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Bug 1546442 - Leading guard pages for normal allocations. r=glandium

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Differential Revision: https://phabricator.services.mozilla.com/D28516
This commit is contained in:
Gian-Carlo Pascutto 2021-11-26 11:46:25 +00:00
parent 4354146592
commit b936d4f576
1 changed files with 23 additions and 14 deletions
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35
memory/build/mozjemalloc.cpp
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@ -541,13 +541,13 @@ DEFINE_GLOBAL(size_t) gPageSizeMask = gPageSize - 1;
// Number of pages in a chunk.
DEFINE_GLOBAL(size_t) gChunkNumPages = kChunkSize >> gPageSize2Pow;
// Number of pages necessary for a chunk header.
// Number of pages necessary for a chunk header plus a guard page.
DEFINE_GLOBAL(size_t)
gChunkHeaderNumPages =
((sizeof(arena_chunk_t) + sizeof(arena_chunk_map_t) * (gChunkNumPages - 1) +
gPageSizeMask) &
1 + (((sizeof(arena_chunk_t) +
sizeof(arena_chunk_map_t) * (gChunkNumPages - 1) + gPageSizeMask) &
~gPageSizeMask) >>
gPageSize2Pow;
gPageSize2Pow);
// One chunk, minus the header, minus a guard page
DEFINE_GLOBAL(size_t)
@ -2469,31 +2469,40 @@ void arena_t::InitChunk(arena_chunk_t* aChunk, bool aZeroed) {
aChunk->ndirty = 0;
// Initialize the map to contain one maximal free untouched run.
#ifdef MALLOC_DECOMMIT
arena_run_t* run = (arena_run_t*)(uintptr_t(aChunk) +
(gChunkHeaderNumPages << gPageSize2Pow));
#endif
for (i = 0; i < gChunkHeaderNumPages; i++) {
// Clear the bits for the real header pages.
for (i = 0; i < gChunkHeaderNumPages - 1; i++) {
aChunk->map[i].bits = 0;
}
aChunk->map[i].bits = gMaxLargeClass | flags;
for (i++; i < gChunkNumPages - 2; i++) {
// Mark the leading guard page (last header page) as decommitted.
aChunk->map[i++].bits = CHUNK_MAP_DECOMMITTED;
// Mark the area usable for runs as available, note size at start and end
aChunk->map[i++].bits = gMaxLargeClass | flags;
for (; i < gChunkNumPages - 2; i++) {
aChunk->map[i].bits = flags;
}
aChunk->map[gChunkNumPages - 2].bits = gMaxLargeClass | flags;
// Mark the guard page as decommited.
// Mark the trailing guard page as decommitted.
aChunk->map[gChunkNumPages - 1].bits = CHUNK_MAP_DECOMMITTED;
#ifdef MALLOC_DECOMMIT
// Start out decommitted, in order to force a closer correspondence
// between dirty pages and committed untouched pages.
pages_decommit(run, gMaxLargeClass + gPageSize);
// between dirty pages and committed untouched pages. This includes
// leading and trailing guard pages.
pages_decommit((void*)(uintptr_t(run) - gPageSize),
gMaxLargeClass + 2 * gPageSize);
#else
// Only decommit the last page as a guard.
// Decommit the last header page (=leading page) as a guard.
pages_decommit((void*)(uintptr_t(run) - gPageSize), gPageSize);
// Decommit the last page as a guard.
pages_decommit((void*)(uintptr_t(aChunk) + kChunkSize - gPageSize),
gPageSize);
#endif
mStats.committed += gChunkHeaderNumPages;
// Insert the run into the tree of available runs.