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[scudo] Release to OS if a large amount of memory is deallocated. #160621

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Sep 25, 2025
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[scudo] Release to OS if a large amount of memory is deallocated. #160621

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7 changes: 7 additions & 0 deletions compiler-rt/lib/scudo/standalone/primary64.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1565,6 +1565,13 @@ bool SizeClassAllocator64<Config>::hasChanceToReleasePages(
if (DiffSinceLastReleaseNs < 2 * IntervalNs)
return false;
} else if (DiffSinceLastReleaseNs < IntervalNs) {
// `TryReleaseThreshold` is capped by (1UL << GroupSizeLog) / 2). If
// RegionPushedBytesDelta grows to twice the threshold, it implies some
// huge deallocations have happened so we better try to release some
// pages. Note this tends to happen for larger block sizes.
if (RegionPushedBytesDelta > (1ULL << GroupSizeLog))
return true;

// In this case, we are over the threshold but we just did some page
// release in the same release interval. This is a hint that we may want
// a higher threshold so that we can release more memory at once.
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