Fix GC.verify_compaction_references not moving every object

The intention of GC.verify_compaction_references is, I believe, to force
every single movable object to be moved, so that it's possible to debug
native extensions which not correctly updating their references to
objects they mark as movable.

To do this, it doubles the number of allocated pages for each size pool,
and sorts the heap pages so that the free ones are swept first; thus,
every object in an old page should be moved into a free slot in one of
the new pages.

This worked fine until movement of objects _between_ size pools during
compaction was implemented. That causes some problems for
verify_compaction_references:

* We were doubling the number of pages in each size pool, but actually
  if some objects need to move into a _different_ pool, there's no
  guarantee that they'll be enough room in that one.
* It's possible for the sweep & compact cursors to meet in one size pool
  before all the objects that want to move into that size pool from
  another are processed by the compaction.

You can see these problems by changing some of the movement tests in
test_gc_compact.rb to try and move e.g. 50,000 objects instead of
500; the test is not able to actually move all of the objects in a
single compaction run.

To fix this, we do two things in verify_compaction_references:

* Firstly, we add enough pages to every size pool to make them the same
  size. This ensures that their compact cursors will all have space to
  move during compaction (even if that means empty pages are
  pointlessly compacted)
* Then, we examine every object and determine where it _wants_ to be
  compacted into. We use this information to add additional pages to
  each size pool to handle all objects which should live there.

With these two changes, we can move arbitrary amounts of objects into
the correct size pool in a single call to verify_compaction_references.

My _motivation_ for performing this work was to try and fix some test
stability issues in test_gc_compact.rb. I now no longer think that we
actually see this particular bug in rubyci.org, but I also think
verify_compaction_references should do what it says on the tin, so it's
worth keeping.

[Bug #20022]

1 files changed, 9 insertions, 9 deletions

diff --git a/test/ruby/test_gc_compact.rb b/test/ruby/test_gc_compact.rb
index 6d26811cbb..a20e2d67d9 100644
--- a/test/ruby/test_gc_compact.rb
+++ b/test/ruby/test_gc_compact.rb
@@ -389,14 +389,14 @@ class TestGCCompact < Test::Unit::TestCase
   def test_moving_strings_up_size_pools
     omit if GC::INTERNAL_CONSTANTS[:SIZE_POOL_COUNT] == 1
 
-    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 10, signal: :SEGV)
+    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 30, signal: :SEGV)
     begin;
-      STR_COUNT = 500
+      STR_COUNT = 50000
 
       GC.verify_compaction_references(expand_heap: true, toward: :empty)
 
       Fiber.new {
-        str = "a" * GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE]
+        str = "a" * GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE] * 4
         $ary = STR_COUNT.times.map { "" << str }
       }.resume
 
@@ -410,14 +410,14 @@ class TestGCCompact < Test::Unit::TestCase
   def test_moving_strings_down_size_pools
     omit if GC::INTERNAL_CONSTANTS[:SIZE_POOL_COUNT] == 1
 
-    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 10, signal: :SEGV)
+    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 30, signal: :SEGV)
     begin;
-      STR_COUNT = 500
+      STR_COUNT = 50000
 
       GC.verify_compaction_references(expand_heap: true, toward: :empty)
 
       Fiber.new {
-        $ary = STR_COUNT.times.map { ("a" * GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE]).squeeze! }
+        $ary = STR_COUNT.times.map { ("a" * GC::INTERNAL_CONSTANTS[:BASE_SLOT_SIZE] * 4).squeeze! }
       }.resume
 
       stats = GC.verify_compaction_references(expand_heap: true, toward: :empty)
@@ -432,9 +432,9 @@ class TestGCCompact < Test::Unit::TestCase
     # AR and ST hashes are in the same size pool on 32 bit
     omit unless RbConfig::SIZEOF["uint64_t"] <= RbConfig::SIZEOF["void*"]
 
-    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 10, signal: :SEGV)
+    assert_separately(%w[-robjspace], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 30, signal: :SEGV)
     begin;
-      HASH_COUNT = 500
+      HASH_COUNT = 50000
 
       GC.verify_compaction_references(expand_heap: true, toward: :empty)
 
@@ -446,7 +446,7 @@ class TestGCCompact < Test::Unit::TestCase
 
       stats = GC.verify_compaction_references(expand_heap: true, toward: :empty)
 
-      assert_operator(stats[:moved_down][:T_HASH], :>=, 500)
+      assert_operator(stats[:moved_down][:T_HASH], :>=, HASH_COUNT)
     end;
   end