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[heap] Minor MinorMC fixes

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Fix broken DCHECK:
When using MinorMC, new space is a paged space and only uses the
TO_PAGE page flag. New large object space however still uses both
TO_PAGE and FROM_PAGE page flags. With MinorMC it still possible
to find reference to FROM_PAGEs, but those pages have to be large
pages.

Fix broken test:
MinorMC may only free empty pages when shrinking. Therefore, shrink
may actually not change the space capacity at all (e.g. when all
pages have live objects on them). More specifically, the capacity is
not guaranteed to be half the previous capacity.

Bug: v8:12612
Change-Id: Ib0edcafd758828f821f82bc8c796c205f162809c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3879493
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83061}
This commit is contained in:
Omer Katz 2022-09-08 11:26:28 +02:00 committed by V8 LUCI CQ
parent cab126f9ee
commit a5b3c3df9b
2 changed files with 9 additions and 2 deletions
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3
src/heap/mark-compact.cc
View File

@ -4946,7 +4946,8 @@ class RememberedSetUpdatingItem : public UpdatingItem {
return REMOVE_SLOT;
}
if (Heap::InFromPage(heap_object)) {
DCHECK(!v8_flags.minor_mc);
DCHECK_IMPLIES(v8_flags.minor_mc,
Page::FromHeapObject(heap_object)->IsLargePage());
MapWord map_word = heap_object.map_word(kRelaxedLoad);
if (map_word.IsForwardingAddress()) {
HeapObjectReference::Update(THeapObjectSlot(slot),

6
test/unittests/heap/heap-unittest.cc
View File

@ -228,7 +228,13 @@ TEST_F(HeapTest, GrowAndShrinkNewSpace) {
old_capacity = new_space->TotalCapacity();
new_space->Shrink();
new_capacity = new_space->TotalCapacity();
if (v8_flags.minor_mc) {
// Shrinking may not be able to remove any pages if all contain live
// objects.
CHECK_GE(old_capacity, new_capacity);
} else {
CHECK_EQ(old_capacity, 2 * new_capacity);
}
// Consecutive shrinking should not affect space capacity.
old_capacity = new_space->TotalCapacity();