blob: da112e2683753b936d0e6ed32a5f061e5683d2c6 [file] [log] [blame]
// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/heap/mark-compact.h"
#include <unordered_map>
#include "src/base/utils/random-number-generator.h"
#include "src/cancelable-task.h"
#include "src/compilation-cache.h"
#include "src/deoptimizer.h"
#include "src/execution.h"
#include "src/frames-inl.h"
#include "src/global-handles.h"
#include "src/heap/array-buffer-collector.h"
#include "src/heap/array-buffer-tracker-inl.h"
#include "src/heap/gc-tracer.h"
#include "src/heap/incremental-marking-inl.h"
#include "src/heap/invalidated-slots-inl.h"
#include "src/heap/item-parallel-job.h"
#include "src/heap/local-allocator-inl.h"
#include "src/heap/mark-compact-inl.h"
#include "src/heap/object-stats.h"
#include "src/heap/objects-visiting-inl.h"
#include "src/heap/read-only-heap.h"
#include "src/heap/spaces-inl.h"
#include "src/heap/sweeper.h"
#include "src/heap/worklist.h"
#include "src/ic/stub-cache.h"
#include "src/objects/embedder-data-array-inl.h"
#include "src/objects/foreign.h"
#include "src/objects/hash-table-inl.h"
#include "src/objects/js-objects-inl.h"
#include "src/objects/maybe-object.h"
#include "src/objects/slots-inl.h"
#include "src/objects/transitions-inl.h"
#include "src/utils-inl.h"
#include "src/v8.h"
#include "src/vm-state-inl.h"
namespace v8 {
namespace internal {
const char* Marking::kWhiteBitPattern = "00";
const char* Marking::kBlackBitPattern = "11";
const char* Marking::kGreyBitPattern = "10";
const char* Marking::kImpossibleBitPattern = "01";
// The following has to hold in order for {MarkingState::MarkBitFrom} to not
// produce invalid {kImpossibleBitPattern} in the marking bitmap by overlapping.
STATIC_ASSERT(Heap::kMinObjectSizeInTaggedWords >= 2);
// =============================================================================
// Verifiers
// =============================================================================
#ifdef VERIFY_HEAP
namespace {
class MarkingVerifier : public ObjectVisitor, public RootVisitor {
public:
virtual void Run() = 0;
protected:
explicit MarkingVerifier(Heap* heap) : heap_(heap) {}
virtual ConcurrentBitmap<AccessMode::NON_ATOMIC>* bitmap(
const MemoryChunk* chunk) = 0;
virtual void VerifyPointers(ObjectSlot start, ObjectSlot end) = 0;
virtual void VerifyPointers(MaybeObjectSlot start, MaybeObjectSlot end) = 0;
virtual void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) = 0;
virtual bool IsMarked(HeapObject object) = 0;
virtual bool IsBlackOrGrey(HeapObject object) = 0;
void VisitPointers(HeapObject host, ObjectSlot start,
ObjectSlot end) override {
VerifyPointers(start, end);
}
void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) override {
VerifyPointers(start, end);
}
void VisitRootPointers(Root root, const char* description,
FullObjectSlot start, FullObjectSlot end) override {
VerifyRootPointers(start, end);
}
void VerifyRoots(VisitMode mode);
void VerifyMarkingOnPage(const Page* page, Address start, Address end);
void VerifyMarking(NewSpace* new_space);
void VerifyMarking(PagedSpace* paged_space);
void VerifyMarking(LargeObjectSpace* lo_space);
Heap* heap_;
};
void MarkingVerifier::VerifyRoots(VisitMode mode) {
heap_->IterateStrongRoots(this, mode);
}
void MarkingVerifier::VerifyMarkingOnPage(const Page* page, Address start,
Address end) {
HeapObject object;
Address next_object_must_be_here_or_later = start;
for (Address current = start; current < end;) {
object = HeapObject::FromAddress(current);
// One word fillers at the end of a black area can be grey.
if (IsBlackOrGrey(object) &&
object->map() != ReadOnlyRoots(heap_).one_pointer_filler_map()) {
CHECK(IsMarked(object));
CHECK(current >= next_object_must_be_here_or_later);
object->Iterate(this);
next_object_must_be_here_or_later = current + object->Size();
// The object is either part of a black area of black allocation or a
// regular black object
CHECK(
bitmap(page)->AllBitsSetInRange(
page->AddressToMarkbitIndex(current),
page->AddressToMarkbitIndex(next_object_must_be_here_or_later)) ||
bitmap(page)->AllBitsClearInRange(
page->AddressToMarkbitIndex(current + kTaggedSize * 2),
page->AddressToMarkbitIndex(next_object_must_be_here_or_later)));
current = next_object_must_be_here_or_later;
} else {
current += kTaggedSize;
}
}
}
void MarkingVerifier::VerifyMarking(NewSpace* space) {
Address end = space->top();
// The bottom position is at the start of its page. Allows us to use
// page->area_start() as start of range on all pages.
CHECK_EQ(space->first_allocatable_address(),
space->first_page()->area_start());
PageRange range(space->first_allocatable_address(), end);
for (auto it = range.begin(); it != range.end();) {
Page* page = *(it++);
Address limit = it != range.end() ? page->area_end() : end;
CHECK(limit == end || !page->Contains(end));
VerifyMarkingOnPage(page, page->area_start(), limit);
}
}
void MarkingVerifier::VerifyMarking(PagedSpace* space) {
for (Page* p : *space) {
VerifyMarkingOnPage(p, p->area_start(), p->area_end());
}
}
void MarkingVerifier::VerifyMarking(LargeObjectSpace* lo_space) {
LargeObjectIterator it(lo_space);
for (HeapObject obj = it.Next(); !obj.is_null(); obj = it.Next()) {
if (IsBlackOrGrey(obj)) {
obj->Iterate(this);
}
}
}
class FullMarkingVerifier : public MarkingVerifier {
public:
explicit FullMarkingVerifier(Heap* heap)
: MarkingVerifier(heap),
marking_state_(
heap->mark_compact_collector()->non_atomic_marking_state()) {}
void Run() override {
VerifyRoots(VISIT_ONLY_STRONG);
VerifyMarking(heap_->new_space());
VerifyMarking(heap_->new_lo_space());
VerifyMarking(heap_->old_space());
VerifyMarking(heap_->code_space());
VerifyMarking(heap_->map_space());
VerifyMarking(heap_->lo_space());
VerifyMarking(heap_->code_lo_space());
}
protected:
ConcurrentBitmap<AccessMode::NON_ATOMIC>* bitmap(
const MemoryChunk* chunk) override {
return marking_state_->bitmap(chunk);
}
bool IsMarked(HeapObject object) override {
return marking_state_->IsBlack(object);
}
bool IsBlackOrGrey(HeapObject object) override {
return marking_state_->IsBlackOrGrey(object);
}
void VerifyPointers(ObjectSlot start, ObjectSlot end) override {
VerifyPointersImpl(start, end);
}
void VerifyPointers(MaybeObjectSlot start, MaybeObjectSlot end) override {
VerifyPointersImpl(start, end);
}
void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) override {
VerifyPointersImpl(start, end);
}
void VisitCodeTarget(Code host, RelocInfo* rinfo) override {
Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
VerifyHeapObjectImpl(target);
}
void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
DCHECK(RelocInfo::IsEmbeddedObjectMode(rinfo->rmode()));
if (!host->IsWeakObject(rinfo->target_object())) {
HeapObject object = rinfo->target_object();
VerifyHeapObjectImpl(object);
}
}
private:
V8_INLINE void VerifyHeapObjectImpl(HeapObject heap_object) {
CHECK(marking_state_->IsBlackOrGrey(heap_object));
}
template <typename TSlot>
V8_INLINE void VerifyPointersImpl(TSlot start, TSlot end) {
for (TSlot slot = start; slot < end; ++slot) {
typename TSlot::TObject object = *slot;
HeapObject heap_object;
if (object.GetHeapObjectIfStrong(&heap_object)) {
VerifyHeapObjectImpl(heap_object);
}
}
}
MarkCompactCollector::NonAtomicMarkingState* marking_state_;
};
class EvacuationVerifier : public ObjectVisitor, public RootVisitor {
public:
virtual void Run() = 0;
void VisitPointers(HeapObject host, ObjectSlot start,
ObjectSlot end) override {
VerifyPointers(start, end);
}
void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) override {
VerifyPointers(start, end);
}
void VisitRootPointers(Root root, const char* description,
FullObjectSlot start, FullObjectSlot end) override {
VerifyRootPointers(start, end);
}
protected:
explicit EvacuationVerifier(Heap* heap) : heap_(heap) {}
inline Heap* heap() { return heap_; }
virtual void VerifyPointers(ObjectSlot start, ObjectSlot end) = 0;
virtual void VerifyPointers(MaybeObjectSlot start, MaybeObjectSlot end) = 0;
virtual void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) = 0;
void VerifyRoots(VisitMode mode);
void VerifyEvacuationOnPage(Address start, Address end);
void VerifyEvacuation(NewSpace* new_space);
void VerifyEvacuation(PagedSpace* paged_space);
Heap* heap_;
};
void EvacuationVerifier::VerifyRoots(VisitMode mode) {
heap_->IterateStrongRoots(this, mode);
}
void EvacuationVerifier::VerifyEvacuationOnPage(Address start, Address end) {
Address current = start;
while (current < end) {
HeapObject object = HeapObject::FromAddress(current);
if (!object->IsFiller()) object->Iterate(this);
current += object->Size();
}
}
void EvacuationVerifier::VerifyEvacuation(NewSpace* space) {
PageRange range(space->first_allocatable_address(), space->top());
for (auto it = range.begin(); it != range.end();) {
Page* page = *(it++);
Address current = page->area_start();
Address limit = it != range.end() ? page->area_end() : space->top();
CHECK(limit == space->top() || !page->Contains(space->top()));
VerifyEvacuationOnPage(current, limit);
}
}
void EvacuationVerifier::VerifyEvacuation(PagedSpace* space) {
for (Page* p : *space) {
if (p->IsEvacuationCandidate()) continue;
if (p->Contains(space->top())) {
CodePageMemoryModificationScope memory_modification_scope(p);
heap_->CreateFillerObjectAt(
space->top(), static_cast<int>(space->limit() - space->top()),
ClearRecordedSlots::kNo);
}
VerifyEvacuationOnPage(p->area_start(), p->area_end());
}
}
class FullEvacuationVerifier : public EvacuationVerifier {
public:
explicit FullEvacuationVerifier(Heap* heap) : EvacuationVerifier(heap) {}
void Run() override {
VerifyRoots(VISIT_ALL);
VerifyEvacuation(heap_->new_space());
VerifyEvacuation(heap_->old_space());
VerifyEvacuation(heap_->code_space());
VerifyEvacuation(heap_->map_space());
}
protected:
V8_INLINE void VerifyHeapObjectImpl(HeapObject heap_object) {
CHECK_IMPLIES(Heap::InYoungGeneration(heap_object),
Heap::InToPage(heap_object));
CHECK(!MarkCompactCollector::IsOnEvacuationCandidate(heap_object));
}
template <typename TSlot>
void VerifyPointersImpl(TSlot start, TSlot end) {
for (TSlot current = start; current < end; ++current) {
typename TSlot::TObject object = *current;
HeapObject heap_object;
if (object.GetHeapObjectIfStrong(&heap_object)) {
VerifyHeapObjectImpl(heap_object);
}
}
}
void VerifyPointers(ObjectSlot start, ObjectSlot end) override {
VerifyPointersImpl(start, end);
}
void VerifyPointers(MaybeObjectSlot start, MaybeObjectSlot end) override {
VerifyPointersImpl(start, end);
}
void VisitCodeTarget(Code host, RelocInfo* rinfo) override {
Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
VerifyHeapObjectImpl(target);
}
void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
VerifyHeapObjectImpl(rinfo->target_object());
}
void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) override {
VerifyPointersImpl(start, end);
}
};
} // namespace
#endif // VERIFY_HEAP
// =============================================================================
// MarkCompactCollectorBase, MinorMarkCompactCollector, MarkCompactCollector
// =============================================================================
using MarkCompactMarkingVisitor =
MarkingVisitor<FixedArrayVisitationMode::kRegular,
TraceRetainingPathMode::kEnabled,
MarkCompactCollector::MarkingState>;
namespace {
int NumberOfAvailableCores() {
static int num_cores = V8::GetCurrentPlatform()->NumberOfWorkerThreads() + 1;
// This number of cores should be greater than zero and never change.
DCHECK_GE(num_cores, 1);
DCHECK_EQ(num_cores, V8::GetCurrentPlatform()->NumberOfWorkerThreads() + 1);
return num_cores;
}
} // namespace
int MarkCompactCollectorBase::NumberOfParallelCompactionTasks(int pages) {
DCHECK_GT(pages, 0);
int tasks =
FLAG_parallel_compaction ? Min(NumberOfAvailableCores(), pages) : 1;
if (!heap_->CanExpandOldGeneration(
static_cast<size_t>(tasks * Page::kPageSize))) {
// Optimize for memory usage near the heap limit.
tasks = 1;
}
return tasks;
}
int MarkCompactCollectorBase::NumberOfParallelPointerUpdateTasks(int pages,
int slots) {
DCHECK_GT(pages, 0);
// Limit the number of update tasks as task creation often dominates the
// actual work that is being done.
const int kMaxPointerUpdateTasks = 8;
const int kSlotsPerTask = 600;
const int wanted_tasks =
(slots >= 0) ? Max(1, Min(pages, slots / kSlotsPerTask)) : pages;
return FLAG_parallel_pointer_update
? Min(kMaxPointerUpdateTasks,
Min(NumberOfAvailableCores(), wanted_tasks))
: 1;
}
int MarkCompactCollectorBase::NumberOfParallelToSpacePointerUpdateTasks(
int pages) {
DCHECK_GT(pages, 0);
// No cap needed because all pages we need to process are fully filled with
// interesting objects.
return FLAG_parallel_pointer_update ? Min(NumberOfAvailableCores(), pages)
: 1;
}
MarkCompactCollector::MarkCompactCollector(Heap* heap)
: MarkCompactCollectorBase(heap),
page_parallel_job_semaphore_(0),
#ifdef DEBUG
state_(IDLE),
#endif
was_marked_incrementally_(false),
evacuation_(false),
compacting_(false),
black_allocation_(false),
have_code_to_deoptimize_(false),
marking_worklist_(heap),
sweeper_(new Sweeper(heap, non_atomic_marking_state())) {
old_to_new_slots_ = -1;
}
MarkCompactCollector::~MarkCompactCollector() { delete sweeper_; }
void MarkCompactCollector::SetUp() {
DCHECK_EQ(0, strcmp(Marking::kWhiteBitPattern, "00"));
DCHECK_EQ(0, strcmp(Marking::kBlackBitPattern, "11"));
DCHECK_EQ(0, strcmp(Marking::kGreyBitPattern, "10"));
DCHECK_EQ(0, strcmp(Marking::kImpossibleBitPattern, "01"));
}
void MarkCompactCollector::TearDown() {
AbortCompaction();
AbortWeakObjects();
if (heap()->incremental_marking()->IsMarking()) {
marking_worklist()->Clear();
}
}
void MarkCompactCollector::AddEvacuationCandidate(Page* p) {
DCHECK(!p->NeverEvacuate());
p->MarkEvacuationCandidate();
evacuation_candidates_.push_back(p);
}
static void TraceFragmentation(PagedSpace* space) {
int number_of_pages = space->CountTotalPages();
intptr_t reserved = (number_of_pages * space->AreaSize());
intptr_t free = reserved - space->SizeOfObjects();
PrintF("[%s]: %d pages, %d (%.1f%%) free\n", space->name(), number_of_pages,
static_cast<int>(free), static_cast<double>(free) * 100 / reserved);
}
bool MarkCompactCollector::StartCompaction() {
if (!compacting_) {
DCHECK(evacuation_candidates_.empty());
CollectEvacuationCandidates(heap()->old_space());
if (FLAG_compact_code_space) {
CollectEvacuationCandidates(heap()->code_space());
} else if (FLAG_trace_fragmentation) {
TraceFragmentation(heap()->code_space());
}
if (FLAG_trace_fragmentation) {
TraceFragmentation(heap()->map_space());
}
compacting_ = !evacuation_candidates_.empty();
}
return compacting_;
}
void MarkCompactCollector::CollectGarbage() {
// Make sure that Prepare() has been called. The individual steps below will
// update the state as they proceed.
DCHECK(state_ == PREPARE_GC);
#ifdef ENABLE_MINOR_MC
heap()->minor_mark_compact_collector()->CleanupSweepToIteratePages();
#endif // ENABLE_MINOR_MC
MarkLiveObjects();
ClearNonLiveReferences();
VerifyMarking();
RecordObjectStats();
StartSweepSpaces();
Evacuate();
Finish();
}
#ifdef VERIFY_HEAP
void MarkCompactCollector::VerifyMarkbitsAreDirty(ReadOnlySpace* space) {
ReadOnlyHeapIterator iterator(space);
for (HeapObject object = iterator.next(); !object.is_null();
object = iterator.next()) {
CHECK(non_atomic_marking_state()->IsBlack(object));
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean(PagedSpace* space) {
for (Page* p : *space) {
CHECK(non_atomic_marking_state()->bitmap(p)->IsClean());
CHECK_EQ(0, non_atomic_marking_state()->live_bytes(p));
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean(NewSpace* space) {
for (Page* p : PageRange(space->first_allocatable_address(), space->top())) {
CHECK(non_atomic_marking_state()->bitmap(p)->IsClean());
CHECK_EQ(0, non_atomic_marking_state()->live_bytes(p));
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean(LargeObjectSpace* space) {
LargeObjectIterator it(space);
for (HeapObject obj = it.Next(); !obj.is_null(); obj = it.Next()) {
CHECK(non_atomic_marking_state()->IsWhite(obj));
CHECK_EQ(0, non_atomic_marking_state()->live_bytes(
MemoryChunk::FromHeapObject(obj)));
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean() {
VerifyMarkbitsAreClean(heap_->old_space());
VerifyMarkbitsAreClean(heap_->code_space());
VerifyMarkbitsAreClean(heap_->map_space());
VerifyMarkbitsAreClean(heap_->new_space());
// Read-only space should always be black since we never collect any objects
// in it or linked from it.
VerifyMarkbitsAreDirty(heap_->read_only_space());
VerifyMarkbitsAreClean(heap_->lo_space());
VerifyMarkbitsAreClean(heap_->code_lo_space());
VerifyMarkbitsAreClean(heap_->new_lo_space());
}
#endif // VERIFY_HEAP
void MarkCompactCollector::EnsureSweepingCompleted() {
if (!sweeper()->sweeping_in_progress()) return;
sweeper()->EnsureCompleted();
heap()->old_space()->RefillFreeList();
heap()->code_space()->RefillFreeList();
heap()->map_space()->RefillFreeList();
#ifdef VERIFY_HEAP
if (FLAG_verify_heap && !evacuation()) {
FullEvacuationVerifier verifier(heap());
verifier.Run();
}
#endif
}
void MarkCompactCollector::ComputeEvacuationHeuristics(
size_t area_size, int* target_fragmentation_percent,
size_t* max_evacuated_bytes) {
// For memory reducing and optimize for memory mode we directly define both
// constants.
const int kTargetFragmentationPercentForReduceMemory = 20;
const size_t kMaxEvacuatedBytesForReduceMemory = 12 * MB;
const int kTargetFragmentationPercentForOptimizeMemory = 20;
const size_t kMaxEvacuatedBytesForOptimizeMemory = 6 * MB;
// For regular mode (which is latency critical) we define less aggressive
// defaults to start and switch to a trace-based (using compaction speed)
// approach as soon as we have enough samples.
const int kTargetFragmentationPercent = 70;
const size_t kMaxEvacuatedBytes = 4 * MB;
// Time to take for a single area (=payload of page). Used as soon as there
// exist enough compaction speed samples.
const float kTargetMsPerArea = .5;
if (heap()->ShouldReduceMemory()) {
*target_fragmentation_percent = kTargetFragmentationPercentForReduceMemory;
*max_evacuated_bytes = kMaxEvacuatedBytesForReduceMemory;
} else if (heap()->ShouldOptimizeForMemoryUsage()) {
*target_fragmentation_percent =
kTargetFragmentationPercentForOptimizeMemory;
*max_evacuated_bytes = kMaxEvacuatedBytesForOptimizeMemory;
} else {
const double estimated_compaction_speed =
heap()->tracer()->CompactionSpeedInBytesPerMillisecond();
if (estimated_compaction_speed != 0) {
// Estimate the target fragmentation based on traced compaction speed
// and a goal for a single page.
const double estimated_ms_per_area =
1 + area_size / estimated_compaction_speed;
*target_fragmentation_percent = static_cast<int>(
100 - 100 * kTargetMsPerArea / estimated_ms_per_area);
if (*target_fragmentation_percent <
kTargetFragmentationPercentForReduceMemory) {
*target_fragmentation_percent =
kTargetFragmentationPercentForReduceMemory;
}
} else {
*target_fragmentation_percent = kTargetFragmentationPercent;
}
*max_evacuated_bytes = kMaxEvacuatedBytes;
}
}
void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
DCHECK(space->identity() == OLD_SPACE || space->identity() == CODE_SPACE);
int number_of_pages = space->CountTotalPages();
size_t area_size = space->AreaSize();
// Pairs of (live_bytes_in_page, page).
using LiveBytesPagePair = std::pair<size_t, Page*>;
std::vector<LiveBytesPagePair> pages;
pages.reserve(number_of_pages);
DCHECK(!sweeping_in_progress());
Page* owner_of_linear_allocation_area =
space->top() == space->limit()
? nullptr
: Page::FromAllocationAreaAddress(space->top());
for (Page* p : *space) {
if (p->NeverEvacuate() || (p == owner_of_linear_allocation_area) ||
!p->CanAllocate())
continue;
// Invariant: Evacuation candidates are just created when marking is
// started. This means that sweeping has finished. Furthermore, at the end
// of a GC all evacuation candidates are cleared and their slot buffers are
// released.
CHECK(!p->IsEvacuationCandidate());
CHECK_NULL(p->slot_set<OLD_TO_OLD>());
CHECK_NULL(p->typed_slot_set<OLD_TO_OLD>());
CHECK(p->SweepingDone());
DCHECK(p->area_size() == area_size);
pages.push_back(std::make_pair(p->allocated_bytes(), p));
}
int candidate_count = 0;
size_t total_live_bytes = 0;
const bool reduce_memory = heap()->ShouldReduceMemory();
if (FLAG_manual_evacuation_candidates_selection) {
for (size_t i = 0; i < pages.size(); i++) {
Page* p = pages[i].second;
if (p->IsFlagSet(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING)) {
candidate_count++;
total_live_bytes += pages[i].first;
p->ClearFlag(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING);
AddEvacuationCandidate(p);
}
}
} else if (FLAG_stress_compaction_random) {
double fraction = isolate()->fuzzer_rng()->NextDouble();
size_t pages_to_mark_count =
static_cast<size_t>(fraction * (pages.size() + 1));
for (uint64_t i : isolate()->fuzzer_rng()->NextSample(
pages.size(), pages_to_mark_count)) {
candidate_count++;
total_live_bytes += pages[i].first;
AddEvacuationCandidate(pages[i].second);
}
} else if (FLAG_stress_compaction) {
for (size_t i = 0; i < pages.size(); i++) {
Page* p = pages[i].second;
if (i % 2 == 0) {
candidate_count++;
total_live_bytes += pages[i].first;
AddEvacuationCandidate(p);
}
}
} else {
// The following approach determines the pages that should be evacuated.
//
// We use two conditions to decide whether a page qualifies as an evacuation
// candidate, or not:
// * Target fragmentation: How fragmented is a page, i.e., how is the ratio
// between live bytes and capacity of this page (= area).
// * Evacuation quota: A global quota determining how much bytes should be
// compacted.
//
// The algorithm sorts all pages by live bytes and then iterates through
// them starting with the page with the most free memory, adding them to the
// set of evacuation candidates as long as both conditions (fragmentation
// and quota) hold.
size_t max_evacuated_bytes;
int target_fragmentation_percent;
ComputeEvacuationHeuristics(area_size, &target_fragmentation_percent,
&max_evacuated_bytes);
const size_t free_bytes_threshold =
target_fragmentation_percent * (area_size / 100);
// Sort pages from the most free to the least free, then select
// the first n pages for evacuation such that:
// - the total size of evacuated objects does not exceed the specified
// limit.
// - fragmentation of (n+1)-th page does not exceed the specified limit.
std::sort(pages.begin(), pages.end(),
[](const LiveBytesPagePair& a, const LiveBytesPagePair& b) {
return a.first < b.first;
});
for (size_t i = 0; i < pages.size(); i++) {
size_t live_bytes = pages[i].first;
DCHECK_GE(area_size, live_bytes);
size_t free_bytes = area_size - live_bytes;
if (FLAG_always_compact ||
((free_bytes >= free_bytes_threshold) &&
((total_live_bytes + live_bytes) <= max_evacuated_bytes))) {
candidate_count++;
total_live_bytes += live_bytes;
}
if (FLAG_trace_fragmentation_verbose) {
PrintIsolate(isolate(),
"compaction-selection-page: space=%s free_bytes_page=%zu "
"fragmentation_limit_kb=%zu "
"fragmentation_limit_percent=%d sum_compaction_kb=%zu "
"compaction_limit_kb=%zu\n",
space->name(), free_bytes / KB, free_bytes_threshold / KB,
target_fragmentation_percent, total_live_bytes / KB,
max_evacuated_bytes / KB);
}
}
// How many pages we will allocated for the evacuated objects
// in the worst case: ceil(total_live_bytes / area_size)
int estimated_new_pages =
static_cast<int>((total_live_bytes + area_size - 1) / area_size);
DCHECK_LE(estimated_new_pages, candidate_count);
int estimated_released_pages = candidate_count - estimated_new_pages;
// Avoid (compact -> expand) cycles.
if ((estimated_released_pages == 0) && !FLAG_always_compact) {
candidate_count = 0;
}
for (int i = 0; i < candidate_count; i++) {
AddEvacuationCandidate(pages[i].second);
}
}
if (FLAG_trace_fragmentation) {
PrintIsolate(isolate(),
"compaction-selection: space=%s reduce_memory=%d pages=%d "
"total_live_bytes=%zu\n",
space->name(), reduce_memory, candidate_count,
total_live_bytes / KB);
}
}
void MarkCompactCollector::AbortCompaction() {
if (compacting_) {
RememberedSet<OLD_TO_OLD>::ClearAll(heap());
for (Page* p : evacuation_candidates_) {
p->ClearEvacuationCandidate();
}
compacting_ = false;
evacuation_candidates_.clear();
}
DCHECK(evacuation_candidates_.empty());
}
void MarkCompactCollector::Prepare() {
was_marked_incrementally_ = heap()->incremental_marking()->IsMarking();
#ifdef DEBUG
DCHECK(state_ == IDLE);
state_ = PREPARE_GC;
#endif
DCHECK(!FLAG_never_compact || !FLAG_always_compact);
// Instead of waiting we could also abort the sweeper threads here.
EnsureSweepingCompleted();
if (heap()->incremental_marking()->IsSweeping()) {
heap()->incremental_marking()->Stop();
}
if (!was_marked_incrementally_) {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_EMBEDDER_PROLOGUE);
heap_->local_embedder_heap_tracer()->TracePrologue(
heap_->flags_for_embedder_tracer());
}
// Don't start compaction if we are in the middle of incremental
// marking cycle. We did not collect any slots.
if (!FLAG_never_compact && !was_marked_incrementally_) {
StartCompaction();
}
PagedSpaces spaces(heap());
for (PagedSpace* space = spaces.next(); space != nullptr;
space = spaces.next()) {
space->PrepareForMarkCompact();
}
heap()->account_external_memory_concurrently_freed();
#ifdef VERIFY_HEAP
if (!was_marked_incrementally_ && FLAG_verify_heap) {
VerifyMarkbitsAreClean();
}
#endif
}
void MarkCompactCollector::FinishConcurrentMarking(
ConcurrentMarking::StopRequest stop_request) {
// FinishConcurrentMarking is called for both, concurrent and parallel,
// marking. It is safe to call this function when tasks are already finished.
if (FLAG_parallel_marking || FLAG_concurrent_marking) {
heap()->concurrent_marking()->Stop(stop_request);
heap()->concurrent_marking()->FlushMemoryChunkData(
non_atomic_marking_state());
}
}
void MarkCompactCollector::VerifyMarking() {
CHECK(marking_worklist()->IsEmpty());
DCHECK(heap_->incremental_marking()->IsStopped());
#ifdef VERIFY_HEAP
if (FLAG_verify_heap) {
FullMarkingVerifier verifier(heap());
verifier.Run();
}
#endif
#ifdef VERIFY_HEAP
if (FLAG_verify_heap) {
heap()->old_space()->VerifyLiveBytes();
heap()->map_space()->VerifyLiveBytes();
heap()->code_space()->VerifyLiveBytes();
}
#endif
}
void MarkCompactCollector::Finish() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_FINISH);
epoch_++;
#ifdef DEBUG
heap()->VerifyCountersBeforeConcurrentSweeping();
#endif
CHECK(weak_objects_.current_ephemerons.IsEmpty());
CHECK(weak_objects_.discovered_ephemerons.IsEmpty());
weak_objects_.next_ephemerons.Clear();
sweeper()->StartSweeperTasks();
sweeper()->StartIterabilityTasks();
// Clear the marking state of live large objects.
heap_->lo_space()->ClearMarkingStateOfLiveObjects();
heap_->code_lo_space()->ClearMarkingStateOfLiveObjects();
#ifdef DEBUG
DCHECK(state_ == SWEEP_SPACES || state_ == RELOCATE_OBJECTS);
state_ = IDLE;
#endif
heap_->isolate()->inner_pointer_to_code_cache()->Flush();
// The stub caches are not traversed during GC; clear them to force
// their lazy re-initialization. This must be done after the
// GC, because it relies on the new address of certain old space
// objects (empty string, illegal builtin).
isolate()->load_stub_cache()->Clear();
isolate()->store_stub_cache()->Clear();
if (have_code_to_deoptimize_) {
// Some code objects were marked for deoptimization during the GC.
Deoptimizer::DeoptimizeMarkedCode(isolate());
have_code_to_deoptimize_ = false;
}
}
class MarkCompactCollector::RootMarkingVisitor final : public RootVisitor {
public:
explicit RootMarkingVisitor(MarkCompactCollector* collector)
: collector_(collector) {}
void VisitRootPointer(Root root, const char* description,
FullObjectSlot p) final {
MarkObjectByPointer(root, p);
}
void VisitRootPointers(Root root, const char* description,
FullObjectSlot start, FullObjectSlot end) final {
for (FullObjectSlot p = start; p < end; ++p) MarkObjectByPointer(root, p);
}
private:
V8_INLINE void MarkObjectByPointer(Root root, FullObjectSlot p) {
if (!(*p)->IsHeapObject()) return;
collector_->MarkRootObject(root, HeapObject::cast(*p));
}
MarkCompactCollector* const collector_;
};
// This visitor is used to visit the body of special objects held alive by
// other roots.
//
// It is currently used for
// - Code held alive by the top optimized frame. This code cannot be deoptimized
// and thus have to be kept alive in an isolate way, i.e., it should not keep
// alive other code objects reachable through the weak list but they should
// keep alive its embedded pointers (which would otherwise be dropped).
// - Prefix of the string table.
class MarkCompactCollector::CustomRootBodyMarkingVisitor final
: public ObjectVisitor {
public:
explicit CustomRootBodyMarkingVisitor(MarkCompactCollector* collector)
: collector_(collector) {}
void VisitPointer(HeapObject host, ObjectSlot p) final {
MarkObject(host, *p);
}
void VisitPointers(HeapObject host, ObjectSlot start, ObjectSlot end) final {
for (ObjectSlot p = start; p < end; ++p) {
DCHECK(!HasWeakHeapObjectTag(*p));
MarkObject(host, *p);
}
}
void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) final {
// At the moment, custom roots cannot contain weak pointers.
UNREACHABLE();
}
// VisitEmbedderPointer is defined by ObjectVisitor to call VisitPointers.
void VisitCodeTarget(Code host, RelocInfo* rinfo) override {
Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
MarkObject(host, target);
}
void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
MarkObject(host, rinfo->target_object());
}
private:
V8_INLINE void MarkObject(HeapObject host, Object object) {
if (!object->IsHeapObject()) return;
collector_->MarkObject(host, HeapObject::cast(object));
}
MarkCompactCollector* const collector_;
};
class InternalizedStringTableCleaner : public ObjectVisitor {
public:
InternalizedStringTableCleaner(Heap* heap, HeapObject table)
: heap_(heap), pointers_removed_(0), table_(table) {}
void VisitPointers(HeapObject host, ObjectSlot start,
ObjectSlot end) override {
// Visit all HeapObject pointers in [start, end).
Object the_hole = ReadOnlyRoots(heap_).the_hole_value();
MarkCompactCollector::NonAtomicMarkingState* marking_state =
heap_->mark_compact_collector()->non_atomic_marking_state();
for (ObjectSlot p = start; p < end; ++p) {
Object o = *p;
if (o->IsHeapObject()) {
HeapObject heap_object = HeapObject::cast(o);
if (marking_state->IsWhite(heap_object)) {
pointers_removed_++;
// Set the entry to the_hole_value (as deleted).
p.store(the_hole);
} else {
// StringTable contains only old space strings.
DCHECK(!Heap::InYoungGeneration(o));
MarkCompactCollector::RecordSlot(table_, p, heap_object);
}
}
}
}
void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) final {
UNREACHABLE();
}
void VisitCodeTarget(Code host, RelocInfo* rinfo) final { UNREACHABLE(); }
void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final {
UNREACHABLE();
}
int PointersRemoved() {
return pointers_removed_;
}
private:
Heap* heap_;
int pointers_removed_;
HeapObject table_;
};
class ExternalStringTableCleaner : public RootVisitor {
public:
explicit ExternalStringTableCleaner(Heap* heap) : heap_(heap) {}
void VisitRootPointers(Root root, const char* description,
FullObjectSlot start, FullObjectSlot end) override {
// Visit all HeapObject pointers in [start, end).
MarkCompactCollector::NonAtomicMarkingState* marking_state =
heap_->mark_compact_collector()->non_atomic_marking_state();
Object the_hole = ReadOnlyRoots(heap_).the_hole_value();
for (FullObjectSlot p = start; p < end; ++p) {
Object o = *p;
if (o->IsHeapObject()) {
HeapObject heap_object = HeapObject::cast(o);
if (marking_state->IsWhite(heap_object)) {
if (o->IsExternalString()) {
heap_->FinalizeExternalString(String::cast(o));
} else {
// The original external string may have been internalized.
DCHECK(o->IsThinString());
}
// Set the entry to the_hole_value (as deleted).
p.store(the_hole);
}
}
}
}
private:
Heap* heap_;
};
// Implementation of WeakObjectRetainer for mark compact GCs. All marked objects
// are retained.
class MarkCompactWeakObjectRetainer : public WeakObjectRetainer {
public:
explicit MarkCompactWeakObjectRetainer(
MarkCompactCollector::NonAtomicMarkingState* marking_state)
: marking_state_(marking_state) {}
Object RetainAs(Object object) override {
HeapObject heap_object = HeapObject::cast(object);
DCHECK(!marking_state_->IsGrey(heap_object));
if (marking_state_->IsBlack(heap_object)) {
return object;
} else if (object->IsAllocationSite() &&
!(AllocationSite::cast(object)->IsZombie())) {
// "dead" AllocationSites need to live long enough for a traversal of new
// space. These sites get a one-time reprieve.
Object nested = object;
while (nested->IsAllocationSite()) {
AllocationSite current_site = AllocationSite::cast(nested);
// MarkZombie will override the nested_site, read it first before
// marking
nested = current_site->nested_site();
current_site->MarkZombie();
marking_state_->WhiteToBlack(current_site);
}
return object;
} else {
return Object();
}
}
private:
MarkCompactCollector::NonAtomicMarkingState* marking_state_;
};
class RecordMigratedSlotVisitor : public ObjectVisitor {
public:
explicit RecordMigratedSlotVisitor(
MarkCompactCollector* collector,
EphemeronRememberedSet* ephemeron_remembered_set)
: collector_(collector),
ephemeron_remembered_set_(ephemeron_remembered_set) {}
inline void VisitPointer(HeapObject host, ObjectSlot p) final {
DCHECK(!HasWeakHeapObjectTag(*p));
RecordMigratedSlot(host, MaybeObject::FromObject(*p), p.address());
}
inline void VisitPointer(HeapObject host, MaybeObjectSlot p) final {
RecordMigratedSlot(host, *p, p.address());
}
inline void VisitPointers(HeapObject host, ObjectSlot start,
ObjectSlot end) final {
while (start < end) {
VisitPointer(host, start);
++start;
}
}
inline void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) final {
while (start < end) {
VisitPointer(host, start);
++start;
}
}
inline void VisitEphemeron(HeapObject host, int index, ObjectSlot key,
ObjectSlot value) override {
DCHECK(host->IsEphemeronHashTable());
DCHECK(!Heap::InYoungGeneration(host));
VisitPointer(host, value);
if (ephemeron_remembered_set_ && Heap::InYoungGeneration(*key)) {
auto table = EphemeronHashTable::unchecked_cast(host);
auto insert_result =
ephemeron_remembered_set_->insert({table, std::unordered_set<int>()});
insert_result.first->second.insert(index);
} else {
VisitPointer(host, key);
}
}
inline void VisitCodeTarget(Code host, RelocInfo* rinfo) override {
DCHECK_EQ(host, rinfo->host());
DCHECK(RelocInfo::IsCodeTargetMode(rinfo->rmode()));
Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
// The target is always in old space, we don't have to record the slot in
// the old-to-new remembered set.
DCHECK(!Heap::InYoungGeneration(target));
collector_->RecordRelocSlot(host, rinfo, target);
}
inline void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
DCHECK_EQ(host, rinfo->host());
DCHECK(RelocInfo::IsEmbeddedObjectMode(rinfo->rmode()));
HeapObject object = HeapObject::cast(rinfo->target_object());
GenerationalBarrierForCode(host, rinfo, object);
collector_->RecordRelocSlot(host, rinfo, object);
}
// Entries that are skipped for recording.
inline void VisitExternalReference(Code host, RelocInfo* rinfo) final {}
inline void VisitExternalReference(Foreign host, Address* p) final {}
inline void VisitRuntimeEntry(Code host, RelocInfo* rinfo) final {}
inline void VisitInternalReference(Code host, RelocInfo* rinfo) final {}
protected:
inline virtual void RecordMigratedSlot(HeapObject host, MaybeObject value,
Address slot) {
if (value->IsStrongOrWeak()) {
MemoryChunk* p = MemoryChunk::FromAddress(value.ptr());
if (p->InYoungGeneration()) {
DCHECK_IMPLIES(
p->IsToPage(),
p->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION) || p->IsLargePage());
RememberedSet<OLD_TO_NEW>::Insert<AccessMode::NON_ATOMIC>(
MemoryChunk::FromHeapObject(host), slot);
} else if (p->IsEvacuationCandidate()) {
RememberedSet<OLD_TO_OLD>::Insert<AccessMode::NON_ATOMIC>(
MemoryChunk::FromHeapObject(host), slot);
}
}
}
MarkCompactCollector* collector_;
EphemeronRememberedSet* ephemeron_remembered_set_;
};
class MigrationObserver {
public:
explicit MigrationObserver(Heap* heap) : heap_(heap) {}
virtual ~MigrationObserver() = default;
virtual void Move(AllocationSpace dest, HeapObject src, HeapObject dst,
int size) = 0;
protected:
Heap* heap_;
};
class ProfilingMigrationObserver final : public MigrationObserver {
public:
explicit ProfilingMigrationObserver(Heap* heap) : MigrationObserver(heap) {}
inline void Move(AllocationSpace dest, HeapObject src, HeapObject dst,
int size) final {
if (dest == CODE_SPACE || (dest == OLD_SPACE && dst->IsBytecodeArray())) {
PROFILE(heap_->isolate(),
CodeMoveEvent(AbstractCode::cast(src), AbstractCode::cast(dst)));
}
heap_->OnMoveEvent(dst, src, size);
}
};
class HeapObjectVisitor {
public:
virtual ~HeapObjectVisitor() = default;
virtual bool Visit(HeapObject object, int size) = 0;
};
class EvacuateVisitorBase : public HeapObjectVisitor {
public:
void AddObserver(MigrationObserver* observer) {
migration_function_ = RawMigrateObject<MigrationMode::kObserved>;
observers_.push_back(observer);
}
protected:
enum MigrationMode { kFast, kObserved };
using MigrateFunction = void (*)(EvacuateVisitorBase* base, HeapObject dst,
HeapObject src, int size,
AllocationSpace dest);
template <MigrationMode mode>
static void RawMigrateObject(EvacuateVisitorBase* base, HeapObject dst,
HeapObject src, int size, AllocationSpace dest) {
Address dst_addr = dst->address();
Address src_addr = src->address();
DCHECK(base->heap_->AllowedToBeMigrated(src, dest));
DCHECK_NE(dest, LO_SPACE);
DCHECK_NE(dest, CODE_LO_SPACE);
if (dest == OLD_SPACE) {
DCHECK_OBJECT_SIZE(size);
DCHECK(IsAligned(size, kTaggedSize));
base->heap_->CopyBlock(dst_addr, src_addr, size);
if (mode != MigrationMode::kFast)
base->ExecuteMigrationObservers(dest, src, dst, size);
dst->IterateBodyFast(dst->map(), size, base->record_visitor_);
} else if (dest == CODE_SPACE) {
DCHECK_CODEOBJECT_SIZE(size, base->heap_->code_space());
base->heap_->CopyBlock(dst_addr, src_addr, size);
Code::cast(dst)->Relocate(dst_addr - src_addr);
if (mode != MigrationMode::kFast)
base->ExecuteMigrationObservers(dest, src, dst, size);
dst->IterateBodyFast(dst->map(), size, base->record_visitor_);
} else {
DCHECK_OBJECT_SIZE(size);
DCHECK(dest == NEW_SPACE);
base->heap_->CopyBlock(dst_addr, src_addr, size);
if (mode != MigrationMode::kFast)
base->ExecuteMigrationObservers(dest, src, dst, size);
}
src->set_map_word(MapWord::FromForwardingAddress(dst));
}
EvacuateVisitorBase(Heap* heap, LocalAllocator* local_allocator,
RecordMigratedSlotVisitor* record_visitor)
: heap_(heap),
local_allocator_(local_allocator),
record_visitor_(record_visitor) {
migration_function_ = RawMigrateObject<MigrationMode::kFast>;
}
inline bool TryEvacuateObject(AllocationSpace target_space, HeapObject object,
int size, HeapObject* target_object) {
#ifdef VERIFY_HEAP
if (AbortCompactionForTesting(object)) return false;
#endif // VERIFY_HEAP
AllocationAlignment alignment =
HeapObject::RequiredAlignment(object->map());
AllocationResult allocation =
local_allocator_->Allocate(target_space, size, alignment);
if (allocation.To(target_object)) {
MigrateObject(*target_object, object, size, target_space);
if (target_space == CODE_SPACE)
MemoryChunk::FromHeapObject(*target_object)
->GetCodeObjectRegistry()
->RegisterNewlyAllocatedCodeObject((*target_object).address());
return true;
}
return false;
}
inline void ExecuteMigrationObservers(AllocationSpace dest, HeapObject src,
HeapObject dst, int size) {
for (MigrationObserver* obs : observers_) {
obs->Move(dest, src, dst, size);
}
}
inline void MigrateObject(HeapObject dst, HeapObject src, int size,
AllocationSpace dest) {
migration_function_(this, dst, src, size, dest);
}
#ifdef VERIFY_HEAP
bool AbortCompactionForTesting(HeapObject object) {
if (FLAG_stress_compaction) {
const uintptr_t mask = static_cast<uintptr_t>(FLAG_random_seed) &
kPageAlignmentMask & ~kObjectAlignmentMask;
if ((object->ptr() & kPageAlignmentMask) == mask) {
Page* page = Page::FromHeapObject(object);
if (page->IsFlagSet(Page::COMPACTION_WAS_ABORTED_FOR_TESTING)) {
page->ClearFlag(Page::COMPACTION_WAS_ABORTED_FOR_TESTING);
} else {
page->SetFlag(Page::COMPACTION_WAS_ABORTED_FOR_TESTING);
return true;
}
}
}
return false;
}
#endif // VERIFY_HEAP
Heap* heap_;
LocalAllocator* local_allocator_;
RecordMigratedSlotVisitor* record_visitor_;
std::vector<MigrationObserver*> observers_;
MigrateFunction migration_function_;
};
class EvacuateNewSpaceVisitor final : public EvacuateVisitorBase {
public:
explicit EvacuateNewSpaceVisitor(
Heap* heap, LocalAllocator* local_allocator,
RecordMigratedSlotVisitor* record_visitor,
Heap::PretenuringFeedbackMap* local_pretenuring_feedback)
: EvacuateVisitorBase(heap, local_allocator, record_visitor),
buffer_(LocalAllocationBuffer::InvalidBuffer()),
promoted_size_(0),
semispace_copied_size_(0),
local_pretenuring_feedback_(local_pretenuring_feedback),
is_incremental_marking_(heap->incremental_marking()->IsMarking()) {}
inline bool Visit(HeapObject object, int size) override {
if (TryEvacuateWithoutCopy(object)) return true;
HeapObject target_object;
if (heap_->ShouldBePromoted(object->address()) &&
TryEvacuateObject(OLD_SPACE, object, size, &target_object)) {
promoted_size_ += size;
return true;
}
heap_->UpdateAllocationSite(object->map(), object,
local_pretenuring_feedback_);
HeapObject target;
AllocationSpace space = AllocateTargetObject(object, size, &target);
MigrateObject(HeapObject::cast(target), object, size, space);
semispace_copied_size_ += size;
return true;
}
intptr_t promoted_size() { return promoted_size_; }
intptr_t semispace_copied_size() { return semispace_copied_size_; }
private:
inline bool TryEvacuateWithoutCopy(HeapObject object) {
if (is_incremental_marking_) return false;
Map map = object->map();
// Some objects can be evacuated without creating a copy.
if (map->visitor_id() == kVisitThinString) {
HeapObject actual = ThinString::cast(object)->unchecked_actual();
if (MarkCompactCollector::IsOnEvacuationCandidate(actual)) return false;
object->map_slot().Relaxed_Store(
MapWord::FromForwardingAddress(actual).ToMap());
return true;
}
// TODO(mlippautz): Handle ConsString.
return false;
}
inline AllocationSpace AllocateTargetObject(HeapObject old_object, int size,
HeapObject* target_object) {
AllocationAlignment alignment =
HeapObject::RequiredAlignment(old_object->map());
AllocationSpace space_allocated_in = NEW_SPACE;
AllocationResult allocation =
local_allocator_->Allocate(NEW_SPACE, size, alignment);
if (allocation.IsRetry()) {
allocation = AllocateInOldSpace(size, alignment);
space_allocated_in = OLD_SPACE;
}
bool ok = allocation.To(target_object);
DCHECK(ok);
USE(ok);
return space_allocated_in;
}
inline AllocationResult AllocateInOldSpace(int size_in_bytes,
AllocationAlignment alignment) {
AllocationResult allocation =
local_allocator_->Allocate(OLD_SPACE, size_in_bytes, alignment);
if (allocation.IsRetry()) {
heap_->FatalProcessOutOfMemory(
"MarkCompactCollector: semi-space copy, fallback in old gen");
}
return allocation;
}
LocalAllocationBuffer buffer_;
intptr_t promoted_size_;
intptr_t semispace_copied_size_;
Heap::PretenuringFeedbackMap* local_pretenuring_feedback_;
bool is_incremental_marking_;
};
template <PageEvacuationMode mode>
class EvacuateNewSpacePageVisitor final : public HeapObjectVisitor {
public:
explicit EvacuateNewSpacePageVisitor(
Heap* heap, RecordMigratedSlotVisitor* record_visitor,
Heap::PretenuringFeedbackMap* local_pretenuring_feedback)
: heap_(heap),
record_visitor_(record_visitor),
moved_bytes_(0),
local_pretenuring_feedback_(local_pretenuring_feedback) {}
static void Move(Page* page) {
switch (mode) {
case NEW_TO_NEW:
page->heap()->new_space()->MovePageFromSpaceToSpace(page);
page->SetFlag(Page::PAGE_NEW_NEW_PROMOTION);
break;
case NEW_TO_OLD: {
page->heap()->new_space()->from_space().RemovePage(page);
Page* new_page = Page::ConvertNewToOld(page);
DCHECK(!new_page->InYoungGeneration());
new_page->SetFlag(Page::PAGE_NEW_OLD_PROMOTION);
break;
}
}
}
inline bool Visit(HeapObject object, int size) override {
if (mode == NEW_TO_NEW) {
heap_->UpdateAllocationSite(object->map(), object,
local_pretenuring_feedback_);
} else if (mode == NEW_TO_OLD) {
object->IterateBodyFast(record_visitor_);
}
return true;
}
intptr_t moved_bytes() { return moved_bytes_; }
void account_moved_bytes(intptr_t bytes) { moved_bytes_ += bytes; }
private:
Heap* heap_;
RecordMigratedSlotVisitor* record_visitor_;
intptr_t moved_bytes_;
Heap::PretenuringFeedbackMap* local_pretenuring_feedback_;
};
class EvacuateOldSpaceVisitor final : public EvacuateVisitorBase {
public:
EvacuateOldSpaceVisitor(Heap* heap, LocalAllocator* local_allocator,
RecordMigratedSlotVisitor* record_visitor)
: EvacuateVisitorBase(heap, local_allocator, record_visitor) {}
inline bool Visit(HeapObject object, int size) override {
HeapObject target_object;
if (TryEvacuateObject(Page::FromHeapObject(object)->owner()->identity(),
object, size, &target_object)) {
DCHECK(object->map_word().IsForwardingAddress());
return true;
}
return false;
}
};
class EvacuateRecordOnlyVisitor final : public HeapObjectVisitor {
public:
explicit EvacuateRecordOnlyVisitor(Heap* heap) : heap_(heap) {}
inline bool Visit(HeapObject object, int size) override {
RecordMigratedSlotVisitor visitor(heap_->mark_compact_collector(),
&heap_->ephemeron_remembered_set_);
object->IterateBodyFast(&visitor);
return true;
}
private:
Heap* heap_;
};
bool MarkCompactCollector::IsUnmarkedHeapObject(Heap* heap, FullObjectSlot p) {
Object o = *p;
if (!o->IsHeapObject()) return false;
HeapObject heap_object = HeapObject::cast(o);
return heap->mark_compact_collector()->non_atomic_marking_state()->IsWhite(
heap_object);
}
void MarkCompactCollector::MarkStringTable(
ObjectVisitor* custom_root_body_visitor) {
StringTable string_table = heap()->string_table();
// Mark the string table itself.
if (marking_state()->WhiteToBlack(string_table)) {
// Explicitly mark the prefix.
string_table->IteratePrefix(custom_root_body_visitor);
}
}
void MarkCompactCollector::MarkRoots(RootVisitor* root_visitor,
ObjectVisitor* custom_root_body_visitor) {
// Mark the heap roots including global variables, stack variables,
// etc., and all objects reachable from them.
heap()->IterateStrongRoots(root_visitor, VISIT_ONLY_STRONG);
// Custom marking for string table and top optimized frame.
MarkStringTable(custom_root_body_visitor);
ProcessTopOptimizedFrame(custom_root_body_visitor);
}
void MarkCompactCollector::ProcessEphemeronsUntilFixpoint() {
bool work_to_do = true;
int iterations = 0;
int max_iterations = FLAG_ephemeron_fixpoint_iterations;
while (work_to_do) {
PerformWrapperTracing();
if (iterations >= max_iterations) {
// Give up fixpoint iteration and switch to linear algorithm.
ProcessEphemeronsLinear();
break;
}
// Move ephemerons from next_ephemerons into current_ephemerons to
// drain them in this iteration.
weak_objects_.current_ephemerons.Swap(weak_objects_.next_ephemerons);
heap()->concurrent_marking()->set_ephemeron_marked(false);
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERON_MARKING);
if (FLAG_parallel_marking) {
heap_->concurrent_marking()->RescheduleTasksIfNeeded();
}
work_to_do = ProcessEphemerons();
FinishConcurrentMarking(
ConcurrentMarking::StopRequest::COMPLETE_ONGOING_TASKS);
}
CHECK(weak_objects_.current_ephemerons.IsEmpty());
CHECK(weak_objects_.discovered_ephemerons.IsEmpty());
work_to_do = work_to_do || !marking_worklist()->IsEmpty() ||
heap()->concurrent_marking()->ephemeron_marked() ||
!marking_worklist()->IsEmbedderEmpty() ||
!heap()->local_embedder_heap_tracer()->IsRemoteTracingDone();
++iterations;
}
CHECK(marking_worklist()->IsEmpty());
CHECK(weak_objects_.current_ephemerons.IsEmpty());
CHECK(weak_objects_.discovered_ephemerons.IsEmpty());
}
bool MarkCompactCollector::ProcessEphemerons() {
Ephemeron ephemeron;
bool ephemeron_marked = false;
// Drain current_ephemerons and push ephemerons where key and value are still
// unreachable into next_ephemerons.
while (weak_objects_.current_ephemerons.Pop(kMainThread, &ephemeron)) {
if (ProcessEphemeron(ephemeron.key, ephemeron.value)) {
ephemeron_marked = true;
}
}
// Drain marking worklist and push discovered ephemerons into
// discovered_ephemerons.
ProcessMarkingWorklist();
// Drain discovered_ephemerons (filled in the drain MarkingWorklist-phase
// before) and push ephemerons where key and value are still unreachable into
// next_ephemerons.
while (weak_objects_.discovered_ephemerons.Pop(kMainThread, &ephemeron)) {
if (ProcessEphemeron(ephemeron.key, ephemeron.value)) {
ephemeron_marked = true;
}
}
// Flush local ephemerons for main task to global pool.
weak_objects_.ephemeron_hash_tables.FlushToGlobal(kMainThread);
weak_objects_.next_ephemerons.FlushToGlobal(kMainThread);
return ephemeron_marked;
}
void MarkCompactCollector::ProcessEphemeronsLinear() {
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERON_LINEAR);
CHECK(heap()->concurrent_marking()->IsStopped());
std::unordered_multimap<HeapObject, HeapObject, Object::Hasher> key_to_values;
Ephemeron ephemeron;
DCHECK(weak_objects_.current_ephemerons.IsEmpty());
weak_objects_.current_ephemerons.Swap(weak_objects_.next_ephemerons);
while (weak_objects_.current_ephemerons.Pop(kMainThread, &ephemeron)) {
ProcessEphemeron(ephemeron.key, ephemeron.value);
if (non_atomic_marking_state()->IsWhite(ephemeron.value)) {
key_to_values.insert(std::make_pair(ephemeron.key, ephemeron.value));
}
}
ephemeron_marking_.newly_discovered_limit = key_to_values.size();
bool work_to_do = true;
while (work_to_do) {
PerformWrapperTracing();
ResetNewlyDiscovered();
ephemeron_marking_.newly_discovered_limit = key_to_values.size();
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERON_MARKING);
// Drain marking worklist and push all discovered objects into
// newly_discovered.
ProcessMarkingWorklistInternal<
MarkCompactCollector::MarkingWorklistProcessingMode::
kTrackNewlyDiscoveredObjects>();
}
while (weak_objects_.discovered_ephemerons.Pop(kMainThread, &ephemeron)) {
ProcessEphemeron(ephemeron.key, ephemeron.value);
if (non_atomic_marking_state()->IsWhite(ephemeron.value)) {
key_to_values.insert(std::make_pair(ephemeron.key, ephemeron.value));
}
}
if (ephemeron_marking_.newly_discovered_overflowed) {
// If newly_discovered was overflowed just visit all ephemerons in
// next_ephemerons.
weak_objects_.next_ephemerons.Iterate([&](Ephemeron ephemeron) {
if (non_atomic_marking_state()->IsBlackOrGrey(ephemeron.key) &&
non_atomic_marking_state()->WhiteToGrey(ephemeron.value)) {
marking_worklist()->Push(ephemeron.value);
}
});
} else {
// This is the good case: newly_discovered stores all discovered
// objects. Now use key_to_values to see if discovered objects keep more
// objects alive due to ephemeron semantics.
for (HeapObject object : ephemeron_marking_.newly_discovered) {
auto range = key_to_values.equal_range(object);
for (auto it = range.first; it != range.second; ++it) {
HeapObject value = it->second;
MarkObject(object, value);
}
}
}
// Do NOT drain marking worklist here, otherwise the current checks
// for work_to_do are not sufficient for determining if another iteration
// is necessary.
work_to_do = !marking_worklist()->IsEmpty() ||
!marking_worklist()->IsEmbedderEmpty() ||
!heap()->local_embedder_heap_tracer()->IsRemoteTracingDone();
CHECK(weak_objects_.discovered_ephemerons.IsEmpty());
}
ResetNewlyDiscovered();
ephemeron_marking_.newly_discovered.shrink_to_fit();
CHECK(marking_worklist()->IsEmpty());
}
void MarkCompactCollector::PerformWrapperTracing() {
if (heap_->local_embedder_heap_tracer()->InUse()) {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_EMBEDDER_TRACING);
{
LocalEmbedderHeapTracer::ProcessingScope scope(
heap_->local_embedder_heap_tracer());
HeapObject object;
while (marking_worklist()->embedder()->Pop(kMainThread, &object)) {
scope.TracePossibleWrapper(JSObject::cast(object));
}
}
heap_->local_embedder_heap_tracer()->Trace(
std::numeric_limits<double>::infinity());
}
}
void MarkCompactCollector::ProcessMarkingWorklist() {
ProcessMarkingWorklistInternal<
MarkCompactCollector::MarkingWorklistProcessingMode::kDefault>();
}
template <MarkCompactCollector::MarkingWorklistProcessingMode mode>
void MarkCompactCollector::ProcessMarkingWorklistInternal() {
HeapObject object;
MarkCompactMarkingVisitor visitor(this, marking_state());
while (!(object = marking_worklist()->Pop()).is_null()) {
// Left trimming may result in grey or black filler objects on the marking
// worklist. Ignore these objects.
if (object->IsFiller()) {
// Due to copying mark bits and the fact that grey and black have their
// first bit set, one word fillers are always black.
DCHECK_IMPLIES(
object->map() == ReadOnlyRoots(heap()).one_pointer_filler_map(),
marking_state()->IsBlack(object));
// Other fillers may be black or grey depending on the color of the object
// that was trimmed.
DCHECK_IMPLIES(
object->map() != ReadOnlyRoots(heap()).one_pointer_filler_map(),
marking_state()->IsBlackOrGrey(object));
continue;
}
DCHECK(object->IsHeapObject());
DCHECK(heap()->Contains(object));
DCHECK(!(marking_state()->IsWhite(object)));
marking_state()->GreyToBlack(object);
if (mode == MarkCompactCollector::MarkingWorklistProcessingMode::
kTrackNewlyDiscoveredObjects) {
AddNewlyDiscovered(object);
}
Map map = object->map();
MarkObject(object, map);
visitor.Visit(map, object);
}
}
bool MarkCompactCollector::ProcessEphemeron(HeapObject key, HeapObject value) {
if (marking_state()->IsBlackOrGrey(key)) {
if (marking_state()->WhiteToGrey(value)) {
marking_worklist()->Push(value);
return true;
}
} else if (marking_state()->IsWhite(value)) {
weak_objects_.next_ephemerons.Push(kMainThread, Ephemeron{key, value});
}
return false;
}
void MarkCompactCollector::ProcessEphemeronMarking() {
DCHECK(marking_worklist()->IsEmpty());
// Incremental marking might leave ephemerons in main task's local
// buffer, flush it into global pool.
weak_objects_.next_ephemerons.FlushToGlobal(kMainThread);
ProcessEphemeronsUntilFixpoint();
CHECK(marking_worklist()->IsEmpty());
CHECK(heap()->local_embedder_heap_tracer()->IsRemoteTracingDone());
}
void MarkCompactCollector::ProcessTopOptimizedFrame(ObjectVisitor* visitor) {
for (StackFrameIterator it(isolate(), isolate()->thread_local_top());
!it.done(); it.Advance()) {
if (it.frame()->type() == StackFrame::INTERPRETED) {
return;
}
if (it.frame()->type() == StackFrame::OPTIMIZED) {
Code code = it.frame()->LookupCode();
if (!code->CanDeoptAt(it.frame()->pc())) {
Code::BodyDescriptor::IterateBody(code->map(), code, visitor);
}
return;
}
}
}
void MarkCompactCollector::RecordObjectStats() {
if (V8_UNLIKELY(TracingFlags::is_gc_stats_enabled())) {
heap()->CreateObjectStats();
ObjectStatsCollector collector(heap(), heap()->live_object_stats_.get(),
heap()->dead_object_stats_.get());
collector.Collect();
if (V8_UNLIKELY(TracingFlags::gc_stats.load(std::memory_order_relaxed) &
v8::tracing::TracingCategoryObserver::ENABLED_BY_TRACING)) {
std::stringstream live, dead;
heap()->live_object_stats_->Dump(live);
heap()->dead_object_stats_->Dump(dead);
TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("v8.gc_stats"),
"V8.GC_Objects_Stats", TRACE_EVENT_SCOPE_THREAD,
"live", TRACE_STR_COPY(live.str().c_str()), "dead",
TRACE_STR_COPY(dead.str().c_str()));
}
if (FLAG_trace_gc_object_stats) {
heap()->live_object_stats_->PrintJSON("live");
heap()->dead_object_stats_->PrintJSON("dead");
}
heap()->live_object_stats_->CheckpointObjectStats();
heap()->dead_object_stats_->ClearObjectStats();
}
}
void MarkCompactCollector::MarkLiveObjects() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK);
// The recursive GC marker detects when it is nearing stack overflow,
// and switches to a different marking system. JS interrupts interfere
// with the C stack limit check.
PostponeInterruptsScope postpone(isolate());
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_FINISH_INCREMENTAL);
IncrementalMarking* incremental_marking = heap_->incremental_marking();
if (was_marked_incrementally_) {
incremental_marking->Finalize();
} else {
CHECK(incremental_marking->IsStopped());
}
}
#ifdef DEBUG
DCHECK(state_ == PREPARE_GC);
state_ = MARK_LIVE_OBJECTS;
#endif
heap_->local_embedder_heap_tracer()->EnterFinalPause();
RootMarkingVisitor root_visitor(this);
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_ROOTS);
CustomRootBodyMarkingVisitor custom_root_body_visitor(this);
MarkRoots(&root_visitor, &custom_root_body_visitor);
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_MAIN);
if (FLAG_parallel_marking) {
heap_->concurrent_marking()->RescheduleTasksIfNeeded();
}
ProcessMarkingWorklist();
FinishConcurrentMarking(
ConcurrentMarking::StopRequest::COMPLETE_ONGOING_TASKS);
ProcessMarkingWorklist();
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WEAK_CLOSURE);
DCHECK(marking_worklist()->IsEmpty());
// Mark objects reachable through the embedder heap. This phase is
// opportunistic as it may not discover graphs that are only reachable
// through ephemerons.
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_EMBEDDER_TRACING_CLOSURE);
do {
// PerformWrapperTracing() also empties the work items collected by
// concurrent markers. As a result this call needs to happen at least
// once.
PerformWrapperTracing();
ProcessMarkingWorklist();
} while (!heap_->local_embedder_heap_tracer()->IsRemoteTracingDone() ||
!marking_worklist()->IsEmbedderEmpty());
DCHECK(marking_worklist()->IsEmbedderEmpty());
DCHECK(marking_worklist()->IsEmpty());
}
// The objects reachable from the roots are marked, yet unreachable objects
// are unmarked. Mark objects reachable due to embedder heap tracing or
// harmony weak maps.
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERON);
ProcessEphemeronMarking();
DCHECK(marking_worklist()->IsEmpty());
}
// The objects reachable from the roots, weak maps, and embedder heap
// tracing are marked. Objects pointed to only by weak global handles cannot
// be immediately reclaimed. Instead, we have to mark them as pending and
// mark objects reachable from them.
//
// First we identify nonlive weak handles and mark them as pending
// destruction.
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_WEAK_HANDLES);
heap()->isolate()->global_handles()->IterateWeakRootsIdentifyFinalizers(
&IsUnmarkedHeapObject);
ProcessMarkingWorklist();
}
// Process finalizers, effectively keeping them alive until the next
// garbage collection.
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_WEAK_ROOTS);
heap()->isolate()->global_handles()->IterateWeakRootsForFinalizers(
&root_visitor);
ProcessMarkingWorklist();
}
// Repeat ephemeron processing from the newly marked objects.
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WEAK_CLOSURE_HARMONY);
ProcessEphemeronMarking();
DCHECK(marking_worklist()->IsEmbedderEmpty());
DCHECK(marking_worklist()->IsEmpty());
}
{
heap()->isolate()->global_handles()->IterateWeakRootsForPhantomHandles(
&IsUnmarkedHeapObject);
}
}
if (was_marked_incrementally_) {
heap()->incremental_marking()->Deactivate();
}
}
void MarkCompactCollector::ClearNonLiveReferences() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR);
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_STRING_TABLE);
// Prune the string table removing all strings only pointed to by the
// string table. Cannot use string_table() here because the string
// table is marked.
StringTable string_table = heap()->string_table();
InternalizedStringTableCleaner internalized_visitor(heap(), string_table);
string_table->IterateElements(&internalized_visitor);
string_table->ElementsRemoved(internalized_visitor.PointersRemoved());
ExternalStringTableCleaner external_visitor(heap());
heap()->external_string_table_.IterateAll(&external_visitor);
heap()->external_string_table_.CleanUpAll();
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_FLUSHABLE_BYTECODE);
ClearOldBytecodeCandidates();
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_FLUSHED_JS_FUNCTIONS);
ClearFlushedJsFunctions();
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_LISTS);
// Process the weak references.
MarkCompactWeakObjectRetainer mark_compact_object_retainer(
non_atomic_marking_state());
heap()->ProcessAllWeakReferences(&mark_compact_object_retainer);
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_MAPS);
// ClearFullMapTransitions must be called before weak references are
// cleared.
ClearFullMapTransitions();
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_REFERENCES);
ClearWeakReferences();
ClearWeakCollections();
ClearJSWeakRefs();
}
MarkDependentCodeForDeoptimization();
DCHECK(weak_objects_.transition_arrays.IsEmpty());
DCHECK(weak_objects_.weak_references.IsEmpty());
DCHECK(weak_objects_.weak_objects_in_code.IsEmpty());
DCHECK(weak_objects_.js_weak_refs.IsEmpty());
DCHECK(weak_objects_.weak_cells.IsEmpty());
DCHECK(weak_objects_.bytecode_flushing_candidates.IsEmpty());
DCHECK(weak_objects_.flushed_js_functions.IsEmpty());
}
void MarkCompactCollector::MarkDependentCodeForDeoptimization() {
std::pair<HeapObject, Code> weak_object_in_code;
while (weak_objects_.weak_objects_in_code.Pop(kMainThread,
&weak_object_in_code)) {
HeapObject object = weak_object_in_code.first;
Code code = weak_object_in_code.second;
if (!non_atomic_marking_state()->IsBlackOrGrey(object) &&
!code->embedded_objects_cleared()) {
if (!code->marked_for_deoptimization()) {
code->SetMarkedForDeoptimization("weak objects");
have_code_to_deoptimize_ = true;
}
code->ClearEmbeddedObjects(heap_);
DCHECK(code->embedded_objects_cleared());
}
}
}
void MarkCompactCollector::ClearPotentialSimpleMapTransition(Map dead_target) {
DCHECK(non_atomic_marking_state()->IsWhite(dead_target));
Object potential_parent = dead_target->constructor_or_backpointer();
if (potential_parent->IsMap()) {
Map parent = Map::cast(potential_parent);
DisallowHeapAllocation no_gc_obviously;
if (non_atomic_marking_state()->IsBlackOrGrey(parent) &&
TransitionsAccessor(isolate(), parent, &no_gc_obviously)
.HasSimpleTransitionTo(dead_target)) {
ClearPotentialSimpleMapTransition(parent, dead_target);
}
}
}
void MarkCompactCollector::ClearPotentialSimpleMapTransition(Map map,
Map dead_target) {
DCHECK(!map->is_prototype_map());
DCHECK(!dead_target->is_prototype_map());
DCHECK_EQ(map->raw_transitions(), HeapObjectReference::Weak(dead_target));
// Take ownership of the descriptor array.
int number_of_own_descriptors = map->NumberOfOwnDescriptors();
DescriptorArray descriptors = map->instance_descriptors();
if (descriptors == dead_target->instance_descriptors() &&
number_of_own_descriptors > 0) {
TrimDescriptorArray(map, descriptors);
DCHECK(descriptors->number_of_descriptors() == number_of_own_descriptors);
}
}
void MarkCompactCollector::FlushBytecodeFromSFI(
SharedFunctionInfo shared_info) {
DCHECK(shared_info->HasBytecodeArray());
// Retain objects required for uncompiled data.
String inferred_name = shared_info->inferred_name();
int start_position = shared_info->StartPosition();
int end_position = shared_info->EndPosition();
shared_info->DiscardCompiledMetadata(
isolate(), [](HeapObject object, ObjectSlot slot, HeapObject target) {
RecordSlot(object, slot, target);
});
// The size of the bytecode array should always be larger than an
// UncompiledData object.
STATIC_ASSERT(BytecodeArray::SizeFor(0) >=
UncompiledDataWithoutPreparseData::kSize);
// Replace bytecode array with an uncompiled data array.
HeapObject compiled_data = shared_info->GetBytecodeArray();
Address compiled_data_start = compiled_data->address();
int compiled_data_size = compiled_data->Size();
MemoryChunk* chunk = MemoryChunk::FromAddress(compiled_data_start);
// Clear any recorded slots for the compiled data as being invalid.
RememberedSet<OLD_TO_NEW>::RemoveRange(
chunk, compiled_data_start, compiled_data_start + compiled_data_size,
SlotSet::PREFREE_EMPTY_BUCKETS);
RememberedSet<OLD_TO_OLD>::RemoveRange(
chunk, compiled_data_start, compiled_data_start + compiled_data_size,
SlotSet::PREFREE_EMPTY_BUCKETS);
// Swap the map, using set_map_after_allocation to avoid verify heap checks
// which are not necessary since we are doing this during the GC atomic pause.
compiled_data->set_map_after_allocation(
ReadOnlyRoots(heap()).uncompiled_data_without_preparse_data_map(),
SKIP_WRITE_BARRIER);
// Create a filler object for any left over space in the bytecode array.
if (!heap()->IsLargeObject(compiled_data)) {
heap()->CreateFillerObjectAt(
compiled_data->address() + UncompiledDataWithoutPreparseData::kSize,
compiled_data_size - UncompiledDataWithoutPreparseData::kSize,
ClearRecordedSlots::kNo);
}
// Initialize the uncompiled data.
UncompiledData uncompiled_data = UncompiledData::cast(compiled_data);
UncompiledData::Initialize(
uncompiled_data, inferred_name, start_position, end_position,
kFunctionLiteralIdInvalid,
[](HeapObject object, ObjectSlot slot, HeapObject target) {
RecordSlot(object, slot, target);
});
// Mark the uncompiled data as black, and ensure all fields have already been
// marked.
DCHECK(non_atomic_marking_state()->IsBlackOrGrey(inferred_name));
non_atomic_marking_state()->WhiteToBlack(uncompiled_data);
// Use the raw function data setter to avoid validity checks, since we're
// performing the unusual task of decompiling.
shared_info->set_function_data(uncompiled_data);
DCHECK(!shared_info->is_compiled());
}
void MarkCompactCollector::ClearOldBytecodeCandidates() {
DCHECK(FLAG_flush_bytecode ||
weak_objects_.bytecode_flushing_candidates.IsEmpty());
SharedFunctionInfo flushing_candidate;
while (weak_objects_.bytecode_flushing_candidates.Pop(kMainThread,
&flushing_candidate)) {
// If the BytecodeArray is dead, flush it, which will replace the field with
// an uncompiled data object.
if (!non_atomic_marking_state()->IsBlackOrGrey(
flushing_candidate->GetBytecodeArray())) {
FlushBytecodeFromSFI(flushing_candidate);
}
// Now record the slot, which has either been updated to an uncompiled data,
// or is the BytecodeArray which is still alive.
ObjectSlot slot =
flushing_candidate.RawField(SharedFunctionInfo::kFunctionDataOffset);
RecordSlot(flushing_candidate, slot, HeapObject::cast(*slot));
}
}
void MarkCompactCollector::ClearFlushedJsFunctions() {
DCHECK(FLAG_flush_bytecode || weak_objects_.flushed_js_functions.IsEmpty());
JSFunction flushed_js_function;
while (weak_objects_.flushed_js_functions.Pop(kMainThread,
&flushed_js_function)) {
flushed_js_function->ResetIfBytecodeFlushed();
}
}
void MarkCompactCollector::ClearFullMapTransitions() {
TransitionArray array;
while (weak_objects_.transition_arrays.Pop(kMainThread, &array)) {
int num_transitions = array->number_of_entries();
if (num_transitions > 0) {
Map map;
// The array might contain "undefined" elements because it's not yet
// filled. Allow it.
if (array->GetTargetIfExists(0, isolate(), &map)) {
DCHECK(!map.is_null()); // Weak pointers aren't cleared yet.
Map parent = Map::cast(map->constructor_or_backpointer());
bool parent_is_alive =
non_atomic_marking_state()->IsBlackOrGrey(parent);
DescriptorArray descriptors = parent_is_alive
? parent->instance_descriptors()
: DescriptorArray();
bool descriptors_owner_died =
CompactTransitionArray(parent, array, descriptors);
if (descriptors_owner_died) {
TrimDescriptorArray(parent, descriptors);
}
}
}
}
}
bool MarkCompactCollector::CompactTransitionArray(Map map,
TransitionArray transitions,
DescriptorArray descriptors) {
DCHECK(!map->is_prototype_map());
int num_transitions = transitions->number_of_entries();
bool descriptors_owner_died = false;
int transition_index = 0;
// Compact all live transitions to the left.
for (int i = 0; i < num_transitions; ++i) {
Map target = transitions->GetTarget(i);
DCHECK_EQ(target->constructor_or_backpointer(), map);
if (non_atomic_marking_state()->IsWhite(target)) {
if (!descriptors.is_null() &&
target->instance_descriptors() == descriptors) {
DCHECK(!target->is_prototype_map());
descriptors_owner_died = true;
}
} else {
if (i != transition_index) {
Name key = transitions->GetKey(i);
transitions->SetKey(transition_index, key);
HeapObjectSlot key_slot = transitions->GetKeySlot(transition_index);
RecordSlot(transitions, key_slot, key);
MaybeObject raw_target = transitions->GetRawTarget(i);
transitions->SetRawTarget(transition_index, raw_target);
HeapObjectSlot target_slot =
transitions->GetTargetSlot(transition_index);
RecordSlot(transitions, target_slot, raw_target->GetHeapObject());
}
transition_index++;
}
}
// If there are no transitions to be cleared, return.
if (transition_index == num_transitions) {
DCHECK(!descriptors_owner_died);
return false;
}
// Note that we never eliminate a transition array, though we might right-trim
// such that number_of_transitions() == 0. If this assumption changes,
// TransitionArray::Insert() will need to deal with the case that a transition
// array disappeared during GC.
int trim = transitions->Capacity() - transition_index;
if (trim > 0) {
heap_->RightTrimWeakFixedArray(transitions,
trim * TransitionArray::kEntrySize);
transitions->SetNumberOfTransitions(transition_index);
}
return descriptors_owner_died;
}
void MarkCompactCollector::RightTrimDescriptorArray(DescriptorArray array,
int descriptors_to_trim) {
int old_nof_all_descriptors = array->number_of_all_descriptors();
int new_nof_all_descriptors = old_nof_all_descriptors - descriptors_to_trim;
DCHECK_LT(0, descriptors_to_trim);
DCHECK_LE(0, new_nof_all_descriptors);
Address start = array->GetDescriptorSlot(new_nof_all_descriptors).address();
Address end = array->GetDescriptorSlot(old_nof_all_descriptors).address();
RememberedSet<OLD_TO_NEW>::RemoveRange(MemoryChunk::FromHeapObject(array),
start, end,
SlotSet::PREFREE_EMPTY_BUCKETS);
RememberedSet<OLD_TO_OLD>::RemoveRange(MemoryChunk::FromHeapObject(array),
start, end,
SlotSet::PREFREE_EMPTY_BUCKETS);
heap()->CreateFillerObjectAt(start, static_cast<int>(end - start),
ClearRecordedSlots::kNo);
array->set_number_of_all_descriptors(new_nof_all_descriptors);
}
void MarkCompactCollector::TrimDescriptorArray(Map map,
DescriptorArray descriptors) {
int number_of_own_descriptors = map->NumberOfOwnDescriptors();
if (number_of_own_descriptors == 0) {
DCHECK(descriptors == ReadOnlyRoots(heap_).empty_descriptor_array());
return;
}
// TODO(ulan): Trim only if slack is greater than some percentage threshold.
int to_trim =
descriptors->number_of_all_descriptors() - number_of_own_descriptors;
if (to_trim > 0) {
descriptors->set_number_of_descriptors(number_of_own_descriptors);
RightTrimDescriptorArray(descriptors, to_trim);
TrimEnumCache(map, descriptors);
descriptors->Sort();
if (FLAG_unbox_double_fields) {
LayoutDescriptor layout_descriptor = map->layout_descriptor();
layout_descriptor = layout_descriptor->Trim(heap_, map, descriptors,
number_of_own_descriptors);
SLOW_DCHECK(layout_descriptor->IsConsistentWithMap(map, true));
}
}
DCHECK(descriptors->number_of_descriptors() == number_of_own_descriptors);
map->set_owns_descriptors(true);
}
void MarkCompactCollector::TrimEnumCache(Map map, DescriptorArray descriptors) {
int live_enum = map->EnumLength();
if (live_enum == kInvalidEnumCacheSentinel) {
live_enum = map->NumberOfEnumerableProperties();
}
if (live_enum == 0) return descriptors->ClearEnumCache();
EnumCache enum_cache = descriptors->enum_cache();
FixedArray keys = enum_cache->keys();
int to_trim = keys->length() - live_enum;
if (to_trim <= 0) return;
heap_->RightTrimFixedArray(keys, to_trim);
FixedArray indices = enum_cache->indices();
to_trim = indices->length() - live_enum;
if (to_trim <= 0) return;
heap_->RightTrimFixedArray(indices, to_trim);
}
void MarkCompactCollector::ClearWeakCollections() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_COLLECTIONS);
EphemeronHashTable table;
while (weak_objects_.ephemeron_hash_tables.Pop(kMainThread, &table)) {
for (int i = 0; i < table->Capacity(); i++) {
HeapObject key = HeapObject::cast(table->KeyAt(i));
#ifdef VERIFY_HEAP
Object value = table->ValueAt(i);
if (value->IsHeapObject()) {
CHECK_IMPLIES(
non_atomic_marking_state()->IsBlackOrGrey(key),
non_atomic_marking_state()->IsBlackOrGrey(HeapObject::cast(value)));
}
#endif
if (!non_atomic_marking_state()->IsBlackOrGrey(key)) {
table->RemoveEntry(i);
}
}
}
for (auto it = heap_->ephemeron_remembered_set_.begin();
it != heap_->ephemeron_remembered_set_.end();) {
if (!non_atomic_marking_state()->IsBlackOrGrey(it->first)) {
it = heap_->ephemeron_remembered_set_.erase(it);
} else {
++it;
}
}
}
void MarkCompactCollector::ClearWeakReferences() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_REFERENCES);
std::pair<HeapObject, HeapObjectSlot> slot;
HeapObjectReference cleared_weak_ref =
HeapObjectReference::ClearedValue(isolate());
while (weak_objects_.weak_references.Pop(kMainThread, &slot)) {
HeapObject value;
// The slot could have been overwritten, so we have to treat it
// as MaybeObjectSlot.
MaybeObjectSlot location(slot.second);
if ((*location)->GetHeapObjectIfWeak(&value)) {
DCHECK(!value->IsCell());
if (non_atomic_marking_state()->IsBlackOrGrey(value)) {
// The value of the weak reference is alive.
RecordSlot(slot.first, HeapObjectSlot(location), value);
} else {
if (value->IsMap()) {
// The map is non-live.
ClearPotentialSimpleMapTransition(Map::cast(value));
}
location.store(cleared_weak_ref);
}
}
}
}
void MarkCompactCollector::ClearJSWeakRefs() {
if (!FLAG_harmony_weak_refs) {
return;
}
JSWeakRef weak_ref;
while (weak_objects_.js_weak_refs.Pop(kMainThread, &weak_ref)) {
HeapObject target = HeapObject::cast(weak_ref->target());
if (!non_atomic_marking_state()->IsBlackOrGrey(target)) {
weak_ref->set_target(ReadOnlyRoots(isolate()).undefined_value());
} else {
// The value of the JSWeakRef is alive.
ObjectSlot slot = weak_ref.RawField(JSWeakRef::kTargetOffset);
RecordSlot(weak_ref, slot, target);
}
}
WeakCell weak_cell;
while (weak_objects_.weak_cells.Pop(kMainThread, &weak_cell)) {
HeapObject target = HeapObject::cast(weak_cell->target());
if (!non_atomic_marking_state()->IsBlackOrGrey(target)) {
DCHECK(!target->IsUndefined());
// The value of the WeakCell is dead.
JSFinalizationGroup finalization_group =
JSFinalizationGroup::cast(weak_cell->finalization_group());
if (!finalization_group->scheduled_for_cleanup()) {
heap()->AddDirtyJSFinalizationGroup(
finalization_group,
[](HeapObject object, ObjectSlot slot, Object target) {
if (target->IsHeapObject()) {
RecordSlot(object, slot, HeapObject::cast(target));
}
});
}
// We're modifying the pointers in WeakCell and JSFinalizationGroup during
// GC; thus we need to record the slots it writes. The normal write
// barrier is not enough, since it's disabled before GC.
weak_cell->Nullify(isolate(),
[](HeapObject object, ObjectSlot slot, Object target) {
if (target->IsHeapObject()) {
RecordSlot(object, slot, HeapObject::cast(target));
}
});
DCHECK(finalization_group->NeedsCleanup());
DCHECK(finalization_group->scheduled_for_cleanup());
} else {
// The value of the WeakCell is alive.
ObjectSlot slot = weak_cell.RawField(WeakCell::kTargetOffset);
RecordSlot(weak_cell, slot, HeapObject::cast(*slot));
}
}
}
void MarkCompactCollector::AbortWeakObjects() {
weak_objects_.transition_arrays.Clear();
weak_objects_.ephemeron_hash_tables.Clear();
weak_objects_.current_ephemerons.Clear();
weak_objects_.next_ephemerons.Clear();
weak_objects_.discovered_ephemerons.Clear();
weak_objects_.weak_references.Clear();
weak_objects_.weak_objects_in_code.Clear();
weak_objects_.js_weak_refs.Clear();
weak_objects_.weak_cells.Clear();
weak_objects_.bytecode_flushing_candidates.Clear();
weak_objects_.flushed_js_functions.Clear();
}
bool MarkCompactCollector::IsOnEvacuationCandidate(MaybeObject obj) {
return Page::FromAddress(obj.ptr())->IsEvacuationCandidate();
}
MarkCompactCollector::RecordRelocSlotInfo
MarkCompactCollector::PrepareRecordRelocSlot(Code host, RelocInfo* rinfo,
HeapObject target) {
RecordRelocSlotInfo result;
result.should_record = false;
Page* target_page = Page::FromHeapObject(target);
Page* source_page = Page::FromHeapObject(host);
if (target_page->IsEvacuationCandidate() &&
(rinfo->host().is_null() ||
!source_page->ShouldSkipEvacuationSlotRecording())) {
RelocInfo::Mode rmode = rinfo->rmode();
Address addr = rinfo->pc();
SlotType slot_type = SlotTypeForRelocInfoMode(rmode);
if (rinfo->IsInConstantPool()) {
addr = rinfo->constant_pool_entry_address();
if (RelocInfo::IsCodeTargetMode(rmode)) {
slot_type = CODE_ENTRY_SLOT;
} else {
// Constant pools don't support compressed values at this time
// (this may change, therefore use a DCHECK).
DCHECK(RelocInfo::IsFullEmbeddedObject(rmode));
slot_type = OBJECT_SLOT;
}
}
uintptr_t offset = addr - source_page->address();
DCHECK_LT(offset, static_cast<uintptr_t>(TypedSlotSet::kMaxOffset));
result.should_record = true;
result.memory_chunk = source_page;
result.slot_type = slot_type;
result.offset = static_cast<uint32_t>(offset);
}
return result;
}
void MarkCompactCollector::RecordRelocSlot(Code host, RelocInfo* rinfo,
HeapObject target) {
RecordRelocSlotInfo info = PrepareRecordRelocSlot(host, rinfo, target);
if (info.should_record) {
RememberedSet<OLD_TO_OLD>::InsertTyped(info.memory_chunk, info.slot_type,
info.offset);
}
}
namespace {
// Missing specialization MakeSlotValue<FullObjectSlot, WEAK>() will turn
// attempt to store a weak reference to strong-only slot to a compilation error.
template <typename TSlot, HeapObjectReferenceType reference_type>
typename TSlot::TObject MakeSlotValue(HeapObject heap_object);
template <>
Object MakeSlotValue<ObjectSlot, HeapObjectReferenceType::STRONG>(
HeapObject heap_object) {
return heap_object;
}
template <>
MaybeObject MakeSlotValue<MaybeObjectSlot, HeapObjectReferenceType::STRONG>(
HeapObject heap_object) {
return HeapObjectReference::Strong(heap_object);
}
template <>
MaybeObject MakeSlotValue<MaybeObjectSlot, HeapObjectReferenceType::WEAK>(
HeapObject heap_object) {
return HeapObjectReference::Weak(heap_object);
}
#ifdef V8_COMPRESS_POINTERS
template <>
Object MakeSlotValue<FullObjectSlot, HeapObjectReferenceType::STRONG>(
HeapObject heap_object) {
return heap_object;
}
template <>
MaybeObject MakeSlotValue<FullMaybeObjectSlot, HeapObjectReferenceType::STRONG>(
HeapObject heap_object) {
return HeapObjectReference::Strong(heap_object);
}
// The following specialization
// MakeSlotValue<FullMaybeObjectSlot, HeapObjectReferenceType::WEAK>()
// is not used.
#endif
template <AccessMode access_mode, HeapObjectReferenceType reference_type,
typename TSlot>
static inline SlotCallbackResult UpdateSlot(TSlot slot,
typename TSlot::TObject old,
HeapObject heap_obj) {
static_assert(
std::is_same<TSlot, FullObjectSlot>::value ||
std::is_same<TSlot, ObjectSlot>::value ||
std::is_same<TSlot, FullMaybeObjectSlot>::value ||
std::is_same<TSlot, MaybeObjectSlot>::value,
"Only [Full]ObjectSlot and [Full]MaybeObjectSlot are expected here");
MapWord map_word = heap_obj->map_word();
if (map_word.IsForwardingAddress()) {
DCHECK_IMPLIES(!Heap::InFromPage(heap_obj),
MarkCompactCollector::IsOnEvacuationCandidate(heap_obj) ||
Page::FromHeapObject(heap_obj)->IsFlagSet(
Page::COMPACTION_WAS_ABORTED));
typename TSlot::TObject target =
MakeSlotValue<TSlot, reference_type>(map_word.ToForwardingAddress());
if (access_mode == AccessMode::NON_ATOMIC) {
slot.store(target);
} else {
slot.Release_CompareAndSwap(old, target);
}
DCHECK(!Heap::InFromPage(target));
DCHECK(!MarkCompactCollector::IsOnEvacuationCandidate(target));
} else {
DCHECK(heap_obj->map()->IsMap());
}
// OLD_TO_OLD slots are always removed after updating.
return REMOVE_SLOT;
}
template <AccessMode access_mode, typename TSlot>
static inline SlotCallbackResult UpdateSlot(TSlot slot) {
typename TSlot::TObject obj = slot.Relaxed_Load();
HeapObject heap_obj;
if (TSlot::kCanBeWeak && obj->GetHeapObjectIfWeak(&heap_obj)) {
UpdateSlot<access_mode, HeapObjectReferenceType::WEAK>(slot, obj, heap_obj);
} else if (obj->GetHeapObjectIfStrong(&heap_obj)) {
return UpdateSlot<access_mode, HeapObjectReferenceType::STRONG>(slot, obj,
heap_obj);
}
return REMOVE_SLOT;
}
template <AccessMode access_mode, typename TSlot>
static inline SlotCallbackResult UpdateStrongSlot(TSlot slot) {
typename TSlot::TObject obj = slot.Relaxed_Load();
DCHECK(!HAS_WEAK_HEAP_OBJECT_TAG(obj.ptr()));
HeapObject heap_obj;
if (obj.GetHeapObject(&heap_obj)) {
return UpdateSlot<access_mode, HeapObjectReferenceType::STRONG>(slot, obj,
heap_obj);
}
return REMOVE_SLOT;
}
} // namespace
// Visitor for updating root pointers and to-space pointers.
// It does not expect to encounter pointers to dead objects.
class PointersUpdatingVisitor : public ObjectVisitor, public RootVisitor {
public:
PointersUpdatingVisitor() {}
void VisitPointer(HeapObject host, ObjectSlot p) override {
UpdateStrongSlotInternal(p);
}
void VisitPointer(HeapObject host, MaybeObjectSlot p) override {
UpdateSlotInternal(p);
}
void VisitPointers(HeapObject host, ObjectSlot start,
ObjectSlot end) override {
for (ObjectSlot p = start; p < end; ++p) {
UpdateStrongSlotInternal(p);
}
}
void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) final {
for (MaybeObjectSlot p = start; p < end; ++p) {
UpdateSlotInternal(p);
}
}