diff options
Diffstat (limited to '')
| -rw-r--r-- | js/src/gc/Compacting.cpp | 967 |
1 files changed, 967 insertions, 0 deletions
diff --git a/js/src/gc/Compacting.cpp b/js/src/gc/Compacting.cpp new file mode 100644 index 0000000000..6af0a98860 --- /dev/null +++ b/js/src/gc/Compacting.cpp @@ -0,0 +1,967 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/* + * Implementation of compacting GC. + */ + +#include "mozilla/Maybe.h" + +#include "debugger/DebugAPI.h" +#include "gc/ArenaList.h" +#include "gc/GCInternals.h" +#include "gc/GCLock.h" +#include "gc/ParallelWork.h" +#include "gc/Zone.h" +#include "jit/JitCode.h" +#include "jit/JitRuntime.h" +#include "jit/JitZone.h" +#include "js/GCAPI.h" +#include "vm/HelperThreads.h" +#include "vm/Realm.h" +#include "wasm/WasmGcObject.h" + +#include "gc/Heap-inl.h" +#include "gc/Marking-inl.h" +#include "gc/PrivateIterators-inl.h" +#include "gc/StableCellHasher-inl.h" +#include "gc/TraceMethods-inl.h" +#include "vm/GeckoProfiler-inl.h" + +using namespace js; +using namespace js::gc; + +using mozilla::Maybe; + +bool GCRuntime::canRelocateZone(Zone* zone) const { + return !zone->isAtomsZone(); +} + +void GCRuntime::beginCompactPhase() { + MOZ_ASSERT(!isBackgroundSweeping()); + assertBackgroundSweepingFinished(); + + gcstats::AutoPhase ap(stats(), gcstats::PhaseKind::COMPACT); + + MOZ_ASSERT(zonesToMaybeCompact.ref().isEmpty()); + for (GCZonesIter zone(this); !zone.done(); zone.next()) { + if (canRelocateZone(zone)) { + zonesToMaybeCompact.ref().append(zone); + } + } + + startedCompacting = true; + zonesCompacted = 0; + +#ifdef DEBUG + AutoLockGC lock(this); + MOZ_ASSERT(!relocatedArenasToRelease); +#endif +} + +IncrementalProgress GCRuntime::compactPhase(JS::GCReason reason, + SliceBudget& sliceBudget, + AutoGCSession& session) { + assertBackgroundSweepingFinished(); + MOZ_ASSERT(startedCompacting); + + AutoMajorGCProfilerEntry s(this); + gcstats::AutoPhase ap(stats(), gcstats::PhaseKind::COMPACT); + + // TODO: JSScripts can move. If the sampler interrupts the GC in the + // middle of relocating an arena, invalid JSScript pointers may be + // accessed. Suppress all sampling until a finer-grained solution can be + // found. See bug 1295775. + AutoSuppressProfilerSampling suppressSampling(rt->mainContextFromOwnThread()); + + ZoneList relocatedZones; + Arena* relocatedArenas = nullptr; + while (!zonesToMaybeCompact.ref().isEmpty()) { + Zone* zone = zonesToMaybeCompact.ref().front(); + zonesToMaybeCompact.ref().removeFront(); + + MOZ_ASSERT(nursery().isEmpty()); + zone->changeGCState(Zone::Finished, Zone::Compact); + + if (relocateArenas(zone, reason, relocatedArenas, sliceBudget)) { + updateZonePointersToRelocatedCells(zone); + relocatedZones.append(zone); + zonesCompacted++; + } else { + zone->changeGCState(Zone::Compact, Zone::Finished); + } + + if (sliceBudget.isOverBudget()) { + break; + } + } + + if (!relocatedZones.isEmpty()) { + updateRuntimePointersToRelocatedCells(session); + + do { + Zone* zone = relocatedZones.front(); + relocatedZones.removeFront(); + zone->changeGCState(Zone::Compact, Zone::Finished); + } while (!relocatedZones.isEmpty()); + } + + clearRelocatedArenas(relocatedArenas, reason); + +#ifdef DEBUG + protectOrReleaseRelocatedArenas(relocatedArenas, reason); +#else + releaseRelocatedArenas(relocatedArenas); +#endif + + // Clear caches that can contain cell pointers. + rt->caches().purgeForCompaction(); + +#ifdef DEBUG + checkHashTablesAfterMovingGC(); +#endif + + return zonesToMaybeCompact.ref().isEmpty() ? Finished : NotFinished; +} + +void GCRuntime::endCompactPhase() { startedCompacting = false; } + +static bool ShouldRelocateAllArenas(JS::GCReason reason) { + return reason == JS::GCReason::DEBUG_GC; +} + +/* + * Choose which arenas to relocate all cells from. Return an arena cursor that + * can be passed to removeRemainingArenas(). + */ +Arena** ArenaList::pickArenasToRelocate(size_t& arenaTotalOut, + size_t& relocTotalOut) { + // Relocate the greatest number of arenas such that the number of used cells + // in relocated arenas is less than or equal to the number of free cells in + // unrelocated arenas. In other words we only relocate cells we can move + // into existing arenas, and we choose the least full areans to relocate. + // + // This is made easier by the fact that the arena list has been sorted in + // descending order of number of used cells, so we will always relocate a + // tail of the arena list. All we need to do is find the point at which to + // start relocating. + + check(); + + if (isCursorAtEnd()) { + return nullptr; + } + + Arena** arenap = cursorp_; // Next arena to consider for relocation. + size_t previousFreeCells = 0; // Count of free cells before arenap. + size_t followingUsedCells = 0; // Count of used cells after arenap. + size_t fullArenaCount = 0; // Number of full arenas (not relocated). + size_t nonFullArenaCount = + 0; // Number of non-full arenas (considered for relocation). + size_t arenaIndex = 0; // Index of the next arena to consider. + + for (Arena* arena = head_; arena != *cursorp_; arena = arena->next) { + fullArenaCount++; + } + + for (Arena* arena = *cursorp_; arena; arena = arena->next) { + followingUsedCells += arena->countUsedCells(); + nonFullArenaCount++; + } + + mozilla::DebugOnly<size_t> lastFreeCells(0); + size_t cellsPerArena = Arena::thingsPerArena((*arenap)->getAllocKind()); + + while (*arenap) { + Arena* arena = *arenap; + if (followingUsedCells <= previousFreeCells) { + break; + } + + size_t freeCells = arena->countFreeCells(); + size_t usedCells = cellsPerArena - freeCells; + followingUsedCells -= usedCells; +#ifdef DEBUG + MOZ_ASSERT(freeCells >= lastFreeCells); + lastFreeCells = freeCells; +#endif + previousFreeCells += freeCells; + arenap = &arena->next; + arenaIndex++; + } + + size_t relocCount = nonFullArenaCount - arenaIndex; + MOZ_ASSERT(relocCount < nonFullArenaCount); + MOZ_ASSERT((relocCount == 0) == (!*arenap)); + arenaTotalOut += fullArenaCount + nonFullArenaCount; + relocTotalOut += relocCount; + + return arenap; +} + +#ifdef DEBUG +inline bool PtrIsInRange(const void* ptr, const void* start, size_t length) { + return uintptr_t(ptr) - uintptr_t(start) < length; +} +#endif + +static void RelocateCell(Zone* zone, TenuredCell* src, AllocKind thingKind, + size_t thingSize) { + JS::AutoSuppressGCAnalysis nogc; + + // Allocate a new cell. + MOZ_ASSERT(zone == src->zone()); + TenuredCell* dst = + reinterpret_cast<TenuredCell*>(AllocateCellInGC(zone, thingKind)); + + // Copy source cell contents to destination. + memcpy(dst, src, thingSize); + + // Move any uid attached to the object. + gc::TransferUniqueId(dst, src); + + if (IsObjectAllocKind(thingKind)) { + auto* srcObj = static_cast<JSObject*>(static_cast<Cell*>(src)); + auto* dstObj = static_cast<JSObject*>(static_cast<Cell*>(dst)); + + if (srcObj->is<NativeObject>()) { + NativeObject* srcNative = &srcObj->as<NativeObject>(); + NativeObject* dstNative = &dstObj->as<NativeObject>(); + + // Fixup the pointer to inline object elements if necessary. + if (srcNative->hasFixedElements()) { + uint32_t numShifted = + srcNative->getElementsHeader()->numShiftedElements(); + dstNative->setFixedElements(numShifted); + } + } else if (srcObj->is<ProxyObject>()) { + if (srcObj->as<ProxyObject>().usingInlineValueArray()) { + dstObj->as<ProxyObject>().setInlineValueArray(); + } + } + + // Call object moved hook if present. + if (JSObjectMovedOp op = srcObj->getClass()->extObjectMovedOp()) { + op(dstObj, srcObj); + } + + MOZ_ASSERT_IF( + dstObj->is<NativeObject>(), + !PtrIsInRange( + (const Value*)dstObj->as<NativeObject>().getDenseElements(), src, + thingSize)); + } + + // Copy the mark bits. + dst->copyMarkBitsFrom(src); + + // Poison the source cell contents except for the forwarding flag and pointer + // which will be stored in the first word. We can't do this for native object + // with fixed elements because this would overwrite the element flags and + // these are needed when updating COW elements referred to by other objects. +#ifdef DEBUG + JSObject* srcObj = IsObjectAllocKind(thingKind) + ? static_cast<JSObject*>(static_cast<Cell*>(src)) + : nullptr; + if (!srcObj || !srcObj->is<NativeObject>() || + !srcObj->as<NativeObject>().hasFixedElements()) { + AlwaysPoison(reinterpret_cast<uint8_t*>(src) + sizeof(uintptr_t), + JS_MOVED_TENURED_PATTERN, thingSize - sizeof(uintptr_t), + MemCheckKind::MakeNoAccess); + } +#endif + + // Mark source cell as forwarded and leave a pointer to the destination. + RelocationOverlay::forwardCell(src, dst); +} + +static void RelocateArena(Arena* arena, SliceBudget& sliceBudget) { + MOZ_ASSERT(arena->allocated()); + MOZ_ASSERT(!arena->onDelayedMarkingList()); + MOZ_ASSERT(arena->bufferedCells()->isEmpty()); + + Zone* zone = arena->zone; + + AllocKind thingKind = arena->getAllocKind(); + size_t thingSize = arena->getThingSize(); + + for (ArenaCellIterUnderGC cell(arena); !cell.done(); cell.next()) { + RelocateCell(zone, cell, thingKind, thingSize); + sliceBudget.step(); + } + +#ifdef DEBUG + for (ArenaCellIterUnderGC cell(arena); !cell.done(); cell.next()) { + TenuredCell* src = cell; + MOZ_ASSERT(src->isForwarded()); + TenuredCell* dest = Forwarded(src); + MOZ_ASSERT(src->isMarkedBlack() == dest->isMarkedBlack()); + MOZ_ASSERT(src->isMarkedGray() == dest->isMarkedGray()); + } +#endif +} + +/* + * Relocate all arenas identified by pickArenasToRelocate: for each arena, + * relocate each cell within it, then add it to a list of relocated arenas. + */ +Arena* ArenaList::relocateArenas(Arena* toRelocate, Arena* relocated, + SliceBudget& sliceBudget, + gcstats::Statistics& stats) { + check(); + + while (Arena* arena = toRelocate) { + toRelocate = arena->next; + RelocateArena(arena, sliceBudget); + // Prepend to list of relocated arenas + arena->next = relocated; + relocated = arena; + stats.count(gcstats::COUNT_ARENA_RELOCATED); + } + + check(); + + return relocated; +} + +// Skip compacting zones unless we can free a certain proportion of their GC +// heap memory. +static const float MIN_ZONE_RECLAIM_PERCENT = 2.0; + +static bool ShouldRelocateZone(size_t arenaCount, size_t relocCount, + JS::GCReason reason) { + if (relocCount == 0) { + return false; + } + + if (IsOOMReason(reason)) { + return true; + } + + return (relocCount * 100.0f) / arenaCount >= MIN_ZONE_RECLAIM_PERCENT; +} + +static AllocKinds CompactingAllocKinds() { + AllocKinds result; + for (AllocKind kind : AllAllocKinds()) { + if (IsCompactingKind(kind)) { + result += kind; + } + } + return result; +} + +bool ArenaLists::relocateArenas(Arena*& relocatedListOut, JS::GCReason reason, + SliceBudget& sliceBudget, + gcstats::Statistics& stats) { + // This is only called from the main thread while we are doing a GC, so + // there is no need to lock. + MOZ_ASSERT(CurrentThreadCanAccessRuntime(runtime())); + MOZ_ASSERT(runtime()->gc.isHeapCompacting()); + MOZ_ASSERT(!runtime()->gc.isBackgroundSweeping()); + + // Relocate all compatible kinds + AllocKinds allocKindsToRelocate = CompactingAllocKinds(); + + // Clear all the free lists. + clearFreeLists(); + + if (ShouldRelocateAllArenas(reason)) { + zone_->prepareForCompacting(); + for (auto kind : allocKindsToRelocate) { + ArenaList& al = arenaList(kind); + Arena* allArenas = al.head(); + al.clear(); + relocatedListOut = + al.relocateArenas(allArenas, relocatedListOut, sliceBudget, stats); + } + } else { + size_t arenaCount = 0; + size_t relocCount = 0; + AllAllocKindArray<Arena**> toRelocate; + + for (auto kind : allocKindsToRelocate) { + toRelocate[kind] = + arenaList(kind).pickArenasToRelocate(arenaCount, relocCount); + } + + if (!ShouldRelocateZone(arenaCount, relocCount, reason)) { + return false; + } + + zone_->prepareForCompacting(); + for (auto kind : allocKindsToRelocate) { + if (toRelocate[kind]) { + ArenaList& al = arenaList(kind); + Arena* arenas = al.removeRemainingArenas(toRelocate[kind]); + relocatedListOut = + al.relocateArenas(arenas, relocatedListOut, sliceBudget, stats); + } + } + } + + return true; +} + +bool GCRuntime::relocateArenas(Zone* zone, JS::GCReason reason, + Arena*& relocatedListOut, + SliceBudget& sliceBudget) { + gcstats::AutoPhase ap(stats(), gcstats::PhaseKind::COMPACT_MOVE); + + MOZ_ASSERT(!zone->isPreservingCode()); + MOZ_ASSERT(canRelocateZone(zone)); + + js::CancelOffThreadIonCompile(rt, JS::Zone::Compact); + + if (!zone->arenas.relocateArenas(relocatedListOut, reason, sliceBudget, + stats())) { + return false; + } + +#ifdef DEBUG + // Check that we did as much compaction as we should have. There + // should always be less than one arena's worth of free cells. + for (auto kind : CompactingAllocKinds()) { + ArenaList& al = zone->arenas.arenaList(kind); + size_t freeCells = 0; + for (Arena* arena = al.arenaAfterCursor(); arena; arena = arena->next) { + freeCells += arena->countFreeCells(); + } + MOZ_ASSERT(freeCells < Arena::thingsPerArena(kind)); + } +#endif + + return true; +} + +MovingTracer::MovingTracer(JSRuntime* rt) + : GenericTracerImpl(rt, JS::TracerKind::Moving, + JS::WeakMapTraceAction::TraceKeysAndValues) {} + +template <typename T> +inline void MovingTracer::onEdge(T** thingp, const char* name) { + T* thing = *thingp; + if (thing->runtimeFromAnyThread() == runtime() && IsForwarded(thing)) { + *thingp = Forwarded(thing); + } +} + +void Zone::prepareForCompacting() { + JS::GCContext* gcx = runtimeFromMainThread()->gcContext(); + discardJitCode(gcx); +} + +void GCRuntime::sweepZoneAfterCompacting(MovingTracer* trc, Zone* zone) { + MOZ_ASSERT(zone->isGCCompacting()); + + zone->traceWeakMaps(trc); + + traceWeakFinalizationObserverEdges(trc, zone); + + for (auto* cache : zone->weakCaches()) { + cache->traceWeak(trc, nullptr); + } + + if (jit::JitZone* jitZone = zone->jitZone()) { + jitZone->traceWeak(trc); + } + + for (CompartmentsInZoneIter c(zone); !c.done(); c.next()) { + c->traceWeakNativeIterators(trc); + + for (RealmsInCompartmentIter r(c); !r.done(); r.next()) { + r->traceWeakRegExps(trc); + r->traceWeakSavedStacks(trc); + r->traceWeakGlobalEdge(trc); + r->traceWeakDebugEnvironmentEdges(trc); + r->traceWeakEdgesInJitRealm(trc); + } + } +} + +template <typename T> +static inline void UpdateCellPointers(MovingTracer* trc, T* cell) { + // We only update unmoved GC things or the new copy of moved GC things, never + // the old copy. If this happened it could clear the forwarded flag which + // could lead to pointers to the old copy not being updated. + MOZ_ASSERT(!cell->isForwarded()); + + cell->fixupAfterMovingGC(); + cell->traceChildren(trc); +} + +template <typename T> +static void UpdateArenaPointersTyped(MovingTracer* trc, Arena* arena) { + for (ArenaCellIterUnderGC cell(arena); !cell.done(); cell.next()) { + UpdateCellPointers(trc, cell.as<T>()); + } +} + +static bool CanUpdateKindInBackground(AllocKind kind) { + // We try to update as many GC things in parallel as we can, but there are + // kinds for which this might not be safe: + // - we assume JSObjects that are foreground finalized are not safe to + // update in parallel + // - updating a SharedPropMap touches child maps in + // SharedPropMap::fixupAfterMovingGC + return js::gc::IsBackgroundFinalized(kind) && !IsShapeAllocKind(kind) && + kind != AllocKind::BASE_SHAPE; +} + +/* + * Update the internal pointers for all cells in an arena. + */ +static void UpdateArenaPointers(MovingTracer* trc, Arena* arena) { + AllocKind kind = arena->getAllocKind(); + + MOZ_ASSERT_IF(!CanUpdateKindInBackground(kind), + CurrentThreadCanAccessRuntime(trc->runtime())); + + switch (kind) { +#define EXPAND_CASE(allocKind, traceKind, type, sizedType, bgFinal, nursery, \ + compact) \ + case AllocKind::allocKind: \ + UpdateArenaPointersTyped<type>(trc, arena); \ + return; + FOR_EACH_ALLOCKIND(EXPAND_CASE) +#undef EXPAND_CASE + + default: + MOZ_CRASH("Invalid alloc kind for UpdateArenaPointers"); + } +} + +struct ArenaListSegment { + Arena* begin; + Arena* end; +}; + +/* + * Update the internal pointers for all arenas in a segment of an arena list. + * + * Returns the number of steps to count against the slice budget. + */ +static size_t UpdateArenaListSegmentPointers(GCRuntime* gc, + const ArenaListSegment& arenas) { + MOZ_ASSERT(arenas.begin); + MovingTracer trc(gc->rt); + size_t count = 0; + for (Arena* arena = arenas.begin; arena != arenas.end; arena = arena->next) { + UpdateArenaPointers(&trc, arena); + count++; + } + return count * 256; +} + +class ArenasToUpdate { + // Maximum number of arenas to update in one block. +#ifdef DEBUG + static const unsigned MaxArenasToProcess = 16; +#else + static const unsigned MaxArenasToProcess = 256; +#endif + + public: + explicit ArenasToUpdate(Zone* zone); + ArenasToUpdate(Zone* zone, const AllocKinds& kinds); + + bool done() const { return !segmentBegin; } + + ArenaListSegment get() const { + MOZ_ASSERT(!done()); + return {segmentBegin, segmentEnd}; + } + + void next(); + + private: + Maybe<AllocKinds> kinds; // Selects which thing kinds to update. + Zone* zone; // Zone to process. + AllocKind kind = AllocKind::FIRST; // Current alloc kind to process. + Arena* segmentBegin = nullptr; + Arena* segmentEnd = nullptr; + + static AllocKind nextAllocKind(AllocKind i) { + return AllocKind(uint8_t(i) + 1); + } + + void settle(); + void findSegmentEnd(); +}; + +ArenasToUpdate::ArenasToUpdate(Zone* zone) : zone(zone) { settle(); } + +ArenasToUpdate::ArenasToUpdate(Zone* zone, const AllocKinds& kinds) + : kinds(Some(kinds)), zone(zone) { + settle(); +} + +void ArenasToUpdate::settle() { + // Called when we have set |kind| to a new kind. Sets |arena| to the next + // arena or null if there are no more arenas to update. + + MOZ_ASSERT(!segmentBegin); + + for (; kind < AllocKind::LIMIT; kind = nextAllocKind(kind)) { + if (kinds && !kinds.ref().contains(kind)) { + continue; + } + + Arena* arena = zone->arenas.getFirstArena(kind); + if (arena) { + segmentBegin = arena; + findSegmentEnd(); + break; + } + } +} + +void ArenasToUpdate::findSegmentEnd() { + // Take up to MaxArenasToProcess arenas from the list starting at + // |segmentBegin| and set |segmentEnd|. + Arena* arena = segmentBegin; + for (size_t i = 0; arena && i < MaxArenasToProcess; i++) { + arena = arena->next; + } + segmentEnd = arena; +} + +void ArenasToUpdate::next() { + MOZ_ASSERT(!done()); + + segmentBegin = segmentEnd; + if (segmentBegin) { + findSegmentEnd(); + return; + } + + kind = nextAllocKind(kind); + settle(); +} + +static AllocKinds ForegroundUpdateKinds(AllocKinds kinds) { + AllocKinds result; + for (AllocKind kind : kinds) { + if (!CanUpdateKindInBackground(kind)) { + result += kind; + } + } + return result; +} + +void GCRuntime::updateCellPointers(Zone* zone, AllocKinds kinds) { + AllocKinds fgKinds = ForegroundUpdateKinds(kinds); + AllocKinds bgKinds = kinds - fgKinds; + + ArenasToUpdate fgArenas(zone, fgKinds); + ArenasToUpdate bgArenas(zone, bgKinds); + + AutoLockHelperThreadState lock; + + AutoRunParallelWork bgTasks(this, UpdateArenaListSegmentPointers, + gcstats::PhaseKind::COMPACT_UPDATE_CELLS, + GCUse::Unspecified, bgArenas, + SliceBudget::unlimited(), lock); + + AutoUnlockHelperThreadState unlock(lock); + + for (; !fgArenas.done(); fgArenas.next()) { + UpdateArenaListSegmentPointers(this, fgArenas.get()); + } +} + +// After cells have been relocated any pointers to a cell's old locations must +// be updated to point to the new location. This happens by iterating through +// all cells in heap and tracing their children (non-recursively) to update +// them. +// +// This is complicated by the fact that updating a GC thing sometimes depends on +// making use of other GC things. After a moving GC these things may not be in +// a valid state since they may contain pointers which have not been updated +// yet. +// +// The main dependencies are: +// +// - Updating a JSObject makes use of its shape +// - Updating a typed object makes use of its type descriptor object +// +// This means we require at least three phases for update: +// +// 1) shapes +// 2) typed object type descriptor objects +// 3) all other objects +// +// Also, there can be data races calling IsForwarded() on the new location of a +// cell whose first word is being updated in parallel on another thread. This +// easiest way to avoid this is to not store a GC pointer in the first word of a +// cell. Otherwise this can be avoided by updating different kinds of cell in +// different phases. +// +// Since we want to minimize the number of phases, arrange kinds into three +// arbitrary phases. + +static constexpr AllocKinds UpdatePhaseOne{AllocKind::SCRIPT, + AllocKind::BASE_SHAPE, + AllocKind::SHAPE, + AllocKind::STRING, + AllocKind::JITCODE, + AllocKind::REGEXP_SHARED, + AllocKind::SCOPE, + AllocKind::GETTER_SETTER, + AllocKind::COMPACT_PROP_MAP, + AllocKind::NORMAL_PROP_MAP, + AllocKind::DICT_PROP_MAP}; + +// UpdatePhaseTwo is typed object descriptor objects. + +static constexpr AllocKinds UpdatePhaseThree{AllocKind::FUNCTION, + AllocKind::FUNCTION_EXTENDED, + AllocKind::OBJECT0, + AllocKind::OBJECT0_BACKGROUND, + AllocKind::OBJECT2, + AllocKind::OBJECT2_BACKGROUND, + AllocKind::ARRAYBUFFER4, + AllocKind::OBJECT4, + AllocKind::OBJECT4_BACKGROUND, + AllocKind::ARRAYBUFFER8, + AllocKind::OBJECT8, + AllocKind::OBJECT8_BACKGROUND, + AllocKind::ARRAYBUFFER12, + AllocKind::OBJECT12, + AllocKind::OBJECT12_BACKGROUND, + AllocKind::ARRAYBUFFER16, + AllocKind::OBJECT16, + AllocKind::OBJECT16_BACKGROUND}; + +void GCRuntime::updateAllCellPointers(MovingTracer* trc, Zone* zone) { + updateCellPointers(zone, UpdatePhaseOne); + + updateCellPointers(zone, UpdatePhaseThree); +} + +/* + * Update pointers to relocated cells in a single zone by doing a traversal of + * that zone's arenas and calling per-zone sweep hooks. + * + * The latter is necessary to update weak references which are not marked as + * part of the traversal. + */ +void GCRuntime::updateZonePointersToRelocatedCells(Zone* zone) { + MOZ_ASSERT(!rt->isBeingDestroyed()); + MOZ_ASSERT(zone->isGCCompacting()); + + AutoTouchingGrayThings tgt; + + gcstats::AutoPhase ap(stats(), gcstats::PhaseKind::COMPACT_UPDATE); + MovingTracer trc(rt); + + zone->fixupAfterMovingGC(); + zone->fixupScriptMapsAfterMovingGC(&trc); + + // Fixup compartment global pointers as these get accessed during marking. + for (CompartmentsInZoneIter comp(zone); !comp.done(); comp.next()) { + comp->fixupAfterMovingGC(&trc); + } + + zone->externalStringCache().purge(); + zone->functionToStringCache().purge(); + zone->shapeZone().purgeShapeCaches(rt->gcContext()); + rt->caches().stringToAtomCache.purge(); + + // Iterate through all cells that can contain relocatable pointers to update + // them. Since updating each cell is independent we try to parallelize this + // as much as possible. + updateAllCellPointers(&trc, zone); + + // Sweep everything to fix up weak pointers. + sweepZoneAfterCompacting(&trc, zone); + + // Call callbacks to get the rest of the system to fixup other untraced + // pointers. + for (CompartmentsInZoneIter comp(zone); !comp.done(); comp.next()) { + callWeakPointerCompartmentCallbacks(&trc, comp); + } +} + +/* + * Update runtime-wide pointers to relocated cells. + */ +void GCRuntime::updateRuntimePointersToRelocatedCells(AutoGCSession& session) { + MOZ_ASSERT(!rt->isBeingDestroyed()); + + gcstats::AutoPhase ap1(stats(), gcstats::PhaseKind::COMPACT_UPDATE); + MovingTracer trc(rt); + + Zone::fixupAllCrossCompartmentWrappersAfterMovingGC(&trc); + + rt->geckoProfiler().fixupStringsMapAfterMovingGC(); + + // Mark roots to update them. + + traceRuntimeForMajorGC(&trc, session); + + { + gcstats::AutoPhase ap2(stats(), gcstats::PhaseKind::MARK_ROOTS); + DebugAPI::traceAllForMovingGC(&trc); + DebugAPI::traceCrossCompartmentEdges(&trc); + + // Mark all gray roots. + traceEmbeddingGrayRoots(&trc); + Compartment::traceIncomingCrossCompartmentEdgesForZoneGC( + &trc, Compartment::GrayEdges); + } + + // Sweep everything to fix up weak pointers. + jit::JitRuntime::TraceWeakJitcodeGlobalTable(rt, &trc); + for (JS::detail::WeakCacheBase* cache : rt->weakCaches()) { + cache->traceWeak(&trc, nullptr); + } + + if (rt->hasJitRuntime() && rt->jitRuntime()->hasInterpreterEntryMap()) { + rt->jitRuntime()->getInterpreterEntryMap()->updateScriptsAfterMovingGC(); + } + + // Type inference may put more blocks here to free. + { + AutoLockHelperThreadState lock; + lifoBlocksToFree.ref().freeAll(); + } + + // Call callbacks to get the rest of the system to fixup other untraced + // pointers. + callWeakPointerZonesCallbacks(&trc); +} + +void GCRuntime::clearRelocatedArenas(Arena* arenaList, JS::GCReason reason) { + AutoLockGC lock(this); + clearRelocatedArenasWithoutUnlocking(arenaList, reason, lock); +} + +void GCRuntime::clearRelocatedArenasWithoutUnlocking(Arena* arenaList, + JS::GCReason reason, + const AutoLockGC& lock) { + // Clear the relocated arenas, now containing only forwarding pointers + while (arenaList) { + Arena* arena = arenaList; + arenaList = arenaList->next; + + // Clear the mark bits + arena->unmarkAll(); + + // Mark arena as empty + arena->setAsFullyUnused(); + +#ifdef DEBUG + // The cell contents have been partially marked no access in RelocateCell, + // so we need to mark the region as undefined again so we can poison it. + SetMemCheckKind(reinterpret_cast<void*>(arena->thingsStart()), + arena->getThingsSpan(), MemCheckKind::MakeUndefined); +#endif + + AlwaysPoison(reinterpret_cast<void*>(arena->thingsStart()), + JS_MOVED_TENURED_PATTERN, arena->getThingsSpan(), + MemCheckKind::MakeNoAccess); + + // Don't count emptied arenas as being freed by the current GC: + // - if we purposely moved everything to new arenas, as that will already + // have allocated a similar number of arenas. (This only happens for + // collections triggered by GC zeal.) + // - if they were allocated since the start of the GC. + bool allArenasRelocated = ShouldRelocateAllArenas(reason); + bool updateRetainedSize = !allArenasRelocated && !arena->isNewlyCreated(); + arena->zone->gcHeapSize.removeBytes(ArenaSize, updateRetainedSize, + heapSize); + + // Release the arena but don't return it to the chunk yet. + arena->release(lock); + } +} + +#ifdef DEBUG + +// In debug mode we don't always release relocated arenas straight away. +// Sometimes protect them instead and hold onto them until the next GC sweep +// phase to catch any pointers to them that didn't get forwarded. + +static inline bool CanProtectArenas() { + // On some systems the page size is larger than the size of an arena so we + // can't change the mapping permissions per arena. + return SystemPageSize() <= ArenaSize; +} + +static inline bool ShouldProtectRelocatedArenas(JS::GCReason reason) { + // For zeal mode collections we don't release the relocated arenas + // immediately. Instead we protect them and keep them around until the next + // collection so we can catch any stray accesses to them. + return reason == JS::GCReason::DEBUG_GC && CanProtectArenas(); +} + +void GCRuntime::protectOrReleaseRelocatedArenas(Arena* arenaList, + JS::GCReason reason) { + if (ShouldProtectRelocatedArenas(reason)) { + protectAndHoldArenas(arenaList); + return; + } + + releaseRelocatedArenas(arenaList); +} + +void GCRuntime::protectAndHoldArenas(Arena* arenaList) { + for (Arena* arena = arenaList; arena;) { + MOZ_ASSERT(!arena->allocated()); + Arena* next = arena->next; + if (!next) { + // Prepend to hold list before we protect the memory. + AutoLockGC lock(this); + arena->next = relocatedArenasToRelease; + relocatedArenasToRelease = arenaList; + } + ProtectPages(arena, ArenaSize); + arena = next; + } +} + +void GCRuntime::unprotectHeldRelocatedArenas(const AutoLockGC& lock) { + for (Arena* arena = relocatedArenasToRelease; arena; arena = arena->next) { + UnprotectPages(arena, ArenaSize); + MOZ_ASSERT(!arena->allocated()); + } +} + +void GCRuntime::releaseHeldRelocatedArenas() { + AutoLockGC lock(this); + unprotectHeldRelocatedArenas(lock); + Arena* arenas = relocatedArenasToRelease; + relocatedArenasToRelease = nullptr; + releaseRelocatedArenasWithoutUnlocking(arenas, lock); +} + +void GCRuntime::releaseHeldRelocatedArenasWithoutUnlocking( + const AutoLockGC& lock) { + unprotectHeldRelocatedArenas(lock); + releaseRelocatedArenasWithoutUnlocking(relocatedArenasToRelease, lock); + relocatedArenasToRelease = nullptr; +} + +#endif + +void GCRuntime::releaseRelocatedArenas(Arena* arenaList) { + AutoLockGC lock(this); + releaseRelocatedArenasWithoutUnlocking(arenaList, lock); +} + +void GCRuntime::releaseRelocatedArenasWithoutUnlocking(Arena* arenaList, + const AutoLockGC& lock) { + // Release relocated arenas previously cleared with clearRelocatedArenas(). + while (arenaList) { + Arena* arena = arenaList; + arenaList = arenaList->next; + + // We already updated the memory accounting so just call + // Chunk::releaseArena. + arena->chunk()->releaseArena(this, arena, lock); + } +} |