blob: d39c9ee601f893c4b813a0e07d20f4b78a135a84 [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 "src/base/atomicops.h"
#include "src/base/bits.h"
#include "src/base/sys-info.h"
#include "src/code-stubs.h"
#include "src/compilation-cache.h"
#include "src/deoptimizer.h"
#include "src/execution.h"
#include "src/frames-inl.h"
#include "src/gdb-jit.h"
#include "src/global-handles.h"
#include "src/heap/array-buffer-tracker.h"
#include "src/heap/gc-tracer.h"
#include "src/heap/incremental-marking.h"
#include "src/heap/mark-compact-inl.h"
#include "src/heap/object-stats.h"
#include "src/heap/objects-visiting-inl.h"
#include "src/heap/objects-visiting.h"
#include "src/heap/page-parallel-job.h"
#include "src/heap/spaces-inl.h"
#include "src/ic/ic.h"
#include "src/ic/stub-cache.h"
#include "src/profiler/cpu-profiler.h"
#include "src/utils-inl.h"
#include "src/v8.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 {Marking::MarkBitFrom} to not produce
// invalid {kImpossibleBitPattern} in the marking bitmap by overlapping.
STATIC_ASSERT(Heap::kMinObjectSizeInWords >= 2);
// -------------------------------------------------------------------------
// MarkCompactCollector
MarkCompactCollector::MarkCompactCollector(Heap* heap)
: // NOLINT
#ifdef DEBUG
state_(IDLE),
#endif
marking_parity_(ODD_MARKING_PARITY),
was_marked_incrementally_(false),
evacuation_(false),
heap_(heap),
marking_deque_memory_(NULL),
marking_deque_memory_committed_(0),
code_flusher_(nullptr),
embedder_heap_tracer_(nullptr),
have_code_to_deoptimize_(false),
compacting_(false),
pending_compaction_tasks_semaphore_(0),
sweeper_(heap) {
}
#ifdef VERIFY_HEAP
class VerifyMarkingVisitor : public ObjectVisitor {
public:
explicit VerifyMarkingVisitor(Heap* heap) : heap_(heap) {}
void VisitPointers(Object** start, Object** end) override {
for (Object** current = start; current < end; current++) {
if ((*current)->IsHeapObject()) {
HeapObject* object = HeapObject::cast(*current);
CHECK(heap_->mark_compact_collector()->IsMarked(object));
}
}
}
void VisitEmbeddedPointer(RelocInfo* rinfo) override {
DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
if (!rinfo->host()->IsWeakObject(rinfo->target_object())) {
Object* p = rinfo->target_object();
VisitPointer(&p);
}
}
void VisitCell(RelocInfo* rinfo) override {
Code* code = rinfo->host();
DCHECK(rinfo->rmode() == RelocInfo::CELL);
if (!code->IsWeakObject(rinfo->target_cell())) {
ObjectVisitor::VisitCell(rinfo);
}
}
private:
Heap* heap_;
};
static void VerifyMarking(Heap* heap, Address bottom, Address top) {
VerifyMarkingVisitor visitor(heap);
HeapObject* object;
Address next_object_must_be_here_or_later = bottom;
for (Address current = bottom; current < top; current += kPointerSize) {
object = HeapObject::FromAddress(current);
if (MarkCompactCollector::IsMarked(object)) {
CHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
CHECK(current >= next_object_must_be_here_or_later);
object->Iterate(&visitor);
next_object_must_be_here_or_later = current + object->Size();
// The next word for sure belongs to the current object, jump over it.
current += kPointerSize;
}
}
}
static void VerifyMarkingBlackPage(Heap* heap, Page* page) {
CHECK(page->IsFlagSet(Page::BLACK_PAGE));
VerifyMarkingVisitor visitor(heap);
HeapObjectIterator it(page);
for (HeapObject* object = it.Next(); object != NULL; object = it.Next()) {
CHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
object->Iterate(&visitor);
}
}
static void VerifyMarking(NewSpace* space) {
Address end = space->top();
NewSpacePageIterator it(space->bottom(), end);
// 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->bottom(), Page::FromAddress(space->bottom())->area_start());
while (it.has_next()) {
Page* page = it.next();
Address limit = it.has_next() ? page->area_end() : end;
CHECK(limit == end || !page->Contains(end));
VerifyMarking(space->heap(), page->area_start(), limit);
}
}
static void VerifyMarking(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
if (p->IsFlagSet(Page::BLACK_PAGE)) {
VerifyMarkingBlackPage(space->heap(), p);
} else {
VerifyMarking(space->heap(), p->area_start(), p->area_end());
}
}
}
static void VerifyMarking(Heap* heap) {
VerifyMarking(heap->old_space());
VerifyMarking(heap->code_space());
VerifyMarking(heap->map_space());
VerifyMarking(heap->new_space());
VerifyMarkingVisitor visitor(heap);
LargeObjectIterator it(heap->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
if (MarkCompactCollector::IsMarked(obj)) {
obj->Iterate(&visitor);
}
}
heap->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
}
class VerifyEvacuationVisitor : public ObjectVisitor {
public:
void VisitPointers(Object** start, Object** end) override {
for (Object** current = start; current < end; current++) {
if ((*current)->IsHeapObject()) {
HeapObject* object = HeapObject::cast(*current);
CHECK(!MarkCompactCollector::IsOnEvacuationCandidate(object));
}
}
}
};
static void VerifyEvacuation(Page* page) {
VerifyEvacuationVisitor visitor;
HeapObjectIterator iterator(page);
for (HeapObject* heap_object = iterator.Next(); heap_object != NULL;
heap_object = iterator.Next()) {
// We skip free space objects.
if (!heap_object->IsFiller()) {
heap_object->Iterate(&visitor);
}
}
}
static void VerifyEvacuation(NewSpace* space) {
NewSpacePageIterator it(space->bottom(), space->top());
VerifyEvacuationVisitor visitor;
while (it.has_next()) {
Page* page = it.next();
Address current = page->area_start();
Address limit = it.has_next() ? page->area_end() : space->top();
CHECK(limit == space->top() || !page->Contains(space->top()));
while (current < limit) {
HeapObject* object = HeapObject::FromAddress(current);
object->Iterate(&visitor);
current += object->Size();
}
}
}
static void VerifyEvacuation(Heap* heap, PagedSpace* space) {
if (FLAG_use_allocation_folding && (space == heap->old_space())) {
return;
}
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
if (p->IsEvacuationCandidate()) continue;
VerifyEvacuation(p);
}
}
static void VerifyEvacuation(Heap* heap) {
VerifyEvacuation(heap, heap->old_space());
VerifyEvacuation(heap, heap->code_space());
VerifyEvacuation(heap, heap->map_space());
VerifyEvacuation(heap->new_space());
VerifyEvacuationVisitor visitor;
heap->IterateStrongRoots(&visitor, VISIT_ALL);
}
#endif // VERIFY_HEAP
void MarkCompactCollector::SetUp() {
DCHECK(strcmp(Marking::kWhiteBitPattern, "00") == 0);
DCHECK(strcmp(Marking::kBlackBitPattern, "11") == 0);
DCHECK(strcmp(Marking::kGreyBitPattern, "10") == 0);
DCHECK(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
EnsureMarkingDequeIsReserved();
EnsureMarkingDequeIsCommitted(kMinMarkingDequeSize);
if (FLAG_flush_code) {
code_flusher_ = new CodeFlusher(isolate());
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing is now on]\n");
}
}
}
void MarkCompactCollector::TearDown() {
AbortCompaction();
delete marking_deque_memory_;
delete code_flusher_;
}
void MarkCompactCollector::AddEvacuationCandidate(Page* p) {
DCHECK(!p->NeverEvacuate());
p->MarkEvacuationCandidate();
evacuation_candidates_.Add(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",
AllocationSpaceName(space->identity()), number_of_pages,
static_cast<int>(free), static_cast<double>(free) * 100 / reserved);
}
bool MarkCompactCollector::StartCompaction(CompactionMode mode) {
if (!compacting_) {
DCHECK(evacuation_candidates_.length() == 0);
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());
}
heap()->old_space()->EvictEvacuationCandidatesFromLinearAllocationArea();
heap()->code_space()->EvictEvacuationCandidatesFromLinearAllocationArea();
compacting_ = evacuation_candidates_.length() > 0;
}
return compacting_;
}
void MarkCompactCollector::ClearInvalidRememberedSetSlots() {
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_STORE_BUFFER);
RememberedSet<OLD_TO_NEW>::ClearInvalidSlots(heap());
}
// There is not need to filter the old to old set because
// it is completely cleared after the mark-compact GC.
// The slots that become invalid due to runtime transitions are
// cleared eagerly immediately after the transition.
#ifdef VERIFY_HEAP
if (FLAG_verify_heap) {
RememberedSet<OLD_TO_NEW>::VerifyValidSlots(heap());
RememberedSet<OLD_TO_OLD>::VerifyValidSlots(heap());
}
#endif
}
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);
MarkLiveObjects();
DCHECK(heap_->incremental_marking()->IsStopped());
ClearNonLiveReferences();
#ifdef VERIFY_HEAP
if (FLAG_verify_heap) {
VerifyMarking(heap_);
}
#endif
SweepSpaces();
EvacuateNewSpaceAndCandidates();
Finish();
}
#ifdef VERIFY_HEAP
void MarkCompactCollector::VerifyMarkbitsAreClean(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
CHECK(p->markbits()->IsClean());
CHECK_EQ(0, p->LiveBytes());
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean(NewSpace* space) {
NewSpacePageIterator it(space->bottom(), space->top());
while (it.has_next()) {
Page* p = it.next();
CHECK(p->markbits()->IsClean());
CHECK_EQ(0, p->LiveBytes());
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean() {
VerifyMarkbitsAreClean(heap_->old_space());
VerifyMarkbitsAreClean(heap_->code_space());
VerifyMarkbitsAreClean(heap_->map_space());
VerifyMarkbitsAreClean(heap_->new_space());
LargeObjectIterator it(heap_->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
MarkBit mark_bit = Marking::MarkBitFrom(obj);
CHECK(Marking::IsWhite(mark_bit));
CHECK_EQ(0, Page::FromAddress(obj->address())->LiveBytes());
}
}
void MarkCompactCollector::VerifyWeakEmbeddedObjectsInCode() {
HeapObjectIterator code_iterator(heap()->code_space());
for (HeapObject* obj = code_iterator.Next(); obj != NULL;
obj = code_iterator.Next()) {
Code* code = Code::cast(obj);
if (!code->is_optimized_code()) continue;
if (WillBeDeoptimized(code)) continue;
code->VerifyEmbeddedObjectsDependency();
}
}
void MarkCompactCollector::VerifyOmittedMapChecks() {
HeapObjectIterator iterator(heap()->map_space());
for (HeapObject* obj = iterator.Next(); obj != NULL; obj = iterator.Next()) {
Map* map = Map::cast(obj);
map->VerifyOmittedMapChecks();
}
}
#endif // VERIFY_HEAP
static void ClearMarkbitsInPagedSpace(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
Bitmap::Clear(p);
if (p->IsFlagSet(Page::BLACK_PAGE)) {
p->ClearFlag(Page::BLACK_PAGE);
}
}
}
static void ClearMarkbitsInNewSpace(NewSpace* space) {
NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
while (it.has_next()) {
Bitmap::Clear(it.next());
}
}
void MarkCompactCollector::ClearMarkbits() {
ClearMarkbitsInPagedSpace(heap_->code_space());
ClearMarkbitsInPagedSpace(heap_->map_space());
ClearMarkbitsInPagedSpace(heap_->old_space());
ClearMarkbitsInNewSpace(heap_->new_space());
LargeObjectIterator it(heap_->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
Marking::MarkWhite(Marking::MarkBitFrom(obj));
MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
chunk->ResetProgressBar();
chunk->ResetLiveBytes();
if (chunk->IsFlagSet(Page::BLACK_PAGE)) {
chunk->ClearFlag(Page::BLACK_PAGE);
}
}
}
class MarkCompactCollector::Sweeper::SweeperTask : public v8::Task {
public:
SweeperTask(Sweeper* sweeper, base::Semaphore* pending_sweeper_tasks,
AllocationSpace space_to_start)
: sweeper_(sweeper),
pending_sweeper_tasks_(pending_sweeper_tasks),
space_to_start_(space_to_start) {}
virtual ~SweeperTask() {}
private:
// v8::Task overrides.
void Run() override {
DCHECK_GE(space_to_start_, FIRST_PAGED_SPACE);
DCHECK_LE(space_to_start_, LAST_PAGED_SPACE);
const int offset = space_to_start_ - FIRST_PAGED_SPACE;
const int num_spaces = LAST_PAGED_SPACE - FIRST_PAGED_SPACE + 1;
for (int i = 0; i < num_spaces; i++) {
const int space_id = FIRST_PAGED_SPACE + ((i + offset) % num_spaces);
DCHECK_GE(space_id, FIRST_PAGED_SPACE);
DCHECK_LE(space_id, LAST_PAGED_SPACE);
sweeper_->ParallelSweepSpace(static_cast<AllocationSpace>(space_id), 0);
}
pending_sweeper_tasks_->Signal();
}
Sweeper* sweeper_;
base::Semaphore* pending_sweeper_tasks_;
AllocationSpace space_to_start_;
DISALLOW_COPY_AND_ASSIGN(SweeperTask);
};
void MarkCompactCollector::Sweeper::StartSweeping() {
sweeping_in_progress_ = true;
ForAllSweepingSpaces([this](AllocationSpace space) {
std::sort(sweeping_list_[space].begin(), sweeping_list_[space].end(),
[](Page* a, Page* b) { return a->LiveBytes() < b->LiveBytes(); });
});
if (FLAG_concurrent_sweeping) {
ForAllSweepingSpaces([this](AllocationSpace space) {
if (space == NEW_SPACE) return;
StartSweepingHelper(space);
});
}
}
void MarkCompactCollector::Sweeper::StartSweepingHelper(
AllocationSpace space_to_start) {
num_sweeping_tasks_++;
V8::GetCurrentPlatform()->CallOnBackgroundThread(
new SweeperTask(this, &pending_sweeper_tasks_semaphore_, space_to_start),
v8::Platform::kShortRunningTask);
}
void MarkCompactCollector::Sweeper::SweepOrWaitUntilSweepingCompleted(
Page* page) {
PagedSpace* owner = reinterpret_cast<PagedSpace*>(page->owner());
if (!page->SweepingDone()) {
ParallelSweepPage(page, owner);
if (!page->SweepingDone()) {
// We were not able to sweep that page, i.e., a concurrent
// sweeper thread currently owns this page. Wait for the sweeper
// thread to be done with this page.
page->WaitUntilSweepingCompleted();
}
}
}
void MarkCompactCollector::SweepAndRefill(CompactionSpace* space) {
if (FLAG_concurrent_sweeping && !sweeper().IsSweepingCompleted()) {
sweeper().ParallelSweepSpace(space->identity(), 0);
space->RefillFreeList();
}
}
Page* MarkCompactCollector::Sweeper::GetSweptPageSafe(PagedSpace* space) {
base::LockGuard<base::Mutex> guard(&mutex_);
SweptList& list = swept_list_[space->identity()];
if (list.length() > 0) {
return list.RemoveLast();
}
return nullptr;
}
void MarkCompactCollector::Sweeper::EnsureCompleted() {
if (!sweeping_in_progress_) return;
// If sweeping is not completed or not running at all, we try to complete it
// here.
if (!FLAG_concurrent_sweeping || !IsSweepingCompleted()) {
ForAllSweepingSpaces(
[this](AllocationSpace space) { ParallelSweepSpace(space, 0); });
}
if (FLAG_concurrent_sweeping) {
while (num_sweeping_tasks_ > 0) {
pending_sweeper_tasks_semaphore_.Wait();
num_sweeping_tasks_--;
}
}
ForAllSweepingSpaces(
[this](AllocationSpace space) { DCHECK(sweeping_list_[space].empty()); });
late_pages_ = false;
sweeping_in_progress_ = false;
}
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()) {
VerifyEvacuation(heap_);
}
#endif
}
bool MarkCompactCollector::Sweeper::IsSweepingCompleted() {
if (!pending_sweeper_tasks_semaphore_.WaitFor(
base::TimeDelta::FromSeconds(0))) {
return false;
}
pending_sweeper_tasks_semaphore_.Signal();
return true;
}
void Marking::TransferMark(Heap* heap, Address old_start, Address new_start) {
// This is only used when resizing an object.
DCHECK(MemoryChunk::FromAddress(old_start) ==
MemoryChunk::FromAddress(new_start));
if (!heap->incremental_marking()->IsMarking() ||
Page::FromAddress(old_start)->IsFlagSet(Page::BLACK_PAGE))
return;
// If the mark doesn't move, we don't check the color of the object.
// It doesn't matter whether the object is black, since it hasn't changed
// size, so the adjustment to the live data count will be zero anyway.
if (old_start == new_start) return;
MarkBit new_mark_bit = MarkBitFrom(new_start);
MarkBit old_mark_bit = MarkBitFrom(old_start);
#ifdef DEBUG
ObjectColor old_color = Color(old_mark_bit);
#endif
if (Marking::IsBlack(old_mark_bit)) {
Marking::BlackToWhite(old_mark_bit);
Marking::MarkBlack(new_mark_bit);
return;
} else if (Marking::IsGrey(old_mark_bit)) {
Marking::GreyToWhite(old_mark_bit);
heap->incremental_marking()->WhiteToGreyAndPush(
HeapObject::FromAddress(new_start), new_mark_bit);
heap->incremental_marking()->RestartIfNotMarking();
}
#ifdef DEBUG
ObjectColor new_color = Color(new_mark_bit);
DCHECK(new_color == old_color);
#endif
}
const char* AllocationSpaceName(AllocationSpace space) {
switch (space) {
case NEW_SPACE:
return "NEW_SPACE";
case OLD_SPACE:
return "OLD_SPACE";
case CODE_SPACE:
return "CODE_SPACE";
case MAP_SPACE:
return "MAP_SPACE";
case LO_SPACE:
return "LO_SPACE";
default:
UNREACHABLE();
}
return NULL;
}
void MarkCompactCollector::ComputeEvacuationHeuristics(
int area_size, int* target_fragmentation_percent,
int* max_evacuated_bytes) {
// For memory reducing mode we directly define both constants.
const int kTargetFragmentationPercentForReduceMemory = 20;
const int kMaxEvacuatedBytesForReduceMemory = 12 * Page::kPageSize;
// 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 int kMaxEvacuatedBytes = 4 * Page::kPageSize;
// Time to take for a single area (=payload of page). Used as soon as there
// exist enough compaction speed samples.
const int kTargetMsPerArea = 1;
if (heap()->ShouldReduceMemory()) {
*target_fragmentation_percent = kTargetFragmentationPercentForReduceMemory;
*max_evacuated_bytes = kMaxEvacuatedBytesForReduceMemory;
} 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();
int area_size = space->AreaSize();
// Pairs of (live_bytes_in_page, page).
typedef std::pair<int, Page*> LiveBytesPagePair;
std::vector<LiveBytesPagePair> pages;
pages.reserve(number_of_pages);
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
if (p->NeverEvacuate()) continue;
if (p->IsFlagSet(Page::BLACK_PAGE)) 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->old_to_old_slots());
CHECK_NULL(p->typed_old_to_old_slots());
CHECK(p->SweepingDone());
DCHECK(p->area_size() == area_size);
pages.push_back(std::make_pair(p->LiveBytesFromFreeList(), p));
}
int candidate_count = 0;
int 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) {
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.
int max_evacuated_bytes;
int target_fragmentation_percent;
ComputeEvacuationHeuristics(area_size, &target_fragmentation_percent,
&max_evacuated_bytes);
const intptr_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++) {
int live_bytes = pages[i].first;
int 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=%d "
"fragmentation_limit_kb=%" V8PRIdPTR
" fragmentation_limit_percent=%d sum_compaction_kb=%d "
"compaction_limit_kb=%d\n",
AllocationSpaceName(space->identity()), 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 = (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=%d\n",
AllocationSpaceName(space->identity()), 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_.Rewind(0);
}
DCHECK_EQ(0, evacuation_candidates_.length());
}
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);
if (sweeping_in_progress()) {
// Instead of waiting we could also abort the sweeper threads here.
EnsureSweepingCompleted();
}
// If concurrent unmapping tasks are still running, we should wait for
// them here.
heap()->WaitUntilUnmappingOfFreeChunksCompleted();
// Clear marking bits if incremental marking is aborted.
if (was_marked_incrementally_ && heap_->ShouldAbortIncrementalMarking()) {
heap()->incremental_marking()->Stop();
ClearMarkbits();
AbortWeakCollections();
AbortWeakCells();
AbortTransitionArrays();
AbortCompaction();
was_marked_incrementally_ = false;
}
// 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(NON_INCREMENTAL_COMPACTION);
}
PagedSpaces spaces(heap());
for (PagedSpace* space = spaces.next(); space != NULL;
space = spaces.next()) {
space->PrepareForMarkCompact();
}
#ifdef VERIFY_HEAP
if (!was_marked_incrementally_ && FLAG_verify_heap) {
VerifyMarkbitsAreClean();
}
#endif
}
void MarkCompactCollector::Finish() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_FINISH);
if (sweeper().contains_late_pages() && FLAG_concurrent_sweeping) {
// If we added some more pages during MC, we need to start at least one
// more task as all other tasks might already be finished.
sweeper().StartSweepingHelper(OLD_SPACE);
}
// The hashing of weak_object_to_code_table is no longer valid.
heap()->weak_object_to_code_table()->Rehash(
heap()->isolate()->factory()->undefined_value());
// Clear the marking state of live large objects.
heap_->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 cache is not traversed during GC; clear the cache to
// force lazy re-initialization of it. This must be done after the
// GC, because it relies on the new address of certain old space
// objects (empty string, illegal builtin).
isolate()->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;
}
heap_->incremental_marking()->ClearIdleMarkingDelayCounter();
if (marking_parity_ == EVEN_MARKING_PARITY) {
marking_parity_ = ODD_MARKING_PARITY;
} else {
DCHECK(marking_parity_ == ODD_MARKING_PARITY);
marking_parity_ = EVEN_MARKING_PARITY;
}
}
// -------------------------------------------------------------------------
// Phase 1: tracing and marking live objects.
// before: all objects are in normal state.
// after: a live object's map pointer is marked as '00'.
// Marking all live objects in the heap as part of mark-sweep or mark-compact
// collection. Before marking, all objects are in their normal state. After
// marking, live objects' map pointers are marked indicating that the object
// has been found reachable.
//
// The marking algorithm is a (mostly) depth-first (because of possible stack
// overflow) traversal of the graph of objects reachable from the roots. It
// uses an explicit stack of pointers rather than recursion. The young
// generation's inactive ('from') space is used as a marking stack. The
// objects in the marking stack are the ones that have been reached and marked
// but their children have not yet been visited.
//
// The marking stack can overflow during traversal. In that case, we set an
// overflow flag. When the overflow flag is set, we continue marking objects
// reachable from the objects on the marking stack, but no longer push them on
// the marking stack. Instead, we mark them as both marked and overflowed.
// When the stack is in the overflowed state, objects marked as overflowed
// have been reached and marked but their children have not been visited yet.
// After emptying the marking stack, we clear the overflow flag and traverse
// the heap looking for objects marked as overflowed, push them on the stack,
// and continue with marking. This process repeats until all reachable
// objects have been marked.
void CodeFlusher::ProcessJSFunctionCandidates() {
Code* lazy_compile = isolate_->builtins()->builtin(Builtins::kCompileLazy);
Object* undefined = isolate_->heap()->undefined_value();
JSFunction* candidate = jsfunction_candidates_head_;
JSFunction* next_candidate;
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
ClearNextCandidate(candidate, undefined);
SharedFunctionInfo* shared = candidate->shared();
Code* code = shared->code();
MarkBit code_mark = Marking::MarkBitFrom(code);
if (Marking::IsWhite(code_mark)) {
if (FLAG_trace_code_flushing && shared->is_compiled()) {
PrintF("[code-flushing clears: ");
shared->ShortPrint();
PrintF(" - age: %d]\n", code->GetAge());
}
// Always flush the optimized code map if there is one.
if (!shared->OptimizedCodeMapIsCleared()) {
shared->ClearOptimizedCodeMap();
}
shared->set_code(lazy_compile);
candidate->set_code(lazy_compile);
} else {
DCHECK(Marking::IsBlack(code_mark));
candidate->set_code(code);
}
// We are in the middle of a GC cycle so the write barrier in the code
// setter did not record the slot update and we have to do that manually.
Address slot = candidate->address() + JSFunction::kCodeEntryOffset;
Code* target = Code::cast(Code::GetObjectFromEntryAddress(slot));
isolate_->heap()->mark_compact_collector()->RecordCodeEntrySlot(
candidate, slot, target);
Object** shared_code_slot =
HeapObject::RawField(shared, SharedFunctionInfo::kCodeOffset);
isolate_->heap()->mark_compact_collector()->RecordSlot(
shared, shared_code_slot, *shared_code_slot);
candidate = next_candidate;
}
jsfunction_candidates_head_ = NULL;
}
void CodeFlusher::ProcessSharedFunctionInfoCandidates() {
Code* lazy_compile = isolate_->builtins()->builtin(Builtins::kCompileLazy);
SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
SharedFunctionInfo* next_candidate;
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
ClearNextCandidate(candidate);
Code* code = candidate->code();
MarkBit code_mark = Marking::MarkBitFrom(code);
if (Marking::IsWhite(code_mark)) {
if (FLAG_trace_code_flushing && candidate->is_compiled()) {
PrintF("[code-flushing clears: ");
candidate->ShortPrint();
PrintF(" - age: %d]\n", code->GetAge());
}
// Always flush the optimized code map if there is one.
if (!candidate->OptimizedCodeMapIsCleared()) {
candidate->ClearOptimizedCodeMap();
}
candidate->set_code(lazy_compile);
}
Object** code_slot =
HeapObject::RawField(candidate, SharedFunctionInfo::kCodeOffset);
isolate_->heap()->mark_compact_collector()->RecordSlot(candidate, code_slot,
*code_slot);
candidate = next_candidate;
}
shared_function_info_candidates_head_ = NULL;
}
void CodeFlusher::EvictCandidate(SharedFunctionInfo* shared_info) {
// Make sure previous flushing decisions are revisited.
isolate_->heap()->incremental_marking()->IterateBlackObject(shared_info);
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing abandons function-info: ");
shared_info->ShortPrint();
PrintF("]\n");
}
SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
SharedFunctionInfo* next_candidate;
if (candidate == shared_info) {
next_candidate = GetNextCandidate(shared_info);
shared_function_info_candidates_head_ = next_candidate;
ClearNextCandidate(shared_info);
} else {
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
if (next_candidate == shared_info) {
next_candidate = GetNextCandidate(shared_info);
SetNextCandidate(candidate, next_candidate);
ClearNextCandidate(shared_info);
break;
}
candidate = next_candidate;
}
}
}
void CodeFlusher::EvictCandidate(JSFunction* function) {
DCHECK(!function->next_function_link()->IsUndefined());
Object* undefined = isolate_->heap()->undefined_value();
// Make sure previous flushing decisions are revisited.
isolate_->heap()->incremental_marking()->IterateBlackObject(function);
isolate_->heap()->incremental_marking()->IterateBlackObject(
function->shared());
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing abandons closure: ");
function->shared()->ShortPrint();
PrintF("]\n");
}
JSFunction* candidate = jsfunction_candidates_head_;
JSFunction* next_candidate;
if (candidate == function) {
next_candidate = GetNextCandidate(function);
jsfunction_candidates_head_ = next_candidate;
ClearNextCandidate(function, undefined);
} else {
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
if (next_candidate == function) {
next_candidate = GetNextCandidate(function);
SetNextCandidate(candidate, next_candidate);
ClearNextCandidate(function, undefined);
break;
}
candidate = next_candidate;
}
}
}
void CodeFlusher::IteratePointersToFromSpace(ObjectVisitor* v) {
Heap* heap = isolate_->heap();
JSFunction** slot = &jsfunction_candidates_head_;
JSFunction* candidate = jsfunction_candidates_head_;
while (candidate != NULL) {
if (heap->InFromSpace(candidate)) {
v->VisitPointer(reinterpret_cast<Object**>(slot));
}
candidate = GetNextCandidate(*slot);
slot = GetNextCandidateSlot(*slot);
}
}
class MarkCompactMarkingVisitor
: public StaticMarkingVisitor<MarkCompactMarkingVisitor> {
public:
static void Initialize();
INLINE(static void VisitPointer(Heap* heap, HeapObject* object, Object** p)) {
MarkObjectByPointer(heap->mark_compact_collector(), object, p);
}
INLINE(static void VisitPointers(Heap* heap, HeapObject* object,
Object** start, Object** end)) {
// Mark all objects pointed to in [start, end).
const int kMinRangeForMarkingRecursion = 64;
if (end - start >= kMinRangeForMarkingRecursion) {
if (VisitUnmarkedObjects(heap, object, start, end)) return;
// We are close to a stack overflow, so just mark the objects.
}
MarkCompactCollector* collector = heap->mark_compact_collector();
for (Object** p = start; p < end; p++) {
MarkObjectByPointer(collector, object, p);
}
}
// Marks the object black and pushes it on the marking stack.
INLINE(static void MarkObject(Heap* heap, HeapObject* object)) {
MarkBit mark = Marking::MarkBitFrom(object);
heap->mark_compact_collector()->MarkObject(object, mark);
}
// Marks the object black without pushing it on the marking stack.
// Returns true if object needed marking and false otherwise.
INLINE(static bool MarkObjectWithoutPush(Heap* heap, HeapObject* object)) {
MarkBit mark_bit = Marking::MarkBitFrom(object);
if (Marking::IsWhite(mark_bit)) {
heap->mark_compact_collector()->SetMark(object, mark_bit);
return true;
}
return false;
}
// Mark object pointed to by p.
INLINE(static void MarkObjectByPointer(MarkCompactCollector* collector,
HeapObject* object, Object** p)) {
if (!(*p)->IsHeapObject()) return;
HeapObject* target_object = HeapObject::cast(*p);
collector->RecordSlot(object, p, target_object);
MarkBit mark = Marking::MarkBitFrom(target_object);
collector->MarkObject(target_object, mark);
}
// Visit an unmarked object.
INLINE(static void VisitUnmarkedObject(MarkCompactCollector* collector,
HeapObject* obj)) {
#ifdef DEBUG
DCHECK(collector->heap()->Contains(obj));
DCHECK(!collector->heap()->mark_compact_collector()->IsMarked(obj));
#endif
Map* map = obj->map();
Heap* heap = obj->GetHeap();
MarkBit mark = Marking::MarkBitFrom(obj);
heap->mark_compact_collector()->SetMark(obj, mark);
// Mark the map pointer and the body.
MarkBit map_mark = Marking::MarkBitFrom(map);
heap->mark_compact_collector()->MarkObject(map, map_mark);
IterateBody(map, obj);
}
// Visit all unmarked objects pointed to by [start, end).
// Returns false if the operation fails (lack of stack space).
INLINE(static bool VisitUnmarkedObjects(Heap* heap, HeapObject* object,
Object** start, Object** end)) {
// Return false is we are close to the stack limit.
StackLimitCheck check(heap->isolate());
if (check.HasOverflowed()) return false;
MarkCompactCollector* collector = heap->mark_compact_collector();
// Visit the unmarked objects.
for (Object** p = start; p < end; p++) {
Object* o = *p;
if (!o->IsHeapObject()) continue;
collector->RecordSlot(object, p, o);
HeapObject* obj = HeapObject::cast(o);
MarkBit mark = Marking::MarkBitFrom(obj);
if (Marking::IsBlackOrGrey(mark)) continue;
VisitUnmarkedObject(collector, obj);
}
return true;
}
private:
// Code flushing support.
static const int kRegExpCodeThreshold = 5;
static void UpdateRegExpCodeAgeAndFlush(Heap* heap, JSRegExp* re,
bool is_one_byte) {
// Make sure that the fixed array is in fact initialized on the RegExp.
// We could potentially trigger a GC when initializing the RegExp.
if (HeapObject::cast(re->data())->map()->instance_type() !=
FIXED_ARRAY_TYPE)
return;
// Make sure this is a RegExp that actually contains code.
if (re->TypeTag() != JSRegExp::IRREGEXP) return;
Object* code = re->DataAt(JSRegExp::code_index(is_one_byte));
if (!code->IsSmi() &&
HeapObject::cast(code)->map()->instance_type() == CODE_TYPE) {
// Save a copy that can be reinstated if we need the code again.
re->SetDataAt(JSRegExp::saved_code_index(is_one_byte), code);
// Saving a copy might create a pointer into compaction candidate
// that was not observed by marker. This might happen if JSRegExp data
// was marked through the compilation cache before marker reached JSRegExp
// object.
FixedArray* data = FixedArray::cast(re->data());
if (Marking::IsBlackOrGrey(Marking::MarkBitFrom(data))) {
Object** slot =
data->data_start() + JSRegExp::saved_code_index(is_one_byte);
heap->mark_compact_collector()->RecordSlot(data, slot, code);
}
// Set a number in the 0-255 range to guarantee no smi overflow.
re->SetDataAt(JSRegExp::code_index(is_one_byte),
Smi::FromInt(heap->ms_count() & 0xff));
} else if (code->IsSmi()) {
int value = Smi::cast(code)->value();
// The regexp has not been compiled yet or there was a compilation error.
if (value == JSRegExp::kUninitializedValue ||
value == JSRegExp::kCompilationErrorValue) {
return;
}
// Check if we should flush now.
if (value == ((heap->ms_count() - kRegExpCodeThreshold) & 0xff)) {
re->SetDataAt(JSRegExp::code_index(is_one_byte),
Smi::FromInt(JSRegExp::kUninitializedValue));
re->SetDataAt(JSRegExp::saved_code_index(is_one_byte),
Smi::FromInt(JSRegExp::kUninitializedValue));
}
}
}
// Works by setting the current sweep_generation (as a smi) in the
// code object place in the data array of the RegExp and keeps a copy
// around that can be reinstated if we reuse the RegExp before flushing.
// If we did not use the code for kRegExpCodeThreshold mark sweep GCs
// we flush the code.
static void VisitRegExpAndFlushCode(Map* map, HeapObject* object) {
Heap* heap = map->GetHeap();
MarkCompactCollector* collector = heap->mark_compact_collector();
if (!collector->is_code_flushing_enabled()) {
VisitJSRegExp(map, object);
return;
}
JSRegExp* re = reinterpret_cast<JSRegExp*>(object);
// Flush code or set age on both one byte and two byte code.
UpdateRegExpCodeAgeAndFlush(heap, re, true);
UpdateRegExpCodeAgeAndFlush(heap, re, false);
// Visit the fields of the RegExp, including the updated FixedArray.
VisitJSRegExp(map, object);
}
};
void MarkCompactMarkingVisitor::Initialize() {
StaticMarkingVisitor<MarkCompactMarkingVisitor>::Initialize();
table_.Register(kVisitJSRegExp, &VisitRegExpAndFlushCode);
if (FLAG_track_gc_object_stats) {
ObjectStatsVisitor::Initialize(&table_);
}
}
class CodeMarkingVisitor : public ThreadVisitor {
public:
explicit CodeMarkingVisitor(MarkCompactCollector* collector)
: collector_(collector) {}
void VisitThread(Isolate* isolate, ThreadLocalTop* top) {
collector_->PrepareThreadForCodeFlushing(isolate, top);
}
private:
MarkCompactCollector* collector_;
};
class SharedFunctionInfoMarkingVisitor : public ObjectVisitor {
public:
explicit SharedFunctionInfoMarkingVisitor(MarkCompactCollector* collector)
: collector_(collector) {}
void VisitPointers(Object** start, Object** end) override {
for (Object** p = start; p < end; p++) VisitPointer(p);
}
void VisitPointer(Object** slot) override {
Object* obj = *slot;
if (obj->IsSharedFunctionInfo()) {
SharedFunctionInfo* shared = reinterpret_cast<SharedFunctionInfo*>(obj);
MarkBit shared_mark = Marking::MarkBitFrom(shared);
MarkBit code_mark = Marking::MarkBitFrom(shared->code());
collector_->MarkObject(shared->code(), code_mark);
collector_->MarkObject(shared, shared_mark);
}
}
private:
MarkCompactCollector* collector_;
};
void MarkCompactCollector::PrepareThreadForCodeFlushing(Isolate* isolate,
ThreadLocalTop* top) {
for (StackFrameIterator it(isolate, top); !it.done(); it.Advance()) {
// Note: for the frame that has a pending lazy deoptimization
// StackFrame::unchecked_code will return a non-optimized code object for
// the outermost function and StackFrame::LookupCode will return
// actual optimized code object.
StackFrame* frame = it.frame();
Code* code = frame->unchecked_code();
MarkBit code_mark = Marking::MarkBitFrom(code);
MarkObject(code, code_mark);
if (frame->is_optimized()) {
Code* optimized_code = frame->LookupCode();
MarkBit optimized_code_mark = Marking::MarkBitFrom(optimized_code);
MarkObject(optimized_code, optimized_code_mark);
}
}
}
void MarkCompactCollector::PrepareForCodeFlushing() {
// If code flushing is disabled, there is no need to prepare for it.
if (!is_code_flushing_enabled()) return;
// Make sure we are not referencing the code from the stack.
DCHECK(this == heap()->mark_compact_collector());
PrepareThreadForCodeFlushing(heap()->isolate(),
heap()->isolate()->thread_local_top());
// Iterate the archived stacks in all threads to check if
// the code is referenced.
CodeMarkingVisitor code_marking_visitor(this);
heap()->isolate()->thread_manager()->IterateArchivedThreads(
&code_marking_visitor);
SharedFunctionInfoMarkingVisitor visitor(this);
heap()->isolate()->compilation_cache()->IterateFunctions(&visitor);
heap()->isolate()->handle_scope_implementer()->Iterate(&visitor);
ProcessMarkingDeque();
}
// Visitor class for marking heap roots.
class RootMarkingVisitor : public ObjectVisitor {
public:
explicit RootMarkingVisitor(Heap* heap)
: collector_(heap->mark_compact_collector()) {}
void VisitPointer(Object** p) override { MarkObjectByPointer(p); }
void VisitPointers(Object** start, Object** end) override {
for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
}
// Skip the weak next code link in a code object, which is visited in
// ProcessTopOptimizedFrame.
void VisitNextCodeLink(Object** p) override {}
private:
void MarkObjectByPointer(Object** p) {
if (!(*p)->IsHeapObject()) return;
// Replace flat cons strings in place.
HeapObject* object = HeapObject::cast(*p);
MarkBit mark_bit = Marking::MarkBitFrom(object);
if (Marking::IsBlackOrGrey(mark_bit)) return;
Map* map = object->map();
// Mark the object.
collector_->SetMark(object, mark_bit);
// Mark the map pointer and body, and push them on the marking stack.
MarkBit map_mark = Marking::MarkBitFrom(map);
collector_->MarkObject(map, map_mark);
MarkCompactMarkingVisitor::IterateBody(map, object);
// Mark all the objects reachable from the map and body. May leave
// overflowed objects in the heap.
collector_->EmptyMarkingDeque();
}
MarkCompactCollector* collector_;
};
// Helper class for pruning the string table.
template <bool finalize_external_strings, bool record_slots>
class StringTableCleaner : public ObjectVisitor {
public:
StringTableCleaner(Heap* heap, HeapObject* table)
: heap_(heap), pointers_removed_(0), table_(table) {
DCHECK(!record_slots || table != nullptr);
}
void VisitPointers(Object** start, Object** end) override {
// Visit all HeapObject pointers in [start, end).
MarkCompactCollector* collector = heap_->mark_compact_collector();
for (Object** p = start; p < end; p++) {
Object* o = *p;
if (o->IsHeapObject()) {
if (Marking::IsWhite(Marking::MarkBitFrom(HeapObject::cast(o)))) {
if (finalize_external_strings) {
DCHECK(o->IsExternalString());
heap_->FinalizeExternalString(String::cast(*p));
} else {
pointers_removed_++;
}
// Set the entry to the_hole_value (as deleted).
*p = heap_->the_hole_value();
} else if (record_slots) {
// StringTable contains only old space strings.
DCHECK(!heap_->InNewSpace(o));
collector->RecordSlot(table_, p, o);
}
}
}
}
int PointersRemoved() {
DCHECK(!finalize_external_strings);
return pointers_removed_;
}
private:
Heap* heap_;
int pointers_removed_;
HeapObject* table_;
};
typedef StringTableCleaner<false, true> InternalizedStringTableCleaner;
typedef StringTableCleaner<true, false> ExternalStringTableCleaner;
// Implementation of WeakObjectRetainer for mark compact GCs. All marked objects
// are retained.
class MarkCompactWeakObjectRetainer : public WeakObjectRetainer {
public:
virtual Object* RetainAs(Object* object) {
MarkBit mark_bit = Marking::MarkBitFrom(HeapObject::cast(object));
DCHECK(!Marking::IsGrey(mark_bit));
if (Marking::IsBlack(mark_bit)) {
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.
AllocationSite* site = AllocationSite::cast(object);
site->MarkZombie();
site->GetHeap()->mark_compact_collector()->MarkAllocationSite(site);
return object;
} else {
return NULL;
}
}
};
// Fill the marking stack with overflowed objects returned by the given
// iterator. Stop when the marking stack is filled or the end of the space
// is reached, whichever comes first.
template <class T>
void MarkCompactCollector::DiscoverGreyObjectsWithIterator(T* it) {
// The caller should ensure that the marking stack is initially not full,
// so that we don't waste effort pointlessly scanning for objects.
DCHECK(!marking_deque()->IsFull());
Map* filler_map = heap()->one_pointer_filler_map();
for (HeapObject* object = it->Next(); object != NULL; object = it->Next()) {
MarkBit markbit = Marking::MarkBitFrom(object);
if ((object->map() != filler_map) && Marking::IsGrey(markbit)) {
Marking::GreyToBlack(markbit);
PushBlack(object);
if (marking_deque()->IsFull()) return;
}
}
}
void MarkCompactCollector::DiscoverGreyObjectsOnPage(MemoryChunk* p) {
DCHECK(!marking_deque()->IsFull());
LiveObjectIterator<kGreyObjects> it(p);
HeapObject* object = NULL;
while ((object = it.Next()) != NULL) {
MarkBit markbit = Marking::MarkBitFrom(object);
DCHECK(Marking::IsGrey(markbit));
Marking::GreyToBlack(markbit);
PushBlack(object);
if (marking_deque()->IsFull()) return;
}
}
class RecordMigratedSlotVisitor final : public ObjectVisitor {
public:
inline void VisitPointer(Object** p) final {
RecordMigratedSlot(*p, reinterpret_cast<Address>(p));
}
inline void VisitPointers(Object** start, Object** end) final {
while (start < end) {
RecordMigratedSlot(*start, reinterpret_cast<Address>(start));
++start;
}
}
inline void VisitCodeEntry(Address code_entry_slot) final {
Address code_entry = Memory::Address_at(code_entry_slot);
if (Page::FromAddress(code_entry)->IsEvacuationCandidate()) {
RememberedSet<OLD_TO_OLD>::InsertTyped(Page::FromAddress(code_entry_slot),
CODE_ENTRY_SLOT, code_entry_slot);
}
}
private:
inline void RecordMigratedSlot(Object* value, Address slot) {
if (value->IsHeapObject()) {
Page* p = Page::FromAddress(reinterpret_cast<Address>(value));
if (p->InNewSpace()) {
RememberedSet<OLD_TO_NEW>::Insert(Page::FromAddress(slot), slot);
} else if (p->IsEvacuationCandidate()) {
RememberedSet<OLD_TO_OLD>::Insert(Page::FromAddress(slot), slot);
}
}
}
};
class MarkCompactCollector::HeapObjectVisitor {
public:
virtual ~HeapObjectVisitor() {}
virtual bool Visit(HeapObject* object) = 0;
};
class MarkCompactCollector::EvacuateVisitorBase
: public MarkCompactCollector::HeapObjectVisitor {
protected:
enum MigrationMode { kFast, kProfiled };
EvacuateVisitorBase(Heap* heap, CompactionSpaceCollection* compaction_spaces)
: heap_(heap),
compaction_spaces_(compaction_spaces),
profiling_(
heap->isolate()->cpu_profiler()->is_profiling() ||
heap->isolate()->logger()->is_logging_code_events() ||
heap->isolate()->heap_profiler()->is_tracking_object_moves()) {}
inline bool TryEvacuateObject(PagedSpace* target_space, HeapObject* object,
HeapObject** target_object) {
int size = object->Size();
AllocationAlignment alignment = object->RequiredAlignment();
AllocationResult allocation = target_space->AllocateRaw(size, alignment);
if (allocation.To(target_object)) {
MigrateObject(*target_object, object, size, target_space->identity());
return true;
}
return false;
}
inline void MigrateObject(HeapObject* dst, HeapObject* src, int size,
AllocationSpace dest) {
if (profiling_) {
MigrateObject<kProfiled>(dst, src, size, dest);
} else {
MigrateObject<kFast>(dst, src, size, dest);
}
}
template <MigrationMode mode>
inline void MigrateObject(HeapObject* dst, HeapObject* src, int size,
AllocationSpace dest) {
Address dst_addr = dst->address();
Address src_addr = src->address();
DCHECK(heap_->AllowedToBeMigrated(src, dest));
DCHECK(dest != LO_SPACE);
if (dest == OLD_SPACE) {
DCHECK_OBJECT_SIZE(size);
DCHECK(IsAligned(size, kPointerSize));
heap_->CopyBlock(dst_addr, src_addr, size);
if ((mode == kProfiled) && FLAG_ignition && dst->IsBytecodeArray()) {
PROFILE(heap_->isolate(),
CodeMoveEvent(AbstractCode::cast(src), dst_addr));
}
RecordMigratedSlotVisitor visitor;
dst->IterateBodyFast(dst->map()->instance_type(), size, &visitor);
} else if (dest == CODE_SPACE) {
DCHECK_CODEOBJECT_SIZE(size, heap_->code_space());
if (mode == kProfiled) {
PROFILE(heap_->isolate(),
CodeMoveEvent(AbstractCode::cast(src), dst_addr));
}
heap_->CopyBlock(dst_addr, src_addr, size);
RememberedSet<OLD_TO_OLD>::InsertTyped(Page::FromAddress(dst_addr),
RELOCATED_CODE_OBJECT, dst_addr);
Code::cast(dst)->Relocate(dst_addr - src_addr);
} else {
DCHECK_OBJECT_SIZE(size);
DCHECK(dest == NEW_SPACE);
heap_->CopyBlock(dst_addr, src_addr, size);
}
if (mode == kProfiled) {
heap_->OnMoveEvent(dst, src, size);
}
Memory::Address_at(src_addr) = dst_addr;
}
Heap* heap_;
CompactionSpaceCollection* compaction_spaces_;
bool profiling_;
};
class MarkCompactCollector::EvacuateNewSpaceVisitor final
: public MarkCompactCollector::EvacuateVisitorBase {
public:
static const intptr_t kLabSize = 4 * KB;
static const intptr_t kMaxLabObjectSize = 256;
explicit EvacuateNewSpaceVisitor(Heap* heap,
CompactionSpaceCollection* compaction_spaces,
HashMap* local_pretenuring_feedback)
: EvacuateVisitorBase(heap, compaction_spaces),
buffer_(LocalAllocationBuffer::InvalidBuffer()),
space_to_allocate_(NEW_SPACE),
promoted_size_(0),
semispace_copied_size_(0),
local_pretenuring_feedback_(local_pretenuring_feedback) {}
inline bool Visit(HeapObject* object) override {
heap_->UpdateAllocationSite<Heap::kCached>(object,
local_pretenuring_feedback_);
int size = object->Size();
HeapObject* target_object = nullptr;
if (heap_->ShouldBePromoted(object->address(), size) &&
TryEvacuateObject(compaction_spaces_->Get(OLD_SPACE), object,
&target_object)) {
// If we end up needing more special cases, we should factor this out.
if (V8_UNLIKELY(target_object->IsJSArrayBuffer())) {
heap_->array_buffer_tracker()->Promote(
JSArrayBuffer::cast(target_object));
}
promoted_size_ += size;
return true;
}
HeapObject* target = nullptr;
AllocationSpace space = AllocateTargetObject(object, &target);
MigrateObject(HeapObject::cast(target), object, size, space);
if (V8_UNLIKELY(target->IsJSArrayBuffer())) {
heap_->array_buffer_tracker()->MarkLive(JSArrayBuffer::cast(target));
}
semispace_copied_size_ += size;
return true;
}
intptr_t promoted_size() { return promoted_size_; }
intptr_t semispace_copied_size() { return semispace_copied_size_; }
private:
enum NewSpaceAllocationMode {
kNonstickyBailoutOldSpace,
kStickyBailoutOldSpace,
};
inline AllocationSpace AllocateTargetObject(HeapObject* old_object,
HeapObject** target_object) {
const int size = old_object->Size();
AllocationAlignment alignment = old_object->RequiredAlignment();
AllocationResult allocation;
if (space_to_allocate_ == NEW_SPACE) {
if (size > kMaxLabObjectSize) {
allocation =
AllocateInNewSpace(size, alignment, kNonstickyBailoutOldSpace);
} else {
allocation = AllocateInLab(size, alignment);
}
}
if (allocation.IsRetry() || (space_to_allocate_ == OLD_SPACE)) {
allocation = AllocateInOldSpace(size, alignment);
}
bool ok = allocation.To(target_object);
DCHECK(ok);
USE(ok);
return space_to_allocate_;
}
inline bool NewLocalAllocationBuffer() {
AllocationResult result =
AllocateInNewSpace(kLabSize, kWordAligned, kStickyBailoutOldSpace);
LocalAllocationBuffer saved_old_buffer = buffer_;
buffer_ = LocalAllocationBuffer::FromResult(heap_, result, kLabSize);
if (buffer_.IsValid()) {
buffer_.TryMerge(&saved_old_buffer);
return true;
}
return false;
}
inline AllocationResult AllocateInNewSpace(int size_in_bytes,
AllocationAlignment alignment,
NewSpaceAllocationMode mode) {
AllocationResult allocation =
heap_->new_space()->AllocateRawSynchronized(size_in_bytes, alignment);
if (allocation.IsRetry()) {
if (!heap_->new_space()->AddFreshPageSynchronized()) {
if (mode == kStickyBailoutOldSpace) space_to_allocate_ = OLD_SPACE;
} else {
allocation = heap_->new_space()->AllocateRawSynchronized(size_in_bytes,
alignment);
if (allocation.IsRetry()) {
if (mode == kStickyBailoutOldSpace) space_to_allocate_ = OLD_SPACE;
}
}
}
return allocation;
}
inline AllocationResult AllocateInOldSpace(int size_in_bytes,
AllocationAlignment alignment) {
AllocationResult allocation =
compaction_spaces_->Get(OLD_SPACE)->AllocateRaw(size_in_bytes,
alignment);
if (allocation.IsRetry()) {
v8::internal::Heap::FatalProcessOutOfMemory(
"MarkCompactCollector: semi-space copy, fallback in old gen", true);
}
return allocation;
}
inline AllocationResult AllocateInLab(int size_in_bytes,
AllocationAlignment alignment) {
AllocationResult allocation;
if (!buffer_.IsValid()) {
if (!NewLocalAllocationBuffer()) {
space_to_allocate_ = OLD_SPACE;
return AllocationResult::Retry(OLD_SPACE);
}
}
allocation = buffer_.AllocateRawAligned(size_in_bytes, alignment);
if (allocation.IsRetry()) {
if (!NewLocalAllocationBuffer()) {
space_to_allocate_ = OLD_SPACE;
return AllocationResult::Retry(OLD_SPACE);
} else {
allocation = buffer_.AllocateRawAligned(size_in_bytes, alignment);
if (allocation.IsRetry()) {
space_to_allocate_ = OLD_SPACE;
return AllocationResult::Retry(OLD_SPACE);
}
}
}
return allocation;
}
LocalAllocationBuffer buffer_;
AllocationSpace space_to_allocate_;
intptr_t promoted_size_;
intptr_t semispace_copied_size_;
HashMap* local_pretenuring_feedback_;
};
class MarkCompactCollector::EvacuateNewSpacePageVisitor final
: public MarkCompactCollector::HeapObjectVisitor {
public:
EvacuateNewSpacePageVisitor() : promoted_size_(0) {}
static void MoveToOldSpace(Page* page, PagedSpace* owner) {
page->heap()->new_space()->ReplaceWithEmptyPage(page);
Page* new_page = Page::ConvertNewToOld(page, owner);
new_page->SetFlag(Page::PAGE_NEW_OLD_PROMOTION);
}
inline bool Visit(HeapObject* object) {
if (V8_UNLIKELY(object->IsJSArrayBuffer())) {
object->GetHeap()->array_buffer_tracker()->Promote(
JSArrayBuffer::cast(object));
}
RecordMigratedSlotVisitor visitor;
object->IterateBodyFast(&visitor);
promoted_size_ += object->Size();
return true;
}
intptr_t promoted_size() { return promoted_size_; }
private:
intptr_t promoted_size_;
};
class MarkCompactCollector::EvacuateOldSpaceVisitor final
: public MarkCompactCollector::EvacuateVisitorBase {
public:
EvacuateOldSpaceVisitor(Heap* heap,
CompactionSpaceCollection* compaction_spaces)
: EvacuateVisitorBase(heap, compaction_spaces) {}
inline bool Visit(HeapObject* object) override {
CompactionSpace* target_space = compaction_spaces_->Get(
Page::FromAddress(object->address())->owner()->identity());
HeapObject* target_object = nullptr;
if (TryEvacuateObject(target_space, object, &target_object)) {
DCHECK(object->map_word().IsForwardingAddress());
return true;
}
return false;
}
};
class MarkCompactCollector::EvacuateRecordOnlyVisitor final
: public MarkCompactCollector::HeapObjectVisitor {
public:
explicit EvacuateRecordOnlyVisitor(AllocationSpace space) : space_(space) {}
inline bool Visit(HeapObject* object) {
if (space_ == OLD_SPACE) {
RecordMigratedSlotVisitor visitor;
object->IterateBody(&visitor);
} else {
DCHECK_EQ(space_, CODE_SPACE);
// Add a typed slot for the whole code object.
RememberedSet<OLD_TO_OLD>::InsertTyped(
Page::FromAddress(object->address()), RELOCATED_CODE_OBJECT,
object->address());
}
return true;
}
private:
AllocationSpace space_;
};
void MarkCompactCollector::DiscoverGreyObjectsInSpace(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
if (!p->IsFlagSet(Page::BLACK_PAGE)) {
DiscoverGreyObjectsOnPage(p);
}
if (marking_deque()->IsFull()) return;
}
}
void MarkCompactCollector::DiscoverGreyObjectsInNewSpace() {
NewSpace* space = heap()->new_space();
NewSpacePageIterator it(space->bottom(), space->top());
while (it.has_next()) {
Page* page = it.next();
DiscoverGreyObjectsOnPage(page);
if (marking_deque()->IsFull()) return;
}
}
bool MarkCompactCollector::IsUnmarkedHeapObject(Object** p) {
Object* o = *p;
if (!o->IsHeapObject()) return false;
HeapObject* heap_object = HeapObject::cast(o);
MarkBit mark = Marking::MarkBitFrom(heap_object);
return Marking::IsWhite(mark);
}
bool MarkCompactCollector::IsUnmarkedHeapObjectWithHeap(Heap* heap,
Object** p) {
Object* o = *p;
DCHECK(o->IsHeapObject());
HeapObject* heap_object = HeapObject::cast(o);
MarkBit mark = Marking::MarkBitFrom(heap_object);
return Marking::IsWhite(mark);
}
void MarkCompactCollector::MarkStringTable(RootMarkingVisitor* visitor) {
StringTable* string_table = heap()->string_table();
// Mark the string table itself.
MarkBit string_table_mark = Marking::MarkBitFrom(string_table);
if (Marking::IsWhite(string_table_mark)) {
// String table could have already been marked by visiting the handles list.
SetMark(string_table, string_table_mark);
}
// Explicitly mark the prefix.
string_table->IteratePrefix(visitor);
ProcessMarkingDeque();
}
void MarkCompactCollector::MarkAllocationSite(AllocationSite* site) {
MarkBit mark_bit = Marking::MarkBitFrom(site);
SetMark(site, mark_bit);
}
void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
// Mark the heap roots including global variables, stack variables,
// etc., and all objects reachable from them.
heap()->IterateStrongRoots(visitor, VISIT_ONLY_STRONG);
// Handle the string table specially.
MarkStringTable(visitor);
// There may be overflowed objects in the heap. Visit them now.
while (marking_deque_.overflowed()) {
RefillMarkingDeque();
EmptyMarkingDeque();
}
}
void MarkCompactCollector::MarkImplicitRefGroups(
MarkObjectFunction mark_object) {
List<ImplicitRefGroup*>* ref_groups =
isolate()->global_handles()->implicit_ref_groups();
int last = 0;
for (int i = 0; i < ref_groups->length(); i++) {
ImplicitRefGroup* entry = ref_groups->at(i);
DCHECK(entry != NULL);
if (!IsMarked(*entry->parent)) {
(*ref_groups)[last++] = entry;
continue;
}
Object*** children = entry->children;
// A parent object is marked, so mark all child heap objects.
for (size_t j = 0; j < entry->length; ++j) {
if ((*children[j])->IsHeapObject()) {
mark_object(heap(), HeapObject::cast(*children[j]));
}
}
// Once the entire group has been marked, dispose it because it's
// not needed anymore.
delete entry;
}
ref_groups->Rewind(last);
}
// Mark all objects reachable from the objects on the marking stack.
// Before: the marking stack contains zero or more heap object pointers.
// After: the marking stack is empty, and all objects reachable from the
// marking stack have been marked, or are overflowed in the heap.
void MarkCompactCollector::EmptyMarkingDeque() {
Map* filler_map = heap_->one_pointer_filler_map();
while (!marking_deque_.IsEmpty()) {
HeapObject* object = marking_deque_.Pop();
// Explicitly skip one word fillers. Incremental markbit patterns are
// correct only for objects that occupy at least two words.
Map* map = object->map();
if (map == filler_map) continue;
DCHECK(object->IsHeapObject());
DCHECK(heap()->Contains(object));
DCHECK(!Marking::IsWhite(Marking::MarkBitFrom(object)));
MarkBit map_mark = Marking::MarkBitFrom(map);
MarkObject(map, map_mark);
MarkCompactMarkingVisitor::IterateBody(map, object);
}
}
// Sweep the heap for overflowed objects, clear their overflow bits, and
// push them on the marking stack. Stop early if the marking stack fills
// before sweeping completes. If sweeping completes, there are no remaining
// overflowed objects in the heap so the overflow flag on the markings stack
// is cleared.
void MarkCompactCollector::RefillMarkingDeque() {
isolate()->CountUsage(v8::Isolate::UseCounterFeature::kMarkDequeOverflow);
DCHECK(marking_deque_.overflowed());
DiscoverGreyObjectsInNewSpace();
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap()->old_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap()->code_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap()->map_space());
if (marking_deque_.IsFull()) return;
LargeObjectIterator lo_it(heap()->lo_space());
DiscoverGreyObjectsWithIterator(&lo_it);
if (marking_deque_.IsFull()) return;
marking_deque_.ClearOverflowed();
}
// Mark all objects reachable (transitively) from objects on the marking
// stack. Before: the marking stack contains zero or more heap object
// pointers. After: the marking stack is empty and there are no overflowed
// objects in the heap.
void MarkCompactCollector::ProcessMarkingDeque() {
EmptyMarkingDeque();
while (marking_deque_.overflowed()) {
RefillMarkingDeque();
EmptyMarkingDeque();
}
}
// Mark all objects reachable (transitively) from objects on the marking
// stack including references only considered in the atomic marking pause.
void MarkCompactCollector::ProcessEphemeralMarking(
ObjectVisitor* visitor, bool only_process_harmony_weak_collections) {
DCHECK(marking_deque_.IsEmpty() && !marking_deque_.overflowed());
bool work_to_do = true;
while (work_to_do) {
if (UsingEmbedderHeapTracer()) {
embedder_heap_tracer()->TraceWrappersFrom(wrappers_to_trace_);
wrappers_to_trace_.clear();
} else if (!only_process_harmony_weak_collections) {
isolate()->global_handles()->IterateObjectGroups(
visitor, &IsUnmarkedHeapObjectWithHeap);
MarkImplicitRefGroups(&MarkCompactMarkingVisitor::MarkObject);
}
ProcessWeakCollections();
work_to_do = !marking_deque_.IsEmpty();
ProcessMarkingDeque();
}
}
void MarkCompactCollector::ProcessTopOptimizedFrame(ObjectVisitor* visitor) {
for (StackFrameIterator it(isolate(), isolate()->thread_local_top());
!it.done(); it.Advance()) {
if (it.frame()->type() == StackFrame::JAVA_SCRIPT) {
return;
}
if (it.frame()->type() == StackFrame::OPTIMIZED) {
Code* code = it.frame()->LookupCode();
if (!code->CanDeoptAt(it.frame()->pc())) {
Code::BodyDescriptor::IterateBody(code, visitor);
}
ProcessMarkingDeque();
return;
}
}
}
void MarkCompactCollector::EnsureMarkingDequeIsReserved() {
DCHECK(!marking_deque_.in_use());
if (marking_deque_memory_ == NULL) {
marking_deque_memory_ = new base::VirtualMemory(kMaxMarkingDequeSize);
marking_deque_memory_committed_ = 0;
}
if (marking_deque_memory_ == NULL) {
V8::FatalProcessOutOfMemory("EnsureMarkingDequeIsReserved");
}
}
void MarkCompactCollector::EnsureMarkingDequeIsCommitted(size_t max_size) {
// If the marking deque is too small, we try to allocate a bigger one.
// If that fails, make do with a smaller one.
CHECK(!marking_deque_.in_use());
for (size_t size = max_size; size >= kMinMarkingDequeSize; size >>= 1) {
base::VirtualMemory* memory = marking_deque_memory_;
size_t currently_committed = marking_deque_memory_committed_;
if (currently_committed == size) return;
if (currently_committed > size) {
bool success = marking_deque_memory_->Uncommit(
reinterpret_cast<Address>(marking_deque_memory_->address()) + size,
currently_committed - size);
if (success) {
marking_deque_memory_committed_ = size;
return;
}
UNREACHABLE();
}
bool success = memory->Commit(
reinterpret_cast<Address>(memory->address()) + currently_committed,
size - currently_committed,
false); // Not executable.
if (success) {
marking_deque_memory_committed_ = size;
return;
}
}
V8::FatalProcessOutOfMemory("EnsureMarkingDequeIsCommitted");
}
void MarkCompactCollector::InitializeMarkingDeque() {
DCHECK(!marking_deque_.in_use());
DCHECK(marking_deque_memory_committed_ > 0);
Address addr = static_cast<Address>(marking_deque_memory_->address());
size_t size = marking_deque_memory_committed_;
if (FLAG_force_marking_deque_overflows) size = 64 * kPointerSize;
marking_deque_.Initialize(addr, addr + size);
}
void MarkingDeque::Initialize(Address low, Address high) {
DCHECK(!in_use_);
HeapObject** obj_low = reinterpret_cast<HeapObject**>(low);
HeapObject** obj_high = reinterpret_cast<HeapObject**>(high);
array_ = obj_low;
mask_ = base::bits::RoundDownToPowerOfTwo32(
static_cast<uint32_t>(obj_high - obj_low)) -
1;
top_ = bottom_ = 0;
overflowed_ = false;
in_use_ = true;
}
void MarkingDeque::Uninitialize(bool aborting) {
if (!aborting) {
DCHECK(IsEmpty());
DCHECK(!overflowed_);
}
DCHECK(in_use_);
top_ = bottom_ = 0xdecbad;
in_use_ = false;
}
void MarkCompactCollector::SetEmbedderHeapTracer(EmbedderHeapTracer* tracer) {
DCHECK_NOT_NULL(tracer);
CHECK_NULL(embedder_heap_tracer_);
embedder_heap_tracer_ = tracer;
}
void MarkCompactCollector::TracePossibleWrapper(JSObject* js_object) {
DCHECK(js_object->WasConstructedFromApiFunction());
if (js_object->GetInternalFieldCount() >= 2 &&
js_object->GetInternalField(0) &&
js_object->GetInternalField(0) != heap_->undefined_value() &&
js_object->GetInternalField(1) != heap_->undefined_value()) {
DCHECK(reinterpret_cast<intptr_t>(js_object->GetInternalField(0)) % 2 == 0);
wrappers_to_trace().push_back(std::pair<void*, void*>(
reinterpret_cast<void*>(js_object->GetInternalField(0)),
reinterpret_cast<void*>(js_object->GetInternalField(1))));
}
}
void MarkCompactCollector::RegisterExternallyReferencedObject(Object** object) {
DCHECK(in_use());
HeapObject* heap_object = HeapObject::cast(*object);
DCHECK(heap_->Contains(heap_object));
MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
MarkObject(heap_object, mark_bit);
}
void MarkCompactCollector::MarkLiveObjects() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK);
double start_time = 0.0;
if (FLAG_print_cumulative_gc_stat) {
start_time = heap_->MonotonicallyIncreasingTimeInMs();
}
// 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 {
// Abort any pending incremental activities e.g. incremental sweeping.
incremental_marking->Stop();
if (marking_deque_.in_use()) {
marking_deque_.Uninitialize(true);
}
}
}
#ifdef DEBUG
DCHECK(state_ == PREPARE_GC);
state_ = MARK_LIVE_OBJECTS;
#endif
EnsureMarkingDequeIsCommittedAndInitialize(
MarkCompactCollector::kMaxMarkingDequeSize);
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_PREPARE_CODE_FLUSH);
PrepareForCodeFlushing();
}
RootMarkingVisitor root_visitor(heap());
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_ROOTS);
MarkRoots(&root_visitor);
ProcessTopOptimizedFrame(&root_visitor);
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WEAK_CLOSURE);
// The objects reachable from the roots are marked, yet unreachable
// objects are unmarked. Mark objects reachable due to host
// application specific logic or through Harmony weak maps.
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_EPHEMERAL);
if (UsingEmbedderHeapTracer()) {
embedder_heap_tracer()->TracePrologue();
ProcessMarkingDeque();
}
ProcessEphemeralMarking(&root_visitor, false);
}
// The objects reachable from the roots, weak maps or object groups
// 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()->IdentifyWeakHandles(
&IsUnmarkedHeapObject);
ProcessMarkingDeque();
}
// Then we mark the objects.
{
TRACE_GC(heap()->tracer(),
GCTracer::Scope::MC_MARK_WEAK_CLOSURE_WEAK_ROOTS);
heap()->isolate()->global_handles()->IterateWeakRoots(&root_visitor);
ProcessMarkingDeque();
}
// Repeat Harmony weak maps marking to mark unmarked objects reachable from
// the weak roots we just marked as pending destruction.
//
// We only process harmony collections, as all object groups have been fully
// processed and no weakly reachable node can discover new objects groups.
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WEAK_CLOSURE_HARMONY);
ProcessEphemeralMarking(&root_visitor, true);
if (UsingEmbedderHeapTracer()) {
embedder_heap_tracer()->TraceEpilogue();
}
}
}
if (FLAG_print_cumulative_gc_stat) {
heap_->tracer()->AddMarkingTime(heap_->MonotonicallyIncreasingTimeInMs() -
start_time);
}
if (FLAG_track_gc_object_stats) {
if (FLAG_trace_gc_object_stats) {
heap()->object_stats_->TraceObjectStats();
}
heap()->object_stats_->CheckpointObjectStats();
}
}
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(), nullptr);
heap()->external_string_table_.Iterate(&external_visitor);
heap()->external_string_table_.CleanUp();
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_LISTS);
// Process the weak references.
MarkCompactWeakObjectRetainer mark_compact_object_retainer;
heap()->ProcessAllWeakReferences(&mark_compact_object_retainer);
}
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_GLOBAL_HANDLES);
// Remove object groups after marking phase.
heap()->isolate()->global_handles()->RemoveObjectGroups();
heap()->isolate()->global_handles()->RemoveImplicitRefGroups();
}
// Flush code from collected candidates.
if (is_code_flushing_enabled()) {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_CODE_FLUSH);
code_flusher_->ProcessCandidates();
}
DependentCode* dependent_code_list;
Object* non_live_map_list;
ClearWeakCells(&non_live_map_list, &dependent_code_list);
{
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_MAPS);
ClearSimpleMapTransitions(non_live_map_list);
ClearFullMapTransitions();
}
MarkDependentCodeForDeoptimization(dependent_code_list);
ClearWeakCollections();
ClearInvalidRememberedSetSlots();
}
void MarkCompactCollector::MarkDependentCodeForDeoptimization(
DependentCode* list_head) {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_DEPENDENT_CODE);
Isolate* isolate = this->isolate();
DependentCode* current = list_head;
while (current->length() > 0) {
have_code_to_deoptimize_ |= current->MarkCodeForDeoptimization(
isolate, DependentCode::kWeakCodeGroup);
current = current->next_link();
}
WeakHashTable* table = heap_->weak_object_to_code_table();
uint32_t capacity = table->Capacity();
for (uint32_t i = 0; i < capacity; i++) {
uint32_t key_index = table->EntryToIndex(i);
Object* key = table->get(key_index);
if (!table->IsKey(key)) continue;
uint32_t value_index = table->EntryToValueIndex(i);
Object* value = table->get(value_index);
DCHECK(key->IsWeakCell());
if (WeakCell::cast(key)->cleared()) {
have_code_to_deoptimize_ |=
DependentCode::cast(value)->MarkCodeForDeoptimization(
isolate, DependentCode::kWeakCodeGroup);
table->set(key_index, heap_->the_hole_value());
table->set(value_index, heap_->the_hole_value());
table->ElementRemoved();
}
}
}
void MarkCompactCollector::ClearSimpleMapTransitions(
Object* non_live_map_list) {
Object* the_hole_value = heap()->the_hole_value();
Object* weak_cell_obj = non_live_map_list;
while (weak_cell_obj != Smi::FromInt(0)) {
WeakCell* weak_cell = WeakCell::cast(weak_cell_obj);
Map* map = Map::cast(weak_cell->value());
DCHECK(Marking::IsWhite(Marking::MarkBitFrom(map)));
Object* potential_parent = map->constructor_or_backpointer();
if (potential_parent->IsMap()) {
Map* parent = Map::cast(potential_parent);
if (Marking::IsBlackOrGrey(Marking::MarkBitFrom(parent)) &&
parent->raw_transitions() == weak_cell) {
ClearSimpleMapTransition(parent, map);
}
}
weak_cell->clear();
weak_cell_obj = weak_cell->next();
weak_cell->clear_next(the_hole_value);
}
}
void MarkCompactCollector::ClearSimpleMapTransition(Map* map,
Map* dead_transition) {
// A previously existing simple transition (stored in a WeakCell) is going
// to be cleared. Clear the useless cell pointer, and take ownership
// of the descriptor array.
map->set_raw_transitions(Smi::FromInt(0));
int number_of_own_descriptors = map->NumberOfOwnDescriptors();
DescriptorArray* descriptors = map->instance_descriptors();
if (descriptors == dead_transition->instance_descriptors() &&
number_of_own_descriptors > 0) {
TrimDescriptorArray(map, descriptors);
DCHECK(descriptors->number_of_descriptors() == number_of_own_descriptors);
map->set_owns_descriptors(true);
}
}
void MarkCompactCollector::ClearFullMapTransitions() {
HeapObject* undefined = heap()->undefined_value();
Object* obj = heap()->encountered_transition_arrays();
while (obj != Smi::FromInt(0)) {
TransitionArray* array = TransitionArray::cast(obj);
int num_transitions = array->number_of_entries();
DCHECK_EQ(TransitionArray::NumberOfTransitions(array), num_transitions);
if (num_transitions > 0) {
Map* map = array->GetTarget(0);
Map* parent = Map::cast(map->constructor_or_backpointer());
bool parent_is_alive =
Marking::IsBlackOrGrey(Marking::MarkBitFrom(parent));
DescriptorArray* descriptors =
parent_is_alive ? parent->instance_descriptors() : nullptr;
bool descriptors_owner_died =
CompactTransitionArray(parent, array, descriptors);
if (descriptors_owner_died) {
TrimDescriptorArray(parent, descriptors);
}
}
obj = array->next_link();
array->set_next_link(undefined, SKIP_WRITE_BARRIER);
}
heap()->set_encountered_transition_arrays(Smi::FromInt(0));
}
bool MarkCompactCollector::CompactTransitionArray(
Map* map, TransitionArray* transitions, DescriptorArray* descriptors) {
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 (Marking::IsWhite(Marking::MarkBitFrom(target))) {
if (descriptors != nullptr &&
target->instance_descriptors() == descriptors) {
descriptors_owner_died = true;
}
} else {
if (i != transition_index) {
Name* key = transitions->GetKey(i);
transitions->SetKey(transition_index, key);
Object** key_slot = transitions->GetKeySlot(transition_index);
RecordSlot(transitions, key_slot, key);
// Target slots do not need to be recorded since maps are not compacted.
transitions->SetTarget(transition_index, transitions->GetTarget(i));
}
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 = TransitionArray::Capacity(transitions) - transition_index;
if (trim > 0) {
heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
transitions, trim * TransitionArray::kTransitionSize);
transitions->SetNumberOfTransitions(transition_index);
}
return descriptors_owner_died;
}
void MarkCompactCollector::TrimDescriptorArray(Map* map,
DescriptorArray* descriptors) {
int number_of_own_descriptors = map->NumberOfOwnDescriptors();
if (number_of_own_descriptors == 0) {
DCHECK(descriptors == heap_->empty_descriptor_array());
return;
}
int number_of_descriptors = descriptors->number_of_descriptors_storage();
int to_trim = number_of_descriptors - number_of_own_descriptors;
if (to_trim > 0) {
heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
descriptors, to_trim * DescriptorArray::kDescriptorSize);
descriptors->SetNumberOfDescriptors(number_of_own_descriptors);
if (descriptors->HasEnumCache()) 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->NumberOfDescribedProperties(OWN_DESCRIPTORS, ENUMERABLE_STRINGS);
}
if (live_enum == 0) return descriptors->ClearEnumCache();
FixedArray* enum_cache = descriptors->GetEnumCache();
int to_trim = enum_cache->length() - live_enum;
if (to_trim <= 0) return;
heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(
descriptors->GetEnumCache(), to_trim);
if (!descriptors->HasEnumIndicesCache()) return;
FixedArray* enum_indices_cache = descriptors->GetEnumIndicesCache();
heap_->RightTrimFixedArray<Heap::SEQUENTIAL_TO_SWEEPER>(enum_indices_cache,
to_trim);
}
void MarkCompactCollector::ProcessWeakCollections() {
Object* weak_collection_obj = heap()->encountered_weak_collections();
while (weak_collection_obj != Smi::FromInt(0)) {
JSWeakCollection* weak_collection =
reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
DCHECK(MarkCompactCollector::IsMarked(weak_collection));
if (weak_collection->table()->IsHashTable()) {
ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
for (int i = 0; i < table->Capacity(); i++) {
if (MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
Object** key_slot =
table->RawFieldOfElementAt(ObjectHashTable::EntryToIndex(i));
RecordSlot(table, key_slot, *key_slot);
Object** value_slot =
table->RawFieldOfElementAt(ObjectHashTable::EntryToValueIndex(i));
MarkCompactMarkingVisitor::MarkObjectByPointer(this, table,
value_slot);
}
}
}
weak_collection_obj = weak_collection->next();
}
}
void MarkCompactCollector::ClearWeakCollections() {
TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_COLLECTIONS);
Object* weak_collection_obj = heap()->encountered_weak_collections();
while (weak_collection_obj != Smi::FromInt(0)) {
JSWeakCollection* weak_collection =
reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
DCHECK(MarkCompactCollector::IsMarked(weak_collection));
if (weak_collection->table()->IsHashTable()) {
ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
for (int i = 0; i < table->Capacity(); i++) {
HeapObject* key = HeapObject::cast(table->KeyAt(i));
if (!MarkCompactCollector::IsMarked(key)) {
table->RemoveEntry(i);
}
}
}
weak_collection_obj = weak_collection->next();
weak_collection->