Fix commit accounting for large pages #78531
Merged
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This change fixes an integer underflow that happens in the commit accounting, here is the sequence of events that will lead to it.
Under
use_large_page_p
, we created a new heap segment, we passedSEGMENT_INITIAL_COMMIT
(which is just a page) tovirtual_commit
, socommitted_by_oh[0]
is increased bySEGMENT_INITIAL_COMMIT
.Later, the
heap_segment_committed
value for the segment is changed tosize
, which is the full region size.Eventually, we
return_free_region
, which will subtractcommitted_by_oh[0]
by the full region size, which will lead to a subtraction integer underflow.This will result in a huge number, and that will fail future
virtual_commit
calls, leading to unexpected OOM.The fix simply makes sure we add the full region size to the
committed_by_oh[0]
to begin with.