ruby.git/gc/mmtk, branch master

[ruby/mmtk] Use rb_gc_obj_needs_cleanup_p

2026-06-04T02:54:35+00:00

https://github.com/ruby/mmtk/commit/031785b41c

[ruby/mmtk] Fix compiler warnings in mmtk.c

2026-05-31T10:35:05+00:00

    gc/mmtk/mmtk.c:505:1: warning: function 'rb_mmtk_gc_thread_panic_handler' could be declared with attribute 'noreturn' [-Wmissing-noreturn]
      505 | {
          | ^
    gc/mmtk/mmtk.c:987:27: warning: variable length array folded to constant array as an extension [-Wgnu-folding-constant]
      987 |         char obj_info_buf[info_size];
          |                           ^~~~~~~~~
    gc/mmtk/mmtk.c:990:34: warning: variable length array folded to constant array as an extension [-Wgnu-folding-constant]
      990 |         char parent_obj_info_buf[info_size];
          |                                  ^~~~~~~~~

https://github.com/ruby/mmtk/commit/8ce21cdf10

[ruby/mmtk] Switch logging from debug to info level

2026-05-23T13:04:55+00:00

https://github.com/ruby/mmtk/commit/9f730cc709

[ruby/mmtk] Add cpu heap mode based on Tavakolisomeh et al. (MPLR '23)

2026-05-23T13:04:55+00:00

Adds MMTK_HEAP_MODE=cpu, a dynamic heap-sizing policy that grows
or shrinks the heap after each GC cycle to keep measured GC CPU
overhead near a configurable target. The control law follows
Tavakolisomeh et al., 'Heap Size Adjustment with CPU Control', MPLR
'23: a sigmoid of the (averaged) GC CPU overhead error in (-inf, +inf)
maps to a heap-size adjustment factor in (0.5, 1.5).

Implementation lives alongside the existing 'ruby' delegated trigger
in gc/mmtk/src/heap/. T_GC is wall-clock GC duration; T_APP is process
CPU time delta read via clock_gettime(CLOCK_PROCESS_CPUTIME_ID), which
correctly credits multi-threaded mutator parallelism. Nursery-only
generational GCs are skipped so the trigger only re-sizes at full
collections.

Configuration:

  MMTK_GC_CPU_TARGET   target GC CPU overhead, percent. Default 5.
  MMTK_GC_CPU_WINDOW   number of recent cycles averaged. Default 3.

The default differs from the paper's recommended 15. The paper
targets ZGC, a concurrent generational collector; MMTk-Ruby currently
ships stop-the-world Immix, where every percent of GC CPU also blocks
the mutator. An empirical sweep of MMTK_GC_CPU_TARGET across
ruby-bench (railsbench, lobsters, psych-load, liquid-render, lee)
found 5-6 to be Pareto-optimal vs the existing 'ruby' heap mode:
about 6 percent geomean throughput improvement at essentially equal
peak RSS. Targets >=10 trade large amounts of throughput for modest
RSS savings on this collector.

bin/smoke-test, bin/ruby-mmtk-mode, bin/compare-heap-modes, and
doc/testing-cpu-heap-mode.md are included so reviewers and future
contributors can reproduce the sweep against ruby/ruby-bench.

https://github.com/ruby/mmtk/commit/1f223f5ad5

Co-Authored-By: Claude Opus 4.7

[ruby/mmtk] Fix compiler warnings for noreturn

2026-05-20T01:10:50+00:00

    gc/mmtk/mmtk.c:480:1: warning: function 'rb_mmtk_gc_thread_bug' could be declared with attribute 'noreturn' [-Wmissing-noreturn]
      480 | {
          | ^
    gc/mmtk/mmtk.c:510:1: warning: function 'rb_mmtk_mutator_thread_panic_handler' could be declared with attribute 'noreturn' [-Wmissing-noreturn]
      510 | {
          | ^

https://github.com/ruby/mmtk/commit/a57746d575

[ruby/mmtk] Move rb_gc_obj_suffix to gc.h

2026-05-17T20:20:06+00:00

https://github.com/ruby/mmtk/commit/40053354bd

[ruby/mmtk] Respect alignment in rb_mmtk_alloc_fast_path

2026-05-16T01:34:36+00:00

https://github.com/ruby/mmtk/commit/9772a1d30a

[ruby/mmtk] Remove dead ractor_check_mode field

2026-05-14T23:54:55+00:00

https://github.com/ruby/mmtk/commit/a46b68fe5b

[ruby/mmtk] Remove call to rb_ractor_setup_belonging

2026-05-14T21:50:04+00:00

Don't need to call it after https://github.com/ruby/ruby/pull/16961.

https://github.com/ruby/mmtk/commit/ae5638ac00

[ruby/mmtk] Introduce event_hook_mutex for RUBY_INTERNAL_EVENT_FREEOBJ

2026-05-09T13:08:44+00:00

We can stop using rb_gc_worker_thread_set_vm_context because rb_gc_event_hook
now uses rb_gc_get_ec since https://github.com/ruby/ruby/pull/16880

https://github.com/ruby/mmtk/commit/04bcf8456a