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Bug 1488780 - pt 6. Make Purge() and RemoveChunk() safe to run concurrently r=glandium

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* Add a mDying flag to Chunks
 * After Purge(), if a chunk is dying don't add it to structures such as
   mChunksMadvised
 * Add a mHasBusyPages flag to Chunks
 * Don't delete busy chunks
 * Instead in Purge() if a chunk has a mDying set then Purge is responsible
   for finishing the deletion.

Differential Revision: https://phabricator.services.mozilla.com/D217245
This commit is contained in:
Paul Bone 2024-11-06 01:46:21 +00:00
parent f98dd6456b
commit cf761de0ed
1 changed files with 48 additions and 9 deletions
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57
memory/build/mozjemalloc.cpp
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@ -147,6 +147,7 @@
#include "mozilla/ArrayUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/CheckedInt.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/DoublyLinkedList.h"
#include "mozilla/HelperMacros.h"
#include "mozilla/Likely.h"
@ -425,6 +426,9 @@ struct arena_chunk_t {
// Number of dirty pages.
size_t ndirty;
bool mIsPurging;
bool mDying;
// Map of pages within chunk that keeps track of free/large/small.
arena_chunk_map_t map[]; // Dynamically sized.
};
@ -1214,7 +1218,7 @@ struct arena_t {
// Remove the chunk from the arena. This removes it from all the page counts.
// It assumes its run has already been removed and lets the caller clear
// mSpare as necessary.
void RemoveChunk(arena_chunk_t* aChunk);
bool RemoveChunk(arena_chunk_t* aChunk);
// This may return a chunk that should be destroyed with chunk_dealloc outside
// of the arena lock. It is not the same chunk as was passed in (since that
@ -2788,6 +2792,9 @@ void arena_t::InitChunk(arena_chunk_t* aChunk, size_t aMinCommittedPages) {
// Claim that no pages are in use, since the header is merely overhead.
aChunk->ndirty = 0;
aChunk->mIsPurging = false;
aChunk->mDying = false;
// Setup the chunk's pages in two phases. First we mark which pages are
// committed & decommitted and perform the decommit. Then we update the map
// to create the runs.
@ -2852,7 +2859,15 @@ void arena_t::InitChunk(arena_chunk_t* aChunk, size_t aMinCommittedPages) {
#endif
}
void arena_t::RemoveChunk(arena_chunk_t* aChunk) {
bool arena_t::RemoveChunk(arena_chunk_t* aChunk) {
aChunk->mDying = true;
// If the chunk has busy pages that means that a Purge() is in progress.
// We can't remove the chunk now, instead Purge() will do it.
if (aChunk->mIsPurging) {
return false;
}
if (aChunk->ndirty > 0) {
aChunk->arena->mChunksDirty.Remove(aChunk);
mNumDirty -= aChunk->ndirty;
@ -2886,11 +2901,18 @@ void arena_t::RemoveChunk(arena_chunk_t* aChunk) {
mStats.mapped -= kChunkSize;
mStats.committed -= gChunkHeaderNumPages - 1;
return true;
}
arena_chunk_t* arena_t::DemoteChunkToSpare(arena_chunk_t* aChunk) {
if (mSpare) {
RemoveChunk(mSpare);
if (!RemoveChunk(mSpare)) {
// If we can't remove the spare chunk now purge will finish removing it
// later. Set it to null so that the return below will return null and
// our caller won't delete the chunk before Purge() is finished.
mSpare = nullptr;
}
}
arena_chunk_t* chunk_dealloc = mSpare;
@ -3100,6 +3122,10 @@ bool arena_t::Purge(bool aForce) {
chunk->ndirty -= npages;
mNumDirty -= npages;
// Mark the chunk as busy so it won't be deleted.
MOZ_ASSERT(!chunk->mIsPurging);
chunk->mIsPurging = true;
}
#ifdef MALLOC_DECOMMIT
@ -3118,6 +3144,9 @@ bool arena_t::Purge(bool aForce) {
// XXX: This block will become the second critical section by the end of this
// series of patches.
{
MOZ_ASSERT(chunk->mIsPurging);
chunk->mIsPurging = false;
#ifndef MALLOC_DECOMMIT
mNumMAdvised += npages;
#endif
@ -3127,15 +3156,25 @@ bool arena_t::Purge(bool aForce) {
if (chunk->ndirty == 0) {
mChunksDirty.Remove(chunk);
}
if (chunk->mDying) {
// Another thread tried to delete this chunk while we weren't holding the
// lock. Now it's our responsibility to finish deleting it.
DebugOnly<bool> release_chunk = RemoveChunk(chunk);
// RemoveChunk() can't return false because mIsPurging was false during
// the call.
MOZ_ASSERT(release_chunk);
chunk_dealloc((void*)chunk, kChunkSize, ARENA_CHUNK);
#ifdef MALLOC_DOUBLE_PURGE
// The chunk might already be in the list, but this
// makes sure it's at the front.
if (mChunksMAdvised.ElementProbablyInList(chunk)) {
mChunksMAdvised.remove(chunk);
}
mChunksMAdvised.pushFront(chunk);
} else {
// The chunk might already be in the list, but this
// makes sure it's at the front.
if (mChunksMAdvised.ElementProbablyInList(chunk)) {
mChunksMAdvised.remove(chunk);
}
mChunksMAdvised.pushFront(chunk);
#endif
}
return mNumDirty > (aForce ? 0 : EffectiveMaxDirty() >> 1);
}