)
+{
+    for (mach_msg_type_number_t i = 0; i < old_exception_count; i++) {
+        task_set_exception_ports(
+            mach_task_self(),
+            old_exception_masks[i], old_exception_ports[i],
+            old_exception_behaviors[i], old_exception_flavors[i]
+        );
+    }
+}
+#endif
+
+static void
+read_barrier_signal(int sig, siginfo_t *info, void *data)
+{
+    // setup SEGV/BUS handlers for errors
+    struct sigaction prev_sigbus, prev_sigsegv;
+    sigaction(SIGBUS, &old_sigbus_handler, &prev_sigbus);
+    sigaction(SIGSEGV, &old_sigsegv_handler, &prev_sigsegv);
+
+    // enable SIGBUS/SEGV
+    sigset_t set, prev_set;
+    sigemptyset(&set);
+    sigaddset(&set, SIGBUS);
+    sigaddset(&set, SIGSEGV);
+    sigprocmask(SIG_UNBLOCK, &set, &prev_set);
+#ifdef HAVE_MACH_TASK_EXCEPTION_PORTS
+    disable_mach_bad_access_exc();
+#endif
+    // run handler
+    read_barrier_handler((uintptr_t)info->si_addr);
+
+    // reset SEGV/BUS handlers
+#ifdef HAVE_MACH_TASK_EXCEPTION_PORTS
+    restore_mach_bad_access_exc();
+#endif
+    sigaction(SIGBUS, &prev_sigbus, NULL);
+    sigaction(SIGSEGV, &prev_sigsegv, NULL);
+    sigprocmask(SIG_SETMASK, &prev_set, NULL);
+}
+
+static void
+uninstall_handlers(void)
+{
+#ifdef HAVE_MACH_TASK_EXCEPTION_PORTS
+    restore_mach_bad_access_exc();
+#endif
+    sigaction(SIGBUS, &old_sigbus_handler, NULL);
+    sigaction(SIGSEGV, &old_sigsegv_handler, NULL);
+}
+
+static void
+install_handlers(void)
+{
+    struct sigaction action;
+    memset(&action, 0, sizeof(struct sigaction));
+    sigemptyset(&action.sa_mask);
+    action.sa_sigaction = read_barrier_signal;
+    action.sa_flags = SA_SIGINFO | SA_ONSTACK;
+
+    sigaction(SIGBUS, &action, &old_sigbus_handler);
+    sigaction(SIGSEGV, &action, &old_sigsegv_handler);
+#ifdef HAVE_MACH_TASK_EXCEPTION_PORTS
+    disable_mach_bad_access_exc();
+#endif
+}
+#endif
+
+static void
+gc_compact_finish(rb_objspace_t *objspace)
+{
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        gc_unprotect_pages(objspace, heap);
+    }
+
+    uninstall_handlers();
+
+    gc_update_references(objspace);
+    objspace->profile.compact_count++;
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        heap->compact_cursor = NULL;
+        heap->free_pages = NULL;
+        heap->compact_cursor_index = 0;
+    }
+
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->moved_objects = objspace->rcompactor.total_moved - record->moved_objects;
+    }
+    objspace->flags.during_compacting = FALSE;
+}
+
+struct gc_sweep_context {
+    struct heap_page *page;
+    int final_slots;
+    int freed_slots;
+    int empty_slots;
+};
+
+static inline void
+gc_sweep_plane(rb_objspace_t *objspace, rb_heap_t *heap, uintptr_t p, bits_t bitset, struct gc_sweep_context *ctx)
+{
+    struct heap_page *sweep_page = ctx->page;
+    short slot_size = sweep_page->slot_size;
+    short slot_bits = slot_size / BASE_SLOT_SIZE;
+    GC_ASSERT(slot_bits > 0);
+
+    do {
+        VALUE vp = (VALUE)p;
+        GC_ASSERT(vp % BASE_SLOT_SIZE == 0);
+
+        asan_unpoison_object(vp, false);
+        if (bitset & 1) {
+            switch (BUILTIN_TYPE(vp)) {
+              default: /* majority case */
+                gc_report(2, objspace, "page_sweep: free %p\n", (void *)p);
+#if RGENGC_CHECK_MODE
+                if (!is_full_marking(objspace)) {
+                    if (RVALUE_OLD_P(objspace, vp)) rb_bug("page_sweep: %p - old while minor GC.", (void *)p);
+                    if (RVALUE_REMEMBERED(objspace, vp)) rb_bug("page_sweep: %p - remembered.", (void *)p);
+                }
+#endif
+
+                if (RVALUE_WB_UNPROTECTED(objspace, vp)) CLEAR_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(vp), vp);
+
+#if RGENGC_CHECK_MODE
+#define CHECK(x) if (x(objspace, vp) != FALSE) rb_bug("obj_free: " #x "(%s) != FALSE", rb_obj_info(vp))
+                CHECK(RVALUE_WB_UNPROTECTED);
+                CHECK(RVALUE_MARKED);
+                CHECK(RVALUE_MARKING);
+                CHECK(RVALUE_UNCOLLECTIBLE);
+#undef CHECK
+#endif
+
+                rb_gc_event_hook(vp, RUBY_INTERNAL_EVENT_FREEOBJ);
+
+                bool has_object_id = FL_TEST(vp, FL_SEEN_OBJ_ID);
+                rb_gc_obj_free_vm_weak_references(vp);
+                if (rb_gc_obj_free(objspace, vp)) {
+                    if (has_object_id) {
+                        obj_free_object_id(objspace, vp);
+                    }
+                    // always add free slots back to the swept pages freelist,
+                    // so that if we're compacting, we can re-use the slots
+                    (void)VALGRIND_MAKE_MEM_UNDEFINED((void*)p, BASE_SLOT_SIZE);
+                    heap_page_add_freeobj(objspace, sweep_page, vp);
+                    gc_report(3, objspace, "page_sweep: %s is added to freelist\n", rb_obj_info(vp));
+                    ctx->freed_slots++;
+                }
+                else {
+                    ctx->final_slots++;
+                }
+                break;
+
+              case T_MOVED:
+                if (objspace->flags.during_compacting) {
+                    /* The sweep cursor shouldn't have made it to any
+                     * T_MOVED slots while the compact flag is enabled.
+                     * The sweep cursor and compact cursor move in
+                     * opposite directions, and when they meet references will
+                     * get updated and "during_compacting" should get disabled */
+                    rb_bug("T_MOVED shouldn't be seen until compaction is finished");
+                }
+                gc_report(3, objspace, "page_sweep: %s is added to freelist\n", rb_obj_info(vp));
+                ctx->empty_slots++;
+                heap_page_add_freeobj(objspace, sweep_page, vp);
+                break;
+              case T_ZOMBIE:
+                /* already counted */
+                break;
+              case T_NONE:
+                ctx->empty_slots++; /* already freed */
+                break;
+            }
+        }
+        p += slot_size;
+        bitset >>= slot_bits;
+    } while (bitset);
+}
+
+static inline void
+gc_sweep_page(rb_objspace_t *objspace, rb_heap_t *heap, struct gc_sweep_context *ctx)
+{
+    struct heap_page *sweep_page = ctx->page;
+    GC_ASSERT(sweep_page->heap == heap);
+
+    uintptr_t p;
+    bits_t *bits, bitset;
+
+    gc_report(2, objspace, "page_sweep: start.\n");
+
+#if RGENGC_CHECK_MODE
+    if (!objspace->flags.immediate_sweep) {
+        GC_ASSERT(sweep_page->flags.before_sweep == TRUE);
+    }
+#endif
+    sweep_page->flags.before_sweep = FALSE;
+    sweep_page->free_slots = 0;
+
+    p = (uintptr_t)sweep_page->start;
+    bits = sweep_page->mark_bits;
+
+    int page_rvalue_count = sweep_page->total_slots * (sweep_page->slot_size / BASE_SLOT_SIZE);
+    int out_of_range_bits = (NUM_IN_PAGE(p) + page_rvalue_count) % BITS_BITLENGTH;
+    if (out_of_range_bits != 0) { // sizeof(RVALUE) == 64
+        bits[BITMAP_INDEX(p) + page_rvalue_count / BITS_BITLENGTH] |= ~(((bits_t)1 << out_of_range_bits) - 1);
+    }
+
+    /* The last bitmap plane may not be used if the last plane does not
+     * have enough space for the slot_size. In that case, the last plane must
+     * be skipped since none of the bits will be set. */
+    int bitmap_plane_count = CEILDIV(NUM_IN_PAGE(p) + page_rvalue_count, BITS_BITLENGTH);
+    GC_ASSERT(bitmap_plane_count == HEAP_PAGE_BITMAP_LIMIT - 1 ||
+                  bitmap_plane_count == HEAP_PAGE_BITMAP_LIMIT);
+
+    // Skip out of range slots at the head of the page
+    bitset = ~bits[0];
+    bitset >>= NUM_IN_PAGE(p);
+    if (bitset) {
+        gc_sweep_plane(objspace, heap, p, bitset, ctx);
+    }
+    p += (BITS_BITLENGTH - NUM_IN_PAGE(p)) * BASE_SLOT_SIZE;
+
+    for (int i = 1; i < bitmap_plane_count; i++) {
+        bitset = ~bits[i];
+        if (bitset) {
+            gc_sweep_plane(objspace, heap, p, bitset, ctx);
+        }
+        p += BITS_BITLENGTH * BASE_SLOT_SIZE;
+    }
+
+    if (!heap->compact_cursor) {
+        gc_setup_mark_bits(sweep_page);
+    }
+
+#if GC_PROFILE_MORE_DETAIL
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->removing_objects += ctx->final_slots + ctx->freed_slots;
+        record->empty_objects += ctx->empty_slots;
+    }
+#endif
+    if (0) fprintf(stderr, "gc_sweep_page(%"PRIdSIZE"): total_slots: %d, freed_slots: %d, empty_slots: %d, final_slots: %d\n",
+                   rb_gc_count(),
+                   sweep_page->total_slots,
+                   ctx->freed_slots, ctx->empty_slots, ctx->final_slots);
+
+    sweep_page->free_slots += ctx->freed_slots + ctx->empty_slots;
+    sweep_page->heap->total_freed_objects += ctx->freed_slots;
+
+    if (heap_pages_deferred_final && !finalizing) {
+        gc_finalize_deferred_register(objspace);
+    }
+
+#if RGENGC_CHECK_MODE
+    short freelist_len = 0;
+    asan_unlock_freelist(sweep_page);
+    struct free_slot *ptr = sweep_page->freelist;
+    while (ptr) {
+        freelist_len++;
+        ptr = ptr->next;
+    }
+    asan_lock_freelist(sweep_page);
+    if (freelist_len != sweep_page->free_slots) {
+        rb_bug("inconsistent freelist length: expected %d but was %d", sweep_page->free_slots, freelist_len);
+    }
+#endif
+
+    gc_report(2, objspace, "page_sweep: end.\n");
+}
+
+static const char *
+gc_mode_name(enum gc_mode mode)
+{
+    switch (mode) {
+      case gc_mode_none: return "none";
+      case gc_mode_marking: return "marking";
+      case gc_mode_sweeping: return "sweeping";
+      case gc_mode_compacting: return "compacting";
+      default: rb_bug("gc_mode_name: unknown mode: %d", (int)mode);
+    }
+}
+
+static void
+gc_mode_transition(rb_objspace_t *objspace, enum gc_mode mode)
+{
+#if RGENGC_CHECK_MODE
+    enum gc_mode prev_mode = gc_mode(objspace);
+    switch (prev_mode) {
+      case gc_mode_none:     GC_ASSERT(mode == gc_mode_marking); break;
+      case gc_mode_marking:  GC_ASSERT(mode == gc_mode_sweeping); break;
+      case gc_mode_sweeping: GC_ASSERT(mode == gc_mode_none || mode == gc_mode_compacting); break;
+      case gc_mode_compacting: GC_ASSERT(mode == gc_mode_none); break;
+    }
+#endif
+    if (0) fprintf(stderr, "gc_mode_transition: %s->%s\n", gc_mode_name(gc_mode(objspace)), gc_mode_name(mode));
+    gc_mode_set(objspace, mode);
+}
+
+static void
+heap_page_freelist_append(struct heap_page *page, struct free_slot *freelist)
+{
+    if (freelist) {
+        asan_unlock_freelist(page);
+        if (page->freelist) {
+            struct free_slot *p = page->freelist;
+            asan_unpoison_object((VALUE)p, false);
+            while (p->next) {
+                struct free_slot *prev = p;
+                p = p->next;
+                asan_poison_object((VALUE)prev);
+                asan_unpoison_object((VALUE)p, false);
+            }
+            p->next = freelist;
+            asan_poison_object((VALUE)p);
+        }
+        else {
+            page->freelist = freelist;
+        }
+        asan_lock_freelist(page);
+    }
+}
+
+static void
+gc_sweep_start_heap(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    heap->sweeping_page = ccan_list_top(&heap->pages, struct heap_page, page_node);
+    heap->free_pages = NULL;
+    heap->pooled_pages = NULL;
+    if (!objspace->flags.immediate_sweep) {
+        struct heap_page *page = NULL;
+
+        ccan_list_for_each(&heap->pages, page, page_node) {
+            page->flags.before_sweep = TRUE;
+        }
+    }
+}
+
+#if defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ == 4
+__attribute__((noinline))
+#endif
+
+#if GC_CAN_COMPILE_COMPACTION
+static void gc_sort_heap_by_compare_func(rb_objspace_t *objspace, gc_compact_compare_func compare_func);
+static int compare_pinned_slots(const void *left, const void *right, void *d);
+#endif
+
+static void
+gc_ractor_newobj_cache_clear(void *c, void *data)
+{
+    rb_ractor_newobj_cache_t *newobj_cache = c;
+
+    newobj_cache->incremental_mark_step_allocated_slots = 0;
+
+    for (size_t heap_idx = 0; heap_idx < HEAP_COUNT; heap_idx++) {
+        rb_ractor_newobj_heap_cache_t *cache = &newobj_cache->heap_caches[heap_idx];
+
+        struct heap_page *page = cache->using_page;
+        struct free_slot *freelist = cache->freelist;
+        RUBY_DEBUG_LOG("ractor using_page:%p freelist:%p", (void *)page, (void *)freelist);
+
+        heap_page_freelist_append(page, freelist);
+
+        cache->using_page = NULL;
+        cache->freelist = NULL;
+    }
+}
+
+static void
+gc_sweep_start(rb_objspace_t *objspace)
+{
+    gc_mode_transition(objspace, gc_mode_sweeping);
+    objspace->rincgc.pooled_slots = 0;
+    objspace->heap_pages.allocatable_slots = 0;
+
+#if GC_CAN_COMPILE_COMPACTION
+    if (objspace->flags.during_compacting) {
+        gc_sort_heap_by_compare_func(
+            objspace,
+            objspace->rcompactor.compare_func ? objspace->rcompactor.compare_func : compare_pinned_slots
+        );
+    }
+#endif
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        gc_sweep_start_heap(objspace, heap);
+
+        /* We should call gc_sweep_finish_heap for size pools with no pages. */
+        if (heap->sweeping_page == NULL) {
+            GC_ASSERT(heap->total_pages == 0);
+            GC_ASSERT(heap->total_slots == 0);
+            gc_sweep_finish_heap(objspace, heap);
+        }
+    }
+
+    rb_gc_ractor_newobj_cache_foreach(gc_ractor_newobj_cache_clear, NULL);
+}
+
+static void
+gc_sweep_finish_heap(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    size_t total_slots = heap->total_slots;
+    size_t swept_slots = heap->freed_slots + heap->empty_slots;
+
+    size_t init_slots = gc_params.heap_init_slots[heap - heaps];
+    size_t min_free_slots = (size_t)(MAX(total_slots, init_slots) * gc_params.heap_free_slots_min_ratio);
+
+    if (swept_slots < min_free_slots &&
+            /* The heap is a growth heap if it freed more slots than had empty slots. */
+            (heap->empty_slots == 0 || heap->freed_slots > heap->empty_slots)) {
+        /* If we don't have enough slots and we have pages on the tomb heap, move
+        * pages from the tomb heap to the eden heap. This may prevent page
+        * creation thrashing (frequently allocating and deallocting pages) and
+        * GC thrashing (running GC more frequently than required). */
+        struct heap_page *resurrected_page;
+        while (swept_slots < min_free_slots &&
+                (resurrected_page = heap_page_resurrect(objspace))) {
+            heap_add_page(objspace, heap, resurrected_page);
+            heap_add_freepage(heap, resurrected_page);
+
+            swept_slots += resurrected_page->free_slots;
+        }
+
+        if (swept_slots < min_free_slots) {
+            /* Grow this heap if we are in a major GC or if we haven't run at least
+            * RVALUE_OLD_AGE minor GC since the last major GC. */
+            if (is_full_marking(objspace) ||
+                    objspace->profile.count - objspace->rgengc.last_major_gc < RVALUE_OLD_AGE) {
+                heap_allocatable_slots_expand(objspace, heap, swept_slots, heap->total_slots);
+            }
+            else {
+                gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_NOFREE;
+                heap->force_major_gc_count++;
+            }
+        }
+    }
+}
+
+static void
+gc_sweep_finish(rb_objspace_t *objspace)
+{
+    gc_report(1, objspace, "gc_sweep_finish\n");
+
+    gc_prof_set_heap_info(objspace);
+    heap_pages_free_unused_pages(objspace);
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+
+        heap->freed_slots = 0;
+        heap->empty_slots = 0;
+
+        if (!will_be_incremental_marking(objspace)) {
+            struct heap_page *end_page = heap->free_pages;
+            if (end_page) {
+                while (end_page->free_next) end_page = end_page->free_next;
+                end_page->free_next = heap->pooled_pages;
+            }
+            else {
+                heap->free_pages = heap->pooled_pages;
+            }
+            heap->pooled_pages = NULL;
+            objspace->rincgc.pooled_slots = 0;
+        }
+    }
+
+    rb_gc_event_hook(0, RUBY_INTERNAL_EVENT_GC_END_SWEEP);
+    gc_mode_transition(objspace, gc_mode_none);
+
+#if RGENGC_CHECK_MODE >= 2
+    gc_verify_internal_consistency(objspace);
+#endif
+}
+
+static int
+gc_sweep_step(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    struct heap_page *sweep_page = heap->sweeping_page;
+    int unlink_limit = GC_SWEEP_PAGES_FREEABLE_PER_STEP;
+    int swept_slots = 0;
+    int pooled_slots = 0;
+
+    if (sweep_page == NULL) return FALSE;
+
+#if GC_ENABLE_LAZY_SWEEP
+    gc_prof_sweep_timer_start(objspace);
+#endif
+
+    do {
+        RUBY_DEBUG_LOG("sweep_page:%p", (void *)sweep_page);
+
+        struct gc_sweep_context ctx = {
+            .page = sweep_page,
+            .final_slots = 0,
+            .freed_slots = 0,
+            .empty_slots = 0,
+        };
+        gc_sweep_page(objspace, heap, &ctx);
+        int free_slots = ctx.freed_slots + ctx.empty_slots;
+
+        heap->sweeping_page = ccan_list_next(&heap->pages, sweep_page, page_node);
+
+        if (free_slots == sweep_page->total_slots &&
+                heap_pages_freeable_pages > 0 &&
+                unlink_limit > 0) {
+            heap_pages_freeable_pages--;
+            unlink_limit--;
+            /* There are no living objects, so move this page to the global empty pages. */
+            heap_unlink_page(objspace, heap, sweep_page);
+
+            sweep_page->start = 0;
+            sweep_page->total_slots = 0;
+            sweep_page->slot_size = 0;
+            sweep_page->heap = NULL;
+            sweep_page->free_slots = 0;
+
+            asan_unlock_freelist(sweep_page);
+            sweep_page->freelist = NULL;
+            asan_lock_freelist(sweep_page);
+
+            asan_poison_memory_region(sweep_page->body, HEAP_PAGE_SIZE);
+
+            objspace->empty_pages_count++;
+            sweep_page->free_next = objspace->empty_pages;
+            objspace->empty_pages = sweep_page;
+        }
+        else if (free_slots > 0) {
+            heap->freed_slots += ctx.freed_slots;
+            heap->empty_slots += ctx.empty_slots;
+
+            if (pooled_slots < GC_INCREMENTAL_SWEEP_POOL_SLOT_COUNT) {
+                heap_add_poolpage(objspace, heap, sweep_page);
+                pooled_slots += free_slots;
+            }
+            else {
+                heap_add_freepage(heap, sweep_page);
+                swept_slots += free_slots;
+                if (swept_slots > GC_INCREMENTAL_SWEEP_SLOT_COUNT) {
+                    break;
+                }
+            }
+        }
+        else {
+            sweep_page->free_next = NULL;
+        }
+    } while ((sweep_page = heap->sweeping_page));
+
+    if (!heap->sweeping_page) {
+        gc_sweep_finish_heap(objspace, heap);
+
+        if (!has_sweeping_pages(objspace)) {
+            gc_sweep_finish(objspace);
+        }
+    }
+
+#if GC_ENABLE_LAZY_SWEEP
+    gc_prof_sweep_timer_stop(objspace);
+#endif
+
+    return heap->free_pages != NULL;
+}
+
+static void
+gc_sweep_rest(rb_objspace_t *objspace)
+{
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+
+        while (heap->sweeping_page) {
+            gc_sweep_step(objspace, heap);
+        }
+    }
+}
+
+static void
+gc_sweep_continue(rb_objspace_t *objspace, rb_heap_t *sweep_heap)
+{
+    GC_ASSERT(dont_gc_val() == FALSE || objspace->profile.latest_gc_info & GPR_FLAG_METHOD);
+    if (!GC_ENABLE_LAZY_SWEEP) return;
+
+    gc_sweeping_enter(objspace);
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        if (!gc_sweep_step(objspace, heap)) {
+            /* sweep_heap requires a free slot but sweeping did not yield any
+             * and we cannot allocate a new page. */
+            if (heap == sweep_heap && objspace->heap_pages.allocatable_slots == 0) {
+                /* Not allowed to create a new page so finish sweeping. */
+                gc_sweep_rest(objspace);
+                break;
+            }
+        }
+    }
+
+    gc_sweeping_exit(objspace);
+}
+
+VALUE
+rb_gc_impl_location(void *objspace_ptr, VALUE value)
+{
+    VALUE destination;
+
+    if (!SPECIAL_CONST_P(value)) {
+        asan_unpoisoning_object(value) {
+            if (BUILTIN_TYPE(value) == T_MOVED) {
+                destination = (VALUE)RMOVED(value)->destination;
+                GC_ASSERT(BUILTIN_TYPE(destination) != T_NONE);
+            }
+            else {
+                destination = value;
+            }
+        }
+    }
+    else {
+        destination = value;
+    }
+
+    return destination;
+}
+
+#if GC_CAN_COMPILE_COMPACTION
+static void
+invalidate_moved_plane(rb_objspace_t *objspace, struct heap_page *page, uintptr_t p, bits_t bitset)
+{
+    if (bitset) {
+        do {
+            if (bitset & 1) {
+                VALUE forwarding_object = (VALUE)p;
+                VALUE object;
+
+                if (BUILTIN_TYPE(forwarding_object) == T_MOVED) {
+                    GC_ASSERT(RVALUE_PINNED(objspace, forwarding_object));
+                    GC_ASSERT(!RVALUE_MARKED(objspace, forwarding_object));
+
+                    CLEAR_IN_BITMAP(GET_HEAP_PINNED_BITS(forwarding_object), forwarding_object);
+
+                    object = rb_gc_impl_location(objspace, forwarding_object);
+
+                    uint32_t original_shape_id = 0;
+                    if (RB_TYPE_P(object, T_OBJECT)) {
+                        original_shape_id = RMOVED(forwarding_object)->original_shape_id;
+                    }
+
+                    gc_move(objspace, object, forwarding_object, GET_HEAP_PAGE(object)->slot_size, page->slot_size);
+                    /* forwarding_object is now our actual object, and "object"
+                     * is the free slot for the original page */
+
+                    if (original_shape_id) {
+                        rb_gc_set_shape(forwarding_object, original_shape_id);
+                    }
+
+                    struct heap_page *orig_page = GET_HEAP_PAGE(object);
+                    orig_page->free_slots++;
+                    heap_page_add_freeobj(objspace, orig_page, object);
+
+                    GC_ASSERT(RVALUE_MARKED(objspace, forwarding_object));
+                    GC_ASSERT(BUILTIN_TYPE(forwarding_object) != T_MOVED);
+                    GC_ASSERT(BUILTIN_TYPE(forwarding_object) != T_NONE);
+                }
+            }
+            p += BASE_SLOT_SIZE;
+            bitset >>= 1;
+        } while (bitset);
+    }
+}
+
+static void
+invalidate_moved_page(rb_objspace_t *objspace, struct heap_page *page)
+{
+    int i;
+    bits_t *mark_bits, *pin_bits;
+    bits_t bitset;
+
+    mark_bits = page->mark_bits;
+    pin_bits = page->pinned_bits;
+
+    uintptr_t p = page->start;
+
+    // Skip out of range slots at the head of the page
+    bitset = pin_bits[0] & ~mark_bits[0];
+    bitset >>= NUM_IN_PAGE(p);
+    invalidate_moved_plane(objspace, page, p, bitset);
+    p += (BITS_BITLENGTH - NUM_IN_PAGE(p)) * BASE_SLOT_SIZE;
+
+    for (i=1; i < HEAP_PAGE_BITMAP_LIMIT; i++) {
+        /* Moved objects are pinned but never marked. We reuse the pin bits
+         * to indicate there is a moved object in this slot. */
+        bitset = pin_bits[i] & ~mark_bits[i];
+
+        invalidate_moved_plane(objspace, page, p, bitset);
+        p += BITS_BITLENGTH * BASE_SLOT_SIZE;
+    }
+}
+#endif
+
+static void
+gc_compact_start(rb_objspace_t *objspace)
+{
+    struct heap_page *page = NULL;
+    gc_mode_transition(objspace, gc_mode_compacting);
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        ccan_list_for_each(&heap->pages, page, page_node) {
+            page->flags.before_sweep = TRUE;
+        }
+
+        heap->compact_cursor = ccan_list_tail(&heap->pages, struct heap_page, page_node);
+        heap->compact_cursor_index = 0;
+    }
+
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->moved_objects = objspace->rcompactor.total_moved;
+    }
+
+    memset(objspace->rcompactor.considered_count_table, 0, T_MASK * sizeof(size_t));
+    memset(objspace->rcompactor.moved_count_table, 0, T_MASK * sizeof(size_t));
+    memset(objspace->rcompactor.moved_up_count_table, 0, T_MASK * sizeof(size_t));
+    memset(objspace->rcompactor.moved_down_count_table, 0, T_MASK * sizeof(size_t));
+
+    /* Set up read barrier for pages containing MOVED objects */
+    install_handlers();
+}
+
+static void gc_sweep_compact(rb_objspace_t *objspace);
+
+static void
+gc_sweep(rb_objspace_t *objspace)
+{
+    gc_sweeping_enter(objspace);
+
+    const unsigned int immediate_sweep = objspace->flags.immediate_sweep;
+
+    gc_report(1, objspace, "gc_sweep: immediate: %d\n", immediate_sweep);
+
+    gc_sweep_start(objspace);
+    if (objspace->flags.during_compacting) {
+        gc_sweep_compact(objspace);
+    }
+
+    if (immediate_sweep) {
+#if !GC_ENABLE_LAZY_SWEEP
+        gc_prof_sweep_timer_start(objspace);
+#endif
+        gc_sweep_rest(objspace);
+#if !GC_ENABLE_LAZY_SWEEP
+        gc_prof_sweep_timer_stop(objspace);
+#endif
+    }
+    else {
+
+        /* Sweep every size pool. */
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            rb_heap_t *heap = &heaps[i];
+            gc_sweep_step(objspace, heap);
+        }
+    }
+
+    gc_sweeping_exit(objspace);
+}
+
+/* Marking - Marking stack */
+
+static stack_chunk_t *
+stack_chunk_alloc(void)
+{
+    stack_chunk_t *res;
+
+    res = malloc(sizeof(stack_chunk_t));
+    if (!res)
+        rb_memerror();
+
+    return res;
+}
+
+static inline int
+is_mark_stack_empty(mark_stack_t *stack)
+{
+    return stack->chunk == NULL;
+}
+
+static size_t
+mark_stack_size(mark_stack_t *stack)
+{
+    size_t size = stack->index;
+    stack_chunk_t *chunk = stack->chunk ? stack->chunk->next : NULL;
+
+    while (chunk) {
+        size += stack->limit;
+        chunk = chunk->next;
+    }
+    return size;
+}
+
+static void
+add_stack_chunk_cache(mark_stack_t *stack, stack_chunk_t *chunk)
+{
+    chunk->next = stack->cache;
+    stack->cache = chunk;
+    stack->cache_size++;
+}
+
+static void
+shrink_stack_chunk_cache(mark_stack_t *stack)
+{
+    stack_chunk_t *chunk;
+
+    if (stack->unused_cache_size > (stack->cache_size/2)) {
+        chunk = stack->cache;
+        stack->cache = stack->cache->next;
+        stack->cache_size--;
+        free(chunk);
+    }
+    stack->unused_cache_size = stack->cache_size;
+}
+
+static void
+push_mark_stack_chunk(mark_stack_t *stack)
+{
+    stack_chunk_t *next;
+
+    GC_ASSERT(stack->index == stack->limit);
+
+    if (stack->cache_size > 0) {
+        next = stack->cache;
+        stack->cache = stack->cache->next;
+        stack->cache_size--;
+        if (stack->unused_cache_size > stack->cache_size)
+            stack->unused_cache_size = stack->cache_size;
+    }
+    else {
+        next = stack_chunk_alloc();
+    }
+    next->next = stack->chunk;
+    stack->chunk = next;
+    stack->index = 0;
+}
+
+static void
+pop_mark_stack_chunk(mark_stack_t *stack)
+{
+    stack_chunk_t *prev;
+
+    prev = stack->chunk->next;
+    GC_ASSERT(stack->index == 0);
+    add_stack_chunk_cache(stack, stack->chunk);
+    stack->chunk = prev;
+    stack->index = stack->limit;
+}
+
+static void
+mark_stack_chunk_list_free(stack_chunk_t *chunk)
+{
+    stack_chunk_t *next = NULL;
+
+    while (chunk != NULL) {
+        next = chunk->next;
+        free(chunk);
+        chunk = next;
+    }
+}
+
+static void
+free_stack_chunks(mark_stack_t *stack)
+{
+    mark_stack_chunk_list_free(stack->chunk);
+}
+
+static void
+mark_stack_free_cache(mark_stack_t *stack)
+{
+    mark_stack_chunk_list_free(stack->cache);
+    stack->cache_size = 0;
+    stack->unused_cache_size = 0;
+}
+
+static void
+push_mark_stack(mark_stack_t *stack, VALUE obj)
+{
+    switch (BUILTIN_TYPE(obj)) {
+      case T_OBJECT:
+      case T_CLASS:
+      case T_MODULE:
+      case T_FLOAT:
+      case T_STRING:
+      case T_REGEXP:
+      case T_ARRAY:
+      case T_HASH:
+      case T_STRUCT:
+      case T_BIGNUM:
+      case T_FILE:
+      case T_DATA:
+      case T_MATCH:
+      case T_COMPLEX:
+      case T_RATIONAL:
+      case T_TRUE:
+      case T_FALSE:
+      case T_SYMBOL:
+      case T_IMEMO:
+      case T_ICLASS:
+        if (stack->index == stack->limit) {
+            push_mark_stack_chunk(stack);
+        }
+        stack->chunk->data[stack->index++] = obj;
+        return;
+
+      case T_NONE:
+      case T_NIL:
+      case T_FIXNUM:
+      case T_MOVED:
+      case T_ZOMBIE:
+      case T_UNDEF:
+      case T_MASK:
+        rb_bug("push_mark_stack() called for broken object");
+        break;
+
+      case T_NODE:
+        rb_bug("push_mark_stack: unexpected T_NODE object");
+        break;
+    }
+
+    rb_bug("rb_gc_mark(): unknown data type 0x%x(%p) %s",
+            BUILTIN_TYPE(obj), (void *)obj,
+            is_pointer_to_heap((rb_objspace_t *)rb_gc_get_objspace(), (void *)obj) ? "corrupted object" : "non object");
+}
+
+static int
+pop_mark_stack(mark_stack_t *stack, VALUE *data)
+{
+    if (is_mark_stack_empty(stack)) {
+        return FALSE;
+    }
+    if (stack->index == 1) {
+        *data = stack->chunk->data[--stack->index];
+        pop_mark_stack_chunk(stack);
+    }
+    else {
+        *data = stack->chunk->data[--stack->index];
+    }
+    return TRUE;
+}
+
+static void
+init_mark_stack(mark_stack_t *stack)
+{
+    int i;
+
+    MEMZERO(stack, mark_stack_t, 1);
+    stack->index = stack->limit = STACK_CHUNK_SIZE;
+
+    for (i=0; i < 4; i++) {
+        add_stack_chunk_cache(stack, stack_chunk_alloc());
+    }
+    stack->unused_cache_size = stack->cache_size;
+}
+
+/* Marking */
+
+static void
+rgengc_check_relation(rb_objspace_t *objspace, VALUE obj)
+{
+    const VALUE old_parent = objspace->rgengc.parent_object;
+
+    if (old_parent) { /* parent object is old */
+        if (RVALUE_WB_UNPROTECTED(objspace, obj) || !RVALUE_OLD_P(objspace, obj)) {
+            rgengc_remember(objspace, old_parent);
+        }
+    }
+
+    GC_ASSERT(old_parent == objspace->rgengc.parent_object);
+}
+
+static inline int
+gc_mark_set(rb_objspace_t *objspace, VALUE obj)
+{
+    if (RVALUE_MARKED(objspace, obj)) return 0;
+    MARK_IN_BITMAP(GET_HEAP_MARK_BITS(obj), obj);
+    return 1;
+}
+
+static void
+gc_aging(rb_objspace_t *objspace, VALUE obj)
+{
+    /* Disable aging if Major GC's are disabled. This will prevent longish lived
+     * objects filling up the heap at the expense of marking many more objects.
+     *
+     * We should always pre-warm our process when disabling majors, by running
+     * GC manually several times so that most objects likely to become oldgen
+     * are already oldgen.
+     */
+    if(!gc_config_full_mark_val)
+        return;
+
+    struct heap_page *page = GET_HEAP_PAGE(obj);
+
+    GC_ASSERT(RVALUE_MARKING(objspace, obj) == FALSE);
+    check_rvalue_consistency(objspace, obj);
+
+    if (!RVALUE_PAGE_WB_UNPROTECTED(page, obj)) {
+        if (!RVALUE_OLD_P(objspace, obj)) {
+            gc_report(3, objspace, "gc_aging: YOUNG: %s\n", rb_obj_info(obj));
+            RVALUE_AGE_INC(objspace, obj);
+        }
+        else if (is_full_marking(objspace)) {
+            GC_ASSERT(RVALUE_PAGE_UNCOLLECTIBLE(page, obj) == FALSE);
+            RVALUE_PAGE_OLD_UNCOLLECTIBLE_SET(objspace, page, obj);
+        }
+    }
+    check_rvalue_consistency(objspace, obj);
+
+    objspace->marked_slots++;
+}
+
+static void
+gc_grey(rb_objspace_t *objspace, VALUE obj)
+{
+#if RGENGC_CHECK_MODE
+    if (RVALUE_MARKED(objspace, obj) == FALSE) rb_bug("gc_grey: %s is not marked.", rb_obj_info(obj));
+    if (RVALUE_MARKING(objspace, obj) == TRUE) rb_bug("gc_grey: %s is marking/remembered.", rb_obj_info(obj));
+#endif
+
+    if (is_incremental_marking(objspace)) {
+        MARK_IN_BITMAP(GET_HEAP_MARKING_BITS(obj), obj);
+    }
+
+    push_mark_stack(&objspace->mark_stack, obj);
+}
+
+static void
+gc_mark(rb_objspace_t *objspace, VALUE obj)
+{
+    GC_ASSERT(during_gc);
+
+    rgengc_check_relation(objspace, obj);
+    if (!gc_mark_set(objspace, obj)) return; /* already marked */
+
+    if (0) { // for debug GC marking miss
+        if (objspace->rgengc.parent_object) {
+            RUBY_DEBUG_LOG("%p (%s) parent:%p (%s)",
+                            (void *)obj, obj_type_name(obj),
+                            (void *)objspace->rgengc.parent_object, obj_type_name(objspace->rgengc.parent_object));
+        }
+        else {
+            RUBY_DEBUG_LOG("%p (%s)", (void *)obj, obj_type_name(obj));
+        }
+    }
+
+    if (RB_UNLIKELY(RB_TYPE_P(obj, T_NONE))) {
+        rb_obj_info_dump(obj);
+        rb_bug("try to mark T_NONE object"); /* check here will help debugging */
+    }
+
+    gc_aging(objspace, obj);
+    gc_grey(objspace, obj);
+}
+
+static inline void
+gc_pin(rb_objspace_t *objspace, VALUE obj)
+{
+    GC_ASSERT(!SPECIAL_CONST_P(obj));
+    if (RB_UNLIKELY(objspace->flags.during_compacting)) {
+        if (RB_LIKELY(during_gc)) {
+            if (!RVALUE_PINNED(objspace, obj)) {
+                GC_ASSERT(GET_HEAP_PAGE(obj)->pinned_slots <= GET_HEAP_PAGE(obj)->total_slots);
+                GET_HEAP_PAGE(obj)->pinned_slots++;
+                MARK_IN_BITMAP(GET_HEAP_PINNED_BITS(obj), obj);
+            }
+        }
+    }
+}
+
+static inline void
+gc_mark_and_pin(rb_objspace_t *objspace, VALUE obj)
+{
+    gc_pin(objspace, obj);
+    gc_mark(objspace, obj);
+}
+
+void
+rb_gc_impl_mark_and_move(void *objspace_ptr, VALUE *ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (RB_UNLIKELY(objspace->flags.during_reference_updating)) {
+        GC_ASSERT(objspace->flags.during_compacting);
+        GC_ASSERT(during_gc);
+
+        *ptr = rb_gc_impl_location(objspace, *ptr);
+    }
+    else {
+        gc_mark(objspace, *ptr);
+    }
+}
+
+void
+rb_gc_impl_mark(void *objspace_ptr, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    gc_mark(objspace, obj);
+}
+
+void
+rb_gc_impl_mark_and_pin(void *objspace_ptr, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    gc_mark_and_pin(objspace, obj);
+}
+
+void
+rb_gc_impl_mark_maybe(void *objspace_ptr, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    (void)VALGRIND_MAKE_MEM_DEFINED(&obj, sizeof(obj));
+
+    if (is_pointer_to_heap(objspace, (void *)obj)) {
+        asan_unpoisoning_object(obj) {
+            /* Garbage can live on the stack, so do not mark or pin */
+            switch (BUILTIN_TYPE(obj)) {
+            case T_ZOMBIE:
+            case T_NONE:
+                break;
+            default:
+                gc_mark_and_pin(objspace, obj);
+                break;
+            }
+        }
+    }
+}
+
+void
+rb_gc_impl_mark_weak(void *objspace_ptr, VALUE *ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    GC_ASSERT(objspace->rgengc.parent_object == 0 || FL_TEST(objspace->rgengc.parent_object, FL_WB_PROTECTED));
+
+    VALUE obj = *ptr;
+
+    if (RB_UNLIKELY(RB_TYPE_P(obj, T_NONE))) {
+        rb_obj_info_dump(obj);
+        rb_bug("try to mark T_NONE object");
+    }
+
+    /* If we are in a minor GC and the other object is old, then obj should
+     * already be marked and cannot be reclaimed in this GC cycle so we don't
+     * need to add it to the weak references list. */
+    if (!is_full_marking(objspace) && RVALUE_OLD_P(objspace, obj)) {
+        GC_ASSERT(RVALUE_MARKED(objspace, obj));
+        GC_ASSERT(!objspace->flags.during_compacting);
+
+        return;
+    }
+
+    rgengc_check_relation(objspace, obj);
+
+    DURING_GC_COULD_MALLOC_REGION_START();
+    {
+        rb_darray_append(&objspace->weak_references, ptr);
+    }
+    DURING_GC_COULD_MALLOC_REGION_END();
+
+    objspace->profile.weak_references_count++;
+}
+
+void
+rb_gc_impl_remove_weak(void *objspace_ptr, VALUE parent_obj, VALUE *ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    /* If we're not incremental marking, then the state of the objects can't
+     * change so we don't need to do anything. */
+    if (!is_incremental_marking(objspace)) return;
+    /* If parent_obj has not been marked, then ptr has not yet been marked
+     * weak, so we don't need to do anything. */
+    if (!RVALUE_MARKED(objspace, parent_obj)) return;
+
+    VALUE **ptr_ptr;
+    rb_darray_foreach(objspace->weak_references, i, ptr_ptr) {
+        if (*ptr_ptr == ptr) {
+            *ptr_ptr = NULL;
+            break;
+        }
+    }
+}
+
+static int
+pin_value(st_data_t key, st_data_t value, st_data_t data)
+{
+    rb_gc_impl_mark_and_pin((void *)data, (VALUE)value);
+
+    return ST_CONTINUE;
+}
+
+static void
+mark_roots(rb_objspace_t *objspace, const char **categoryp)
+{
+#define MARK_CHECKPOINT(category) do { \
+    if (categoryp) *categoryp = category; \
+} while (0)
+
+    MARK_CHECKPOINT("objspace");
+    objspace->rgengc.parent_object = Qfalse;
+
+    if (finalizer_table != NULL) {
+        st_foreach(finalizer_table, pin_value, (st_data_t)objspace);
+    }
+
+    st_foreach(objspace->obj_to_id_tbl, gc_mark_tbl_no_pin_i, (st_data_t)objspace);
+
+    if (stress_to_class) rb_gc_mark(stress_to_class);
+
+    rb_gc_save_machine_context();
+    rb_gc_mark_roots(objspace, categoryp);
+}
+
+static inline void
+gc_mark_set_parent(rb_objspace_t *objspace, VALUE obj)
+{
+    if (RVALUE_OLD_P(objspace, obj)) {
+        objspace->rgengc.parent_object = obj;
+    }
+    else {
+        objspace->rgengc.parent_object = Qfalse;
+    }
+}
+
+static void
+gc_mark_children(rb_objspace_t *objspace, VALUE obj)
+{
+    gc_mark_set_parent(objspace, obj);
+    rb_gc_mark_children(objspace, obj);
+}
+
+/**
+ * incremental: 0 -> not incremental (do all)
+ * incremental: n -> mark at most `n' objects
+ */
+static inline int
+gc_mark_stacked_objects(rb_objspace_t *objspace, int incremental, size_t count)
+{
+    mark_stack_t *mstack = &objspace->mark_stack;
+    VALUE obj;
+    size_t marked_slots_at_the_beginning = objspace->marked_slots;
+    size_t popped_count = 0;
+
+    while (pop_mark_stack(mstack, &obj)) {
+        if (obj == Qundef) continue; /* skip */
+
+        if (RGENGC_CHECK_MODE && !RVALUE_MARKED(objspace, obj)) {
+            rb_bug("gc_mark_stacked_objects: %s is not marked.", rb_obj_info(obj));
+        }
+        gc_mark_children(objspace, obj);
+
+        if (incremental) {
+            if (RGENGC_CHECK_MODE && !RVALUE_MARKING(objspace, obj)) {
+                rb_bug("gc_mark_stacked_objects: incremental, but marking bit is 0");
+            }
+            CLEAR_IN_BITMAP(GET_HEAP_MARKING_BITS(obj), obj);
+            popped_count++;
+
+            if (popped_count + (objspace->marked_slots - marked_slots_at_the_beginning) > count) {
+                break;
+            }
+        }
+        else {
+            /* just ignore marking bits */
+        }
+    }
+
+    if (RGENGC_CHECK_MODE >= 3) gc_verify_internal_consistency(objspace);
+
+    if (is_mark_stack_empty(mstack)) {
+        shrink_stack_chunk_cache(mstack);
+        return TRUE;
+    }
+    else {
+        return FALSE;
+    }
+}
+
+static int
+gc_mark_stacked_objects_incremental(rb_objspace_t *objspace, size_t count)
+{
+    return gc_mark_stacked_objects(objspace, TRUE, count);
+}
+
+static int
+gc_mark_stacked_objects_all(rb_objspace_t *objspace)
+{
+    return gc_mark_stacked_objects(objspace, FALSE, 0);
+}
+
+#if RGENGC_CHECK_MODE >= 4
+
+#define MAKE_ROOTSIG(obj) (((VALUE)(obj) << 1) | 0x01)
+#define IS_ROOTSIG(obj)   ((VALUE)(obj) & 0x01)
+#define GET_ROOTSIG(obj)  ((const char *)((VALUE)(obj) >> 1))
+
+struct reflist {
+    VALUE *list;
+    int pos;
+    int size;
+};
+
+static struct reflist *
+reflist_create(VALUE obj)
+{
+    struct reflist *refs = xmalloc(sizeof(struct reflist));
+    refs->size = 1;
+    refs->list = ALLOC_N(VALUE, refs->size);
+    refs->list[0] = obj;
+    refs->pos = 1;
+    return refs;
+}
+
+static void
+reflist_destruct(struct reflist *refs)
+{
+    xfree(refs->list);
+    xfree(refs);
+}
+
+static void
+reflist_add(struct reflist *refs, VALUE obj)
+{
+    if (refs->pos == refs->size) {
+        refs->size *= 2;
+        SIZED_REALLOC_N(refs->list, VALUE, refs->size, refs->size/2);
+    }
+
+    refs->list[refs->pos++] = obj;
+}
+
+static void
+reflist_dump(struct reflist *refs)
+{
+    int i;
+    for (i=0; i<refs->pos; i++) {
+        VALUE obj = refs->list[i];
+        if (IS_ROOTSIG(obj)) { /* root */
+            fprintf(stderr, "<root@%s>", GET_ROOTSIG(obj));
+        }
+        else {
+            fprintf(stderr, "<%s>", rb_obj_info(obj));
+        }
+        if (i+1 < refs->pos) fprintf(stderr, ", ");
+    }
+}
+
+static int
+reflist_referred_from_machine_context(struct reflist *refs)
+{
+    int i;
+    for (i=0; i<refs->pos; i++) {
+        VALUE obj = refs->list[i];
+        if (IS_ROOTSIG(obj) && strcmp(GET_ROOTSIG(obj), "machine_context") == 0) return 1;
+    }
+    return 0;
+}
+
+struct allrefs {
+    rb_objspace_t *objspace;
+    /* a -> obj1
+     * b -> obj1
+     * c -> obj1
+     * c -> obj2
+     * d -> obj3
+     * #=> {obj1 => [a, b, c], obj2 => [c, d]}
+     */
+    struct st_table *references;
+    const char *category;
+    VALUE root_obj;
+    mark_stack_t mark_stack;
+};
+
+static int
+allrefs_add(struct allrefs *data, VALUE obj)
+{
+    struct reflist *refs;
+    st_data_t r;
+
+    if (st_lookup(data->references, obj, &r)) {
+        refs = (struct reflist *)r;
+        reflist_add(refs, data->root_obj);
+        return 0;
+    }
+    else {
+        refs = reflist_create(data->root_obj);
+        st_insert(data->references, obj, (st_data_t)refs);
+        return 1;
+    }
+}
+
+static void
+allrefs_i(VALUE obj, void *ptr)
+{
+    struct allrefs *data = (struct allrefs *)ptr;
+
+    if (allrefs_add(data, obj)) {
+        push_mark_stack(&data->mark_stack, obj);
+    }
+}
+
+static void
+allrefs_roots_i(VALUE obj, void *ptr)
+{
+    struct allrefs *data = (struct allrefs *)ptr;
+    if (strlen(data->category) == 0) rb_bug("!!!");
+    data->root_obj = MAKE_ROOTSIG(data->category);
+
+    if (allrefs_add(data, obj)) {
+        push_mark_stack(&data->mark_stack, obj);
+    }
+}
+#define PUSH_MARK_FUNC_DATA(v) do { \
+    struct gc_mark_func_data_struct *prev_mark_func_data = GET_VM()->gc.mark_func_data; \
+    GET_VM()->gc.mark_func_data = (v);
+
+#define POP_MARK_FUNC_DATA() GET_VM()->gc.mark_func_data = prev_mark_func_data;} while (0)
+
+static st_table *
+objspace_allrefs(rb_objspace_t *objspace)
+{
+    struct allrefs data;
+    struct gc_mark_func_data_struct mfd;
+    VALUE obj;
+    int prev_dont_gc = dont_gc_val();
+    dont_gc_on();
+
+    data.objspace = objspace;
+    data.references = st_init_numtable();
+    init_mark_stack(&data.mark_stack);
+
+    mfd.mark_func = allrefs_roots_i;
+    mfd.data = &data;
+
+    /* traverse root objects */
+    PUSH_MARK_FUNC_DATA(&mfd);
+    GET_VM()->gc.mark_func_data = &mfd;
+    mark_roots(objspace, &data.category);
+    POP_MARK_FUNC_DATA();
+
+    /* traverse rest objects reachable from root objects */
+    while (pop_mark_stack(&data.mark_stack, &obj)) {
+        rb_objspace_reachable_objects_from(data.root_obj = obj, allrefs_i, &data);
+    }
+    free_stack_chunks(&data.mark_stack);
+
+    dont_gc_set(prev_dont_gc);
+    return data.references;
+}
+
+static int
+objspace_allrefs_destruct_i(st_data_t key, st_data_t value, st_data_t ptr)
+{
+    struct reflist *refs = (struct reflist *)value;
+    reflist_destruct(refs);
+    return ST_CONTINUE;
+}
+
+static void
+objspace_allrefs_destruct(struct st_table *refs)
+{
+    st_foreach(refs, objspace_allrefs_destruct_i, 0);
+    st_free_table(refs);
+}
+
+#if RGENGC_CHECK_MODE >= 5
+static int
+allrefs_dump_i(st_data_t k, st_data_t v, st_data_t ptr)
+{
+    VALUE obj = (VALUE)k;
+    struct reflist *refs = (struct reflist *)v;
+    fprintf(stderr, "[allrefs_dump_i] %s <- ", rb_obj_info(obj));
+    reflist_dump(refs);
+    fprintf(stderr, "\n");
+    return ST_CONTINUE;
+}
+
+static void
+allrefs_dump(rb_objspace_t *objspace)
+{
+    VALUE size = objspace->rgengc.allrefs_table->num_entries;
+    fprintf(stderr, "[all refs] (size: %"PRIuVALUE")\n", size);
+    st_foreach(objspace->rgengc.allrefs_table, allrefs_dump_i, 0);
+}
+#endif
+
+static int
+gc_check_after_marks_i(st_data_t k, st_data_t v, st_data_t ptr)
+{
+    VALUE obj = k;
+    struct reflist *refs = (struct reflist *)v;
+    rb_objspace_t *objspace = (rb_objspace_t *)ptr;
+
+    /* object should be marked or oldgen */
+    if (!RVALUE_MARKED(objspace, obj)) {
+        fprintf(stderr, "gc_check_after_marks_i: %s is not marked and not oldgen.\n", rb_obj_info(obj));
+        fprintf(stderr, "gc_check_after_marks_i: %p is referred from ", (void *)obj);
+        reflist_dump(refs);
+
+        if (reflist_referred_from_machine_context(refs)) {
+            fprintf(stderr, " (marked from machine stack).\n");
+            /* marked from machine context can be false positive */
+        }
+        else {
+            objspace->rgengc.error_count++;
+            fprintf(stderr, "\n");
+        }
+    }
+    return ST_CONTINUE;
+}
+
+static void
+gc_marks_check(rb_objspace_t *objspace, st_foreach_callback_func *checker_func, const char *checker_name)
+{
+    size_t saved_malloc_increase = objspace->malloc_params.increase;
+#if RGENGC_ESTIMATE_OLDMALLOC
+    size_t saved_oldmalloc_increase = objspace->rgengc.oldmalloc_increase;
+#endif
+    VALUE already_disabled = rb_objspace_gc_disable(objspace);
+
+    objspace->rgengc.allrefs_table = objspace_allrefs(objspace);
+
+    if (checker_func) {
+        st_foreach(objspace->rgengc.allrefs_table, checker_func, (st_data_t)objspace);
+    }
+
+    if (objspace->rgengc.error_count > 0) {
+#if RGENGC_CHECK_MODE >= 5
+        allrefs_dump(objspace);
+#endif
+        if (checker_name) rb_bug("%s: GC has problem.", checker_name);
+    }
+
+    objspace_allrefs_destruct(objspace->rgengc.allrefs_table);
+    objspace->rgengc.allrefs_table = 0;
+
+    if (already_disabled == Qfalse) rb_objspace_gc_enable(objspace);
+    objspace->malloc_params.increase = saved_malloc_increase;
+#if RGENGC_ESTIMATE_OLDMALLOC
+    objspace->rgengc.oldmalloc_increase = saved_oldmalloc_increase;
+#endif
+}
+#endif /* RGENGC_CHECK_MODE >= 4 */
+
+struct verify_internal_consistency_struct {
+    rb_objspace_t *objspace;
+    int err_count;
+    size_t live_object_count;
+    size_t zombie_object_count;
+
+    VALUE parent;
+    size_t old_object_count;
+    size_t remembered_shady_count;
+};
+
+static void
+check_generation_i(const VALUE child, void *ptr)
+{
+    struct verify_internal_consistency_struct *data = (struct verify_internal_consistency_struct *)ptr;
+    const VALUE parent = data->parent;
+
+    if (RGENGC_CHECK_MODE) GC_ASSERT(RVALUE_OLD_P(data->objspace, parent));
+
+    if (!RVALUE_OLD_P(data->objspace, child)) {
+        if (!RVALUE_REMEMBERED(data->objspace, parent) &&
+            !RVALUE_REMEMBERED(data->objspace, child) &&
+            !RVALUE_UNCOLLECTIBLE(data->objspace, child)) {
+            fprintf(stderr, "verify_internal_consistency_reachable_i: WB miss (O->Y) %s -> %s\n", rb_obj_info(parent), rb_obj_info(child));
+            data->err_count++;
+        }
+    }
+}
+
+static void
+check_color_i(const VALUE child, void *ptr)
+{
+    struct verify_internal_consistency_struct *data = (struct verify_internal_consistency_struct *)ptr;
+    const VALUE parent = data->parent;
+
+    if (!RVALUE_WB_UNPROTECTED(data->objspace, parent) && RVALUE_WHITE_P(data->objspace, child)) {
+        fprintf(stderr, "verify_internal_consistency_reachable_i: WB miss (B->W) - %s -> %s\n",
+                rb_obj_info(parent), rb_obj_info(child));
+        data->err_count++;
+    }
+}
+
+static void
+check_children_i(const VALUE child, void *ptr)
+{
+    struct verify_internal_consistency_struct *data = (struct verify_internal_consistency_struct *)ptr;
+    if (check_rvalue_consistency_force(data->objspace, child, FALSE) != 0) {
+        fprintf(stderr, "check_children_i: %s has error (referenced from %s)",
+                rb_obj_info(child), rb_obj_info(data->parent));
+
+        data->err_count++;
+    }
+}
+
+static int
+verify_internal_consistency_i(void *page_start, void *page_end, size_t stride,
+                              struct verify_internal_consistency_struct *data)
+{
+    VALUE obj;
+    rb_objspace_t *objspace = data->objspace;
+
+    for (obj = (VALUE)page_start; obj != (VALUE)page_end; obj += stride) {
+        asan_unpoisoning_object(obj) {
+            if (!rb_gc_impl_garbage_object_p(objspace, obj)) {
+                /* count objects */
+                data->live_object_count++;
+                data->parent = obj;
+
+                /* Normally, we don't expect T_MOVED objects to be in the heap.
+                * But they can stay alive on the stack, */
+                if (!gc_object_moved_p(objspace, obj)) {
+                    /* moved slots don't have children */
+                    rb_objspace_reachable_objects_from(obj, check_children_i, (void *)data);
+                }
+
+                /* check health of children */
+                if (RVALUE_OLD_P(objspace, obj)) data->old_object_count++;
+                if (RVALUE_WB_UNPROTECTED(objspace, obj) && RVALUE_UNCOLLECTIBLE(objspace, obj)) data->remembered_shady_count++;
+
+                if (!is_marking(objspace) && RVALUE_OLD_P(objspace, obj)) {
+                    /* reachable objects from an oldgen object should be old or (young with remember) */
+                    data->parent = obj;
+                    rb_objspace_reachable_objects_from(obj, check_generation_i, (void *)data);
+                }
+
+                if (is_incremental_marking(objspace)) {
+                    if (RVALUE_BLACK_P(objspace, obj)) {
+                        /* reachable objects from black objects should be black or grey objects */
+                        data->parent = obj;
+                        rb_objspace_reachable_objects_from(obj, check_color_i, (void *)data);
+                    }
+                }
+            }
+            else {
+                if (BUILTIN_TYPE(obj) == T_ZOMBIE) {
+                    data->zombie_object_count++;
+
+                    if ((RBASIC(obj)->flags & ~ZOMBIE_OBJ_KEPT_FLAGS) != T_ZOMBIE) {
+                        fprintf(stderr, "verify_internal_consistency_i: T_ZOMBIE has extra flags set: %s\n",
+                                rb_obj_info(obj));
+                        data->err_count++;
+                    }
+
+                    if (!!FL_TEST(obj, FL_FINALIZE) != !!st_is_member(finalizer_table, obj)) {
+                        fprintf(stderr, "verify_internal_consistency_i: FL_FINALIZE %s but %s finalizer_table: %s\n",
+                                FL_TEST(obj, FL_FINALIZE) ? "set" : "not set", st_is_member(finalizer_table, obj) ? "in" : "not in",
+                                rb_obj_info(obj));
+                        data->err_count++;
+                    }
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+
+static int
+gc_verify_heap_page(rb_objspace_t *objspace, struct heap_page *page, VALUE obj)
+{
+    unsigned int has_remembered_shady = FALSE;
+    unsigned int has_remembered_old = FALSE;
+    int remembered_old_objects = 0;
+    int free_objects = 0;
+    int zombie_objects = 0;
+
+    short slot_size = page->slot_size;
+    uintptr_t start = (uintptr_t)page->start;
+    uintptr_t end = start + page->total_slots * slot_size;
+
+    for (uintptr_t ptr = start; ptr < end; ptr += slot_size) {
+        VALUE val = (VALUE)ptr;
+        asan_unpoisoning_object(val) {
+            enum ruby_value_type type = BUILTIN_TYPE(val);
+
+            if (type == T_NONE) free_objects++;
+            if (type == T_ZOMBIE) zombie_objects++;
+            if (RVALUE_PAGE_UNCOLLECTIBLE(page, val) && RVALUE_PAGE_WB_UNPROTECTED(page, val)) {
+                has_remembered_shady = TRUE;
+            }
+            if (RVALUE_PAGE_MARKING(page, val)) {
+                has_remembered_old = TRUE;
+                remembered_old_objects++;
+            }
+        }
+    }
+
+    if (!is_incremental_marking(objspace) &&
+        page->flags.has_remembered_objects == FALSE && has_remembered_old == TRUE) {
+
+        for (uintptr_t ptr = start; ptr < end; ptr += slot_size) {
+            VALUE val = (VALUE)ptr;
+            if (RVALUE_PAGE_MARKING(page, val)) {
+                fprintf(stderr, "marking -> %s\n", rb_obj_info(val));
+            }
+        }
+        rb_bug("page %p's has_remembered_objects should be false, but there are remembered old objects (%d). %s",
+               (void *)page, remembered_old_objects, obj ? rb_obj_info(obj) : "");
+    }
+
+    if (page->flags.has_uncollectible_wb_unprotected_objects == FALSE && has_remembered_shady == TRUE) {
+        rb_bug("page %p's has_remembered_shady should be false, but there are remembered shady objects. %s",
+               (void *)page, obj ? rb_obj_info(obj) : "");
+    }
+
+    if (0) {
+        /* free_slots may not equal to free_objects */
+        if (page->free_slots != free_objects) {
+            rb_bug("page %p's free_slots should be %d, but %d", (void *)page, page->free_slots, free_objects);
+        }
+    }
+    if (page->final_slots != zombie_objects) {
+        rb_bug("page %p's final_slots should be %d, but %d", (void *)page, page->final_slots, zombie_objects);
+    }
+
+    return remembered_old_objects;
+}
+
+static int
+gc_verify_heap_pages_(rb_objspace_t *objspace, struct ccan_list_head *head)
+{
+    int remembered_old_objects = 0;
+    struct heap_page *page = 0;
+
+    ccan_list_for_each(head, page, page_node) {
+        asan_unlock_freelist(page);
+        struct free_slot *p = page->freelist;
+        while (p) {
+            VALUE vp = (VALUE)p;
+            VALUE prev = vp;
+            asan_unpoison_object(vp, false);
+            if (BUILTIN_TYPE(vp) != T_NONE) {
+                fprintf(stderr, "freelist slot expected to be T_NONE but was: %s\n", rb_obj_info(vp));
+            }
+            p = p->next;
+            asan_poison_object(prev);
+        }
+        asan_lock_freelist(page);
+
+        if (page->flags.has_remembered_objects == FALSE) {
+            remembered_old_objects += gc_verify_heap_page(objspace, page, Qfalse);
+        }
+    }
+
+    return remembered_old_objects;
+}
+
+static int
+gc_verify_heap_pages(rb_objspace_t *objspace)
+{
+    int remembered_old_objects = 0;
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        remembered_old_objects += gc_verify_heap_pages_(objspace, &((&heaps[i])->pages));
+    }
+    return remembered_old_objects;
+}
+
+static void
+gc_verify_internal_consistency_(rb_objspace_t *objspace)
+{
+    struct verify_internal_consistency_struct data = {0};
+
+    data.objspace = objspace;
+    gc_report(5, objspace, "gc_verify_internal_consistency: start\n");
+
+    /* check relations */
+    for (size_t i = 0; i < rb_darray_size(objspace->heap_pages.sorted); i++) {
+        struct heap_page *page = rb_darray_get(objspace->heap_pages.sorted, i);
+        short slot_size = page->slot_size;
+
+        uintptr_t start = (uintptr_t)page->start;
+        uintptr_t end = start + page->total_slots * slot_size;
+
+        verify_internal_consistency_i((void *)start, (void *)end, slot_size, &data);
+    }
+
+    if (data.err_count != 0) {
+#if RGENGC_CHECK_MODE >= 5
+        objspace->rgengc.error_count = data.err_count;
+        gc_marks_check(objspace, NULL, NULL);
+        allrefs_dump(objspace);
+#endif
+        rb_bug("gc_verify_internal_consistency: found internal inconsistency.");
+    }
+
+    /* check heap_page status */
+    gc_verify_heap_pages(objspace);
+
+    /* check counters */
+
+    if (!is_lazy_sweeping(objspace) &&
+            !finalizing &&
+            !rb_gc_multi_ractor_p()) {
+        if (objspace_live_slots(objspace) != data.live_object_count) {
+            fprintf(stderr, "heap_pages_final_slots: %"PRIdSIZE", total_freed_objects: %"PRIdSIZE"\n",
+                    total_final_slots_count(objspace), total_freed_objects(objspace));
+            rb_bug("inconsistent live slot number: expect %"PRIuSIZE", but %"PRIuSIZE".",
+                   objspace_live_slots(objspace), data.live_object_count);
+        }
+    }
+
+    if (!is_marking(objspace)) {
+        if (objspace->rgengc.old_objects != data.old_object_count) {
+            rb_bug("inconsistent old slot number: expect %"PRIuSIZE", but %"PRIuSIZE".",
+                   objspace->rgengc.old_objects, data.old_object_count);
+        }
+        if (objspace->rgengc.uncollectible_wb_unprotected_objects != data.remembered_shady_count) {
+            rb_bug("inconsistent number of wb unprotected objects: expect %"PRIuSIZE", but %"PRIuSIZE".",
+                   objspace->rgengc.uncollectible_wb_unprotected_objects, data.remembered_shady_count);
+        }
+    }
+
+    if (!finalizing) {
+        size_t list_count = 0;
+
+        {
+            VALUE z = heap_pages_deferred_final;
+            while (z) {
+                list_count++;
+                z = RZOMBIE(z)->next;
+            }
+        }
+
+        if (total_final_slots_count(objspace) != data.zombie_object_count ||
+            total_final_slots_count(objspace) != list_count) {
+
+            rb_bug("inconsistent finalizing object count:\n"
+                    "  expect %"PRIuSIZE"\n"
+                    "  but    %"PRIuSIZE" zombies\n"
+                    "  heap_pages_deferred_final list has %"PRIuSIZE" items.",
+                    total_final_slots_count(objspace),
+                    data.zombie_object_count,
+                    list_count);
+        }
+    }
+
+    gc_report(5, objspace, "gc_verify_internal_consistency: OK\n");
+}
+
+static void
+gc_verify_internal_consistency(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    unsigned int lev = rb_gc_vm_lock();
+    {
+        rb_gc_vm_barrier(); // stop other ractors
+
+        unsigned int prev_during_gc = during_gc;
+        during_gc = FALSE; // stop gc here
+        {
+            gc_verify_internal_consistency_(objspace);
+        }
+        during_gc = prev_during_gc;
+    }
+    rb_gc_vm_unlock(lev);
+}
+
+static void
+heap_move_pooled_pages_to_free_pages(rb_heap_t *heap)
+{
+    if (heap->pooled_pages) {
+        if (heap->free_pages) {
+            struct heap_page *free_pages_tail = heap->free_pages;
+            while (free_pages_tail->free_next) {
+                free_pages_tail = free_pages_tail->free_next;
+            }
+            free_pages_tail->free_next = heap->pooled_pages;
+        }
+        else {
+            heap->free_pages = heap->pooled_pages;
+        }
+
+        heap->pooled_pages = NULL;
+    }
+}
+
+static int
+gc_remember_unprotected(rb_objspace_t *objspace, VALUE obj)
+{
+    struct heap_page *page = GET_HEAP_PAGE(obj);
+    bits_t *uncollectible_bits = &page->uncollectible_bits[0];
+
+    if (!MARKED_IN_BITMAP(uncollectible_bits, obj)) {
+        page->flags.has_uncollectible_wb_unprotected_objects = TRUE;
+        MARK_IN_BITMAP(uncollectible_bits, obj);
+        objspace->rgengc.uncollectible_wb_unprotected_objects++;
+
+#if RGENGC_PROFILE > 0
+        objspace->profile.total_remembered_shady_object_count++;
+#if RGENGC_PROFILE >= 2
+        objspace->profile.remembered_shady_object_count_types[BUILTIN_TYPE(obj)]++;
+#endif
+#endif
+        return TRUE;
+    }
+    else {
+        return FALSE;
+    }
+}
+
+static inline void
+gc_marks_wb_unprotected_objects_plane(rb_objspace_t *objspace, uintptr_t p, bits_t bits)
+{
+    if (bits) {
+        do {
+            if (bits & 1) {
+                gc_report(2, objspace, "gc_marks_wb_unprotected_objects: marked shady: %s\n", rb_obj_info((VALUE)p));
+                GC_ASSERT(RVALUE_WB_UNPROTECTED(objspace, (VALUE)p));
+                GC_ASSERT(RVALUE_MARKED(objspace, (VALUE)p));
+                gc_mark_children(objspace, (VALUE)p);
+            }
+            p += BASE_SLOT_SIZE;
+            bits >>= 1;
+        } while (bits);
+    }
+}
+
+static void
+gc_marks_wb_unprotected_objects(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    struct heap_page *page = 0;
+
+    ccan_list_for_each(&heap->pages, page, page_node) {
+        bits_t *mark_bits = page->mark_bits;
+        bits_t *wbun_bits = page->wb_unprotected_bits;
+        uintptr_t p = page->start;
+        size_t j;
+
+        bits_t bits = mark_bits[0] & wbun_bits[0];
+        bits >>= NUM_IN_PAGE(p);
+        gc_marks_wb_unprotected_objects_plane(objspace, p, bits);
+        p += (BITS_BITLENGTH - NUM_IN_PAGE(p)) * BASE_SLOT_SIZE;
+
+        for (j=1; j<HEAP_PAGE_BITMAP_LIMIT; j++) {
+            bits_t bits = mark_bits[j] & wbun_bits[j];
+
+            gc_marks_wb_unprotected_objects_plane(objspace, p, bits);
+            p += BITS_BITLENGTH * BASE_SLOT_SIZE;
+        }
+    }
+
+    gc_mark_stacked_objects_all(objspace);
+}
+
+static void
+gc_update_weak_references(rb_objspace_t *objspace)
+{
+    size_t retained_weak_references_count = 0;
+    VALUE **ptr_ptr;
+    rb_darray_foreach(objspace->weak_references, i, ptr_ptr) {
+        if (!*ptr_ptr) continue;
+
+        VALUE obj = **ptr_ptr;
+
+        if (RB_SPECIAL_CONST_P(obj)) continue;
+
+        if (!RVALUE_MARKED(objspace, obj)) {
+            **ptr_ptr = Qundef;
+        }
+        else {
+            retained_weak_references_count++;
+        }
+    }
+
+    objspace->profile.retained_weak_references_count = retained_weak_references_count;
+
+    rb_darray_clear(objspace->weak_references);
+    DURING_GC_COULD_MALLOC_REGION_START();
+    {
+        rb_darray_resize_capa(&objspace->weak_references, retained_weak_references_count);
+    }
+    DURING_GC_COULD_MALLOC_REGION_END();
+}
+
+static void
+gc_marks_finish(rb_objspace_t *objspace)
+{
+    /* finish incremental GC */
+    if (is_incremental_marking(objspace)) {
+        if (RGENGC_CHECK_MODE && is_mark_stack_empty(&objspace->mark_stack) == 0) {
+            rb_bug("gc_marks_finish: mark stack is not empty (%"PRIdSIZE").",
+                   mark_stack_size(&objspace->mark_stack));
+        }
+
+        mark_roots(objspace, NULL);
+        while (gc_mark_stacked_objects_incremental(objspace, INT_MAX) == false);
+
+#if RGENGC_CHECK_MODE >= 2
+        if (gc_verify_heap_pages(objspace) != 0) {
+            rb_bug("gc_marks_finish (incremental): there are remembered old objects.");
+        }
+#endif
+
+        objspace->flags.during_incremental_marking = FALSE;
+        /* check children of all marked wb-unprotected objects */
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            gc_marks_wb_unprotected_objects(objspace, &heaps[i]);
+        }
+    }
+
+    gc_update_weak_references(objspace);
+
+#if RGENGC_CHECK_MODE >= 2
+    gc_verify_internal_consistency(objspace);
+#endif
+
+#if RGENGC_CHECK_MODE >= 4
+    during_gc = FALSE;
+    gc_marks_check(objspace, gc_check_after_marks_i, "after_marks");
+    during_gc = TRUE;
+#endif
+
+    {
+        const unsigned long r_mul = objspace->live_ractor_cache_count > 8 ? 8 : objspace->live_ractor_cache_count; // upto 8
+
+        size_t total_slots = objspace_available_slots(objspace);
+        size_t sweep_slots = total_slots - objspace->marked_slots; /* will be swept slots */
+        size_t max_free_slots = (size_t)(total_slots * gc_params.heap_free_slots_max_ratio);
+        size_t min_free_slots = (size_t)(total_slots * gc_params.heap_free_slots_min_ratio);
+        if (min_free_slots < gc_params.heap_free_slots * r_mul) {
+            min_free_slots = gc_params.heap_free_slots * r_mul;
+        }
+
+        int full_marking = is_full_marking(objspace);
+
+        GC_ASSERT(objspace_available_slots(objspace) >= objspace->marked_slots);
+
+        /* Setup freeable slots. */
+        size_t total_init_slots = 0;
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            total_init_slots += gc_params.heap_init_slots[i] * r_mul;
+        }
+
+        if (max_free_slots < total_init_slots) {
+            max_free_slots = total_init_slots;
+        }
+
+        if (sweep_slots > max_free_slots) {
+            heap_pages_freeable_pages = (sweep_slots - max_free_slots) / HEAP_PAGE_OBJ_LIMIT;
+        }
+        else {
+            heap_pages_freeable_pages = 0;
+        }
+
+        if (objspace->heap_pages.allocatable_slots == 0 && sweep_slots < min_free_slots) {
+            if (!full_marking) {
+                if (objspace->profile.count - objspace->rgengc.last_major_gc < RVALUE_OLD_AGE) {
+                    full_marking = TRUE;
+                }
+                else {
+                    gc_report(1, objspace, "gc_marks_finish: next is full GC!!)\n");
+                    gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_NOFREE;
+                }
+            }
+        }
+
+        if (full_marking) {
+            /* See the comment about RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR */
+            const double r = gc_params.oldobject_limit_factor;
+            objspace->rgengc.uncollectible_wb_unprotected_objects_limit = MAX(
+                (size_t)(objspace->rgengc.uncollectible_wb_unprotected_objects * r),
+                (size_t)(objspace->rgengc.old_objects * gc_params.uncollectible_wb_unprotected_objects_limit_ratio)
+            );
+            objspace->rgengc.old_objects_limit = (size_t)(objspace->rgengc.old_objects * r);
+        }
+
+        if (objspace->rgengc.uncollectible_wb_unprotected_objects > objspace->rgengc.uncollectible_wb_unprotected_objects_limit) {
+            gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_SHADY;
+        }
+        if (objspace->rgengc.old_objects > objspace->rgengc.old_objects_limit) {
+            gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_OLDGEN;
+        }
+
+        gc_report(1, objspace, "gc_marks_finish (marks %"PRIdSIZE" objects, "
+                  "old %"PRIdSIZE" objects, total %"PRIdSIZE" slots, "
+                  "sweep %"PRIdSIZE" slots, allocatable %"PRIdSIZE" slots, next GC: %s)\n",
+                  objspace->marked_slots, objspace->rgengc.old_objects, objspace_available_slots(objspace), sweep_slots, objspace->heap_pages.allocatable_slots,
+                  gc_needs_major_flags ? "major" : "minor");
+    }
+
+    // TODO: refactor so we don't need to call this
+    rb_ractor_finish_marking();
+
+    rb_gc_event_hook(0, RUBY_INTERNAL_EVENT_GC_END_MARK);
+}
+
+static bool
+gc_compact_heap_cursors_met_p(rb_heap_t *heap)
+{
+    return heap->sweeping_page == heap->compact_cursor;
+}
+
+
+static rb_heap_t *
+gc_compact_destination_pool(rb_objspace_t *objspace, rb_heap_t *src_pool, VALUE obj)
+{
+    size_t obj_size = rb_gc_obj_optimal_size(obj);
+    if (obj_size == 0) {
+        return src_pool;
+    }
+
+    size_t idx = 0;
+    if (rb_gc_impl_size_allocatable_p(obj_size)) {
+        idx = heap_idx_for_size(obj_size);
+    }
+
+    return &heaps[idx];
+}
+
+static bool
+gc_compact_move(rb_objspace_t *objspace, rb_heap_t *heap, VALUE src)
+{
+    GC_ASSERT(BUILTIN_TYPE(src) != T_MOVED);
+    GC_ASSERT(gc_is_moveable_obj(objspace, src));
+
+    rb_heap_t *dest_pool = gc_compact_destination_pool(objspace, heap, src);
+    uint32_t orig_shape = 0;
+    uint32_t new_shape = 0;
+
+    if (gc_compact_heap_cursors_met_p(dest_pool)) {
+        return dest_pool != heap;
+    }
+
+    if (RB_TYPE_P(src, T_OBJECT)) {
+        orig_shape = rb_gc_get_shape(src);
+
+        if (dest_pool != heap) {
+            new_shape = rb_gc_rebuild_shape(src, dest_pool - heaps);
+
+            if (new_shape == 0) {
+                dest_pool = heap;
+            }
+        }
+    }
+
+    while (!try_move(objspace, dest_pool, dest_pool->free_pages, src)) {
+        struct gc_sweep_context ctx = {
+            .page = dest_pool->sweeping_page,
+            .final_slots = 0,
+            .freed_slots = 0,
+            .empty_slots = 0,
+        };
+
+        /* The page of src could be partially compacted, so it may contain
+         * T_MOVED. Sweeping a page may read objects on this page, so we
+         * need to lock the page. */
+        lock_page_body(objspace, GET_PAGE_BODY(src));
+        gc_sweep_page(objspace, dest_pool, &ctx);
+        unlock_page_body(objspace, GET_PAGE_BODY(src));
+
+        if (dest_pool->sweeping_page->free_slots > 0) {
+            heap_add_freepage(dest_pool, dest_pool->sweeping_page);
+        }
+
+        dest_pool->sweeping_page = ccan_list_next(&dest_pool->pages, dest_pool->sweeping_page, page_node);
+        if (gc_compact_heap_cursors_met_p(dest_pool)) {
+            return dest_pool != heap;
+        }
+    }
+
+    if (orig_shape != 0) {
+        if (new_shape != 0) {
+            VALUE dest = rb_gc_impl_location(objspace, src);
+            rb_gc_set_shape(dest, new_shape);
+        }
+        RMOVED(src)->original_shape_id = orig_shape;
+    }
+
+    return true;
+}
+
+static bool
+gc_compact_plane(rb_objspace_t *objspace, rb_heap_t *heap, uintptr_t p, bits_t bitset, struct heap_page *page)
+{
+    short slot_size = page->slot_size;
+    short slot_bits = slot_size / BASE_SLOT_SIZE;
+    GC_ASSERT(slot_bits > 0);
+
+    do {
+        VALUE vp = (VALUE)p;
+        GC_ASSERT(vp % BASE_SLOT_SIZE == 0);
+
+        if (bitset & 1) {
+            objspace->rcompactor.considered_count_table[BUILTIN_TYPE(vp)]++;
+
+            if (gc_is_moveable_obj(objspace, vp)) {
+                if (!gc_compact_move(objspace, heap, vp)) {
+                    //the cursors met. bubble up
+                    return false;
+                }
+            }
+        }
+        p += slot_size;
+        bitset >>= slot_bits;
+    } while (bitset);
+
+    return true;
+}
+
+// Iterate up all the objects in page, moving them to where they want to go
+static bool
+gc_compact_page(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *page)
+{
+    GC_ASSERT(page == heap->compact_cursor);
+
+    bits_t *mark_bits, *pin_bits;
+    bits_t bitset;
+    uintptr_t p = page->start;
+
+    mark_bits = page->mark_bits;
+    pin_bits = page->pinned_bits;
+
+    // objects that can be moved are marked and not pinned
+    bitset = (mark_bits[0] & ~pin_bits[0]);
+    bitset >>= NUM_IN_PAGE(p);
+    if (bitset) {
+        if (!gc_compact_plane(objspace, heap, (uintptr_t)p, bitset, page))
+            return false;
+    }
+    p += (BITS_BITLENGTH - NUM_IN_PAGE(p)) * BASE_SLOT_SIZE;
+
+    for (int j = 1; j < HEAP_PAGE_BITMAP_LIMIT; j++) {
+        bitset = (mark_bits[j] & ~pin_bits[j]);
+        if (bitset) {
+            if (!gc_compact_plane(objspace, heap, (uintptr_t)p, bitset, page))
+                return false;
+        }
+        p += BITS_BITLENGTH * BASE_SLOT_SIZE;
+    }
+
+    return true;
+}
+
+static bool
+gc_compact_all_compacted_p(rb_objspace_t *objspace)
+{
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+
+        if (heap->total_pages > 0 &&
+                !gc_compact_heap_cursors_met_p(heap)) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+static void
+gc_sweep_compact(rb_objspace_t *objspace)
+{
+    gc_compact_start(objspace);
+#if RGENGC_CHECK_MODE >= 2
+    gc_verify_internal_consistency(objspace);
+#endif
+
+    while (!gc_compact_all_compacted_p(objspace)) {
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            rb_heap_t *heap = &heaps[i];
+
+            if (gc_compact_heap_cursors_met_p(heap)) {
+                continue;
+            }
+
+            struct heap_page *start_page = heap->compact_cursor;
+
+            if (!gc_compact_page(objspace, heap, start_page)) {
+                lock_page_body(objspace, start_page->body);
+
+                continue;
+            }
+
+            // If we get here, we've finished moving all objects on the compact_cursor page
+            // So we can lock it and move the cursor on to the next one.
+            lock_page_body(objspace, start_page->body);
+            heap->compact_cursor = ccan_list_prev(&heap->pages, heap->compact_cursor, page_node);
+        }
+    }
+
+    gc_compact_finish(objspace);
+
+#if RGENGC_CHECK_MODE >= 2
+    gc_verify_internal_consistency(objspace);
+#endif
+}
+
+static void
+gc_marks_rest(rb_objspace_t *objspace)
+{
+    gc_report(1, objspace, "gc_marks_rest\n");
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        (&heaps[i])->pooled_pages = NULL;
+    }
+
+    if (is_incremental_marking(objspace)) {
+        while (gc_mark_stacked_objects_incremental(objspace, INT_MAX) == FALSE);
+    }
+    else {
+        gc_mark_stacked_objects_all(objspace);
+    }
+
+    gc_marks_finish(objspace);
+}
+
+static bool
+gc_marks_step(rb_objspace_t *objspace, size_t slots)
+{
+    bool marking_finished = false;
+
+    GC_ASSERT(is_marking(objspace));
+    if (gc_mark_stacked_objects_incremental(objspace, slots)) {
+        gc_marks_finish(objspace);
+
+        marking_finished = true;
+    }
+
+    return marking_finished;
+}
+
+static bool
+gc_marks_continue(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    GC_ASSERT(dont_gc_val() == FALSE || objspace->profile.latest_gc_info & GPR_FLAG_METHOD);
+    bool marking_finished = true;
+
+    gc_marking_enter(objspace);
+
+    if (heap->free_pages) {
+        gc_report(2, objspace, "gc_marks_continue: has pooled pages");
+
+        marking_finished = gc_marks_step(objspace, objspace->rincgc.step_slots);
+    }
+    else {
+        gc_report(2, objspace, "gc_marks_continue: no more pooled pages (stack depth: %"PRIdSIZE").\n",
+                  mark_stack_size(&objspace->mark_stack));
+        heap->force_incremental_marking_finish_count++;
+        gc_marks_rest(objspace);
+    }
+
+    gc_marking_exit(objspace);
+
+    return marking_finished;
+}
+
+static void
+gc_marks_start(rb_objspace_t *objspace, int full_mark)
+{
+    /* start marking */
+    gc_report(1, objspace, "gc_marks_start: (%s)\n", full_mark ? "full" : "minor");
+    gc_mode_transition(objspace, gc_mode_marking);
+
+    if (full_mark) {
+        size_t incremental_marking_steps = (objspace->rincgc.pooled_slots / INCREMENTAL_MARK_STEP_ALLOCATIONS) + 1;
+        objspace->rincgc.step_slots = (objspace->marked_slots * 2) / incremental_marking_steps;
+
+        if (0) fprintf(stderr, "objspace->marked_slots: %"PRIdSIZE", "
+                       "objspace->rincgc.pooled_page_num: %"PRIdSIZE", "
+                       "objspace->rincgc.step_slots: %"PRIdSIZE", \n",
+                       objspace->marked_slots, objspace->rincgc.pooled_slots, objspace->rincgc.step_slots);
+        objspace->flags.during_minor_gc = FALSE;
+        if (ruby_enable_autocompact) {
+            objspace->flags.during_compacting |= TRUE;
+        }
+        objspace->profile.major_gc_count++;
+        objspace->rgengc.uncollectible_wb_unprotected_objects = 0;
+        objspace->rgengc.old_objects = 0;
+        objspace->rgengc.last_major_gc = objspace->profile.count;
+        objspace->marked_slots = 0;
+
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            rb_heap_t *heap = &heaps[i];
+            rgengc_mark_and_rememberset_clear(objspace, heap);
+            heap_move_pooled_pages_to_free_pages(heap);
+
+            if (objspace->flags.during_compacting) {
+                struct heap_page *page = NULL;
+
+                ccan_list_for_each(&heap->pages, page, page_node) {
+                    page->pinned_slots = 0;
+                }
+            }
+        }
+    }
+    else {
+        objspace->flags.during_minor_gc = TRUE;
+        objspace->marked_slots =
+          objspace->rgengc.old_objects + objspace->rgengc.uncollectible_wb_unprotected_objects; /* uncollectible objects are marked already */
+        objspace->profile.minor_gc_count++;
+
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            rgengc_rememberset_mark(objspace, &heaps[i]);
+        }
+    }
+
+    mark_roots(objspace, NULL);
+
+    gc_report(1, objspace, "gc_marks_start: (%s) end, stack in %"PRIdSIZE"\n",
+              full_mark ? "full" : "minor", mark_stack_size(&objspace->mark_stack));
+}
+
+static bool
+gc_marks(rb_objspace_t *objspace, int full_mark)
+{
+    gc_prof_mark_timer_start(objspace);
+    gc_marking_enter(objspace);
+
+    bool marking_finished = false;
+
+    /* setup marking */
+
+    gc_marks_start(objspace, full_mark);
+    if (!is_incremental_marking(objspace)) {
+        gc_marks_rest(objspace);
+        marking_finished = true;
+    }
+
+#if RGENGC_PROFILE > 0
+    if (gc_prof_record(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->old_objects = objspace->rgengc.old_objects;
+    }
+#endif
+
+    gc_marking_exit(objspace);
+    gc_prof_mark_timer_stop(objspace);
+
+    return marking_finished;
+}
+
+/* RGENGC */
+
+static void
+gc_report_body(int level, rb_objspace_t *objspace, const char *fmt, ...)
+{
+    if (level <= RGENGC_DEBUG) {
+        char buf[1024];
+        FILE *out = stderr;
+        va_list args;
+        const char *status = " ";
+
+        if (during_gc) {
+            status = is_full_marking(objspace) ? "+" : "-";
+        }
+        else {
+            if (is_lazy_sweeping(objspace)) {
+                status = "S";
+            }
+            if (is_incremental_marking(objspace)) {
+                status = "M";
+            }
+        }
+
+        va_start(args, fmt);
+        vsnprintf(buf, 1024, fmt, args);
+        va_end(args);
+
+        fprintf(out, "%s|", status);
+        fputs(buf, out);
+    }
+}
+
+/* bit operations */
+
+static int
+rgengc_remembersetbits_set(rb_objspace_t *objspace, VALUE obj)
+{
+    struct heap_page *page = GET_HEAP_PAGE(obj);
+    bits_t *bits = &page->remembered_bits[0];
+
+    if (MARKED_IN_BITMAP(bits, obj)) {
+        return FALSE;
+    }
+    else {
+        page->flags.has_remembered_objects = TRUE;
+        MARK_IN_BITMAP(bits, obj);
+        return TRUE;
+    }
+}
+
+/* wb, etc */
+
+/* return FALSE if already remembered */
+static int
+rgengc_remember(rb_objspace_t *objspace, VALUE obj)
+{
+    gc_report(6, objspace, "rgengc_remember: %s %s\n", rb_obj_info(obj),
+              RVALUE_REMEMBERED(objspace, obj) ? "was already remembered" : "is remembered now");
+
+    check_rvalue_consistency(objspace, obj);
+
+    if (RGENGC_CHECK_MODE) {
+        if (RVALUE_WB_UNPROTECTED(objspace, obj)) rb_bug("rgengc_remember: %s is not wb protected.", rb_obj_info(obj));
+    }
+
+#if RGENGC_PROFILE > 0
+    if (!RVALUE_REMEMBERED(objspace, obj)) {
+        if (RVALUE_WB_UNPROTECTED(objspace, obj) == 0) {
+            objspace->profile.total_remembered_normal_object_count++;
+#if RGENGC_PROFILE >= 2
+            objspace->profile.remembered_normal_object_count_types[BUILTIN_TYPE(obj)]++;
+#endif
+        }
+    }
+#endif /* RGENGC_PROFILE > 0 */
+
+    return rgengc_remembersetbits_set(objspace, obj);
+}
+
+#ifndef PROFILE_REMEMBERSET_MARK
+#define PROFILE_REMEMBERSET_MARK 0
+#endif
+
+static inline void
+rgengc_rememberset_mark_plane(rb_objspace_t *objspace, uintptr_t p, bits_t bitset)
+{
+    if (bitset) {
+        do {
+            if (bitset & 1) {
+                VALUE obj = (VALUE)p;
+                gc_report(2, objspace, "rgengc_rememberset_mark: mark %s\n", rb_obj_info(obj));
+                GC_ASSERT(RVALUE_UNCOLLECTIBLE(objspace, obj));
+                GC_ASSERT(RVALUE_OLD_P(objspace, obj) || RVALUE_WB_UNPROTECTED(objspace, obj));
+
+                gc_mark_children(objspace, obj);
+            }
+            p += BASE_SLOT_SIZE;
+            bitset >>= 1;
+        } while (bitset);
+    }
+}
+
+static void
+rgengc_rememberset_mark(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    size_t j;
+    struct heap_page *page = 0;
+#if PROFILE_REMEMBERSET_MARK
+    int has_old = 0, has_shady = 0, has_both = 0, skip = 0;
+#endif
+    gc_report(1, objspace, "rgengc_rememberset_mark: start\n");
+
+    ccan_list_for_each(&heap->pages, page, page_node) {
+        if (page->flags.has_remembered_objects | page->flags.has_uncollectible_wb_unprotected_objects) {
+            uintptr_t p = page->start;
+            bits_t bitset, bits[HEAP_PAGE_BITMAP_LIMIT];
+            bits_t *remembered_bits = page->remembered_bits;
+            bits_t *uncollectible_bits = page->uncollectible_bits;
+            bits_t *wb_unprotected_bits = page->wb_unprotected_bits;
+#if PROFILE_REMEMBERSET_MARK
+            if (page->flags.has_remembered_objects && page->flags.has_uncollectible_wb_unprotected_objects) has_both++;
+            else if (page->flags.has_remembered_objects) has_old++;
+            else if (page->flags.has_uncollectible_wb_unprotected_objects) has_shady++;
+#endif
+            for (j=0; j<HEAP_PAGE_BITMAP_LIMIT; j++) {
+                bits[j] = remembered_bits[j] | (uncollectible_bits[j] & wb_unprotected_bits[j]);
+                remembered_bits[j] = 0;
+            }
+            page->flags.has_remembered_objects = FALSE;
+
+            bitset = bits[0];
+            bitset >>= NUM_IN_PAGE(p);
+            rgengc_rememberset_mark_plane(objspace, p, bitset);
+            p += (BITS_BITLENGTH - NUM_IN_PAGE(p)) * BASE_SLOT_SIZE;
+
+            for (j=1; j < HEAP_PAGE_BITMAP_LIMIT; j++) {
+                bitset = bits[j];
+                rgengc_rememberset_mark_plane(objspace, p, bitset);
+                p += BITS_BITLENGTH * BASE_SLOT_SIZE;
+            }
+        }
+#if PROFILE_REMEMBERSET_MARK
+        else {
+            skip++;
+        }
+#endif
+    }
+
+#if PROFILE_REMEMBERSET_MARK
+    fprintf(stderr, "%d\t%d\t%d\t%d\n", has_both, has_old, has_shady, skip);
+#endif
+    gc_report(1, objspace, "rgengc_rememberset_mark: finished\n");
+}
+
+static void
+rgengc_mark_and_rememberset_clear(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    struct heap_page *page = 0;
+
+    ccan_list_for_each(&heap->pages, page, page_node) {
+        memset(&page->mark_bits[0],       0, HEAP_PAGE_BITMAP_SIZE);
+        memset(&page->uncollectible_bits[0], 0, HEAP_PAGE_BITMAP_SIZE);
+        memset(&page->marking_bits[0],    0, HEAP_PAGE_BITMAP_SIZE);
+        memset(&page->remembered_bits[0], 0, HEAP_PAGE_BITMAP_SIZE);
+        memset(&page->pinned_bits[0],     0, HEAP_PAGE_BITMAP_SIZE);
+        page->flags.has_uncollectible_wb_unprotected_objects = FALSE;
+        page->flags.has_remembered_objects = FALSE;
+    }
+}
+
+/* RGENGC: APIs */
+
+NOINLINE(static void gc_writebarrier_generational(VALUE a, VALUE b, rb_objspace_t *objspace));
+
+static void
+gc_writebarrier_generational(VALUE a, VALUE b, rb_objspace_t *objspace)
+{
+    if (RGENGC_CHECK_MODE) {
+        if (!RVALUE_OLD_P(objspace, a)) rb_bug("gc_writebarrier_generational: %s is not an old object.", rb_obj_info(a));
+        if ( RVALUE_OLD_P(objspace, b)) rb_bug("gc_writebarrier_generational: %s is an old object.", rb_obj_info(b));
+        if (is_incremental_marking(objspace)) rb_bug("gc_writebarrier_generational: called while incremental marking: %s -> %s", rb_obj_info(a), rb_obj_info(b));
+    }
+
+    /* mark `a' and remember (default behavior) */
+    if (!RVALUE_REMEMBERED(objspace, a)) {
+        int lev = rb_gc_vm_lock_no_barrier();
+        {
+            rgengc_remember(objspace, a);
+        }
+        rb_gc_vm_unlock_no_barrier(lev);
+
+        gc_report(1, objspace, "gc_writebarrier_generational: %s (remembered) -> %s\n", rb_obj_info(a), rb_obj_info(b));
+    }
+
+    check_rvalue_consistency(objspace, a);
+    check_rvalue_consistency(objspace, b);
+}
+
+static void
+gc_mark_from(rb_objspace_t *objspace, VALUE obj, VALUE parent)
+{
+    gc_mark_set_parent(objspace, parent);
+    rgengc_check_relation(objspace, obj);
+    if (gc_mark_set(objspace, obj) == FALSE) return;
+    gc_aging(objspace, obj);
+    gc_grey(objspace, obj);
+}
+
+NOINLINE(static void gc_writebarrier_incremental(VALUE a, VALUE b, rb_objspace_t *objspace));
+
+static void
+gc_writebarrier_incremental(VALUE a, VALUE b, rb_objspace_t *objspace)
+{
+    gc_report(2, objspace, "gc_writebarrier_incremental: [LG] %p -> %s\n", (void *)a, rb_obj_info(b));
+
+    if (RVALUE_BLACK_P(objspace, a)) {
+        if (RVALUE_WHITE_P(objspace, b)) {
+            if (!RVALUE_WB_UNPROTECTED(objspace, a)) {
+                gc_report(2, objspace, "gc_writebarrier_incremental: [IN] %p -> %s\n", (void *)a, rb_obj_info(b));
+                gc_mark_from(objspace, b, a);
+            }
+        }
+        else if (RVALUE_OLD_P(objspace, a) && !RVALUE_OLD_P(objspace, b)) {
+            rgengc_remember(objspace, a);
+        }
+
+        if (RB_UNLIKELY(objspace->flags.during_compacting)) {
+            MARK_IN_BITMAP(GET_HEAP_PINNED_BITS(b), b);
+        }
+    }
+}
+
+void
+rb_gc_impl_writebarrier(void *objspace_ptr, VALUE a, VALUE b)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (RGENGC_CHECK_MODE) {
+        if (SPECIAL_CONST_P(a)) rb_bug("rb_gc_writebarrier: a is special const: %"PRIxVALUE, a);
+        if (SPECIAL_CONST_P(b)) rb_bug("rb_gc_writebarrier: b is special const: %"PRIxVALUE, b);
+    }
+
+    GC_ASSERT(RB_BUILTIN_TYPE(a) != T_NONE);
+    GC_ASSERT(RB_BUILTIN_TYPE(a) != T_MOVED);
+    GC_ASSERT(RB_BUILTIN_TYPE(a) != T_ZOMBIE);
+    GC_ASSERT(RB_BUILTIN_TYPE(b) != T_NONE);
+    GC_ASSERT(RB_BUILTIN_TYPE(b) != T_MOVED);
+    GC_ASSERT(RB_BUILTIN_TYPE(b) != T_ZOMBIE);
+
+  retry:
+    if (!is_incremental_marking(objspace)) {
+        if (!RVALUE_OLD_P(objspace, a) || RVALUE_OLD_P(objspace, b)) {
+            // do nothing
+        }
+        else {
+            gc_writebarrier_generational(a, b, objspace);
+        }
+    }
+    else {
+        bool retry = false;
+        /* slow path */
+        int lev = rb_gc_vm_lock_no_barrier();
+        {
+            if (is_incremental_marking(objspace)) {
+                gc_writebarrier_incremental(a, b, objspace);
+            }
+            else {
+                retry = true;
+            }
+        }
+        rb_gc_vm_unlock_no_barrier(lev);
+
+        if (retry) goto retry;
+    }
+    return;
+}
+
+void
+rb_gc_impl_writebarrier_unprotect(void *objspace_ptr, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (RVALUE_WB_UNPROTECTED(objspace, obj)) {
+        return;
+    }
+    else {
+        gc_report(2, objspace, "rb_gc_writebarrier_unprotect: %s %s\n", rb_obj_info(obj),
+                  RVALUE_REMEMBERED(objspace, obj) ? " (already remembered)" : "");
+
+        unsigned int lev = rb_gc_vm_lock_no_barrier();
+        {
+            if (RVALUE_OLD_P(objspace, obj)) {
+                gc_report(1, objspace, "rb_gc_writebarrier_unprotect: %s\n", rb_obj_info(obj));
+                RVALUE_DEMOTE(objspace, obj);
+                gc_mark_set(objspace, obj);
+                gc_remember_unprotected(objspace, obj);
+
+#if RGENGC_PROFILE
+                objspace->profile.total_shade_operation_count++;
+#if RGENGC_PROFILE >= 2
+                objspace->profile.shade_operation_count_types[BUILTIN_TYPE(obj)]++;
+#endif /* RGENGC_PROFILE >= 2 */
+#endif /* RGENGC_PROFILE */
+            }
+            else {
+                RVALUE_AGE_RESET(obj);
+            }
+
+            RB_DEBUG_COUNTER_INC(obj_wb_unprotect);
+            MARK_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(obj), obj);
+        }
+        rb_gc_vm_unlock_no_barrier(lev);
+    }
+}
+
+void
+rb_gc_impl_copy_attributes(void *objspace_ptr, VALUE dest, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (RVALUE_WB_UNPROTECTED(objspace, obj)) {
+        rb_gc_impl_writebarrier_unprotect(objspace, dest);
+    }
+    rb_gc_impl_copy_finalizer(objspace, dest, obj);
+}
+
+const char *
+rb_gc_impl_active_gc_name(void)
+{
+    return "default";
+}
+
+void
+rb_gc_impl_writebarrier_remember(void *objspace_ptr, VALUE obj)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    gc_report(1, objspace, "rb_gc_writebarrier_remember: %s\n", rb_obj_info(obj));
+
+    if (is_incremental_marking(objspace)) {
+        if (RVALUE_BLACK_P(objspace, obj)) {
+            gc_grey(objspace, obj);
+        }
+    }
+    else {
+        if (RVALUE_OLD_P(objspace, obj)) {
+            rgengc_remember(objspace, obj);
+        }
+    }
+}
+
+// TODO: rearchitect this function to work for a generic GC
+size_t
+rb_gc_impl_obj_flags(void *objspace_ptr, VALUE obj, ID* flags, size_t max)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    size_t n = 0;
+    static ID ID_marked;
+    static ID ID_wb_protected, ID_old, ID_marking, ID_uncollectible, ID_pinned;
+
+    if (!ID_marked) {
+#define I(s) ID_##s = rb_intern(#s);
+        I(marked);
+        I(wb_protected);
+        I(old);
+        I(marking);
+        I(uncollectible);
+        I(pinned);
+#undef I
+    }
+
+    if (RVALUE_WB_UNPROTECTED(objspace, obj) == 0 && n < max)                   flags[n++] = ID_wb_protected;
+    if (RVALUE_OLD_P(objspace, obj) && n < max)                                 flags[n++] = ID_old;
+    if (RVALUE_UNCOLLECTIBLE(objspace, obj) && n < max)                         flags[n++] = ID_uncollectible;
+    if (RVALUE_MARKING(objspace, obj) && n < max) flags[n++] = ID_marking;
+    if (RVALUE_MARKED(objspace, obj) && n < max)    flags[n++] = ID_marked;
+    if (RVALUE_PINNED(objspace, obj) && n < max)  flags[n++] = ID_pinned;
+    return n;
+}
+
+void *
+rb_gc_impl_ractor_cache_alloc(void *objspace_ptr, void *ractor)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    objspace->live_ractor_cache_count++;
+
+    return calloc1(sizeof(rb_ractor_newobj_cache_t));
+}
+
+void
+rb_gc_impl_ractor_cache_free(void *objspace_ptr, void *cache)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    objspace->live_ractor_cache_count--;
+
+    gc_ractor_newobj_cache_clear(cache, NULL);
+    free(cache);
+}
+
+static void
+heap_ready_to_gc(rb_objspace_t *objspace, rb_heap_t *heap)
+{
+    if (!heap->free_pages) {
+        if (!heap_page_allocate_and_initialize(objspace, heap)) {
+            objspace->heap_pages.allocatable_slots = 1;
+            heap_page_allocate_and_initialize(objspace, heap);
+        }
+    }
+}
+
+static int
+ready_to_gc(rb_objspace_t *objspace)
+{
+    if (dont_gc_val() || during_gc || ruby_disable_gc) {
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            rb_heap_t *heap = &heaps[i];
+            heap_ready_to_gc(objspace, heap);
+        }
+        return FALSE;
+    }
+    else {
+        return TRUE;
+    }
+}
+
+static void
+gc_reset_malloc_info(rb_objspace_t *objspace, bool full_mark)
+{
+    gc_prof_set_malloc_info(objspace);
+    {
+        size_t inc = RUBY_ATOMIC_SIZE_EXCHANGE(malloc_increase, 0);
+        size_t old_limit = malloc_limit;
+
+        if (inc > malloc_limit) {
+            malloc_limit = (size_t)(inc * gc_params.malloc_limit_growth_factor);
+            if (malloc_limit > gc_params.malloc_limit_max) {
+                malloc_limit = gc_params.malloc_limit_max;
+            }
+        }
+        else {
+            malloc_limit = (size_t)(malloc_limit * 0.98); /* magic number */
+            if (malloc_limit < gc_params.malloc_limit_min) {
+                malloc_limit = gc_params.malloc_limit_min;
+            }
+        }
+
+        if (0) {
+            if (old_limit != malloc_limit) {
+                fprintf(stderr, "[%"PRIuSIZE"] malloc_limit: %"PRIuSIZE" -> %"PRIuSIZE"\n",
+                        rb_gc_count(), old_limit, malloc_limit);
+            }
+            else {
+                fprintf(stderr, "[%"PRIuSIZE"] malloc_limit: not changed (%"PRIuSIZE")\n",
+                        rb_gc_count(), malloc_limit);
+            }
+        }
+    }
+
+    /* reset oldmalloc info */
+#if RGENGC_ESTIMATE_OLDMALLOC
+    if (!full_mark) {
+        if (objspace->rgengc.oldmalloc_increase > objspace->rgengc.oldmalloc_increase_limit) {
+            gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_OLDMALLOC;
+            objspace->rgengc.oldmalloc_increase_limit =
+              (size_t)(objspace->rgengc.oldmalloc_increase_limit * gc_params.oldmalloc_limit_growth_factor);
+
+            if (objspace->rgengc.oldmalloc_increase_limit > gc_params.oldmalloc_limit_max) {
+                objspace->rgengc.oldmalloc_increase_limit = gc_params.oldmalloc_limit_max;
+            }
+        }
+
+        if (0) fprintf(stderr, "%"PRIdSIZE"\t%d\t%"PRIuSIZE"\t%"PRIuSIZE"\t%"PRIdSIZE"\n",
+                       rb_gc_count(),
+                       gc_needs_major_flags,
+                       objspace->rgengc.oldmalloc_increase,
+                       objspace->rgengc.oldmalloc_increase_limit,
+                       gc_params.oldmalloc_limit_max);
+    }
+    else {
+        /* major GC */
+        objspace->rgengc.oldmalloc_increase = 0;
+
+        if ((objspace->profile.latest_gc_info & GPR_FLAG_MAJOR_BY_OLDMALLOC) == 0) {
+            objspace->rgengc.oldmalloc_increase_limit =
+              (size_t)(objspace->rgengc.oldmalloc_increase_limit / ((gc_params.oldmalloc_limit_growth_factor - 1)/10 + 1));
+            if (objspace->rgengc.oldmalloc_increase_limit < gc_params.oldmalloc_limit_min) {
+                objspace->rgengc.oldmalloc_increase_limit = gc_params.oldmalloc_limit_min;
+            }
+        }
+    }
+#endif
+}
+
+static int
+garbage_collect(rb_objspace_t *objspace, unsigned int reason)
+{
+    int ret;
+
+    int lev = rb_gc_vm_lock();
+    {
+#if GC_PROFILE_MORE_DETAIL
+        objspace->profile.prepare_time = getrusage_time();
+#endif
+
+        gc_rest(objspace);
+
+#if GC_PROFILE_MORE_DETAIL
+        objspace->profile.prepare_time = getrusage_time() - objspace->profile.prepare_time;
+#endif
+
+        ret = gc_start(objspace, reason);
+    }
+    rb_gc_vm_unlock(lev);
+
+    return ret;
+}
+
+static int
+gc_start(rb_objspace_t *objspace, unsigned int reason)
+{
+    unsigned int do_full_mark = !!(reason & GPR_FLAG_FULL_MARK);
+
+    /* reason may be clobbered, later, so keep set immediate_sweep here */
+    objspace->flags.immediate_sweep = !!(reason & GPR_FLAG_IMMEDIATE_SWEEP);
+
+    if (!rb_darray_size(objspace->heap_pages.sorted)) return TRUE; /* heap is not ready */
+    if (!(reason & GPR_FLAG_METHOD) && !ready_to_gc(objspace)) return TRUE; /* GC is not allowed */
+
+    GC_ASSERT(gc_mode(objspace) == gc_mode_none);
+    GC_ASSERT(!is_lazy_sweeping(objspace));
+    GC_ASSERT(!is_incremental_marking(objspace));
+
+    unsigned int lock_lev;
+    gc_enter(objspace, gc_enter_event_start, &lock_lev);
+
+#if RGENGC_CHECK_MODE >= 2
+    gc_verify_internal_consistency(objspace);
+#endif
+
+    if (ruby_gc_stressful) {
+        int flag = FIXNUM_P(ruby_gc_stress_mode) ? FIX2INT(ruby_gc_stress_mode) : 0;
+
+        if ((flag & (1 << gc_stress_no_major)) == 0) {
+            do_full_mark = TRUE;
+        }
+
+        objspace->flags.immediate_sweep = !(flag & (1<<gc_stress_no_immediate_sweep));
+    }
+
+    if (gc_needs_major_flags) {
+        reason |= gc_needs_major_flags;
+        do_full_mark = TRUE;
+    }
+
+    /* if major gc has been disabled, never do a full mark */
+    if (!gc_config_full_mark_val) {
+        do_full_mark = FALSE;
+    }
+    gc_needs_major_flags = GPR_FLAG_NONE;
+
+    if (do_full_mark && (reason & GPR_FLAG_MAJOR_MASK) == 0) {
+        reason |= GPR_FLAG_MAJOR_BY_FORCE; /* GC by CAPI, METHOD, and so on. */
+    }
+
+    if (objspace->flags.dont_incremental ||
+            reason & GPR_FLAG_IMMEDIATE_MARK ||
+            ruby_gc_stressful) {
+        objspace->flags.during_incremental_marking = FALSE;
+    }
+    else {
+        objspace->flags.during_incremental_marking = do_full_mark;
+    }
+
+    /* Explicitly enable compaction (GC.compact) */
+    if (do_full_mark && ruby_enable_autocompact) {
+        objspace->flags.during_compacting = TRUE;
+#if RGENGC_CHECK_MODE
+        objspace->rcompactor.compare_func = ruby_autocompact_compare_func;
+#endif
+    }
+    else {
+        objspace->flags.during_compacting = !!(reason & GPR_FLAG_COMPACT);
+    }
+
+    if (!GC_ENABLE_LAZY_SWEEP || objspace->flags.dont_incremental) {
+        objspace->flags.immediate_sweep = TRUE;
+    }
+
+    if (objspace->flags.immediate_sweep) reason |= GPR_FLAG_IMMEDIATE_SWEEP;
+
+    gc_report(1, objspace, "gc_start(reason: %x) => %u, %d, %d\n",
+              reason,
+              do_full_mark, !is_incremental_marking(objspace), objspace->flags.immediate_sweep);
+
+#if USE_DEBUG_COUNTER
+    RB_DEBUG_COUNTER_INC(gc_count);
+
+    if (reason & GPR_FLAG_MAJOR_MASK) {
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_major_nofree, reason & GPR_FLAG_MAJOR_BY_NOFREE);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_major_oldgen, reason & GPR_FLAG_MAJOR_BY_OLDGEN);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_major_shady,  reason & GPR_FLAG_MAJOR_BY_SHADY);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_major_force,  reason & GPR_FLAG_MAJOR_BY_FORCE);
+#if RGENGC_ESTIMATE_OLDMALLOC
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_major_oldmalloc, reason & GPR_FLAG_MAJOR_BY_OLDMALLOC);
+#endif
+    }
+    else {
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_minor_newobj, reason & GPR_FLAG_NEWOBJ);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_minor_malloc, reason & GPR_FLAG_MALLOC);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_minor_method, reason & GPR_FLAG_METHOD);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_minor_capi,   reason & GPR_FLAG_CAPI);
+        (void)RB_DEBUG_COUNTER_INC_IF(gc_minor_stress, reason & GPR_FLAG_STRESS);
+    }
+#endif
+
+    objspace->profile.count++;
+    objspace->profile.latest_gc_info = reason;
+    objspace->profile.total_allocated_objects_at_gc_start = total_allocated_objects(objspace);
+    objspace->profile.heap_used_at_gc_start = rb_darray_size(objspace->heap_pages.sorted);
+    objspace->profile.weak_references_count = 0;
+    objspace->profile.retained_weak_references_count = 0;
+    gc_prof_setup_new_record(objspace, reason);
+    gc_reset_malloc_info(objspace, do_full_mark);
+
+    rb_gc_event_hook(0, RUBY_INTERNAL_EVENT_GC_START);
+
+    GC_ASSERT(during_gc);
+
+    gc_prof_timer_start(objspace);
+    {
+        if (gc_marks(objspace, do_full_mark)) {
+            gc_sweep(objspace);
+        }
+    }
+    gc_prof_timer_stop(objspace);
+
+    gc_exit(objspace, gc_enter_event_start, &lock_lev);
+    return TRUE;
+}
+
+static void
+gc_rest(rb_objspace_t *objspace)
+{
+    if (is_incremental_marking(objspace) || is_lazy_sweeping(objspace)) {
+        unsigned int lock_lev;
+        gc_enter(objspace, gc_enter_event_rest, &lock_lev);
+
+        if (RGENGC_CHECK_MODE >= 2) gc_verify_internal_consistency(objspace);
+
+        if (is_incremental_marking(objspace)) {
+            gc_marking_enter(objspace);
+            gc_marks_rest(objspace);
+            gc_marking_exit(objspace);
+
+            gc_sweep(objspace);
+        }
+
+        if (is_lazy_sweeping(objspace)) {
+            gc_sweeping_enter(objspace);
+            gc_sweep_rest(objspace);
+            gc_sweeping_exit(objspace);
+        }
+
+        gc_exit(objspace, gc_enter_event_rest, &lock_lev);
+    }
+}
+
+struct objspace_and_reason {
+    rb_objspace_t *objspace;
+    unsigned int reason;
+};
+
+static void
+gc_current_status_fill(rb_objspace_t *objspace, char *buff)
+{
+    int i = 0;
+    if (is_marking(objspace)) {
+        buff[i++] = 'M';
+        if (is_full_marking(objspace))        buff[i++] = 'F';
+        if (is_incremental_marking(objspace)) buff[i++] = 'I';
+    }
+    else if (is_sweeping(objspace)) {
+        buff[i++] = 'S';
+        if (is_lazy_sweeping(objspace))      buff[i++] = 'L';
+    }
+    else {
+        buff[i++] = 'N';
+    }
+    buff[i] = '\0';
+}
+
+static const char *
+gc_current_status(rb_objspace_t *objspace)
+{
+    static char buff[0x10];
+    gc_current_status_fill(objspace, buff);
+    return buff;
+}
+
+#if PRINT_ENTER_EXIT_TICK
+
+static tick_t last_exit_tick;
+static tick_t enter_tick;
+static int enter_count = 0;
+static char last_gc_status[0x10];
+
+static inline void
+gc_record(rb_objspace_t *objspace, int direction, const char *event)
+{
+    if (direction == 0) { /* enter */
+        enter_count++;
+        enter_tick = tick();
+        gc_current_status_fill(objspace, last_gc_status);
+    }
+    else { /* exit */
+        tick_t exit_tick = tick();
+        char current_gc_status[0x10];
+        gc_current_status_fill(objspace, current_gc_status);
+#if 1
+        /* [last mutator time] [gc time] [event] */
+        fprintf(stderr, "%"PRItick"\t%"PRItick"\t%s\t[%s->%s|%c]\n",
+                enter_tick - last_exit_tick,
+                exit_tick - enter_tick,
+                event,
+                last_gc_status, current_gc_status,
+                (objspace->profile.latest_gc_info & GPR_FLAG_MAJOR_MASK) ? '+' : '-');
+        last_exit_tick = exit_tick;
+#else
+        /* [enter_tick] [gc time] [event] */
+        fprintf(stderr, "%"PRItick"\t%"PRItick"\t%s\t[%s->%s|%c]\n",
+                enter_tick,
+                exit_tick - enter_tick,
+                event,
+                last_gc_status, current_gc_status,
+                (objspace->profile.latest_gc_info & GPR_FLAG_MAJOR_MASK) ? '+' : '-');
+#endif
+    }
+}
+#else /* PRINT_ENTER_EXIT_TICK */
+static inline void
+gc_record(rb_objspace_t *objspace, int direction, const char *event)
+{
+    /* null */
+}
+#endif /* PRINT_ENTER_EXIT_TICK */
+
+static const char *
+gc_enter_event_cstr(enum gc_enter_event event)
+{
+    switch (event) {
+      case gc_enter_event_start: return "start";
+      case gc_enter_event_continue: return "continue";
+      case gc_enter_event_rest: return "rest";
+      case gc_enter_event_finalizer: return "finalizer";
+    }
+    return NULL;
+}
+
+static void
+gc_enter_count(enum gc_enter_event event)
+{
+    switch (event) {
+      case gc_enter_event_start:          RB_DEBUG_COUNTER_INC(gc_enter_start); break;
+      case gc_enter_event_continue:       RB_DEBUG_COUNTER_INC(gc_enter_continue); break;
+      case gc_enter_event_rest:           RB_DEBUG_COUNTER_INC(gc_enter_rest); break;
+      case gc_enter_event_finalizer:      RB_DEBUG_COUNTER_INC(gc_enter_finalizer); break;
+    }
+}
+
+static bool current_process_time(struct timespec *ts);
+
+static void
+gc_clock_start(struct timespec *ts)
+{
+    if (!current_process_time(ts)) {
+        ts->tv_sec = 0;
+        ts->tv_nsec = 0;
+    }
+}
+
+static unsigned long long
+gc_clock_end(struct timespec *ts)
+{
+    struct timespec end_time;
+
+    if ((ts->tv_sec > 0 || ts->tv_nsec > 0) &&
+            current_process_time(&end_time) &&
+            end_time.tv_sec >= ts->tv_sec) {
+        return (unsigned long long)(end_time.tv_sec - ts->tv_sec) * (1000 * 1000 * 1000) +
+                    (end_time.tv_nsec - ts->tv_nsec);
+    }
+
+    return 0;
+}
+
+static inline void
+gc_enter(rb_objspace_t *objspace, enum gc_enter_event event, unsigned int *lock_lev)
+{
+    *lock_lev = rb_gc_vm_lock();
+
+    switch (event) {
+      case gc_enter_event_rest:
+        if (!is_marking(objspace)) break;
+        // fall through
+      case gc_enter_event_start:
+      case gc_enter_event_continue:
+        // stop other ractors
+        rb_gc_vm_barrier();
+        break;
+      default:
+        break;
+    }
+
+    gc_enter_count(event);
+    if (RB_UNLIKELY(during_gc != 0)) rb_bug("during_gc != 0");
+    if (RGENGC_CHECK_MODE >= 3) gc_verify_internal_consistency(objspace);
+
+    during_gc = TRUE;
+    RUBY_DEBUG_LOG("%s (%s)",gc_enter_event_cstr(event), gc_current_status(objspace));
+    gc_report(1, objspace, "gc_enter: %s [%s]\n", gc_enter_event_cstr(event), gc_current_status(objspace));
+    gc_record(objspace, 0, gc_enter_event_cstr(event));
+
+    rb_gc_event_hook(0, RUBY_INTERNAL_EVENT_GC_ENTER);
+}
+
+static inline void
+gc_exit(rb_objspace_t *objspace, enum gc_enter_event event, unsigned int *lock_lev)
+{
+    GC_ASSERT(during_gc != 0);
+
+    rb_gc_event_hook(0, RUBY_INTERNAL_EVENT_GC_EXIT);
+
+    gc_record(objspace, 1, gc_enter_event_cstr(event));
+    RUBY_DEBUG_LOG("%s (%s)", gc_enter_event_cstr(event), gc_current_status(objspace));
+    gc_report(1, objspace, "gc_exit: %s [%s]\n", gc_enter_event_cstr(event), gc_current_status(objspace));
+    during_gc = FALSE;
+
+    rb_gc_vm_unlock(*lock_lev);
+}
+
+#ifndef MEASURE_GC
+#define MEASURE_GC (objspace->flags.measure_gc)
+#endif
+
+static void
+gc_marking_enter(rb_objspace_t *objspace)
+{
+    GC_ASSERT(during_gc != 0);
+
+    if (MEASURE_GC) {
+        gc_clock_start(&objspace->profile.marking_start_time);
+    }
+}
+
+static void
+gc_marking_exit(rb_objspace_t *objspace)
+{
+    GC_ASSERT(during_gc != 0);
+
+    if (MEASURE_GC) {
+        objspace->profile.marking_time_ns += gc_clock_end(&objspace->profile.marking_start_time);
+    }
+}
+
+static void
+gc_sweeping_enter(rb_objspace_t *objspace)
+{
+    GC_ASSERT(during_gc != 0);
+
+    if (MEASURE_GC) {
+        gc_clock_start(&objspace->profile.sweeping_start_time);
+    }
+}
+
+static void
+gc_sweeping_exit(rb_objspace_t *objspace)
+{
+    GC_ASSERT(during_gc != 0);
+
+    if (MEASURE_GC) {
+        objspace->profile.sweeping_time_ns += gc_clock_end(&objspace->profile.sweeping_start_time);
+    }
+}
+
+static void *
+gc_with_gvl(void *ptr)
+{
+    struct objspace_and_reason *oar = (struct objspace_and_reason *)ptr;
+    return (void *)(VALUE)garbage_collect(oar->objspace, oar->reason);
+}
+
+int ruby_thread_has_gvl_p(void);
+
+static int
+garbage_collect_with_gvl(rb_objspace_t *objspace, unsigned int reason)
+{
+    if (dont_gc_val()) return TRUE;
+    if (ruby_thread_has_gvl_p()) {
+        return garbage_collect(objspace, reason);
+    }
+    else {
+        if (ruby_native_thread_p()) {
+            struct objspace_and_reason oar;
+            oar.objspace = objspace;
+            oar.reason = reason;
+            return (int)(VALUE)rb_thread_call_with_gvl(gc_with_gvl, (void *)&oar);
+        }
+        else {
+            /* no ruby thread */
+            fprintf(stderr, "[FATAL] failed to allocate memory\n");
+            exit(EXIT_FAILURE);
+        }
+    }
+}
+
+static int
+gc_set_candidate_object_i(void *vstart, void *vend, size_t stride, void *data)
+{
+    rb_objspace_t *objspace = (rb_objspace_t *)data;
+
+    VALUE v = (VALUE)vstart;
+    for (; v != (VALUE)vend; v += stride) {
+        asan_unpoisoning_object(v) {
+            switch (BUILTIN_TYPE(v)) {
+              case T_NONE:
+              case T_ZOMBIE:
+                break;
+              default:
+                rb_gc_prepare_heap_process_object(v);
+                if (!RVALUE_OLD_P(objspace, v) && !RVALUE_WB_UNPROTECTED(objspace, v)) {
+                    RVALUE_AGE_SET_CANDIDATE(objspace, v);
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+
+void
+rb_gc_impl_start(void *objspace_ptr, bool full_mark, bool immediate_mark, bool immediate_sweep, bool compact)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    unsigned int reason = (GPR_FLAG_FULL_MARK |
+                           GPR_FLAG_IMMEDIATE_MARK |
+                           GPR_FLAG_IMMEDIATE_SWEEP |
+                           GPR_FLAG_METHOD);
+
+    int full_marking_p = gc_config_full_mark_val;
+    gc_config_full_mark_set(TRUE);
+
+    /* For now, compact implies full mark / sweep, so ignore other flags */
+    if (compact) {
+        GC_ASSERT(GC_COMPACTION_SUPPORTED);
+
+        reason |= GPR_FLAG_COMPACT;
+    }
+    else {
+        if (!full_mark)       reason &= ~GPR_FLAG_FULL_MARK;
+        if (!immediate_mark)  reason &= ~GPR_FLAG_IMMEDIATE_MARK;
+        if (!immediate_sweep) reason &= ~GPR_FLAG_IMMEDIATE_SWEEP;
+    }
+
+    garbage_collect(objspace, reason);
+    gc_finalize_deferred(objspace);
+
+    gc_config_full_mark_set(full_marking_p);
+}
+
+void
+rb_gc_impl_prepare_heap(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    size_t orig_total_slots = objspace_available_slots(objspace);
+    size_t orig_allocatable_slots = objspace->heap_pages.allocatable_slots;
+
+    rb_gc_impl_each_objects(objspace, gc_set_candidate_object_i, objspace_ptr);
+
+    double orig_max_free_slots = gc_params.heap_free_slots_max_ratio;
+    /* Ensure that all empty pages are moved onto empty_pages. */
+    gc_params.heap_free_slots_max_ratio = 0.0;
+    rb_gc_impl_start(objspace, true, true, true, true);
+    gc_params.heap_free_slots_max_ratio = orig_max_free_slots;
+
+    objspace->heap_pages.allocatable_slots = 0;
+    heap_pages_free_unused_pages(objspace_ptr);
+    GC_ASSERT(objspace->empty_pages_count == 0);
+    objspace->heap_pages.allocatable_slots = orig_allocatable_slots;
+
+    size_t total_slots = objspace_available_slots(objspace);
+    if (orig_total_slots > total_slots) {
+        objspace->heap_pages.allocatable_slots += orig_total_slots - total_slots;
+    }
+
+#if defined(HAVE_MALLOC_TRIM) && !defined(RUBY_ALTERNATIVE_MALLOC_HEADER)
+    malloc_trim(0);
+#endif
+}
+
+static int
+gc_is_moveable_obj(rb_objspace_t *objspace, VALUE obj)
+{
+    GC_ASSERT(!SPECIAL_CONST_P(obj));
+
+    switch (BUILTIN_TYPE(obj)) {
+      case T_NONE:
+      case T_MOVED:
+      case T_ZOMBIE:
+        return FALSE;
+      case T_SYMBOL:
+        // TODO: restore original behavior
+        // if (RSYMBOL(obj)->id & ~ID_SCOPE_MASK) {
+        //     return FALSE;
+        // }
+        return false;
+        /* fall through */
+      case T_STRING:
+      case T_OBJECT:
+      case T_FLOAT:
+      case T_IMEMO:
+      case T_ARRAY:
+      case T_BIGNUM:
+      case T_ICLASS:
+      case T_MODULE:
+      case T_REGEXP:
+      case T_DATA:
+      case T_MATCH:
+      case T_STRUCT:
+      case T_HASH:
+      case T_FILE:
+      case T_COMPLEX:
+      case T_RATIONAL:
+      case T_NODE:
+      case T_CLASS:
+        if (FL_TEST(obj, FL_FINALIZE)) {
+            /* The finalizer table is a numtable. It looks up objects by address.
+             * We can't mark the keys in the finalizer table because that would
+             * prevent the objects from being collected.  This check prevents
+             * objects that are keys in the finalizer table from being moved
+             * without directly pinning them. */
+            GC_ASSERT(st_is_member(finalizer_table, obj));
+
+            return FALSE;
+        }
+        GC_ASSERT(RVALUE_MARKED(objspace, obj));
+        GC_ASSERT(!RVALUE_PINNED(objspace, obj));
+
+        return TRUE;
+
+      default:
+        rb_bug("gc_is_moveable_obj: unreachable (%d)", (int)BUILTIN_TYPE(obj));
+        break;
+    }
+
+    return FALSE;
+}
+
+void rb_mv_generic_ivar(VALUE src, VALUE dst);
+
+static VALUE
+gc_move(rb_objspace_t *objspace, VALUE src, VALUE dest, size_t src_slot_size, size_t slot_size)
+{
+    int marked;
+    int wb_unprotected;
+    int uncollectible;
+    int age;
+
+    gc_report(4, objspace, "Moving object: %p -> %p\n", (void *)src, (void *)dest);
+
+    GC_ASSERT(BUILTIN_TYPE(src) != T_NONE);
+    GC_ASSERT(!MARKED_IN_BITMAP(GET_HEAP_MARK_BITS(dest), dest));
+
+    GC_ASSERT(!RVALUE_MARKING(objspace, src));
+
+    /* Save off bits for current object. */
+    marked = RVALUE_MARKED(objspace, src);
+    wb_unprotected = RVALUE_WB_UNPROTECTED(objspace, src);
+    uncollectible = RVALUE_UNCOLLECTIBLE(objspace, src);
+    bool remembered = RVALUE_REMEMBERED(objspace, src);
+    age = RVALUE_AGE_GET(src);
+
+    /* Clear bits for eventual T_MOVED */
+    CLEAR_IN_BITMAP(GET_HEAP_MARK_BITS(src), src);
+    CLEAR_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(src), src);
+    CLEAR_IN_BITMAP(GET_HEAP_UNCOLLECTIBLE_BITS(src), src);
+    CLEAR_IN_BITMAP(GET_HEAP_PAGE(src)->remembered_bits, src);
+
+    if (FL_TEST(src, FL_EXIVAR)) {
+        /* Resizing the st table could cause a malloc */
+        DURING_GC_COULD_MALLOC_REGION_START();
+        {
+            rb_mv_generic_ivar(src, dest);
+        }
+        DURING_GC_COULD_MALLOC_REGION_END();
+    }
+
+    if (FL_TEST(src, FL_SEEN_OBJ_ID)) {
+        /* If the source object's object_id has been seen, we need to update
+         * the object to object id mapping. */
+        st_data_t srcid = (st_data_t)src, id;
+
+        gc_report(4, objspace, "Moving object with seen id: %p -> %p\n", (void *)src, (void *)dest);
+        /* Resizing the st table could cause a malloc */
+        DURING_GC_COULD_MALLOC_REGION_START();
+        {
+            if (!st_delete(objspace->obj_to_id_tbl, &srcid, &id)) {
+                rb_bug("gc_move: object ID seen, but not in mapping table: %s", rb_obj_info((VALUE)src));
+            }
+
+            st_insert(objspace->obj_to_id_tbl, (st_data_t)dest, id);
+        }
+        DURING_GC_COULD_MALLOC_REGION_END();
+    }
+    else {
+        GC_ASSERT(!st_lookup(objspace->obj_to_id_tbl, (st_data_t)src, NULL));
+    }
+
+    /* Move the object */
+    memcpy((void *)dest, (void *)src, MIN(src_slot_size, slot_size));
+
+    if (RVALUE_OVERHEAD > 0) {
+        void *dest_overhead = (void *)(((uintptr_t)dest) + slot_size - RVALUE_OVERHEAD);
+        void *src_overhead = (void *)(((uintptr_t)src) + src_slot_size - RVALUE_OVERHEAD);
+
+        memcpy(dest_overhead, src_overhead, RVALUE_OVERHEAD);
+    }
+
+    memset((void *)src, 0, src_slot_size);
+    RVALUE_AGE_RESET(src);
+
+    /* Set bits for object in new location */
+    if (remembered) {
+        MARK_IN_BITMAP(GET_HEAP_PAGE(dest)->remembered_bits, dest);
+    }
+    else {
+        CLEAR_IN_BITMAP(GET_HEAP_PAGE(dest)->remembered_bits, dest);
+    }
+
+    if (marked) {
+        MARK_IN_BITMAP(GET_HEAP_MARK_BITS(dest), dest);
+    }
+    else {
+        CLEAR_IN_BITMAP(GET_HEAP_MARK_BITS(dest), dest);
+    }
+
+    if (wb_unprotected) {
+        MARK_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(dest), dest);
+    }
+    else {
+        CLEAR_IN_BITMAP(GET_HEAP_WB_UNPROTECTED_BITS(dest), dest);
+    }
+
+    if (uncollectible) {
+        MARK_IN_BITMAP(GET_HEAP_UNCOLLECTIBLE_BITS(dest), dest);
+    }
+    else {
+        CLEAR_IN_BITMAP(GET_HEAP_UNCOLLECTIBLE_BITS(dest), dest);
+    }
+
+    RVALUE_AGE_SET(dest, age);
+    /* Assign forwarding address */
+    RMOVED(src)->flags = T_MOVED;
+    RMOVED(src)->dummy = Qundef;
+    RMOVED(src)->destination = dest;
+    GC_ASSERT(BUILTIN_TYPE(dest) != T_NONE);
+
+    GET_HEAP_PAGE(src)->heap->total_freed_objects++;
+    GET_HEAP_PAGE(dest)->heap->total_allocated_objects++;
+
+    return src;
+}
+
+#if GC_CAN_COMPILE_COMPACTION
+static int
+compare_pinned_slots(const void *left, const void *right, void *dummy)
+{
+    struct heap_page *left_page;
+    struct heap_page *right_page;
+
+    left_page = *(struct heap_page * const *)left;
+    right_page = *(struct heap_page * const *)right;
+
+    return left_page->pinned_slots - right_page->pinned_slots;
+}
+
+static int
+compare_free_slots(const void *left, const void *right, void *dummy)
+{
+    struct heap_page *left_page;
+    struct heap_page *right_page;
+
+    left_page = *(struct heap_page * const *)left;
+    right_page = *(struct heap_page * const *)right;
+
+    return left_page->free_slots - right_page->free_slots;
+}
+
+static void
+gc_sort_heap_by_compare_func(rb_objspace_t *objspace, gc_compact_compare_func compare_func)
+{
+    for (int j = 0; j < HEAP_COUNT; j++) {
+        rb_heap_t *heap = &heaps[j];
+
+        size_t total_pages = heap->total_pages;
+        size_t size = rb_size_mul_or_raise(total_pages, sizeof(struct heap_page *), rb_eRuntimeError);
+        struct heap_page *page = 0, **page_list = malloc(size);
+        size_t i = 0;
+
+        heap->free_pages = NULL;
+        ccan_list_for_each(&heap->pages, page, page_node) {
+            page_list[i++] = page;
+            GC_ASSERT(page);
+        }
+
+        GC_ASSERT((size_t)i == total_pages);
+
+        /* Sort the heap so "filled pages" are first. `heap_add_page` adds to the
+         * head of the list, so empty pages will end up at the start of the heap */
+        ruby_qsort(page_list, total_pages, sizeof(struct heap_page *), compare_func, NULL);
+
+        /* Reset the eden heap */
+        ccan_list_head_init(&heap->pages);
+
+        for (i = 0; i < total_pages; i++) {
+            ccan_list_add(&heap->pages, &page_list[i]->page_node);
+            if (page_list[i]->free_slots != 0) {
+                heap_add_freepage(heap, page_list[i]);
+            }
+        }
+
+        free(page_list);
+    }
+}
+#endif
+
+bool
+rb_gc_impl_object_moved_p(void *objspace_ptr, VALUE obj)
+{
+    return gc_object_moved_p(objspace_ptr, obj);
+}
+
+static int
+gc_ref_update(void *vstart, void *vend, size_t stride, rb_objspace_t *objspace, struct heap_page *page)
+{
+    VALUE v = (VALUE)vstart;
+
+    page->flags.has_uncollectible_wb_unprotected_objects = FALSE;
+    page->flags.has_remembered_objects = FALSE;
+
+    /* For each object on the page */
+    for (; v != (VALUE)vend; v += stride) {
+        asan_unpoisoning_object(v) {
+            switch (BUILTIN_TYPE(v)) {
+              case T_NONE:
+              case T_MOVED:
+              case T_ZOMBIE:
+                break;
+              default:
+                if (RVALUE_WB_UNPROTECTED(objspace, v)) {
+                    page->flags.has_uncollectible_wb_unprotected_objects = TRUE;
+                }
+                if (RVALUE_REMEMBERED(objspace, v)) {
+                    page->flags.has_remembered_objects = TRUE;
+                }
+                if (page->flags.before_sweep) {
+                    if (RVALUE_MARKED(objspace, v)) {
+                        rb_gc_update_object_references(objspace, v);
+                    }
+                }
+                else {
+                    rb_gc_update_object_references(objspace, v);
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+
+static void
+gc_update_references(rb_objspace_t *objspace)
+{
+    objspace->flags.during_reference_updating = true;
+
+    struct heap_page *page = NULL;
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        bool should_set_mark_bits = TRUE;
+        rb_heap_t *heap = &heaps[i];
+
+        ccan_list_for_each(&heap->pages, page, page_node) {
+            uintptr_t start = (uintptr_t)page->start;
+            uintptr_t end = start + (page->total_slots * heap->slot_size);
+
+            gc_ref_update((void *)start, (void *)end, heap->slot_size, objspace, page);
+            if (page == heap->sweeping_page) {
+                should_set_mark_bits = FALSE;
+            }
+            if (should_set_mark_bits) {
+                gc_setup_mark_bits(page);
+            }
+        }
+    }
+    gc_ref_update_table_values_only(objspace->obj_to_id_tbl);
+    gc_update_table_refs(objspace->id_to_obj_tbl);
+    gc_update_table_refs(finalizer_table);
+
+    rb_gc_update_vm_references((void *)objspace);
+
+    objspace->flags.during_reference_updating = false;
+}
+
+#if GC_CAN_COMPILE_COMPACTION
+static void
+root_obj_check_moved_i(const char *category, VALUE obj, void *data)
+{
+    rb_objspace_t *objspace = data;
+
+    if (gc_object_moved_p(objspace, obj)) {
+        rb_bug("ROOT %s points to MOVED: %p -> %s", category, (void *)obj, rb_obj_info(rb_gc_impl_location(objspace, obj)));
+    }
+}
+
+static void
+reachable_object_check_moved_i(VALUE ref, void *data)
+{
+    VALUE parent = (VALUE)data;
+    if (gc_object_moved_p(rb_gc_get_objspace(), ref)) {
+        rb_bug("Object %s points to MOVED: %p -> %s", rb_obj_info(parent), (void *)ref, rb_obj_info(rb_gc_impl_location(rb_gc_get_objspace(), ref)));
+    }
+}
+
+static int
+heap_check_moved_i(void *vstart, void *vend, size_t stride, void *data)
+{
+    rb_objspace_t *objspace = data;
+
+    VALUE v = (VALUE)vstart;
+    for (; v != (VALUE)vend; v += stride) {
+        if (gc_object_moved_p(objspace, v)) {
+            /* Moved object still on the heap, something may have a reference. */
+        }
+        else {
+            asan_unpoisoning_object(v) {
+                switch (BUILTIN_TYPE(v)) {
+                  case T_NONE:
+                  case T_ZOMBIE:
+                    break;
+                  default:
+                    if (!rb_gc_impl_garbage_object_p(objspace, v)) {
+                        rb_objspace_reachable_objects_from(v, reachable_object_check_moved_i, (void *)v);
+                    }
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+#endif
+
+bool
+rb_gc_impl_during_gc_p(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    return during_gc;
+}
+
+#if RGENGC_PROFILE >= 2
+
+static const char*
+type_name(int type, VALUE obj)
+{
+    switch ((enum ruby_value_type)type) {
+      case RUBY_T_NONE:     return "T_NONE";
+      case RUBY_T_OBJECT:   return "T_OBJECT";
+      case RUBY_T_CLASS:    return "T_CLASS";
+      case RUBY_T_MODULE:   return "T_MODULE";
+      case RUBY_T_FLOAT:    return "T_FLOAT";
+      case RUBY_T_STRING:   return "T_STRING";
+      case RUBY_T_REGEXP:   return "T_REGEXP";
+      case RUBY_T_ARRAY:    return "T_ARRAY";
+      case RUBY_T_HASH:     return "T_HASH";
+      case RUBY_T_STRUCT:   return "T_STRUCT";
+      case RUBY_T_BIGNUM:   return "T_BIGNUM";
+      case RUBY_T_FILE:     return "T_FILE";
+      case RUBY_T_DATA:     return "T_DATA";
+      case RUBY_T_MATCH:    return "T_MATCH";
+      case RUBY_T_COMPLEX:  return "T_COMPLEX";
+      case RUBY_T_RATIONAL: return "T_RATIONAL";
+      case RUBY_T_NIL:      return "T_NIL";
+      case RUBY_T_TRUE:     return "T_TRUE";
+      case RUBY_T_FALSE:    return "T_FALSE";
+      case RUBY_T_SYMBOL:   return "T_SYMBOL";
+      case RUBY_T_FIXNUM:   return "T_FIXNUM";
+      case RUBY_T_UNDEF:    return "T_UNDEF";
+      case RUBY_T_IMEMO:    return "T_IMEMO";
+      case RUBY_T_NODE:     return "T_NODE";
+      case RUBY_T_ICLASS:   return "T_ICLASS";
+      case RUBY_T_ZOMBIE:   return "T_ZOMBIE";
+      case RUBY_T_MOVED:    return "T_MOVED";
+      default:              return "unknown";
+    }
+}
+
+static void
+gc_count_add_each_types(VALUE hash, const char *name, const size_t *types)
+{
+    VALUE result = rb_hash_new_with_size(T_MASK);
+    int i;
+    for (i=0; i<T_MASK; i++) {
+        const char *type = type_name(i, 0);
+        rb_hash_aset(result, ID2SYM(rb_intern(type)), SIZET2NUM(types[i]));
+    }
+    rb_hash_aset(hash, ID2SYM(rb_intern(name)), result);
+}
+#endif
+
+size_t
+rb_gc_impl_gc_count(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    return objspace->profile.count;
+}
+
+static VALUE
+gc_info_decode(rb_objspace_t *objspace, const VALUE hash_or_key, const unsigned int orig_flags)
+{
+    static VALUE sym_major_by = Qnil, sym_gc_by, sym_immediate_sweep, sym_have_finalizer, sym_state, sym_need_major_by;
+    static VALUE sym_nofree, sym_oldgen, sym_shady, sym_force, sym_stress;
+#if RGENGC_ESTIMATE_OLDMALLOC
+    static VALUE sym_oldmalloc;
+#endif
+    static VALUE sym_newobj, sym_malloc, sym_method, sym_capi;
+    static VALUE sym_none, sym_marking, sym_sweeping;
+    static VALUE sym_weak_references_count, sym_retained_weak_references_count;
+    VALUE hash = Qnil, key = Qnil;
+    VALUE major_by, need_major_by;
+    unsigned int flags = orig_flags ? orig_flags : objspace->profile.latest_gc_info;
+
+    if (SYMBOL_P(hash_or_key)) {
+        key = hash_or_key;
+    }
+    else if (RB_TYPE_P(hash_or_key, T_HASH)) {
+        hash = hash_or_key;
+    }
+    else {
+        rb_bug("gc_info_decode: non-hash or symbol given");
+    }
+
+    if (NIL_P(sym_major_by)) {
+#define S(s) sym_##s = ID2SYM(rb_intern_const(#s))
+        S(major_by);
+        S(gc_by);
+        S(immediate_sweep);
+        S(have_finalizer);
+        S(state);
+        S(need_major_by);
+
+        S(stress);
+        S(nofree);
+        S(oldgen);
+        S(shady);
+        S(force);
+#if RGENGC_ESTIMATE_OLDMALLOC
+        S(oldmalloc);
+#endif
+        S(newobj);
+        S(malloc);
+        S(method);
+        S(capi);
+
+        S(none);
+        S(marking);
+        S(sweeping);
+
+        S(weak_references_count);
+        S(retained_weak_references_count);
+#undef S
+    }
+
+#define SET(name, attr) \
+    if (key == sym_##name) \
+        return (attr); \
+    else if (hash != Qnil) \
+        rb_hash_aset(hash, sym_##name, (attr));
+
+    major_by =
+      (flags & GPR_FLAG_MAJOR_BY_NOFREE) ? sym_nofree :
+      (flags & GPR_FLAG_MAJOR_BY_OLDGEN) ? sym_oldgen :
+      (flags & GPR_FLAG_MAJOR_BY_SHADY)  ? sym_shady :
+      (flags & GPR_FLAG_MAJOR_BY_FORCE)  ? sym_force :
+#if RGENGC_ESTIMATE_OLDMALLOC
+      (flags & GPR_FLAG_MAJOR_BY_OLDMALLOC) ? sym_oldmalloc :
+#endif
+      Qnil;
+    SET(major_by, major_by);
+
+    if (orig_flags == 0) { /* set need_major_by only if flags not set explicitly */
+        unsigned int need_major_flags = gc_needs_major_flags;
+        need_major_by =
+            (need_major_flags & GPR_FLAG_MAJOR_BY_NOFREE) ? sym_nofree :
+            (need_major_flags & GPR_FLAG_MAJOR_BY_OLDGEN) ? sym_oldgen :
+            (need_major_flags & GPR_FLAG_MAJOR_BY_SHADY)  ? sym_shady :
+            (need_major_flags & GPR_FLAG_MAJOR_BY_FORCE)  ? sym_force :
+#if RGENGC_ESTIMATE_OLDMALLOC
+            (need_major_flags & GPR_FLAG_MAJOR_BY_OLDMALLOC) ? sym_oldmalloc :
+#endif
+            Qnil;
+        SET(need_major_by, need_major_by);
+    }
+
+    SET(gc_by,
+        (flags & GPR_FLAG_NEWOBJ) ? sym_newobj :
+        (flags & GPR_FLAG_MALLOC) ? sym_malloc :
+        (flags & GPR_FLAG_METHOD) ? sym_method :
+        (flags & GPR_FLAG_CAPI)   ? sym_capi :
+        (flags & GPR_FLAG_STRESS) ? sym_stress :
+        Qnil
+    );
+
+    SET(have_finalizer, (flags & GPR_FLAG_HAVE_FINALIZE) ? Qtrue : Qfalse);
+    SET(immediate_sweep, (flags & GPR_FLAG_IMMEDIATE_SWEEP) ? Qtrue : Qfalse);
+
+    if (orig_flags == 0) {
+        SET(state, gc_mode(objspace) == gc_mode_none ? sym_none :
+                   gc_mode(objspace) == gc_mode_marking ? sym_marking : sym_sweeping);
+    }
+
+    SET(weak_references_count, LONG2FIX(objspace->profile.weak_references_count));
+    SET(retained_weak_references_count, LONG2FIX(objspace->profile.retained_weak_references_count));
+#undef SET
+
+    if (!NIL_P(key)) {
+        // Matched key should return above
+        return Qundef;
+    }
+
+    return hash;
+}
+
+VALUE
+rb_gc_impl_latest_gc_info(void *objspace_ptr, VALUE key)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    return gc_info_decode(objspace, key, 0);
+}
+
+
+enum gc_stat_sym {
+    gc_stat_sym_count,
+    gc_stat_sym_time,
+    gc_stat_sym_marking_time,
+    gc_stat_sym_sweeping_time,
+    gc_stat_sym_heap_allocated_pages,
+    gc_stat_sym_heap_empty_pages,
+    gc_stat_sym_heap_allocatable_slots,
+    gc_stat_sym_heap_available_slots,
+    gc_stat_sym_heap_live_slots,
+    gc_stat_sym_heap_free_slots,
+    gc_stat_sym_heap_final_slots,
+    gc_stat_sym_heap_marked_slots,
+    gc_stat_sym_heap_eden_pages,
+    gc_stat_sym_total_allocated_pages,
+    gc_stat_sym_total_freed_pages,
+    gc_stat_sym_total_allocated_objects,
+    gc_stat_sym_total_freed_objects,
+    gc_stat_sym_malloc_increase_bytes,
+    gc_stat_sym_malloc_increase_bytes_limit,
+    gc_stat_sym_minor_gc_count,
+    gc_stat_sym_major_gc_count,
+    gc_stat_sym_compact_count,
+    gc_stat_sym_read_barrier_faults,
+    gc_stat_sym_total_moved_objects,
+    gc_stat_sym_remembered_wb_unprotected_objects,
+    gc_stat_sym_remembered_wb_unprotected_objects_limit,
+    gc_stat_sym_old_objects,
+    gc_stat_sym_old_objects_limit,
+#if RGENGC_ESTIMATE_OLDMALLOC
+    gc_stat_sym_oldmalloc_increase_bytes,
+    gc_stat_sym_oldmalloc_increase_bytes_limit,
+#endif
+    gc_stat_sym_weak_references_count,
+#if RGENGC_PROFILE
+    gc_stat_sym_total_generated_normal_object_count,
+    gc_stat_sym_total_generated_shady_object_count,
+    gc_stat_sym_total_shade_operation_count,
+    gc_stat_sym_total_promoted_count,
+    gc_stat_sym_total_remembered_normal_object_count,
+    gc_stat_sym_total_remembered_shady_object_count,
+#endif
+    gc_stat_sym_last
+};
+
+static VALUE gc_stat_symbols[gc_stat_sym_last];
+
+static void
+setup_gc_stat_symbols(void)
+{
+    if (gc_stat_symbols[0] == 0) {
+#define S(s) gc_stat_symbols[gc_stat_sym_##s] = ID2SYM(rb_intern_const(#s))
+        S(count);
+        S(time);
+        S(marking_time),
+        S(sweeping_time),
+        S(heap_allocated_pages);
+        S(heap_empty_pages);
+        S(heap_allocatable_slots);
+        S(heap_available_slots);
+        S(heap_live_slots);
+        S(heap_free_slots);
+        S(heap_final_slots);
+        S(heap_marked_slots);
+        S(heap_eden_pages);
+        S(total_allocated_pages);
+        S(total_freed_pages);
+        S(total_allocated_objects);
+        S(total_freed_objects);
+        S(malloc_increase_bytes);
+        S(malloc_increase_bytes_limit);
+        S(minor_gc_count);
+        S(major_gc_count);
+        S(compact_count);
+        S(read_barrier_faults);
+        S(total_moved_objects);
+        S(remembered_wb_unprotected_objects);
+        S(remembered_wb_unprotected_objects_limit);
+        S(old_objects);
+        S(old_objects_limit);
+#if RGENGC_ESTIMATE_OLDMALLOC
+        S(oldmalloc_increase_bytes);
+        S(oldmalloc_increase_bytes_limit);
+#endif
+        S(weak_references_count);
+#if RGENGC_PROFILE
+        S(total_generated_normal_object_count);
+        S(total_generated_shady_object_count);
+        S(total_shade_operation_count);
+        S(total_promoted_count);
+        S(total_remembered_normal_object_count);
+        S(total_remembered_shady_object_count);
+#endif /* RGENGC_PROFILE */
+#undef S
+    }
+}
+
+static uint64_t
+ns_to_ms(uint64_t ns)
+{
+    return ns / (1000 * 1000);
+}
+
+VALUE
+rb_gc_impl_stat(void *objspace_ptr, VALUE hash_or_sym)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    VALUE hash = Qnil, key = Qnil;
+
+    setup_gc_stat_symbols();
+
+    if (RB_TYPE_P(hash_or_sym, T_HASH)) {
+        hash = hash_or_sym;
+    }
+    else if (SYMBOL_P(hash_or_sym)) {
+        key = hash_or_sym;
+    }
+    else {
+        rb_bug("non-hash or symbol given");
+    }
+
+#define SET(name, attr) \
+    if (key == gc_stat_symbols[gc_stat_sym_##name]) \
+        return SIZET2NUM(attr); \
+    else if (hash != Qnil) \
+        rb_hash_aset(hash, gc_stat_symbols[gc_stat_sym_##name], SIZET2NUM(attr));
+
+    SET(count, objspace->profile.count);
+    SET(time, (size_t)ns_to_ms(objspace->profile.marking_time_ns + objspace->profile.sweeping_time_ns)); // TODO: UINT64T2NUM
+    SET(marking_time, (size_t)ns_to_ms(objspace->profile.marking_time_ns));
+    SET(sweeping_time, (size_t)ns_to_ms(objspace->profile.sweeping_time_ns));
+
+    /* implementation dependent counters */
+    SET(heap_allocated_pages, rb_darray_size(objspace->heap_pages.sorted));
+    SET(heap_empty_pages, objspace->empty_pages_count)
+    SET(heap_allocatable_slots, objspace->heap_pages.allocatable_slots);
+    SET(heap_available_slots, objspace_available_slots(objspace));
+    SET(heap_live_slots, objspace_live_slots(objspace));
+    SET(heap_free_slots, objspace_free_slots(objspace));
+    SET(heap_final_slots, total_final_slots_count(objspace));
+    SET(heap_marked_slots, objspace->marked_slots);
+    SET(heap_eden_pages, heap_eden_total_pages(objspace));
+    SET(total_allocated_pages, objspace->heap_pages.allocated_pages);
+    SET(total_freed_pages, objspace->heap_pages.freed_pages);
+    SET(total_allocated_objects, total_allocated_objects(objspace));
+    SET(total_freed_objects, total_freed_objects(objspace));
+    SET(malloc_increase_bytes, malloc_increase);
+    SET(malloc_increase_bytes_limit, malloc_limit);
+    SET(minor_gc_count, objspace->profile.minor_gc_count);
+    SET(major_gc_count, objspace->profile.major_gc_count);
+    SET(compact_count, objspace->profile.compact_count);
+    SET(read_barrier_faults, objspace->profile.read_barrier_faults);
+    SET(total_moved_objects, objspace->rcompactor.total_moved);
+    SET(remembered_wb_unprotected_objects, objspace->rgengc.uncollectible_wb_unprotected_objects);
+    SET(remembered_wb_unprotected_objects_limit, objspace->rgengc.uncollectible_wb_unprotected_objects_limit);
+    SET(old_objects, objspace->rgengc.old_objects);
+    SET(old_objects_limit, objspace->rgengc.old_objects_limit);
+#if RGENGC_ESTIMATE_OLDMALLOC
+    SET(oldmalloc_increase_bytes, objspace->rgengc.oldmalloc_increase);
+    SET(oldmalloc_increase_bytes_limit, objspace->rgengc.oldmalloc_increase_limit);
+#endif
+
+#if RGENGC_PROFILE
+    SET(total_generated_normal_object_count, objspace->profile.total_generated_normal_object_count);
+    SET(total_generated_shady_object_count, objspace->profile.total_generated_shady_object_count);
+    SET(total_shade_operation_count, objspace->profile.total_shade_operation_count);
+    SET(total_promoted_count, objspace->profile.total_promoted_count);
+    SET(total_remembered_normal_object_count, objspace->profile.total_remembered_normal_object_count);
+    SET(total_remembered_shady_object_count, objspace->profile.total_remembered_shady_object_count);
+#endif /* RGENGC_PROFILE */
+#undef SET
+
+    if (!NIL_P(key)) {
+        // Matched key should return above
+        return Qundef;
+    }
+
+#if defined(RGENGC_PROFILE) && RGENGC_PROFILE >= 2
+    if (hash != Qnil) {
+        gc_count_add_each_types(hash, "generated_normal_object_count_types", objspace->profile.generated_normal_object_count_types);
+        gc_count_add_each_types(hash, "generated_shady_object_count_types", objspace->profile.generated_shady_object_count_types);
+        gc_count_add_each_types(hash, "shade_operation_count_types", objspace->profile.shade_operation_count_types);
+        gc_count_add_each_types(hash, "promoted_types", objspace->profile.promoted_types);
+        gc_count_add_each_types(hash, "remembered_normal_object_count_types", objspace->profile.remembered_normal_object_count_types);
+        gc_count_add_each_types(hash, "remembered_shady_object_count_types", objspace->profile.remembered_shady_object_count_types);
+    }
+#endif
+
+    return hash;
+}
+
+enum gc_stat_heap_sym {
+    gc_stat_heap_sym_slot_size,
+    gc_stat_heap_sym_heap_eden_pages,
+    gc_stat_heap_sym_heap_eden_slots,
+    gc_stat_heap_sym_total_allocated_pages,
+    gc_stat_heap_sym_force_major_gc_count,
+    gc_stat_heap_sym_force_incremental_marking_finish_count,
+    gc_stat_heap_sym_total_allocated_objects,
+    gc_stat_heap_sym_total_freed_objects,
+    gc_stat_heap_sym_last
+};
+
+static VALUE gc_stat_heap_symbols[gc_stat_heap_sym_last];
+
+static void
+setup_gc_stat_heap_symbols(void)
+{
+    if (gc_stat_heap_symbols[0] == 0) {
+#define S(s) gc_stat_heap_symbols[gc_stat_heap_sym_##s] = ID2SYM(rb_intern_const(#s))
+        S(slot_size);
+        S(heap_eden_pages);
+        S(heap_eden_slots);
+        S(total_allocated_pages);
+        S(force_major_gc_count);
+        S(force_incremental_marking_finish_count);
+        S(total_allocated_objects);
+        S(total_freed_objects);
+#undef S
+    }
+}
+
+static VALUE
+stat_one_heap(rb_heap_t *heap, VALUE hash, VALUE key)
+{
+#define SET(name, attr) \
+    if (key == gc_stat_heap_symbols[gc_stat_heap_sym_##name]) \
+        return SIZET2NUM(attr); \
+    else if (hash != Qnil) \
+        rb_hash_aset(hash, gc_stat_heap_symbols[gc_stat_heap_sym_##name], SIZET2NUM(attr));
+
+    SET(slot_size, heap->slot_size);
+    SET(heap_eden_pages, heap->total_pages);
+    SET(heap_eden_slots, heap->total_slots);
+    SET(total_allocated_pages, heap->total_allocated_pages);
+    SET(force_major_gc_count, heap->force_major_gc_count);
+    SET(force_incremental_marking_finish_count, heap->force_incremental_marking_finish_count);
+    SET(total_allocated_objects, heap->total_allocated_objects);
+    SET(total_freed_objects, heap->total_freed_objects);
+#undef SET
+
+    if (!NIL_P(key)) {
+        // Matched key should return above
+        return Qundef;
+    }
+
+    return hash;
+}
+
+VALUE
+rb_gc_impl_stat_heap(void *objspace_ptr, VALUE heap_name, VALUE hash_or_sym)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    setup_gc_stat_heap_symbols();
+
+    if (NIL_P(heap_name)) {
+        if (!RB_TYPE_P(hash_or_sym, T_HASH)) {
+            rb_bug("non-hash given");
+        }
+
+        for (int i = 0; i < HEAP_COUNT; i++) {
+            VALUE hash = rb_hash_aref(hash_or_sym, INT2FIX(i));
+            if (NIL_P(hash)) {
+                hash = rb_hash_new();
+                rb_hash_aset(hash_or_sym, INT2FIX(i), hash);
+            }
+
+            stat_one_heap(&heaps[i], hash, Qnil);
+        }
+    }
+    else if (FIXNUM_P(heap_name)) {
+        int heap_idx = FIX2INT(heap_name);
+
+        if (heap_idx < 0 || heap_idx >= HEAP_COUNT) {
+            rb_raise(rb_eArgError, "size pool index out of range");
+        }
+
+        if (SYMBOL_P(hash_or_sym)) {
+            return stat_one_heap(&heaps[heap_idx], Qnil, hash_or_sym);
+        }
+        else if (RB_TYPE_P(hash_or_sym, T_HASH)) {
+            return stat_one_heap(&heaps[heap_idx], hash_or_sym, Qnil);
+        }
+        else {
+            rb_bug("non-hash or symbol given");
+        }
+    }
+    else {
+        rb_bug("heap_name must be nil or an Integer");
+    }
+
+    return hash_or_sym;
+}
+
+/* I could include internal.h for this, but doing so undefines some Array macros
+ * necessary for initialising objects, and I don't want to include all the array
+ * headers to get them back
+ * TODO: Investigate why RARRAY_AREF gets undefined in internal.h
+ */
+#ifndef RBOOL
+#define RBOOL(v) (v ? Qtrue : Qfalse)
+#endif
+
+VALUE
+rb_gc_impl_config_get(void *objspace_ptr)
+{
+#define sym(name) ID2SYM(rb_intern_const(name))
+    rb_objspace_t *objspace = objspace_ptr;
+    VALUE hash = rb_hash_new();
+
+    rb_hash_aset(hash, sym("rgengc_allow_full_mark"), RBOOL(gc_config_full_mark_val));
+
+    return hash;
+}
+
+static int
+gc_config_set_key(st_data_t key, st_data_t value, st_data_t data)
+{
+    rb_objspace_t *objspace = (rb_objspace_t *)data;
+    if (rb_sym2id(key) == rb_intern("rgengc_allow_full_mark")) {
+        gc_rest(objspace);
+        gc_config_full_mark_set(RTEST(value));
+    }
+    return ST_CONTINUE;
+}
+
+void
+rb_gc_impl_config_set(void *objspace_ptr, VALUE hash)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (!RB_TYPE_P(hash, T_HASH)) {
+        rb_raise(rb_eArgError, "expected keyword arguments");
+    }
+
+    rb_hash_stlike_foreach(hash, gc_config_set_key, (st_data_t)objspace);
+}
+
+VALUE
+rb_gc_impl_stress_get(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    return ruby_gc_stress_mode;
+}
+
+void
+rb_gc_impl_stress_set(void *objspace_ptr, VALUE flag)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    objspace->flags.gc_stressful = RTEST(flag);
+    objspace->gc_stress_mode = flag;
+}
+
+static int
+get_envparam_size(const char *name, size_t *default_value, size_t lower_bound)
+{
+    const char *ptr = getenv(name);
+    ssize_t val;
+
+    if (ptr != NULL && *ptr) {
+        size_t unit = 0;
+        char *end;
+#if SIZEOF_SIZE_T == SIZEOF_LONG_LONG
+        val = strtoll(ptr, &end, 0);
+#else
+        val = strtol(ptr, &end, 0);
+#endif
+        switch (*end) {
+          case 'k': case 'K':
+            unit = 1024;
+            ++end;
+            break;
+          case 'm': case 'M':
+            unit = 1024*1024;
+            ++end;
+            break;
+          case 'g': case 'G':
+            unit = 1024*1024*1024;
+            ++end;
+            break;
+        }
+        while (*end && isspace((unsigned char)*end)) end++;
+        if (*end) {
+            if (RTEST(ruby_verbose)) fprintf(stderr, "invalid string for %s: %s\n", name, ptr);
+            return 0;
+        }
+        if (unit > 0) {
+            if (val < -(ssize_t)(SIZE_MAX / 2 / unit) || (ssize_t)(SIZE_MAX / 2 / unit) < val) {
+                if (RTEST(ruby_verbose)) fprintf(stderr, "%s=%s is ignored because it overflows\n", name, ptr);
+                return 0;
+            }
+            val *= unit;
+        }
+        if (val > 0 && (size_t)val > lower_bound) {
+            if (RTEST(ruby_verbose)) {
+                fprintf(stderr, "%s=%"PRIdSIZE" (default value: %"PRIuSIZE")\n", name, val, *default_value);
+            }
+            *default_value = (size_t)val;
+            return 1;
+        }
+        else {
+            if (RTEST(ruby_verbose)) {
+                fprintf(stderr, "%s=%"PRIdSIZE" (default value: %"PRIuSIZE") is ignored because it must be greater than %"PRIuSIZE".\n",
+                        name, val, *default_value, lower_bound);
+            }
+            return 0;
+        }
+    }
+    return 0;
+}
+
+static int
+get_envparam_double(const char *name, double *default_value, double lower_bound, double upper_bound, int accept_zero)
+{
+    const char *ptr = getenv(name);
+    double val;
+
+    if (ptr != NULL && *ptr) {
+        char *end;
+        val = strtod(ptr, &end);
+        if (!*ptr || *end) {
+            if (RTEST(ruby_verbose)) fprintf(stderr, "invalid string for %s: %s\n", name, ptr);
+            return 0;
+        }
+
+        if (accept_zero && val == 0.0) {
+            goto accept;
+        }
+        else if (val <= lower_bound) {
+            if (RTEST(ruby_verbose)) {
+                fprintf(stderr, "%s=%f (default value: %f) is ignored because it must be greater than %f.\n",
+                        name, val, *default_value, lower_bound);
+            }
+        }
+        else if (upper_bound != 0.0 && /* ignore upper_bound if it is 0.0 */
+                 val > upper_bound) {
+            if (RTEST(ruby_verbose)) {
+                fprintf(stderr, "%s=%f (default value: %f) is ignored because it must be lower than %f.\n",
+                        name, val, *default_value, upper_bound);
+            }
+        }
+        else {
+            goto accept;
+        }
+    }
+    return 0;
+
+  accept:
+    if (RTEST(ruby_verbose)) fprintf(stderr, "%s=%f (default value: %f)\n", name, val, *default_value);
+    *default_value = val;
+    return 1;
+}
+
+/*
+ * GC tuning environment variables
+ *
+ * * RUBY_GC_HEAP_FREE_SLOTS
+ *   - Prepare at least this amount of slots after GC.
+ *   - Allocate slots if there are not enough slots.
+ * * RUBY_GC_HEAP_GROWTH_FACTOR (new from 2.1)
+ *   - Allocate slots by this factor.
+ *   - (next slots number) = (current slots number) * (this factor)
+ * * RUBY_GC_HEAP_GROWTH_MAX_SLOTS (new from 2.1)
+ *   - Allocation rate is limited to this number of slots.
+ * * RUBY_GC_HEAP_FREE_SLOTS_MIN_RATIO (new from 2.4)
+ *   - Allocate additional pages when the number of free slots is
+ *     lower than the value (total_slots * (this ratio)).
+ * * RUBY_GC_HEAP_FREE_SLOTS_GOAL_RATIO (new from 2.4)
+ *   - Allocate slots to satisfy this formula:
+ *       free_slots = total_slots * goal_ratio
+ *   - In other words, prepare (total_slots * goal_ratio) free slots.
+ *   - if this value is 0.0, then use RUBY_GC_HEAP_GROWTH_FACTOR directly.
+ * * RUBY_GC_HEAP_FREE_SLOTS_MAX_RATIO (new from 2.4)
+ *   - Allow to free pages when the number of free slots is
+ *     greater than the value (total_slots * (this ratio)).
+ * * RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR (new from 2.1.1)
+ *   - Do full GC when the number of old objects is more than R * N
+ *     where R is this factor and
+ *           N is the number of old objects just after last full GC.
+ *
+ *  * obsolete
+ *    * RUBY_FREE_MIN       -> RUBY_GC_HEAP_FREE_SLOTS (from 2.1)
+ *    * RUBY_HEAP_MIN_SLOTS -> RUBY_GC_HEAP_INIT_SLOTS (from 2.1)
+ *
+ * * RUBY_GC_MALLOC_LIMIT
+ * * RUBY_GC_MALLOC_LIMIT_MAX (new from 2.1)
+ * * RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR (new from 2.1)
+ *
+ * * RUBY_GC_OLDMALLOC_LIMIT (new from 2.1)
+ * * RUBY_GC_OLDMALLOC_LIMIT_MAX (new from 2.1)
+ * * RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR (new from 2.1)
+ */
+
+void
+rb_gc_impl_set_params(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    /* RUBY_GC_HEAP_FREE_SLOTS */
+    if (get_envparam_size("RUBY_GC_HEAP_FREE_SLOTS", &gc_params.heap_free_slots, 0)) {
+        /* ok */
+    }
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        char env_key[sizeof("RUBY_GC_HEAP_" "_INIT_SLOTS") + DECIMAL_SIZE_OF_BITS(sizeof(int) * CHAR_BIT)];
+        snprintf(env_key, sizeof(env_key), "RUBY_GC_HEAP_%d_INIT_SLOTS", i);
+
+        get_envparam_size(env_key, &gc_params.heap_init_slots[i], 0);
+    }
+
+    get_envparam_double("RUBY_GC_HEAP_GROWTH_FACTOR", &gc_params.growth_factor, 1.0, 0.0, FALSE);
+    get_envparam_size  ("RUBY_GC_HEAP_GROWTH_MAX_SLOTS", &gc_params.growth_max_slots, 0);
+    get_envparam_double("RUBY_GC_HEAP_FREE_SLOTS_MIN_RATIO", &gc_params.heap_free_slots_min_ratio,
+                        0.0, 1.0, FALSE);
+    get_envparam_double("RUBY_GC_HEAP_FREE_SLOTS_MAX_RATIO", &gc_params.heap_free_slots_max_ratio,
+                        gc_params.heap_free_slots_min_ratio, 1.0, FALSE);
+    get_envparam_double("RUBY_GC_HEAP_FREE_SLOTS_GOAL_RATIO", &gc_params.heap_free_slots_goal_ratio,
+                        gc_params.heap_free_slots_min_ratio, gc_params.heap_free_slots_max_ratio, TRUE);
+    get_envparam_double("RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR", &gc_params.oldobject_limit_factor, 0.0, 0.0, TRUE);
+    get_envparam_double("RUBY_GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO", &gc_params.uncollectible_wb_unprotected_objects_limit_ratio, 0.0, 0.0, TRUE);
+
+    if (get_envparam_size("RUBY_GC_MALLOC_LIMIT", &gc_params.malloc_limit_min, 0)) {
+        malloc_limit = gc_params.malloc_limit_min;
+    }
+    get_envparam_size  ("RUBY_GC_MALLOC_LIMIT_MAX", &gc_params.malloc_limit_max, 0);
+    if (!gc_params.malloc_limit_max) { /* ignore max-check if 0 */
+        gc_params.malloc_limit_max = SIZE_MAX;
+    }
+    get_envparam_double("RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR", &gc_params.malloc_limit_growth_factor, 1.0, 0.0, FALSE);
+
+#if RGENGC_ESTIMATE_OLDMALLOC
+    if (get_envparam_size("RUBY_GC_OLDMALLOC_LIMIT", &gc_params.oldmalloc_limit_min, 0)) {
+        objspace->rgengc.oldmalloc_increase_limit = gc_params.oldmalloc_limit_min;
+    }
+    get_envparam_size  ("RUBY_GC_OLDMALLOC_LIMIT_MAX", &gc_params.oldmalloc_limit_max, 0);
+    get_envparam_double("RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR", &gc_params.oldmalloc_limit_growth_factor, 1.0, 0.0, FALSE);
+#endif
+}
+
+static inline size_t
+objspace_malloc_size(rb_objspace_t *objspace, void *ptr, size_t hint)
+{
+#ifdef HAVE_MALLOC_USABLE_SIZE
+    return malloc_usable_size(ptr);
+#else
+    return hint;
+#endif
+}
+
+enum memop_type {
+    MEMOP_TYPE_MALLOC  = 0,
+    MEMOP_TYPE_FREE,
+    MEMOP_TYPE_REALLOC
+};
+
+static inline void
+atomic_sub_nounderflow(size_t *var, size_t sub)
+{
+    if (sub == 0) return;
+
+    while (1) {
+        size_t val = *var;
+        if (val < sub) sub = val;
+        if (RUBY_ATOMIC_SIZE_CAS(*var, val, val-sub) == val) break;
+    }
+}
+
+#define gc_stress_full_mark_after_malloc_p() \
+    (FIXNUM_P(ruby_gc_stress_mode) && (FIX2LONG(ruby_gc_stress_mode) & (1<<gc_stress_full_mark_after_malloc)))
+
+static void
+objspace_malloc_gc_stress(rb_objspace_t *objspace)
+{
+    if (ruby_gc_stressful && ruby_native_thread_p()) {
+        unsigned int reason = (GPR_FLAG_IMMEDIATE_MARK | GPR_FLAG_IMMEDIATE_SWEEP |
+                               GPR_FLAG_STRESS | GPR_FLAG_MALLOC);
+
+        if (gc_stress_full_mark_after_malloc_p()) {
+            reason |= GPR_FLAG_FULL_MARK;
+        }
+        garbage_collect_with_gvl(objspace, reason);
+    }
+}
+
+static inline bool
+objspace_malloc_increase_report(rb_objspace_t *objspace, void *mem, size_t new_size, size_t old_size, enum memop_type type)
+{
+    if (0) fprintf(stderr, "increase - ptr: %p, type: %s, new_size: %"PRIdSIZE", old_size: %"PRIdSIZE"\n",
+                   mem,
+                   type == MEMOP_TYPE_MALLOC  ? "malloc" :
+                   type == MEMOP_TYPE_FREE    ? "free  " :
+                   type == MEMOP_TYPE_REALLOC ? "realloc": "error",
+                   new_size, old_size);
+    return false;
+}
+
+static bool
+objspace_malloc_increase_body(rb_objspace_t *objspace, void *mem, size_t new_size, size_t old_size, enum memop_type type)
+{
+    if (new_size > old_size) {
+        RUBY_ATOMIC_SIZE_ADD(malloc_increase, new_size - old_size);
+#if RGENGC_ESTIMATE_OLDMALLOC
+        RUBY_ATOMIC_SIZE_ADD(objspace->rgengc.oldmalloc_increase, new_size - old_size);
+#endif
+    }
+    else {
+        atomic_sub_nounderflow(&malloc_increase, old_size - new_size);
+#if RGENGC_ESTIMATE_OLDMALLOC
+        atomic_sub_nounderflow(&objspace->rgengc.oldmalloc_increase, old_size - new_size);
+#endif
+    }
+
+    if (type == MEMOP_TYPE_MALLOC) {
+      retry:
+        if (malloc_increase > malloc_limit && ruby_native_thread_p() && !dont_gc_val()) {
+            if (ruby_thread_has_gvl_p() && is_lazy_sweeping(objspace)) {
+                gc_rest(objspace); /* gc_rest can reduce malloc_increase */
+                goto retry;
+            }
+            garbage_collect_with_gvl(objspace, GPR_FLAG_MALLOC);
+        }
+    }
+
+#if MALLOC_ALLOCATED_SIZE
+    if (new_size >= old_size) {
+        RUBY_ATOMIC_SIZE_ADD(objspace->malloc_params.allocated_size, new_size - old_size);
+    }
+    else {
+        size_t dec_size = old_size - new_size;
+        size_t allocated_size = objspace->malloc_params.allocated_size;
+
+#if MALLOC_ALLOCATED_SIZE_CHECK
+        if (allocated_size < dec_size) {
+            rb_bug("objspace_malloc_increase: underflow malloc_params.allocated_size.");
+        }
+#endif
+        atomic_sub_nounderflow(&objspace->malloc_params.allocated_size, dec_size);
+    }
+
+    switch (type) {
+      case MEMOP_TYPE_MALLOC:
+        RUBY_ATOMIC_SIZE_INC(objspace->malloc_params.allocations);
+        break;
+      case MEMOP_TYPE_FREE:
+        {
+            size_t allocations = objspace->malloc_params.allocations;
+            if (allocations > 0) {
+                atomic_sub_nounderflow(&objspace->malloc_params.allocations, 1);
+            }
+#if MALLOC_ALLOCATED_SIZE_CHECK
+            else {
+                GC_ASSERT(objspace->malloc_params.allocations > 0);
+            }
+#endif
+        }
+        break;
+      case MEMOP_TYPE_REALLOC: /* ignore */ break;
+    }
+#endif
+    return true;
+}
+
+#define objspace_malloc_increase(...) \
+    for (bool malloc_increase_done = objspace_malloc_increase_report(__VA_ARGS__); \
+         !malloc_increase_done; \
+         malloc_increase_done = objspace_malloc_increase_body(__VA_ARGS__))
+
+struct malloc_obj_info { /* 4 words */
+    size_t size;
+};
+
+static inline size_t
+objspace_malloc_prepare(rb_objspace_t *objspace, size_t size)
+{
+    if (size == 0) size = 1;
+
+#if CALC_EXACT_MALLOC_SIZE
+    size += sizeof(struct malloc_obj_info);
+#endif
+
+    return size;
+}
+
+static bool
+malloc_during_gc_p(rb_objspace_t *objspace)
+{
+    /* malloc is not allowed during GC when we're not using multiple ractors
+     * (since ractors can run while another thread is sweeping) and when we
+     * have the GVL (since if we don't have the GVL, we'll try to acquire the
+     * GVL which will block and ensure the other thread finishes GC). */
+    return during_gc && !dont_gc_val() && !rb_gc_multi_ractor_p() && ruby_thread_has_gvl_p();
+}
+
+static inline void *
+objspace_malloc_fixup(rb_objspace_t *objspace, void *mem, size_t size)
+{
+    size = objspace_malloc_size(objspace, mem, size);
+    objspace_malloc_increase(objspace, mem, size, 0, MEMOP_TYPE_MALLOC) {}
+
+#if CALC_EXACT_MALLOC_SIZE
+    {
+        struct malloc_obj_info *info = mem;
+        info->size = size;
+        mem = info + 1;
+    }
+#endif
+
+    return mem;
+}
+
+#if defined(__GNUC__) && RUBY_DEBUG
+#define RB_BUG_INSTEAD_OF_RB_MEMERROR 1
+#endif
+
+#ifndef RB_BUG_INSTEAD_OF_RB_MEMERROR
+# define RB_BUG_INSTEAD_OF_RB_MEMERROR 0
+#endif
+
+#define GC_MEMERROR(...) \
+    ((RB_BUG_INSTEAD_OF_RB_MEMERROR+0) ? rb_bug("" __VA_ARGS__) : rb_memerror())
+
+#define TRY_WITH_GC(siz, expr) do {                          \
+        const gc_profile_record_flag gpr =                   \
+            GPR_FLAG_FULL_MARK           |                   \
+            GPR_FLAG_IMMEDIATE_MARK      |                   \
+            GPR_FLAG_IMMEDIATE_SWEEP     |                   \
+            GPR_FLAG_MALLOC;                                 \
+        objspace_malloc_gc_stress(objspace);                 \
+                                                             \
+        if (RB_LIKELY((expr))) {                                \
+            /* Success on 1st try */                         \
+        }                                                    \
+        else if (!garbage_collect_with_gvl(objspace, gpr)) { \
+            /* @shyouhei thinks this doesn't happen */       \
+            GC_MEMERROR("TRY_WITH_GC: could not GC");        \
+        }                                                    \
+        else if ((expr)) {                                   \
+            /* Success on 2nd try */                         \
+        }                                                    \
+        else {                                               \
+            GC_MEMERROR("TRY_WITH_GC: could not allocate:"   \
+                        "%"PRIdSIZE" bytes for %s",          \
+                        siz, # expr);                        \
+        }                                                    \
+    } while (0)
+
+static void
+check_malloc_not_in_gc(rb_objspace_t *objspace, const char *msg)
+{
+    if (RB_UNLIKELY(malloc_during_gc_p(objspace))) {
+        dont_gc_on();
+        during_gc = false;
+        rb_bug("Cannot %s during GC", msg);
+    }
+}
+
+void
+rb_gc_impl_free(void *objspace_ptr, void *ptr, size_t old_size)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (!ptr) {
+        /*
+         * ISO/IEC 9899 says "If ptr is a null pointer, no action occurs" since
+         * its first version.  We would better follow.
+         */
+        return;
+    }
+#if CALC_EXACT_MALLOC_SIZE
+    struct malloc_obj_info *info = (struct malloc_obj_info *)ptr - 1;
+    ptr = info;
+    old_size = info->size;
+#endif
+    old_size = objspace_malloc_size(objspace, ptr, old_size);
+
+    objspace_malloc_increase(objspace, ptr, 0, old_size, MEMOP_TYPE_FREE) {
+        free(ptr);
+        ptr = NULL;
+        RB_DEBUG_COUNTER_INC(heap_xfree);
+    }
+}
+
+void *
+rb_gc_impl_malloc(void *objspace_ptr, size_t size)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+    check_malloc_not_in_gc(objspace, "malloc");
+
+    void *mem;
+
+    size = objspace_malloc_prepare(objspace, size);
+    TRY_WITH_GC(size, mem = malloc(size));
+    RB_DEBUG_COUNTER_INC(heap_xmalloc);
+    return objspace_malloc_fixup(objspace, mem, size);
+}
+
+void *
+rb_gc_impl_calloc(void *objspace_ptr, size_t size)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (RB_UNLIKELY(malloc_during_gc_p(objspace))) {
+        rb_warn("calloc during GC detected, this could cause crashes if it triggers another GC");
+#if RGENGC_CHECK_MODE || RUBY_DEBUG
+        rb_bug("Cannot calloc during GC");
+#endif
+    }
+
+    void *mem;
+
+    size = objspace_malloc_prepare(objspace, size);
+    TRY_WITH_GC(size, mem = calloc1(size));
+    return objspace_malloc_fixup(objspace, mem, size);
+}
+
+void *
+rb_gc_impl_realloc(void *objspace_ptr, void *ptr, size_t new_size, size_t old_size)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    check_malloc_not_in_gc(objspace, "realloc");
+
+    void *mem;
+
+    if (!ptr) return rb_gc_impl_malloc(objspace, new_size);
+
+    /*
+     * The behavior of realloc(ptr, 0) is implementation defined.
+     * Therefore we don't use realloc(ptr, 0) for portability reason.
+     * see http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_400.htm
+     */
+    if (new_size == 0) {
+        if ((mem = rb_gc_impl_malloc(objspace, 0)) != NULL) {
+            /*
+             * - OpenBSD's malloc(3) man page says that when 0 is passed, it
+             *   returns a non-NULL pointer to an access-protected memory page.
+             *   The returned pointer cannot be read / written at all, but
+             *   still be a valid argument of free().
+             *
+             *   https://man.openbsd.org/malloc.3
+             *
+             * - Linux's malloc(3) man page says that it _might_ perhaps return
+             *   a non-NULL pointer when its argument is 0.  That return value
+             *   is safe (and is expected) to be passed to free().
+             *
+             *   https://man7.org/linux/man-pages/man3/malloc.3.html
+             *
+             * - As I read the implementation jemalloc's malloc() returns fully
+             *   normal 16 bytes memory region when its argument is 0.
+             *
+             * - As I read the implementation musl libc's malloc() returns
+             *   fully normal 32 bytes memory region when its argument is 0.
+             *
+             * - Other malloc implementations can also return non-NULL.
+             */
+            rb_gc_impl_free(objspace, ptr, old_size);
+            return mem;
+        }
+        else {
+            /*
+             * It is dangerous to return NULL here, because that could lead to
+             * RCE.  Fallback to 1 byte instead of zero.
+             *
+             * https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11932
+             */
+            new_size = 1;
+        }
+    }
+
+#if CALC_EXACT_MALLOC_SIZE
+    {
+        struct malloc_obj_info *info = (struct malloc_obj_info *)ptr - 1;
+        new_size += sizeof(struct malloc_obj_info);
+        ptr = info;
+        old_size = info->size;
+    }
+#endif
+
+    old_size = objspace_malloc_size(objspace, ptr, old_size);
+    TRY_WITH_GC(new_size, mem = RB_GNUC_EXTENSION_BLOCK(realloc(ptr, new_size)));
+    new_size = objspace_malloc_size(objspace, mem, new_size);
+
+#if CALC_EXACT_MALLOC_SIZE
+    {
+        struct malloc_obj_info *info = mem;
+        info->size = new_size;
+        mem = info + 1;
+    }
+#endif
+
+    objspace_malloc_increase(objspace, mem, new_size, old_size, MEMOP_TYPE_REALLOC);
+
+    RB_DEBUG_COUNTER_INC(heap_xrealloc);
+    return mem;
+}
+
+void
+rb_gc_impl_adjust_memory_usage(void *objspace_ptr, ssize_t diff)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (diff > 0) {
+        objspace_malloc_increase(objspace, 0, diff, 0, MEMOP_TYPE_REALLOC);
+    }
+    else if (diff < 0) {
+        objspace_malloc_increase(objspace, 0, 0, -diff, MEMOP_TYPE_REALLOC);
+    }
+}
+
+// TODO: move GC profiler stuff back into gc.c
+/*
+  ------------------------------ GC profiler ------------------------------
+*/
+
+#define GC_PROFILE_RECORD_DEFAULT_SIZE 100
+
+static bool
+current_process_time(struct timespec *ts)
+{
+#if defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_PROCESS_CPUTIME_ID)
+    {
+        static int try_clock_gettime = 1;
+        if (try_clock_gettime && clock_gettime(CLOCK_PROCESS_CPUTIME_ID, ts) == 0) {
+            return true;
+        }
+        else {
+            try_clock_gettime = 0;
+        }
+    }
+#endif
+
+#ifdef RUSAGE_SELF
+    {
+        struct rusage usage;
+        struct timeval time;
+        if (getrusage(RUSAGE_SELF, &usage) == 0) {
+            time = usage.ru_utime;
+            ts->tv_sec = time.tv_sec;
+            ts->tv_nsec = (int32_t)time.tv_usec * 1000;
+            return true;
+        }
+    }
+#endif
+
+#ifdef _WIN32
+    {
+        FILETIME creation_time, exit_time, kernel_time, user_time;
+        ULARGE_INTEGER ui;
+
+        if (GetProcessTimes(GetCurrentProcess(),
+                            &creation_time, &exit_time, &kernel_time, &user_time) != 0) {
+            memcpy(&ui, &user_time, sizeof(FILETIME));
+#define PER100NSEC (uint64_t)(1000 * 1000 * 10)
+            ts->tv_nsec = (long)(ui.QuadPart % PER100NSEC);
+            ts->tv_sec  = (time_t)(ui.QuadPart / PER100NSEC);
+            return true;
+        }
+    }
+#endif
+
+    return false;
+}
+
+static double
+getrusage_time(void)
+{
+    struct timespec ts;
+    if (current_process_time(&ts)) {
+        return ts.tv_sec + ts.tv_nsec * 1e-9;
+    }
+    else {
+        return 0.0;
+    }
+}
+
+
+static inline void
+gc_prof_setup_new_record(rb_objspace_t *objspace, unsigned int reason)
+{
+    if (objspace->profile.run) {
+        size_t index = objspace->profile.next_index;
+        gc_profile_record *record;
+
+        /* create new record */
+        objspace->profile.next_index++;
+
+        if (!objspace->profile.records) {
+            objspace->profile.size = GC_PROFILE_RECORD_DEFAULT_SIZE;
+            objspace->profile.records = malloc(xmalloc2_size(sizeof(gc_profile_record), objspace->profile.size));
+        }
+        if (index >= objspace->profile.size) {
+            void *ptr;
+            objspace->profile.size += 1000;
+            ptr = realloc(objspace->profile.records, xmalloc2_size(sizeof(gc_profile_record), objspace->profile.size));
+            if (!ptr) rb_memerror();
+            objspace->profile.records = ptr;
+        }
+        if (!objspace->profile.records) {
+            rb_bug("gc_profile malloc or realloc miss");
+        }
+        record = objspace->profile.current_record = &objspace->profile.records[objspace->profile.next_index - 1];
+        MEMZERO(record, gc_profile_record, 1);
+
+        /* setup before-GC parameter */
+        record->flags = reason | (ruby_gc_stressful ? GPR_FLAG_STRESS : 0);
+#if MALLOC_ALLOCATED_SIZE
+        record->allocated_size = malloc_allocated_size;
+#endif
+#if GC_PROFILE_MORE_DETAIL && GC_PROFILE_DETAIL_MEMORY
+#ifdef RUSAGE_SELF
+        {
+            struct rusage usage;
+            if (getrusage(RUSAGE_SELF, &usage) == 0) {
+                record->maxrss = usage.ru_maxrss;
+                record->minflt = usage.ru_minflt;
+                record->majflt = usage.ru_majflt;
+            }
+        }
+#endif
+#endif
+    }
+}
+
+static inline void
+gc_prof_timer_start(rb_objspace_t *objspace)
+{
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+#if GC_PROFILE_MORE_DETAIL
+        record->prepare_time = objspace->profile.prepare_time;
+#endif
+        record->gc_time = 0;
+        record->gc_invoke_time = getrusage_time();
+    }
+}
+
+static double
+elapsed_time_from(double time)
+{
+    double now = getrusage_time();
+    if (now > time) {
+        return now - time;
+    }
+    else {
+        return 0;
+    }
+}
+
+static inline void
+gc_prof_timer_stop(rb_objspace_t *objspace)
+{
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->gc_time = elapsed_time_from(record->gc_invoke_time);
+        record->gc_invoke_time -= objspace->profile.invoke_time;
+    }
+}
+
+#ifdef BUILDING_SHARED_GC
+# define RUBY_DTRACE_GC_HOOK(name)
+#else
+# define RUBY_DTRACE_GC_HOOK(name) \
+    do {if (RUBY_DTRACE_GC_##name##_ENABLED()) RUBY_DTRACE_GC_##name();} while (0)
+#endif
+
+static inline void
+gc_prof_mark_timer_start(rb_objspace_t *objspace)
+{
+    RUBY_DTRACE_GC_HOOK(MARK_BEGIN);
+#if GC_PROFILE_MORE_DETAIL
+    if (gc_prof_enabled(objspace)) {
+        gc_prof_record(objspace)->gc_mark_time = getrusage_time();
+    }
+#endif
+}
+
+static inline void
+gc_prof_mark_timer_stop(rb_objspace_t *objspace)
+{
+    RUBY_DTRACE_GC_HOOK(MARK_END);
+#if GC_PROFILE_MORE_DETAIL
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->gc_mark_time = elapsed_time_from(record->gc_mark_time);
+    }
+#endif
+}
+
+static inline void
+gc_prof_sweep_timer_start(rb_objspace_t *objspace)
+{
+    RUBY_DTRACE_GC_HOOK(SWEEP_BEGIN);
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+
+        if (record->gc_time > 0 || GC_PROFILE_MORE_DETAIL) {
+            objspace->profile.gc_sweep_start_time = getrusage_time();
+        }
+    }
+}
+
+static inline void
+gc_prof_sweep_timer_stop(rb_objspace_t *objspace)
+{
+    RUBY_DTRACE_GC_HOOK(SWEEP_END);
+
+    if (gc_prof_enabled(objspace)) {
+        double sweep_time;
+        gc_profile_record *record = gc_prof_record(objspace);
+
+        if (record->gc_time > 0) {
+            sweep_time = elapsed_time_from(objspace->profile.gc_sweep_start_time);
+            /* need to accumulate GC time for lazy sweep after gc() */
+            record->gc_time += sweep_time;
+        }
+        else if (GC_PROFILE_MORE_DETAIL) {
+            sweep_time = elapsed_time_from(objspace->profile.gc_sweep_start_time);
+        }
+
+#if GC_PROFILE_MORE_DETAIL
+        record->gc_sweep_time += sweep_time;
+        if (heap_pages_deferred_final) record->flags |= GPR_FLAG_HAVE_FINALIZE;
+#endif
+        if (heap_pages_deferred_final) objspace->profile.latest_gc_info |= GPR_FLAG_HAVE_FINALIZE;
+    }
+}
+
+static inline void
+gc_prof_set_malloc_info(rb_objspace_t *objspace)
+{
+#if GC_PROFILE_MORE_DETAIL
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        record->allocate_increase = malloc_increase;
+        record->allocate_limit = malloc_limit;
+    }
+#endif
+}
+
+static inline void
+gc_prof_set_heap_info(rb_objspace_t *objspace)
+{
+    if (gc_prof_enabled(objspace)) {
+        gc_profile_record *record = gc_prof_record(objspace);
+        size_t live = objspace->profile.total_allocated_objects_at_gc_start - total_freed_objects(objspace);
+        size_t total = objspace->profile.heap_used_at_gc_start * HEAP_PAGE_OBJ_LIMIT;
+
+#if GC_PROFILE_MORE_DETAIL
+        record->heap_use_pages = objspace->profile.heap_used_at_gc_start;
+        record->heap_live_objects = live;
+        record->heap_free_objects = total - live;
+#endif
+
+        record->heap_total_objects = total;
+        record->heap_use_size = live * BASE_SLOT_SIZE;
+        record->heap_total_size = total * BASE_SLOT_SIZE;
+    }
+}
+
+/*
+ *  call-seq:
+ *    GC::Profiler.clear          -> nil
+ *
+ *  Clears the \GC profiler data.
+ *
+ */
+
+static VALUE
+gc_profile_clear(VALUE _)
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    void *p = objspace->profile.records;
+    objspace->profile.records = NULL;
+    objspace->profile.size = 0;
+    objspace->profile.next_index = 0;
+    objspace->profile.current_record = 0;
+    free(p);
+    return Qnil;
+}
+
+/*
+ *  call-seq:
+ *     GC::Profiler.raw_data	-> [Hash, ...]
+ *
+ *  Returns an Array of individual raw profile data Hashes ordered
+ *  from earliest to latest by +:GC_INVOKE_TIME+.
+ *
+ *  For example:
+ *
+ *    [
+ *	{
+ *	   :GC_TIME=>1.3000000000000858e-05,
+ *	   :GC_INVOKE_TIME=>0.010634999999999999,
+ *	   :HEAP_USE_SIZE=>289640,
+ *	   :HEAP_TOTAL_SIZE=>588960,
+ *	   :HEAP_TOTAL_OBJECTS=>14724,
+ *	   :GC_IS_MARKED=>false
+ *	},
+ *      # ...
+ *    ]
+ *
+ *  The keys mean:
+ *
+ *  +:GC_TIME+::
+ *	Time elapsed in seconds for this GC run
+ *  +:GC_INVOKE_TIME+::
+ *	Time elapsed in seconds from startup to when the GC was invoked
+ *  +:HEAP_USE_SIZE+::
+ *	Total bytes of heap used
+ *  +:HEAP_TOTAL_SIZE+::
+ *	Total size of heap in bytes
+ *  +:HEAP_TOTAL_OBJECTS+::
+ *	Total number of objects
+ *  +:GC_IS_MARKED+::
+ *	Returns +true+ if the GC is in mark phase
+ *
+ *  If ruby was built with +GC_PROFILE_MORE_DETAIL+, you will also have access
+ *  to the following hash keys:
+ *
+ *  +:GC_MARK_TIME+::
+ *  +:GC_SWEEP_TIME+::
+ *  +:ALLOCATE_INCREASE+::
+ *  +:ALLOCATE_LIMIT+::
+ *  +:HEAP_USE_PAGES+::
+ *  +:HEAP_LIVE_OBJECTS+::
+ *  +:HEAP_FREE_OBJECTS+::
+ *  +:HAVE_FINALIZE+::
+ *
+ */
+
+static VALUE
+gc_profile_record_get(VALUE _)
+{
+    VALUE prof;
+    VALUE gc_profile = rb_ary_new();
+    size_t i;
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+
+    if (!objspace->profile.run) {
+        return Qnil;
+    }
+
+    for (i =0; i < objspace->profile.next_index; i++) {
+        gc_profile_record *record = &objspace->profile.records[i];
+
+        prof = rb_hash_new();
+        rb_hash_aset(prof, ID2SYM(rb_intern("GC_FLAGS")), gc_info_decode(objspace, rb_hash_new(), record->flags));
+        rb_hash_aset(prof, ID2SYM(rb_intern("GC_TIME")), DBL2NUM(record->gc_time));
+        rb_hash_aset(prof, ID2SYM(rb_intern("GC_INVOKE_TIME")), DBL2NUM(record->gc_invoke_time));
+        rb_hash_aset(prof, ID2SYM(rb_intern("HEAP_USE_SIZE")), SIZET2NUM(record->heap_use_size));
+        rb_hash_aset(prof, ID2SYM(rb_intern("HEAP_TOTAL_SIZE")), SIZET2NUM(record->heap_total_size));
+        rb_hash_aset(prof, ID2SYM(rb_intern("HEAP_TOTAL_OBJECTS")), SIZET2NUM(record->heap_total_objects));
+        rb_hash_aset(prof, ID2SYM(rb_intern("MOVED_OBJECTS")), SIZET2NUM(record->moved_objects));
+        rb_hash_aset(prof, ID2SYM(rb_intern("GC_IS_MARKED")), Qtrue);
+#if GC_PROFILE_MORE_DETAIL
+        rb_hash_aset(prof, ID2SYM(rb_intern("GC_MARK_TIME")), DBL2NUM(record->gc_mark_time));
+        rb_hash_aset(prof, ID2SYM(rb_intern("GC_SWEEP_TIME")), DBL2NUM(record->gc_sweep_time));
+        rb_hash_aset(prof, ID2SYM(rb_intern("ALLOCATE_INCREASE")), SIZET2NUM(record->allocate_increase));
+        rb_hash_aset(prof, ID2SYM(rb_intern("ALLOCATE_LIMIT")), SIZET2NUM(record->allocate_limit));
+        rb_hash_aset(prof, ID2SYM(rb_intern("HEAP_USE_PAGES")), SIZET2NUM(record->heap_use_pages));
+        rb_hash_aset(prof, ID2SYM(rb_intern("HEAP_LIVE_OBJECTS")), SIZET2NUM(record->heap_live_objects));
+        rb_hash_aset(prof, ID2SYM(rb_intern("HEAP_FREE_OBJECTS")), SIZET2NUM(record->heap_free_objects));
+
+        rb_hash_aset(prof, ID2SYM(rb_intern("REMOVING_OBJECTS")), SIZET2NUM(record->removing_objects));
+        rb_hash_aset(prof, ID2SYM(rb_intern("EMPTY_OBJECTS")), SIZET2NUM(record->empty_objects));
+
+        rb_hash_aset(prof, ID2SYM(rb_intern("HAVE_FINALIZE")), (record->flags & GPR_FLAG_HAVE_FINALIZE) ? Qtrue : Qfalse);
+#endif
+
+#if RGENGC_PROFILE > 0
+        rb_hash_aset(prof, ID2SYM(rb_intern("OLD_OBJECTS")), SIZET2NUM(record->old_objects));
+        rb_hash_aset(prof, ID2SYM(rb_intern("REMEMBERED_NORMAL_OBJECTS")), SIZET2NUM(record->remembered_normal_objects));
+        rb_hash_aset(prof, ID2SYM(rb_intern("REMEMBERED_SHADY_OBJECTS")), SIZET2NUM(record->remembered_shady_objects));
+#endif
+        rb_ary_push(gc_profile, prof);
+    }
+
+    return gc_profile;
+}
+
+#if GC_PROFILE_MORE_DETAIL
+#define MAJOR_REASON_MAX 0x10
+
+static char *
+gc_profile_dump_major_reason(unsigned int flags, char *buff)
+{
+    unsigned int reason = flags & GPR_FLAG_MAJOR_MASK;
+    int i = 0;
+
+    if (reason == GPR_FLAG_NONE) {
+        buff[0] = '-';
+        buff[1] = 0;
+    }
+    else {
+#define C(x, s) \
+  if (reason & GPR_FLAG_MAJOR_BY_##x) { \
+      buff[i++] = #x[0]; \
+      if (i >= MAJOR_REASON_MAX) rb_bug("gc_profile_dump_major_reason: overflow"); \
+      buff[i] = 0; \
+  }
+        C(NOFREE, N);
+        C(OLDGEN, O);
+        C(SHADY,  S);
+#if RGENGC_ESTIMATE_OLDMALLOC
+        C(OLDMALLOC, M);
+#endif
+#undef C
+    }
+    return buff;
+}
+#endif
+
+
+
+static void
+gc_profile_dump_on(VALUE out, VALUE (*append)(VALUE, VALUE))
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    size_t count = objspace->profile.next_index;
+#ifdef MAJOR_REASON_MAX
+    char reason_str[MAJOR_REASON_MAX];
+#endif
+
+    if (objspace->profile.run && count /* > 1 */) {
+        size_t i;
+        const gc_profile_record *record;
+
+        append(out, rb_sprintf("GC %"PRIuSIZE" invokes.\n", objspace->profile.count));
+        append(out, rb_str_new_cstr("Index    Invoke Time(sec)       Use Size(byte)     Total Size(byte)         Total Object                    GC Time(ms)\n"));
+
+        for (i = 0; i < count; i++) {
+            record = &objspace->profile.records[i];
+            append(out, rb_sprintf("%5"PRIuSIZE" %19.3f %20"PRIuSIZE" %20"PRIuSIZE" %20"PRIuSIZE" %30.20f\n",
+                                   i+1, record->gc_invoke_time, record->heap_use_size,
+                                   record->heap_total_size, record->heap_total_objects, record->gc_time*1000));
+        }
+
+#if GC_PROFILE_MORE_DETAIL
+        const char *str = "\n\n" \
+                                    "More detail.\n" \
+                                    "Prepare Time = Previously GC's rest sweep time\n"
+                                    "Index Flags          Allocate Inc.  Allocate Limit"
+#if CALC_EXACT_MALLOC_SIZE
+                                    "  Allocated Size"
+#endif
+                                    "  Use Page     Mark Time(ms)    Sweep Time(ms)  Prepare Time(ms)  LivingObj    FreeObj RemovedObj   EmptyObj"
+#if RGENGC_PROFILE
+                                    " OldgenObj RemNormObj RemShadObj"
+#endif
+#if GC_PROFILE_DETAIL_MEMORY
+                                    " MaxRSS(KB) MinorFLT MajorFLT"
+#endif
+                                    "\n";
+        append(out, rb_str_new_cstr(str));
+
+        for (i = 0; i < count; i++) {
+            record = &objspace->profile.records[i];
+            append(out, rb_sprintf("%5"PRIuSIZE" %4s/%c/%6s%c %13"PRIuSIZE" %15"PRIuSIZE
+#if CALC_EXACT_MALLOC_SIZE
+                                   " %15"PRIuSIZE
+#endif
+                                   " %9"PRIuSIZE" %17.12f %17.12f %17.12f %10"PRIuSIZE" %10"PRIuSIZE" %10"PRIuSIZE" %10"PRIuSIZE
+#if RGENGC_PROFILE
+                                   "%10"PRIuSIZE" %10"PRIuSIZE" %10"PRIuSIZE
+#endif
+#if GC_PROFILE_DETAIL_MEMORY
+                                   "%11ld %8ld %8ld"
+#endif
+
+                                   "\n",
+                                   i+1,
+                                   gc_profile_dump_major_reason(record->flags, reason_str),
+                                   (record->flags & GPR_FLAG_HAVE_FINALIZE) ? 'F' : '.',
+                                   (record->flags & GPR_FLAG_NEWOBJ) ? "NEWOBJ" :
+                                   (record->flags & GPR_FLAG_MALLOC) ? "MALLOC" :
+                                   (record->flags & GPR_FLAG_METHOD) ? "METHOD" :
+                                   (record->flags & GPR_FLAG_CAPI)   ? "CAPI__" : "??????",
+                                   (record->flags & GPR_FLAG_STRESS) ? '!' : ' ',
+                                   record->allocate_increase, record->allocate_limit,
+#if CALC_EXACT_MALLOC_SIZE
+                                   record->allocated_size,
+#endif
+                                   record->heap_use_pages,
+                                   record->gc_mark_time*1000,
+                                   record->gc_sweep_time*1000,
+                                   record->prepare_time*1000,
+
+                                   record->heap_live_objects,
+                                   record->heap_free_objects,
+                                   record->removing_objects,
+                                   record->empty_objects
+#if RGENGC_PROFILE
+                                   ,
+                                   record->old_objects,
+                                   record->remembered_normal_objects,
+                                   record->remembered_shady_objects
+#endif
+#if GC_PROFILE_DETAIL_MEMORY
+                                   ,
+                                   record->maxrss / 1024,
+                                   record->minflt,
+                                   record->majflt
+#endif
+
+                       ));
+        }
+#endif
+    }
+}
+
+/*
+ *  call-seq:
+ *     GC::Profiler.result  -> String
+ *
+ *  Returns a profile data report such as:
+ *
+ *    GC 1 invokes.
+ *    Index    Invoke Time(sec)       Use Size(byte)     Total Size(byte)         Total Object                    GC time(ms)
+ *        1               0.012               159240               212940                10647         0.00000000000001530000
+ */
+
+static VALUE
+gc_profile_result(VALUE _)
+{
+    VALUE str = rb_str_buf_new(0);
+    gc_profile_dump_on(str, rb_str_buf_append);
+    return str;
+}
+
+/*
+ *  call-seq:
+ *     GC::Profiler.report
+ *     GC::Profiler.report(io)
+ *
+ *  Writes the GC::Profiler.result to <tt>$stdout</tt> or the given IO object.
+ *
+ */
+
+static VALUE
+gc_profile_report(int argc, VALUE *argv, VALUE self)
+{
+    VALUE out;
+
+    out = (!rb_check_arity(argc, 0, 1) ? rb_stdout : argv[0]);
+    gc_profile_dump_on(out, rb_io_write);
+
+    return Qnil;
+}
+
+/*
+ *  call-seq:
+ *     GC::Profiler.total_time	-> float
+ *
+ *  The total time used for garbage collection in seconds
+ */
+
+static VALUE
+gc_profile_total_time(VALUE self)
+{
+    double time = 0;
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+
+    if (objspace->profile.run && objspace->profile.next_index > 0) {
+        size_t i;
+        size_t count = objspace->profile.next_index;
+
+        for (i = 0; i < count; i++) {
+            time += objspace->profile.records[i].gc_time;
+        }
+    }
+    return DBL2NUM(time);
+}
+
+/*
+ *  call-seq:
+ *    GC::Profiler.enabled?	-> true or false
+ *
+ *  The current status of \GC profile mode.
+ */
+
+static VALUE
+gc_profile_enable_get(VALUE self)
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    return objspace->profile.run ? Qtrue : Qfalse;
+}
+
+/*
+ *  call-seq:
+ *    GC::Profiler.enable	-> nil
+ *
+ *  Starts the \GC profiler.
+ *
+ */
+
+static VALUE
+gc_profile_enable(VALUE _)
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    objspace->profile.run = TRUE;
+    objspace->profile.current_record = 0;
+    return Qnil;
+}
+
+/*
+ *  call-seq:
+ *    GC::Profiler.disable	-> nil
+ *
+ *  Stops the \GC profiler.
+ *
+ */
+
+static VALUE
+gc_profile_disable(VALUE _)
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+
+    objspace->profile.run = FALSE;
+    objspace->profile.current_record = 0;
+    return Qnil;
+}
+
+/*
+ *  call-seq:
+ *     GC.verify_internal_consistency                  -> nil
+ *
+ *  Verify internal consistency.
+ *
+ *  This method is implementation specific.
+ *  Now this method checks generational consistency
+ *  if RGenGC is supported.
+ */
+static VALUE
+gc_verify_internal_consistency_m(VALUE dummy)
+{
+    gc_verify_internal_consistency(rb_gc_get_objspace());
+    return Qnil;
+}
+
+#if GC_CAN_COMPILE_COMPACTION
+/*
+ *  call-seq:
+ *     GC.auto_compact = flag
+ *
+ *  Updates automatic compaction mode.
+ *
+ *  When enabled, the compactor will execute on every major collection.
+ *
+ *  Enabling compaction will degrade performance on major collections.
+ */
+static VALUE
+gc_set_auto_compact(VALUE _, VALUE v)
+{
+    GC_ASSERT(GC_COMPACTION_SUPPORTED);
+
+    ruby_enable_autocompact = RTEST(v);
+
+#if RGENGC_CHECK_MODE
+    ruby_autocompact_compare_func = NULL;
+
+    if (SYMBOL_P(v)) {
+        ID id = RB_SYM2ID(v);
+        if (id == rb_intern("empty")) {
+            ruby_autocompact_compare_func = compare_free_slots;
+        }
+    }
+#endif
+
+    return v;
+}
+#else
+#  define gc_set_auto_compact rb_f_notimplement
+#endif
+
+#if GC_CAN_COMPILE_COMPACTION
+/*
+ *  call-seq:
+ *     GC.auto_compact    -> true or false
+ *
+ *  Returns whether or not automatic compaction has been enabled.
+ */
+static VALUE
+gc_get_auto_compact(VALUE _)
+{
+    return ruby_enable_autocompact ? Qtrue : Qfalse;
+}
+#else
+#  define gc_get_auto_compact rb_f_notimplement
+#endif
+
+#if GC_CAN_COMPILE_COMPACTION
+/*
+ *  call-seq:
+ *     GC.latest_compact_info -> hash
+ *
+ * Returns information about object moved in the most recent \GC compaction.
+ *
+ * The returned +hash+ contains the following keys:
+ *
+ * [considered]
+ *   Hash containing the type of the object as the key and the number of
+ *   objects of that type that were considered for movement.
+ * [moved]
+ *   Hash containing the type of the object as the key and the number of
+ *   objects of that type that were actually moved.
+ * [moved_up]
+ *   Hash containing the type of the object as the key and the number of
+ *   objects of that type that were increased in size.
+ * [moved_down]
+ *   Hash containing the type of the object as the key and the number of
+ *   objects of that type that were decreased in size.
+ *
+ * Some objects can't be moved (due to pinning) so these numbers can be used to
+ * calculate compaction efficiency.
+ */
+static VALUE
+gc_compact_stats(VALUE self)
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    VALUE h = rb_hash_new();
+    VALUE considered = rb_hash_new();
+    VALUE moved = rb_hash_new();
+    VALUE moved_up = rb_hash_new();
+    VALUE moved_down = rb_hash_new();
+
+    for (size_t i = 0; i < T_MASK; i++) {
+        if (objspace->rcompactor.considered_count_table[i]) {
+            rb_hash_aset(considered, type_sym(i), SIZET2NUM(objspace->rcompactor.considered_count_table[i]));
+        }
+
+        if (objspace->rcompactor.moved_count_table[i]) {
+            rb_hash_aset(moved, type_sym(i), SIZET2NUM(objspace->rcompactor.moved_count_table[i]));
+        }
+
+        if (objspace->rcompactor.moved_up_count_table[i]) {
+            rb_hash_aset(moved_up, type_sym(i), SIZET2NUM(objspace->rcompactor.moved_up_count_table[i]));
+        }
+
+        if (objspace->rcompactor.moved_down_count_table[i]) {
+            rb_hash_aset(moved_down, type_sym(i), SIZET2NUM(objspace->rcompactor.moved_down_count_table[i]));
+        }
+    }
+
+    rb_hash_aset(h, ID2SYM(rb_intern("considered")), considered);
+    rb_hash_aset(h, ID2SYM(rb_intern("moved")), moved);
+    rb_hash_aset(h, ID2SYM(rb_intern("moved_up")), moved_up);
+    rb_hash_aset(h, ID2SYM(rb_intern("moved_down")), moved_down);
+
+    return h;
+}
+#else
+#  define gc_compact_stats rb_f_notimplement
+#endif
+
+#if GC_CAN_COMPILE_COMPACTION
+/*
+ *  call-seq:
+ *     GC.compact -> hash
+ *
+ * This function compacts objects together in Ruby's heap. It eliminates
+ * unused space (or fragmentation) in the heap by moving objects in to that
+ * unused space.
+ *
+ * The returned +hash+ contains statistics about the objects that were moved;
+ * see GC.latest_compact_info.
+ *
+ * This method is only expected to work on CRuby.
+ *
+ * To test whether \GC compaction is supported, use the idiom:
+ *
+ *   GC.respond_to?(:compact)
+ */
+static VALUE
+gc_compact(VALUE self)
+{
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+    int full_marking_p = gc_config_full_mark_val;
+    gc_config_full_mark_set(TRUE);
+
+    /* Run GC with compaction enabled */
+    rb_gc_impl_start(rb_gc_get_objspace(), true, true, true, true);
+    gc_config_full_mark_set(full_marking_p);
+
+    return gc_compact_stats(self);
+}
+#else
+#  define gc_compact rb_f_notimplement
+#endif
+
+#if GC_CAN_COMPILE_COMPACTION
+struct desired_compaction_pages_i_data {
+    rb_objspace_t *objspace;
+    size_t required_slots[HEAP_COUNT];
+};
+
+static int
+desired_compaction_pages_i(struct heap_page *page, void *data)
+{
+    struct desired_compaction_pages_i_data *tdata = data;
+    rb_objspace_t *objspace = tdata->objspace;
+    VALUE vstart = (VALUE)page->start;
+    VALUE vend = vstart + (VALUE)(page->total_slots * page->heap->slot_size);
+
+
+    for (VALUE v = vstart; v != vend; v += page->heap->slot_size) {
+        asan_unpoisoning_object(v) {
+            /* skip T_NONEs; they won't be moved */
+            if (BUILTIN_TYPE(v) != T_NONE) {
+                rb_heap_t *dest_pool = gc_compact_destination_pool(objspace, page->heap, v);
+                size_t dest_pool_idx = dest_pool - heaps;
+                tdata->required_slots[dest_pool_idx]++;
+            }
+        }
+    }
+
+    return 0;
+}
+
+/* call-seq:
+ *    GC.verify_compaction_references(toward: nil, double_heap: false) -> hash
+ *
+ * Verify compaction reference consistency.
+ *
+ * This method is implementation specific.  During compaction, objects that
+ * were moved are replaced with T_MOVED objects.  No object should have a
+ * reference to a T_MOVED object after compaction.
+ *
+ * This function expands the heap to ensure room to move all objects,
+ * compacts the heap to make sure everything moves, updates all references,
+ * then performs a full \GC.  If any object contains a reference to a T_MOVED
+ * object, that object should be pushed on the mark stack, and will
+ * make a SEGV.
+ */
+static VALUE
+gc_verify_compaction_references(int argc, VALUE* argv, VALUE self)
+{
+    static ID keywords[3] = {0};
+    if (!keywords[0]) {
+        keywords[0] = rb_intern("toward");
+        keywords[1] = rb_intern("double_heap");
+        keywords[2] = rb_intern("expand_heap");
+    }
+
+    VALUE options;
+    rb_scan_args_kw(rb_keyword_given_p(), argc, argv, ":", &options);
+
+    VALUE arguments[3] = { Qnil, Qfalse, Qfalse };
+    int kwarg_count = rb_get_kwargs(options, keywords, 0, 3, arguments);
+    bool toward_empty = kwarg_count > 0 && SYMBOL_P(arguments[0]) && SYM2ID(arguments[0]) == rb_intern("empty");
+    bool expand_heap = (kwarg_count > 1 && RTEST(arguments[1])) || (kwarg_count > 2 && RTEST(arguments[2]));
+
+    rb_objspace_t *objspace = rb_gc_get_objspace();
+
+    /* Clear the heap. */
+    rb_gc_impl_start(objspace, true, true, true, false);
+
+    unsigned int lev = rb_gc_vm_lock();
+    {
+        gc_rest(objspace);
+
+        /* if both double_heap and expand_heap are set, expand_heap takes precedence */
+        if (expand_heap) {
+            struct desired_compaction_pages_i_data desired_compaction = {
+                .objspace = objspace,
+                .required_slots = {0},
+            };
+            /* Work out how many objects want to be in each size pool, taking account of moves */
+            objspace_each_pages(objspace, desired_compaction_pages_i, &desired_compaction, TRUE);
+
+            /* Find out which pool has the most pages */
+            size_t max_existing_pages = 0;
+            for (int i = 0; i < HEAP_COUNT; i++) {
+                rb_heap_t *heap = &heaps[i];
+                max_existing_pages = MAX(max_existing_pages, heap->total_pages);
+            }
+
+            /* Add pages to each size pool so that compaction is guaranteed to move every object */
+            for (int i = 0; i < HEAP_COUNT; i++) {
+                rb_heap_t *heap = &heaps[i];
+
+                size_t pages_to_add = 0;
+                /*
+                 * Step 1: Make sure every pool has the same number of pages, by adding empty pages
+                 * to smaller pools. This is required to make sure the compact cursor can advance
+                 * through all of the pools in `gc_sweep_compact` without hitting the "sweep &
+                 * compact cursors met" condition on some pools before fully compacting others
+                 */
+                pages_to_add += max_existing_pages - heap->total_pages;
+                /*
+                 * Step 2: Now add additional free pages to each size pool sufficient to hold all objects
+                 * that want to be in that size pool, whether moved into it or moved within it
+                 */
+                objspace->heap_pages.allocatable_slots = desired_compaction.required_slots[i];
+                while (objspace->heap_pages.allocatable_slots > 0) {
+                    heap_page_allocate_and_initialize(objspace, heap);
+                }
+                /*
+                 * Step 3: Add two more pages so that the compact & sweep cursors will meet _after_ all objects
+                 * have been moved, and not on the last iteration of the `gc_sweep_compact` loop
+                 */
+                pages_to_add += 2;
+
+                for (; pages_to_add > 0; pages_to_add--) {
+                    heap_page_allocate_and_initialize_force(objspace, heap);
+                }
+            }
+        }
+
+        if (toward_empty) {
+            objspace->rcompactor.compare_func = compare_free_slots;
+        }
+    }
+    rb_gc_vm_unlock(lev);
+
+    rb_gc_impl_start(rb_gc_get_objspace(), true, true, true, true);
+
+    rb_objspace_reachable_objects_from_root(root_obj_check_moved_i, objspace);
+    objspace_each_objects(objspace, heap_check_moved_i, objspace, TRUE);
+
+    objspace->rcompactor.compare_func = NULL;
+
+    return gc_compact_stats(self);
+}
+#else
+# define gc_verify_compaction_references rb_f_notimplement
+#endif
+
+void
+rb_gc_impl_objspace_free(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    if (is_lazy_sweeping(objspace))
+        rb_bug("lazy sweeping underway when freeing object space");
+
+    free(objspace->profile.records);
+    objspace->profile.records = NULL;
+
+    for (size_t i = 0; i < rb_darray_size(objspace->heap_pages.sorted); i++) {
+        heap_page_free(objspace, rb_darray_get(objspace->heap_pages.sorted, i));
+    }
+    rb_darray_free(objspace->heap_pages.sorted);
+    heap_pages_lomem = 0;
+    heap_pages_himem = 0;
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+        heap->total_pages = 0;
+        heap->total_slots = 0;
+    }
+
+    st_free_table(objspace->id_to_obj_tbl);
+    st_free_table(objspace->obj_to_id_tbl);
+
+    free_stack_chunks(&objspace->mark_stack);
+    mark_stack_free_cache(&objspace->mark_stack);
+
+    rb_darray_free(objspace->weak_references);
+
+    free(objspace);
+}
+
+#if MALLOC_ALLOCATED_SIZE
+/*
+ *  call-seq:
+ *     GC.malloc_allocated_size -> Integer
+ *
+ *  Returns the size of memory allocated by malloc().
+ *
+ *  Only available if ruby was built with +CALC_EXACT_MALLOC_SIZE+.
+ */
+
+static VALUE
+gc_malloc_allocated_size(VALUE self)
+{
+    return UINT2NUM(rb_objspace.malloc_params.allocated_size);
+}
+
+/*
+ *  call-seq:
+ *     GC.malloc_allocations -> Integer
+ *
+ *  Returns the number of malloc() allocations.
+ *
+ *  Only available if ruby was built with +CALC_EXACT_MALLOC_SIZE+.
+ */
+
+static VALUE
+gc_malloc_allocations(VALUE self)
+{
+    return UINT2NUM(rb_objspace.malloc_params.allocations);
+}
+#endif
+
+void rb_gc_impl_before_fork(void *objspace_ptr) { /* no-op */ }
+void rb_gc_impl_after_fork(void *objspace_ptr, rb_pid_t pid) { /* no-op */ }
+
+void *
+rb_gc_impl_objspace_alloc(void)
+{
+    rb_objspace_t *objspace = calloc1(sizeof(rb_objspace_t));
+
+    return objspace;
+}
+
+void
+rb_gc_impl_objspace_init(void *objspace_ptr)
+{
+    rb_objspace_t *objspace = objspace_ptr;
+
+    gc_config_full_mark_set(TRUE);
+
+    objspace->flags.measure_gc = true;
+    malloc_limit = gc_params.malloc_limit_min;
+    objspace->finalize_deferred_pjob = rb_postponed_job_preregister(0, gc_finalize_deferred, objspace);
+    if (objspace->finalize_deferred_pjob == POSTPONED_JOB_HANDLE_INVALID) {
+        rb_bug("Could not preregister postponed job for GC");
+    }
+
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        rb_heap_t *heap = &heaps[i];
+
+        heap->slot_size = (1 << i) * BASE_SLOT_SIZE;
+
+        ccan_list_head_init(&heap->pages);
+    }
+
+    rb_darray_make(&objspace->heap_pages.sorted, 0);
+    rb_darray_make(&objspace->weak_references, 0);
+
+    // TODO: debug why on Windows Ruby crashes on boot when GC is on.
+#ifdef _WIN32
+    dont_gc_on();
+#endif
+
+#if defined(INIT_HEAP_PAGE_ALLOC_USE_MMAP)
+    /* Need to determine if we can use mmap at runtime. */
+    heap_page_alloc_use_mmap = INIT_HEAP_PAGE_ALLOC_USE_MMAP;
+#endif
+    objspace->next_object_id = OBJ_ID_INITIAL;
+    objspace->id_to_obj_tbl = st_init_table(&object_id_hash_type);
+    objspace->obj_to_id_tbl = st_init_numtable();
+#if RGENGC_ESTIMATE_OLDMALLOC
+    objspace->rgengc.oldmalloc_increase_limit = gc_params.oldmalloc_limit_min;
+#endif
+    /* Set size pools allocatable pages. */
+    for (int i = 0; i < HEAP_COUNT; i++) {
+        /* Set the default value of heap_init_slots. */
+        gc_params.heap_init_slots[i] = GC_HEAP_INIT_SLOTS;
+    }
+
+    init_mark_stack(&objspace->mark_stack);
+
+    objspace->profile.invoke_time = getrusage_time();
+    finalizer_table = st_init_numtable();
+}
+
+void
+rb_gc_impl_init(void)
+{
+    VALUE gc_constants = rb_hash_new();
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("DEBUG")), GC_DEBUG ? Qtrue : Qfalse);
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("BASE_SLOT_SIZE")), SIZET2NUM(BASE_SLOT_SIZE - RVALUE_OVERHEAD));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVALUE_OVERHEAD")), SIZET2NUM(RVALUE_OVERHEAD));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_OBJ_LIMIT")), SIZET2NUM(HEAP_PAGE_OBJ_LIMIT));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_BITMAP_SIZE")), SIZET2NUM(HEAP_PAGE_BITMAP_SIZE));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_SIZE")), SIZET2NUM(HEAP_PAGE_SIZE));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_COUNT")), LONG2FIX(HEAP_COUNT));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVARGC_MAX_ALLOCATE_SIZE")), LONG2FIX(heap_slot_size(HEAP_COUNT - 1)));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVALUE_OLD_AGE")), LONG2FIX(RVALUE_OLD_AGE));
+    if (RB_BUG_INSTEAD_OF_RB_MEMERROR+0) {
+        rb_hash_aset(gc_constants, ID2SYM(rb_intern("RB_BUG_INSTEAD_OF_RB_MEMERROR")), Qtrue);
+    }
+    OBJ_FREEZE(gc_constants);
+    /* Internal constants in the garbage collector. */
+    rb_define_const(rb_mGC, "INTERNAL_CONSTANTS", gc_constants);
+
+    if (GC_COMPACTION_SUPPORTED) {
+        rb_define_singleton_method(rb_mGC, "compact", gc_compact, 0);
+        rb_define_singleton_method(rb_mGC, "auto_compact", gc_get_auto_compact, 0);
+        rb_define_singleton_method(rb_mGC, "auto_compact=", gc_set_auto_compact, 1);
+        rb_define_singleton_method(rb_mGC, "latest_compact_info", gc_compact_stats, 0);
+        rb_define_singleton_method(rb_mGC, "verify_compaction_references", gc_verify_compaction_references, -1);
+    }
+    else {
+        rb_define_singleton_method(rb_mGC, "compact", rb_f_notimplement, 0);
+        rb_define_singleton_method(rb_mGC, "auto_compact", rb_f_notimplement, 0);
+        rb_define_singleton_method(rb_mGC, "auto_compact=", rb_f_notimplement, 1);
+        rb_define_singleton_method(rb_mGC, "latest_compact_info", rb_f_notimplement, 0);
+        rb_define_singleton_method(rb_mGC, "verify_compaction_references", rb_f_notimplement, -1);
+    }
+
+    /* internal methods */
+    rb_define_singleton_method(rb_mGC, "verify_internal_consistency", gc_verify_internal_consistency_m, 0);
+
+#if MALLOC_ALLOCATED_SIZE
+    rb_define_singleton_method(rb_mGC, "malloc_allocated_size", gc_malloc_allocated_size, 0);
+    rb_define_singleton_method(rb_mGC, "malloc_allocations", gc_malloc_allocations, 0);
+#endif
+
+    VALUE rb_mProfiler = rb_define_module_under(rb_mGC, "Profiler");
+    rb_define_singleton_method(rb_mProfiler, "enabled?", gc_profile_enable_get, 0);
+    rb_define_singleton_method(rb_mProfiler, "enable", gc_profile_enable, 0);
+    rb_define_singleton_method(rb_mProfiler, "raw_data", gc_profile_record_get, 0);
+    rb_define_singleton_method(rb_mProfiler, "disable", gc_profile_disable, 0);
+    rb_define_singleton_method(rb_mProfiler, "clear", gc_profile_clear, 0);
+    rb_define_singleton_method(rb_mProfiler, "result", gc_profile_result, 0);
+    rb_define_singleton_method(rb_mProfiler, "report", gc_profile_report, -1);
+    rb_define_singleton_method(rb_mProfiler, "total_time", gc_profile_total_time, 0);
+
+    {
+        VALUE opts;
+        /* \GC build options */
+        rb_define_const(rb_mGC, "OPTS", opts = rb_ary_new());
+#define OPT(o) if (o) rb_ary_push(opts, rb_interned_str(#o, sizeof(#o) - 1))
+        OPT(GC_DEBUG);
+        OPT(USE_RGENGC);
+        OPT(RGENGC_DEBUG);
+        OPT(RGENGC_CHECK_MODE);
+        OPT(RGENGC_PROFILE);
+        OPT(RGENGC_ESTIMATE_OLDMALLOC);
+        OPT(GC_PROFILE_MORE_DETAIL);
+        OPT(GC_ENABLE_LAZY_SWEEP);
+        OPT(CALC_EXACT_MALLOC_SIZE);
+        OPT(MALLOC_ALLOCATED_SIZE);
+        OPT(MALLOC_ALLOCATED_SIZE_CHECK);
+        OPT(GC_PROFILE_DETAIL_MEMORY);
+        OPT(GC_COMPACTION_SUPPORTED);
+#undef OPT
+        OBJ_FREEZE(opts);
+    }
+}
diff --git a/gc/default/extconf.rb b/gc/default/extconf.rb
new file mode 100644
index 0000000000..2940a4c962
--- /dev/null
+++ b/gc/default/extconf.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+require_relative "../extconf_base"
+
+create_gc_makefile("default")
diff --git a/gc/extconf_base.rb b/gc/extconf_base.rb
new file mode 100644
index 0000000000..99183a3033
--- /dev/null
+++ b/gc/extconf_base.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "mkmf"
+
+srcdir = File.join(__dir__, "..")
+$CFLAGS << " -I#{srcdir}"
+
+$CFLAGS << " -DBUILDING_SHARED_GC"
+$CFLAGS << " -fPIC"
+
+def create_gc_makefile(name)
+  create_makefile("librubygc.#{name}")
+end
diff --git a/gc/gc.h b/gc/gc.h
index 1cacf8a2a5..592435bc9d 100644
--- a/gc/gc.h
+++ b/gc/gc.h
@@ -29,6 +29,7 @@ size_t rb_size_mul_or_raise(size_t x, size_t y, VALUE exc);
 void rb_gc_run_obj_finalizer(VALUE objid, long count, VALUE (*callback)(long i, void *data), void *data);
 void rb_gc_set_pending_interrupt(void);
 void rb_gc_unset_pending_interrupt(void);
+void rb_gc_obj_free_vm_weak_references(VALUE obj);
 bool rb_gc_obj_free(void *objspace, VALUE obj);
 void rb_gc_mark_roots(void *objspace, const char **categoryp);
 void rb_gc_ractor_newobj_cache_foreach(void (*func)(void *cache, void *data), void *data);
diff --git a/gc/gc_impl.h b/gc/gc_impl.h
index d7ad82d5e0..14416d217c 100644
--- a/gc/gc_impl.h
+++ b/gc/gc_impl.h
@@ -28,7 +28,7 @@
 GC_IMPL_FN void *rb_gc_impl_objspace_alloc(void);
 GC_IMPL_FN void rb_gc_impl_objspace_init(void *objspace_ptr);
 GC_IMPL_FN void rb_gc_impl_objspace_free(void *objspace_ptr);
-GC_IMPL_FN void *rb_gc_impl_ractor_cache_alloc(void *objspace_ptr);
+GC_IMPL_FN void *rb_gc_impl_ractor_cache_alloc(void *objspace_ptr, void *ractor);
 GC_IMPL_FN void rb_gc_impl_ractor_cache_free(void *objspace_ptr, void *cache);
 GC_IMPL_FN void rb_gc_impl_set_params(void *objspace_ptr);
 GC_IMPL_FN void rb_gc_impl_init(void);