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      1 // Copyright 2012 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "src/heap/incremental-marking.h"
      6 
      7 #include "src/code-stubs.h"
      8 #include "src/compilation-cache.h"
      9 #include "src/conversions.h"
     10 #include "src/heap/gc-idle-time-handler.h"
     11 #include "src/heap/gc-tracer.h"
     12 #include "src/heap/mark-compact-inl.h"
     13 #include "src/heap/objects-visiting.h"
     14 #include "src/heap/objects-visiting-inl.h"
     15 #include "src/v8.h"
     16 
     17 namespace v8 {
     18 namespace internal {
     19 
     20 IncrementalMarking::StepActions IncrementalMarking::IdleStepActions() {
     21   return StepActions(IncrementalMarking::NO_GC_VIA_STACK_GUARD,
     22                      IncrementalMarking::FORCE_MARKING,
     23                      IncrementalMarking::DO_NOT_FORCE_COMPLETION);
     24 }
     25 
     26 
     27 IncrementalMarking::IncrementalMarking(Heap* heap)
     28     : heap_(heap),
     29       observer_(*this, kAllocatedThreshold),
     30       state_(STOPPED),
     31       is_compacting_(false),
     32       steps_count_(0),
     33       old_generation_space_available_at_start_of_incremental_(0),
     34       old_generation_space_used_at_start_of_incremental_(0),
     35       bytes_rescanned_(0),
     36       should_hurry_(false),
     37       marking_speed_(0),
     38       bytes_scanned_(0),
     39       allocated_(0),
     40       write_barriers_invoked_since_last_step_(0),
     41       idle_marking_delay_counter_(0),
     42       no_marking_scope_depth_(0),
     43       unscanned_bytes_of_large_object_(0),
     44       was_activated_(false),
     45       finalize_marking_completed_(false),
     46       incremental_marking_finalization_rounds_(0),
     47       request_type_(COMPLETE_MARKING) {}
     48 
     49 
     50 bool IncrementalMarking::BaseRecordWrite(HeapObject* obj, Object* value) {
     51   HeapObject* value_heap_obj = HeapObject::cast(value);
     52   MarkBit value_bit = Marking::MarkBitFrom(value_heap_obj);
     53   DCHECK(!Marking::IsImpossible(value_bit));
     54 
     55   MarkBit obj_bit = Marking::MarkBitFrom(obj);
     56   DCHECK(!Marking::IsImpossible(obj_bit));
     57   bool is_black = Marking::IsBlack(obj_bit);
     58 
     59   if (is_black && Marking::IsWhite(value_bit)) {
     60     WhiteToGreyAndPush(value_heap_obj, value_bit);
     61     RestartIfNotMarking();
     62   }
     63   return is_compacting_ && is_black;
     64 }
     65 
     66 
     67 void IncrementalMarking::RecordWriteSlow(HeapObject* obj, Object** slot,
     68                                          Object* value) {
     69   if (BaseRecordWrite(obj, value) && slot != NULL) {
     70     // Object is not going to be rescanned we need to record the slot.
     71     heap_->mark_compact_collector()->RecordSlot(obj, slot, value);
     72   }
     73 }
     74 
     75 
     76 void IncrementalMarking::RecordWriteFromCode(HeapObject* obj, Object** slot,
     77                                              Isolate* isolate) {
     78   DCHECK(obj->IsHeapObject());
     79   IncrementalMarking* marking = isolate->heap()->incremental_marking();
     80 
     81   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
     82   int counter = chunk->write_barrier_counter();
     83   if (counter < (MemoryChunk::kWriteBarrierCounterGranularity / 2)) {
     84     marking->write_barriers_invoked_since_last_step_ +=
     85         MemoryChunk::kWriteBarrierCounterGranularity -
     86         chunk->write_barrier_counter();
     87     chunk->set_write_barrier_counter(
     88         MemoryChunk::kWriteBarrierCounterGranularity);
     89   }
     90 
     91   marking->RecordWrite(obj, slot, *slot);
     92 }
     93 
     94 
     95 void IncrementalMarking::RecordCodeTargetPatch(Code* host, Address pc,
     96                                                HeapObject* value) {
     97   if (IsMarking()) {
     98     RelocInfo rinfo(heap_->isolate(), pc, RelocInfo::CODE_TARGET, 0, host);
     99     RecordWriteIntoCode(host, &rinfo, value);
    100   }
    101 }
    102 
    103 
    104 void IncrementalMarking::RecordCodeTargetPatch(Address pc, HeapObject* value) {
    105   if (IsMarking()) {
    106     Code* host = heap_->isolate()
    107                      ->inner_pointer_to_code_cache()
    108                      ->GcSafeFindCodeForInnerPointer(pc);
    109     RelocInfo rinfo(heap_->isolate(), pc, RelocInfo::CODE_TARGET, 0, host);
    110     RecordWriteIntoCode(host, &rinfo, value);
    111   }
    112 }
    113 
    114 
    115 void IncrementalMarking::RecordWriteOfCodeEntrySlow(JSFunction* host,
    116                                                     Object** slot,
    117                                                     Code* value) {
    118   if (BaseRecordWrite(host, value)) {
    119     DCHECK(slot != NULL);
    120     heap_->mark_compact_collector()->RecordCodeEntrySlot(
    121         host, reinterpret_cast<Address>(slot), value);
    122   }
    123 }
    124 
    125 
    126 void IncrementalMarking::RecordWriteIntoCodeSlow(HeapObject* obj,
    127                                                  RelocInfo* rinfo,
    128                                                  Object* value) {
    129   if (BaseRecordWrite(obj, value)) {
    130       // Object is not going to be rescanned.  We need to record the slot.
    131       heap_->mark_compact_collector()->RecordRelocSlot(rinfo,
    132                                                        Code::cast(value));
    133   }
    134 }
    135 
    136 
    137 void IncrementalMarking::RecordWrites(HeapObject* obj) {
    138   if (IsMarking()) {
    139     MarkBit obj_bit = Marking::MarkBitFrom(obj);
    140     if (Marking::IsBlack(obj_bit)) {
    141       MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
    142       if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
    143         chunk->set_progress_bar(0);
    144       }
    145       BlackToGreyAndUnshift(obj, obj_bit);
    146       RestartIfNotMarking();
    147     }
    148   }
    149 }
    150 
    151 
    152 void IncrementalMarking::BlackToGreyAndUnshift(HeapObject* obj,
    153                                                MarkBit mark_bit) {
    154   DCHECK(Marking::MarkBitFrom(obj) == mark_bit);
    155   DCHECK(obj->Size() >= 2 * kPointerSize);
    156   DCHECK(IsMarking());
    157   Marking::BlackToGrey(mark_bit);
    158   int obj_size = obj->Size();
    159   MemoryChunk::IncrementLiveBytesFromGC(obj, -obj_size);
    160   bytes_scanned_ -= obj_size;
    161   int64_t old_bytes_rescanned = bytes_rescanned_;
    162   bytes_rescanned_ = old_bytes_rescanned + obj_size;
    163   if ((bytes_rescanned_ >> 20) != (old_bytes_rescanned >> 20)) {
    164     if (bytes_rescanned_ > 2 * heap_->PromotedSpaceSizeOfObjects()) {
    165       // If we have queued twice the heap size for rescanning then we are
    166       // going around in circles, scanning the same objects again and again
    167       // as the program mutates the heap faster than we can incrementally
    168       // trace it.  In this case we switch to non-incremental marking in
    169       // order to finish off this marking phase.
    170       if (FLAG_trace_incremental_marking) {
    171         PrintIsolate(
    172             heap()->isolate(),
    173             "Hurrying incremental marking because of lack of progress\n");
    174       }
    175       marking_speed_ = kMaxMarkingSpeed;
    176     }
    177   }
    178 
    179   heap_->mark_compact_collector()->marking_deque()->Unshift(obj);
    180 }
    181 
    182 
    183 void IncrementalMarking::WhiteToGreyAndPush(HeapObject* obj, MarkBit mark_bit) {
    184   Marking::WhiteToGrey(mark_bit);
    185   heap_->mark_compact_collector()->marking_deque()->Push(obj);
    186 }
    187 
    188 
    189 static void MarkObjectGreyDoNotEnqueue(Object* obj) {
    190   if (obj->IsHeapObject()) {
    191     HeapObject* heap_obj = HeapObject::cast(obj);
    192     MarkBit mark_bit = Marking::MarkBitFrom(HeapObject::cast(obj));
    193     if (Marking::IsBlack(mark_bit)) {
    194       MemoryChunk::IncrementLiveBytesFromGC(heap_obj, -heap_obj->Size());
    195     }
    196     Marking::AnyToGrey(mark_bit);
    197   }
    198 }
    199 
    200 
    201 static inline void MarkBlackOrKeepBlack(HeapObject* heap_object,
    202                                         MarkBit mark_bit, int size) {
    203   DCHECK(!Marking::IsImpossible(mark_bit));
    204   if (Marking::IsBlack(mark_bit)) return;
    205   Marking::MarkBlack(mark_bit);
    206   MemoryChunk::IncrementLiveBytesFromGC(heap_object, size);
    207 }
    208 
    209 
    210 class IncrementalMarkingMarkingVisitor
    211     : public StaticMarkingVisitor<IncrementalMarkingMarkingVisitor> {
    212  public:
    213   static void Initialize() {
    214     StaticMarkingVisitor<IncrementalMarkingMarkingVisitor>::Initialize();
    215     table_.Register(kVisitFixedArray, &VisitFixedArrayIncremental);
    216     table_.Register(kVisitNativeContext, &VisitNativeContextIncremental);
    217     table_.Register(kVisitJSRegExp, &VisitJSRegExp);
    218   }
    219 
    220   static const int kProgressBarScanningChunk = 32 * 1024;
    221 
    222   static void VisitFixedArrayIncremental(Map* map, HeapObject* object) {
    223     MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());
    224     // TODO(mstarzinger): Move setting of the flag to the allocation site of
    225     // the array. The visitor should just check the flag.
    226     if (FLAG_use_marking_progress_bar &&
    227         chunk->owner()->identity() == LO_SPACE) {
    228       chunk->SetFlag(MemoryChunk::HAS_PROGRESS_BAR);
    229     }
    230     if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
    231       Heap* heap = map->GetHeap();
    232       // When using a progress bar for large fixed arrays, scan only a chunk of
    233       // the array and try to push it onto the marking deque again until it is
    234       // fully scanned. Fall back to scanning it through to the end in case this
    235       // fails because of a full deque.
    236       int object_size = FixedArray::BodyDescriptor::SizeOf(map, object);
    237       int start_offset =
    238           Max(FixedArray::BodyDescriptor::kStartOffset, chunk->progress_bar());
    239       int end_offset =
    240           Min(object_size, start_offset + kProgressBarScanningChunk);
    241       int already_scanned_offset = start_offset;
    242       bool scan_until_end = false;
    243       do {
    244         VisitPointers(heap, object, HeapObject::RawField(object, start_offset),
    245                       HeapObject::RawField(object, end_offset));
    246         start_offset = end_offset;
    247         end_offset = Min(object_size, end_offset + kProgressBarScanningChunk);
    248         scan_until_end =
    249             heap->mark_compact_collector()->marking_deque()->IsFull();
    250       } while (scan_until_end && start_offset < object_size);
    251       chunk->set_progress_bar(start_offset);
    252       if (start_offset < object_size) {
    253         if (Marking::IsGrey(Marking::MarkBitFrom(object))) {
    254           heap->mark_compact_collector()->marking_deque()->Unshift(object);
    255         } else {
    256           DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
    257           heap->mark_compact_collector()->UnshiftBlack(object);
    258         }
    259         heap->incremental_marking()->NotifyIncompleteScanOfObject(
    260             object_size - (start_offset - already_scanned_offset));
    261       }
    262     } else {
    263       FixedArrayVisitor::Visit(map, object);
    264     }
    265   }
    266 
    267   static void VisitNativeContextIncremental(Map* map, HeapObject* object) {
    268     Context* context = Context::cast(object);
    269 
    270     // We will mark cache black with a separate pass when we finish marking.
    271     // Note that GC can happen when the context is not fully initialized,
    272     // so the cache can be undefined.
    273     Object* cache = context->get(Context::NORMALIZED_MAP_CACHE_INDEX);
    274     if (!cache->IsUndefined()) {
    275       MarkObjectGreyDoNotEnqueue(cache);
    276     }
    277     VisitNativeContext(map, context);
    278   }
    279 
    280   INLINE(static void VisitPointer(Heap* heap, HeapObject* object, Object** p)) {
    281     Object* target = *p;
    282     if (target->IsHeapObject()) {
    283       heap->mark_compact_collector()->RecordSlot(object, p, target);
    284       MarkObject(heap, target);
    285     }
    286   }
    287 
    288   INLINE(static void VisitPointers(Heap* heap, HeapObject* object,
    289                                    Object** start, Object** end)) {
    290     for (Object** p = start; p < end; p++) {
    291       Object* target = *p;
    292       if (target->IsHeapObject()) {
    293         heap->mark_compact_collector()->RecordSlot(object, p, target);
    294         MarkObject(heap, target);
    295       }
    296     }
    297   }
    298 
    299   // Marks the object grey and pushes it on the marking stack.
    300   INLINE(static void MarkObject(Heap* heap, Object* obj)) {
    301     IncrementalMarking::MarkObject(heap, HeapObject::cast(obj));
    302   }
    303 
    304   // Marks the object black without pushing it on the marking stack.
    305   // Returns true if object needed marking and false otherwise.
    306   INLINE(static bool MarkObjectWithoutPush(Heap* heap, Object* obj)) {
    307     HeapObject* heap_object = HeapObject::cast(obj);
    308     MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
    309     if (Marking::IsWhite(mark_bit)) {
    310       Marking::MarkBlack(mark_bit);
    311       MemoryChunk::IncrementLiveBytesFromGC(heap_object, heap_object->Size());
    312       return true;
    313     }
    314     return false;
    315   }
    316 };
    317 
    318 
    319 class IncrementalMarkingRootMarkingVisitor : public ObjectVisitor {
    320  public:
    321   explicit IncrementalMarkingRootMarkingVisitor(
    322       IncrementalMarking* incremental_marking)
    323       : heap_(incremental_marking->heap()) {}
    324 
    325   void VisitPointer(Object** p) override { MarkObjectByPointer(p); }
    326 
    327   void VisitPointers(Object** start, Object** end) override {
    328     for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
    329   }
    330 
    331  private:
    332   void MarkObjectByPointer(Object** p) {
    333     Object* obj = *p;
    334     if (!obj->IsHeapObject()) return;
    335 
    336     IncrementalMarking::MarkObject(heap_, HeapObject::cast(obj));
    337   }
    338 
    339   Heap* heap_;
    340 };
    341 
    342 
    343 void IncrementalMarking::Initialize() {
    344   IncrementalMarkingMarkingVisitor::Initialize();
    345 }
    346 
    347 
    348 void IncrementalMarking::SetOldSpacePageFlags(MemoryChunk* chunk,
    349                                               bool is_marking,
    350                                               bool is_compacting) {
    351   if (is_marking) {
    352     chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    353     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    354   } else {
    355     chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    356     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    357   }
    358 }
    359 
    360 
    361 void IncrementalMarking::SetNewSpacePageFlags(MemoryChunk* chunk,
    362                                               bool is_marking) {
    363   chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    364   if (is_marking) {
    365     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    366   } else {
    367     chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    368   }
    369   chunk->SetFlag(MemoryChunk::SCAN_ON_SCAVENGE);
    370 }
    371 
    372 
    373 void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
    374     PagedSpace* space) {
    375   PageIterator it(space);
    376   while (it.has_next()) {
    377     Page* p = it.next();
    378     SetOldSpacePageFlags(p, false, false);
    379   }
    380 }
    381 
    382 
    383 void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
    384     NewSpace* space) {
    385   NewSpacePageIterator it(space);
    386   while (it.has_next()) {
    387     NewSpacePage* p = it.next();
    388     SetNewSpacePageFlags(p, false);
    389   }
    390 }
    391 
    392 
    393 void IncrementalMarking::DeactivateIncrementalWriteBarrier() {
    394   DeactivateIncrementalWriteBarrierForSpace(heap_->old_space());
    395   DeactivateIncrementalWriteBarrierForSpace(heap_->map_space());
    396   DeactivateIncrementalWriteBarrierForSpace(heap_->code_space());
    397   DeactivateIncrementalWriteBarrierForSpace(heap_->new_space());
    398 
    399   LargePage* lop = heap_->lo_space()->first_page();
    400   while (lop->is_valid()) {
    401     SetOldSpacePageFlags(lop, false, false);
    402     lop = lop->next_page();
    403   }
    404 }
    405 
    406 
    407 void IncrementalMarking::ActivateIncrementalWriteBarrier(PagedSpace* space) {
    408   PageIterator it(space);
    409   while (it.has_next()) {
    410     Page* p = it.next();
    411     SetOldSpacePageFlags(p, true, is_compacting_);
    412   }
    413 }
    414 
    415 
    416 void IncrementalMarking::ActivateIncrementalWriteBarrier(NewSpace* space) {
    417   NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
    418   while (it.has_next()) {
    419     NewSpacePage* p = it.next();
    420     SetNewSpacePageFlags(p, true);
    421   }
    422 }
    423 
    424 
    425 void IncrementalMarking::ActivateIncrementalWriteBarrier() {
    426   ActivateIncrementalWriteBarrier(heap_->old_space());
    427   ActivateIncrementalWriteBarrier(heap_->map_space());
    428   ActivateIncrementalWriteBarrier(heap_->code_space());
    429   ActivateIncrementalWriteBarrier(heap_->new_space());
    430 
    431   LargePage* lop = heap_->lo_space()->first_page();
    432   while (lop->is_valid()) {
    433     SetOldSpacePageFlags(lop, true, is_compacting_);
    434     lop = lop->next_page();
    435   }
    436 }
    437 
    438 
    439 bool IncrementalMarking::ShouldActivateEvenWithoutIdleNotification() {
    440   return CanBeActivated() &&
    441          heap_->HeapIsFullEnoughToStartIncrementalMarking(
    442              heap_->old_generation_allocation_limit());
    443 }
    444 
    445 
    446 bool IncrementalMarking::WasActivated() { return was_activated_; }
    447 
    448 
    449 bool IncrementalMarking::CanBeActivated() {
    450 #ifndef DEBUG
    451   static const intptr_t kActivationThreshold = 8 * MB;
    452 #else
    453   // TODO(gc) consider setting this to some low level so that some
    454   // debug tests run with incremental marking and some without.
    455   static const intptr_t kActivationThreshold = 0;
    456 #endif
    457   // Only start incremental marking in a safe state: 1) when incremental
    458   // marking is turned on, 2) when we are currently not in a GC, and
    459   // 3) when we are currently not serializing or deserializing the heap.
    460   // Don't switch on for very small heaps.
    461   return FLAG_incremental_marking && heap_->gc_state() == Heap::NOT_IN_GC &&
    462          heap_->deserialization_complete() &&
    463          !heap_->isolate()->serializer_enabled() &&
    464          heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
    465 }
    466 
    467 
    468 void IncrementalMarking::ActivateGeneratedStub(Code* stub) {
    469   DCHECK(RecordWriteStub::GetMode(stub) == RecordWriteStub::STORE_BUFFER_ONLY);
    470 
    471   if (!IsMarking()) {
    472     // Initially stub is generated in STORE_BUFFER_ONLY mode thus
    473     // we don't need to do anything if incremental marking is
    474     // not active.
    475   } else if (IsCompacting()) {
    476     RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL_COMPACTION);
    477   } else {
    478     RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL);
    479   }
    480 }
    481 
    482 
    483 void IncrementalMarking::NotifyOfHighPromotionRate() {
    484   if (IsMarking()) {
    485     if (marking_speed_ < kFastMarking) {
    486       if (FLAG_trace_gc) {
    487         PrintIsolate(heap()->isolate(),
    488                      "Increasing marking speed to %d "
    489                      "due to high promotion rate\n",
    490                      static_cast<int>(kFastMarking));
    491       }
    492       marking_speed_ = kFastMarking;
    493     }
    494   }
    495 }
    496 
    497 
    498 static void PatchIncrementalMarkingRecordWriteStubs(
    499     Heap* heap, RecordWriteStub::Mode mode) {
    500   UnseededNumberDictionary* stubs = heap->code_stubs();
    501 
    502   int capacity = stubs->Capacity();
    503   for (int i = 0; i < capacity; i++) {
    504     Object* k = stubs->KeyAt(i);
    505     if (stubs->IsKey(k)) {
    506       uint32_t key = NumberToUint32(k);
    507 
    508       if (CodeStub::MajorKeyFromKey(key) == CodeStub::RecordWrite) {
    509         Object* e = stubs->ValueAt(i);
    510         if (e->IsCode()) {
    511           RecordWriteStub::Patch(Code::cast(e), mode);
    512         }
    513       }
    514     }
    515   }
    516 }
    517 
    518 
    519 void IncrementalMarking::Start(const char* reason) {
    520   if (FLAG_trace_incremental_marking) {
    521     PrintF("[IncrementalMarking] Start (%s)\n",
    522            (reason == nullptr) ? "unknown reason" : reason);
    523   }
    524   DCHECK(FLAG_incremental_marking);
    525   DCHECK(state_ == STOPPED);
    526   DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
    527   DCHECK(!heap_->isolate()->serializer_enabled());
    528 
    529   HistogramTimerScope incremental_marking_scope(
    530       heap_->isolate()->counters()->gc_incremental_marking_start());
    531   ResetStepCounters();
    532 
    533   was_activated_ = true;
    534 
    535   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
    536     StartMarking();
    537   } else {
    538     if (FLAG_trace_incremental_marking) {
    539       PrintF("[IncrementalMarking] Start sweeping.\n");
    540     }
    541     state_ = SWEEPING;
    542   }
    543 
    544   heap_->new_space()->AddInlineAllocationObserver(&observer_);
    545 
    546   incremental_marking_job()->Start(heap_);
    547 }
    548 
    549 
    550 void IncrementalMarking::StartMarking() {
    551   if (FLAG_trace_incremental_marking) {
    552     PrintF("[IncrementalMarking] Start marking\n");
    553   }
    554 
    555   is_compacting_ = !FLAG_never_compact &&
    556                    heap_->mark_compact_collector()->StartCompaction(
    557                        MarkCompactCollector::INCREMENTAL_COMPACTION);
    558 
    559   state_ = MARKING;
    560 
    561   RecordWriteStub::Mode mode = is_compacting_
    562                                    ? RecordWriteStub::INCREMENTAL_COMPACTION
    563                                    : RecordWriteStub::INCREMENTAL;
    564 
    565   PatchIncrementalMarkingRecordWriteStubs(heap_, mode);
    566 
    567   heap_->mark_compact_collector()->EnsureMarkingDequeIsCommittedAndInitialize(
    568       MarkCompactCollector::kMaxMarkingDequeSize);
    569 
    570   ActivateIncrementalWriteBarrier();
    571 
    572 // Marking bits are cleared by the sweeper.
    573 #ifdef VERIFY_HEAP
    574   if (FLAG_verify_heap) {
    575     heap_->mark_compact_collector()->VerifyMarkbitsAreClean();
    576   }
    577 #endif
    578 
    579   heap_->CompletelyClearInstanceofCache();
    580   heap_->isolate()->compilation_cache()->MarkCompactPrologue();
    581 
    582   if (FLAG_cleanup_code_caches_at_gc) {
    583     // We will mark cache black with a separate pass
    584     // when we finish marking.
    585     MarkObjectGreyDoNotEnqueue(heap_->polymorphic_code_cache());
    586   }
    587 
    588   // Mark strong roots grey.
    589   IncrementalMarkingRootMarkingVisitor visitor(this);
    590   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
    591 
    592   // Ready to start incremental marking.
    593   if (FLAG_trace_incremental_marking) {
    594     PrintF("[IncrementalMarking] Running\n");
    595   }
    596 }
    597 
    598 
    599 void IncrementalMarking::MarkRoots() {
    600   DCHECK(!finalize_marking_completed_);
    601   DCHECK(IsMarking());
    602 
    603   IncrementalMarkingRootMarkingVisitor visitor(this);
    604   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
    605 }
    606 
    607 
    608 void IncrementalMarking::MarkObjectGroups() {
    609   DCHECK(!finalize_marking_completed_);
    610   DCHECK(IsMarking());
    611 
    612   IncrementalMarkingRootMarkingVisitor visitor(this);
    613   heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
    614   heap_->isolate()->global_handles()->IterateObjectGroups(
    615       &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
    616   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
    617   heap_->isolate()->global_handles()->RemoveObjectGroups();
    618 }
    619 
    620 
    621 void IncrementalMarking::ProcessWeakCells() {
    622   DCHECK(!finalize_marking_completed_);
    623   DCHECK(IsMarking());
    624 
    625   Object* the_hole_value = heap()->the_hole_value();
    626   Object* weak_cell_obj = heap()->encountered_weak_cells();
    627   Object* weak_cell_head = Smi::FromInt(0);
    628   WeakCell* prev_weak_cell_obj = NULL;
    629   while (weak_cell_obj != Smi::FromInt(0)) {
    630     WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
    631     // We do not insert cleared weak cells into the list, so the value
    632     // cannot be a Smi here.
    633     HeapObject* value = HeapObject::cast(weak_cell->value());
    634     // Remove weak cells with live objects from the list, they do not need
    635     // clearing.
    636     if (MarkCompactCollector::IsMarked(value)) {
    637       // Record slot, if value is pointing to an evacuation candidate.
    638       Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
    639       heap_->mark_compact_collector()->RecordSlot(weak_cell, slot, *slot);
    640       // Remove entry somewhere after top.
    641       if (prev_weak_cell_obj != NULL) {
    642         prev_weak_cell_obj->set_next(weak_cell->next());
    643       }
    644       weak_cell_obj = weak_cell->next();
    645       weak_cell->clear_next(the_hole_value);
    646     } else {
    647       if (weak_cell_head == Smi::FromInt(0)) {
    648         weak_cell_head = weak_cell;
    649       }
    650       prev_weak_cell_obj = weak_cell;
    651       weak_cell_obj = weak_cell->next();
    652     }
    653   }
    654   // Top may have changed.
    655   heap()->set_encountered_weak_cells(weak_cell_head);
    656 }
    657 
    658 
    659 bool ShouldRetainMap(Map* map, int age) {
    660   if (age == 0) {
    661     // The map has aged. Do not retain this map.
    662     return false;
    663   }
    664   Object* constructor = map->GetConstructor();
    665   if (!constructor->IsHeapObject() ||
    666       Marking::IsWhite(Marking::MarkBitFrom(HeapObject::cast(constructor)))) {
    667     // The constructor is dead, no new objects with this map can
    668     // be created. Do not retain this map.
    669     return false;
    670   }
    671   return true;
    672 }
    673 
    674 
    675 void IncrementalMarking::RetainMaps() {
    676   // Do not retain dead maps if flag disables it or there is
    677   // - memory pressure (reduce_memory_footprint_),
    678   // - GC is requested by tests or dev-tools (abort_incremental_marking_).
    679   bool map_retaining_is_disabled = heap()->ShouldReduceMemory() ||
    680                                    heap()->ShouldAbortIncrementalMarking() ||
    681                                    FLAG_retain_maps_for_n_gc == 0;
    682   ArrayList* retained_maps = heap()->retained_maps();
    683   int length = retained_maps->Length();
    684   // The number_of_disposed_maps separates maps in the retained_maps
    685   // array that were created before and after context disposal.
    686   // We do not age and retain disposed maps to avoid memory leaks.
    687   int number_of_disposed_maps = heap()->number_of_disposed_maps_;
    688   for (int i = 0; i < length; i += 2) {
    689     DCHECK(retained_maps->Get(i)->IsWeakCell());
    690     WeakCell* cell = WeakCell::cast(retained_maps->Get(i));
    691     if (cell->cleared()) continue;
    692     int age = Smi::cast(retained_maps->Get(i + 1))->value();
    693     int new_age;
    694     Map* map = Map::cast(cell->value());
    695     MarkBit map_mark = Marking::MarkBitFrom(map);
    696     if (i >= number_of_disposed_maps && !map_retaining_is_disabled &&
    697         Marking::IsWhite(map_mark)) {
    698       if (ShouldRetainMap(map, age)) {
    699         MarkObject(heap(), map);
    700       }
    701       Object* prototype = map->prototype();
    702       if (age > 0 && prototype->IsHeapObject() &&
    703           Marking::IsWhite(Marking::MarkBitFrom(HeapObject::cast(prototype)))) {
    704         // The prototype is not marked, age the map.
    705         new_age = age - 1;
    706       } else {
    707         // The prototype and the constructor are marked, this map keeps only
    708         // transition tree alive, not JSObjects. Do not age the map.
    709         new_age = age;
    710       }
    711     } else {
    712       new_age = FLAG_retain_maps_for_n_gc;
    713     }
    714     // Compact the array and update the age.
    715     if (new_age != age) {
    716       retained_maps->Set(i + 1, Smi::FromInt(new_age));
    717     }
    718   }
    719 }
    720 
    721 
    722 void IncrementalMarking::FinalizeIncrementally() {
    723   DCHECK(!finalize_marking_completed_);
    724   DCHECK(IsMarking());
    725 
    726   double start = heap_->MonotonicallyIncreasingTimeInMs();
    727 
    728   int old_marking_deque_top =
    729       heap_->mark_compact_collector()->marking_deque()->top();
    730 
    731   // After finishing incremental marking, we try to discover all unmarked
    732   // objects to reduce the marking load in the final pause.
    733   // 1) We scan and mark the roots again to find all changes to the root set.
    734   // 2) We mark the object groups.
    735   // 3) Age and retain maps embedded in optimized code.
    736   // 4) Remove weak cell with live values from the list of weak cells, they
    737   // do not need processing during GC.
    738   MarkRoots();
    739   MarkObjectGroups();
    740   if (incremental_marking_finalization_rounds_ == 0) {
    741     // Map retaining is needed for perfromance, not correctness,
    742     // so we can do it only once at the beginning of the finalization.
    743     RetainMaps();
    744   }
    745   ProcessWeakCells();
    746 
    747   int marking_progress =
    748       abs(old_marking_deque_top -
    749           heap_->mark_compact_collector()->marking_deque()->top());
    750 
    751   double end = heap_->MonotonicallyIncreasingTimeInMs();
    752   double delta = end - start;
    753   heap_->tracer()->AddMarkingTime(delta);
    754   heap_->tracer()->AddIncrementalMarkingFinalizationStep(delta);
    755   if (FLAG_trace_incremental_marking) {
    756     PrintF(
    757         "[IncrementalMarking] Finalize incrementally round %d, "
    758         "spent %d ms, marking progress %d.\n",
    759         static_cast<int>(delta), incremental_marking_finalization_rounds_,
    760         marking_progress);
    761   }
    762 
    763   ++incremental_marking_finalization_rounds_;
    764   if ((incremental_marking_finalization_rounds_ >=
    765        FLAG_max_incremental_marking_finalization_rounds) ||
    766       (marking_progress <
    767        FLAG_min_progress_during_incremental_marking_finalization)) {
    768     finalize_marking_completed_ = true;
    769   }
    770 }
    771 
    772 
    773 void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
    774   if (!IsMarking()) return;
    775 
    776   MarkingDeque* marking_deque =
    777       heap_->mark_compact_collector()->marking_deque();
    778   int current = marking_deque->bottom();
    779   int mask = marking_deque->mask();
    780   int limit = marking_deque->top();
    781   HeapObject** array = marking_deque->array();
    782   int new_top = current;
    783 
    784   Map* filler_map = heap_->one_pointer_filler_map();
    785 
    786   while (current != limit) {
    787     HeapObject* obj = array[current];
    788     DCHECK(obj->IsHeapObject());
    789     current = ((current + 1) & mask);
    790     if (heap_->InNewSpace(obj)) {
    791       MapWord map_word = obj->map_word();
    792       if (map_word.IsForwardingAddress()) {
    793         HeapObject* dest = map_word.ToForwardingAddress();
    794         array[new_top] = dest;
    795         new_top = ((new_top + 1) & mask);
    796         DCHECK(new_top != marking_deque->bottom());
    797 #ifdef DEBUG
    798         MarkBit mark_bit = Marking::MarkBitFrom(obj);
    799         DCHECK(Marking::IsGrey(mark_bit) ||
    800                (obj->IsFiller() && Marking::IsWhite(mark_bit)));
    801 #endif
    802       }
    803     } else if (obj->map() != filler_map) {
    804       // Skip one word filler objects that appear on the
    805       // stack when we perform in place array shift.
    806       array[new_top] = obj;
    807       new_top = ((new_top + 1) & mask);
    808       DCHECK(new_top != marking_deque->bottom());
    809 #ifdef DEBUG
    810       MarkBit mark_bit = Marking::MarkBitFrom(obj);
    811       MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
    812       DCHECK(Marking::IsGrey(mark_bit) ||
    813              (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||
    814              (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
    815               Marking::IsBlack(mark_bit)));
    816 #endif
    817     }
    818   }
    819   marking_deque->set_top(new_top);
    820 }
    821 
    822 
    823 void IncrementalMarking::VisitObject(Map* map, HeapObject* obj, int size) {
    824   MarkObject(heap_, map);
    825 
    826   IncrementalMarkingMarkingVisitor::IterateBody(map, obj);
    827 
    828   MarkBit mark_bit = Marking::MarkBitFrom(obj);
    829 #if ENABLE_SLOW_DCHECKS
    830   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
    831   SLOW_DCHECK(Marking::IsGrey(mark_bit) ||
    832               (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||
    833               (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
    834                Marking::IsBlack(mark_bit)));
    835 #endif
    836   MarkBlackOrKeepBlack(obj, mark_bit, size);
    837 }
    838 
    839 
    840 void IncrementalMarking::MarkObject(Heap* heap, HeapObject* obj) {
    841   MarkBit mark_bit = Marking::MarkBitFrom(obj);
    842   if (Marking::IsWhite(mark_bit)) {
    843     heap->incremental_marking()->WhiteToGreyAndPush(obj, mark_bit);
    844   }
    845 }
    846 
    847 
    848 intptr_t IncrementalMarking::ProcessMarkingDeque(intptr_t bytes_to_process) {
    849   intptr_t bytes_processed = 0;
    850   Map* filler_map = heap_->one_pointer_filler_map();
    851   MarkingDeque* marking_deque =
    852       heap_->mark_compact_collector()->marking_deque();
    853   while (!marking_deque->IsEmpty() && bytes_processed < bytes_to_process) {
    854     HeapObject* obj = marking_deque->Pop();
    855 
    856     // Explicitly skip one word fillers. Incremental markbit patterns are
    857     // correct only for objects that occupy at least two words.
    858     Map* map = obj->map();
    859     if (map == filler_map) continue;
    860 
    861     int size = obj->SizeFromMap(map);
    862     unscanned_bytes_of_large_object_ = 0;
    863     VisitObject(map, obj, size);
    864     bytes_processed += size - unscanned_bytes_of_large_object_;
    865   }
    866   return bytes_processed;
    867 }
    868 
    869 
    870 void IncrementalMarking::ProcessMarkingDeque() {
    871   Map* filler_map = heap_->one_pointer_filler_map();
    872   MarkingDeque* marking_deque =
    873       heap_->mark_compact_collector()->marking_deque();
    874   while (!marking_deque->IsEmpty()) {
    875     HeapObject* obj = marking_deque->Pop();
    876 
    877     // Explicitly skip one word fillers. Incremental markbit patterns are
    878     // correct only for objects that occupy at least two words.
    879     Map* map = obj->map();
    880     if (map == filler_map) continue;
    881 
    882     VisitObject(map, obj, obj->SizeFromMap(map));
    883   }
    884 }
    885 
    886 
    887 void IncrementalMarking::Hurry() {
    888   if (state() == MARKING) {
    889     double start = 0.0;
    890     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
    891       start = heap_->MonotonicallyIncreasingTimeInMs();
    892       if (FLAG_trace_incremental_marking) {
    893         PrintF("[IncrementalMarking] Hurry\n");
    894       }
    895     }
    896     // TODO(gc) hurry can mark objects it encounters black as mutator
    897     // was stopped.
    898     ProcessMarkingDeque();
    899     state_ = COMPLETE;
    900     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
    901       double end = heap_->MonotonicallyIncreasingTimeInMs();
    902       double delta = end - start;
    903       heap_->tracer()->AddMarkingTime(delta);
    904       if (FLAG_trace_incremental_marking) {
    905         PrintF("[IncrementalMarking] Complete (hurry), spent %d ms.\n",
    906                static_cast<int>(delta));
    907       }
    908     }
    909   }
    910 
    911   if (FLAG_cleanup_code_caches_at_gc) {
    912     PolymorphicCodeCache* poly_cache = heap_->polymorphic_code_cache();
    913     Marking::GreyToBlack(Marking::MarkBitFrom(poly_cache));
    914     MemoryChunk::IncrementLiveBytesFromGC(poly_cache,
    915                                           PolymorphicCodeCache::kSize);
    916   }
    917 
    918   Object* context = heap_->native_contexts_list();
    919   while (!context->IsUndefined()) {
    920     // GC can happen when the context is not fully initialized,
    921     // so the cache can be undefined.
    922     HeapObject* cache = HeapObject::cast(
    923         Context::cast(context)->get(Context::NORMALIZED_MAP_CACHE_INDEX));
    924     if (!cache->IsUndefined()) {
    925       MarkBit mark_bit = Marking::MarkBitFrom(cache);
    926       if (Marking::IsGrey(mark_bit)) {
    927         Marking::GreyToBlack(mark_bit);
    928         MemoryChunk::IncrementLiveBytesFromGC(cache, cache->Size());
    929       }
    930     }
    931     context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
    932   }
    933 }
    934 
    935 
    936 void IncrementalMarking::Stop() {
    937   if (IsStopped()) return;
    938   if (FLAG_trace_incremental_marking) {
    939     PrintF("[IncrementalMarking] Stopping.\n");
    940   }
    941 
    942   heap_->new_space()->RemoveInlineAllocationObserver(&observer_);
    943   IncrementalMarking::set_should_hurry(false);
    944   ResetStepCounters();
    945   if (IsMarking()) {
    946     PatchIncrementalMarkingRecordWriteStubs(heap_,
    947                                             RecordWriteStub::STORE_BUFFER_ONLY);
    948     DeactivateIncrementalWriteBarrier();
    949 
    950     if (is_compacting_) {
    951       LargeObjectIterator it(heap_->lo_space());
    952       for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
    953         Page* p = Page::FromAddress(obj->address());
    954         if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
    955           p->ClearFlag(Page::RESCAN_ON_EVACUATION);
    956         }
    957       }
    958     }
    959   }
    960   heap_->isolate()->stack_guard()->ClearGC();
    961   state_ = STOPPED;
    962   is_compacting_ = false;
    963 }
    964 
    965 
    966 void IncrementalMarking::Finalize() {
    967   Hurry();
    968   state_ = STOPPED;
    969   is_compacting_ = false;
    970 
    971   heap_->new_space()->RemoveInlineAllocationObserver(&observer_);
    972   IncrementalMarking::set_should_hurry(false);
    973   ResetStepCounters();
    974   PatchIncrementalMarkingRecordWriteStubs(heap_,
    975                                           RecordWriteStub::STORE_BUFFER_ONLY);
    976   DeactivateIncrementalWriteBarrier();
    977   DCHECK(heap_->mark_compact_collector()->marking_deque()->IsEmpty());
    978   heap_->isolate()->stack_guard()->ClearGC();
    979 }
    980 
    981 
    982 void IncrementalMarking::FinalizeMarking(CompletionAction action) {
    983   DCHECK(!finalize_marking_completed_);
    984   if (FLAG_trace_incremental_marking) {
    985     PrintF(
    986         "[IncrementalMarking] requesting finalization of incremental "
    987         "marking.\n");
    988   }
    989   request_type_ = FINALIZATION;
    990   if (action == GC_VIA_STACK_GUARD) {
    991     heap_->isolate()->stack_guard()->RequestGC();
    992   }
    993 }
    994 
    995 
    996 void IncrementalMarking::MarkingComplete(CompletionAction action) {
    997   state_ = COMPLETE;
    998   // We will set the stack guard to request a GC now.  This will mean the rest
    999   // of the GC gets performed as soon as possible (we can't do a GC here in a
   1000   // record-write context).  If a few things get allocated between now and then
   1001   // that shouldn't make us do a scavenge and keep being incremental, so we set
   1002   // the should-hurry flag to indicate that there can't be much work left to do.
   1003   set_should_hurry(true);
   1004   if (FLAG_trace_incremental_marking) {
   1005     PrintF("[IncrementalMarking] Complete (normal).\n");
   1006   }
   1007   request_type_ = COMPLETE_MARKING;
   1008   if (action == GC_VIA_STACK_GUARD) {
   1009     heap_->isolate()->stack_guard()->RequestGC();
   1010   }
   1011 }
   1012 
   1013 
   1014 void IncrementalMarking::Epilogue() {
   1015   was_activated_ = false;
   1016   finalize_marking_completed_ = false;
   1017   incremental_marking_finalization_rounds_ = 0;
   1018 }
   1019 
   1020 
   1021 double IncrementalMarking::AdvanceIncrementalMarking(
   1022     intptr_t step_size_in_bytes, double deadline_in_ms,
   1023     IncrementalMarking::StepActions step_actions) {
   1024   DCHECK(!IsStopped());
   1025 
   1026   if (step_size_in_bytes == 0) {
   1027     step_size_in_bytes = GCIdleTimeHandler::EstimateMarkingStepSize(
   1028         static_cast<size_t>(GCIdleTimeHandler::kIncrementalMarkingStepTimeInMs),
   1029         static_cast<size_t>(
   1030             heap()
   1031                 ->tracer()
   1032                 ->FinalIncrementalMarkCompactSpeedInBytesPerMillisecond()));
   1033   }
   1034 
   1035   double remaining_time_in_ms = 0.0;
   1036   do {
   1037     Step(step_size_in_bytes, step_actions.completion_action,
   1038          step_actions.force_marking, step_actions.force_completion);
   1039     remaining_time_in_ms =
   1040         deadline_in_ms - heap()->MonotonicallyIncreasingTimeInMs();
   1041   } while (remaining_time_in_ms >=
   1042                2.0 * GCIdleTimeHandler::kIncrementalMarkingStepTimeInMs &&
   1043            !IsComplete() &&
   1044            !heap()->mark_compact_collector()->marking_deque()->IsEmpty());
   1045   return remaining_time_in_ms;
   1046 }
   1047 
   1048 
   1049 void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
   1050   if (IsStopped() && ShouldActivateEvenWithoutIdleNotification()) {
   1051     heap()->StartIncrementalMarking(Heap::kNoGCFlags, kNoGCCallbackFlags,
   1052                                     "old space step");
   1053   } else {
   1054     Step(allocated * kFastMarking / kInitialMarkingSpeed, GC_VIA_STACK_GUARD);
   1055   }
   1056 }
   1057 
   1058 
   1059 void IncrementalMarking::SpeedUp() {
   1060   bool speed_up = false;
   1061 
   1062   if ((steps_count_ % kMarkingSpeedAccellerationInterval) == 0) {
   1063     if (FLAG_trace_incremental_marking) {
   1064       PrintIsolate(heap()->isolate(), "Speed up marking after %d steps\n",
   1065                    static_cast<int>(kMarkingSpeedAccellerationInterval));
   1066     }
   1067     speed_up = true;
   1068   }
   1069 
   1070   bool space_left_is_very_small =
   1071       (old_generation_space_available_at_start_of_incremental_ < 10 * MB);
   1072 
   1073   bool only_1_nth_of_space_that_was_available_still_left =
   1074       (SpaceLeftInOldSpace() * (marking_speed_ + 1) <
   1075        old_generation_space_available_at_start_of_incremental_);
   1076 
   1077   if (space_left_is_very_small ||
   1078       only_1_nth_of_space_that_was_available_still_left) {
   1079     if (FLAG_trace_incremental_marking)
   1080       PrintIsolate(heap()->isolate(),
   1081                    "Speed up marking because of low space left\n");
   1082     speed_up = true;
   1083   }
   1084 
   1085   bool size_of_old_space_multiplied_by_n_during_marking =
   1086       (heap_->PromotedTotalSize() >
   1087        (marking_speed_ + 1) *
   1088            old_generation_space_used_at_start_of_incremental_);
   1089   if (size_of_old_space_multiplied_by_n_during_marking) {
   1090     speed_up = true;
   1091     if (FLAG_trace_incremental_marking) {
   1092       PrintIsolate(heap()->isolate(),
   1093                    "Speed up marking because of heap size increase\n");
   1094     }
   1095   }
   1096 
   1097   int64_t promoted_during_marking =
   1098       heap_->PromotedTotalSize() -
   1099       old_generation_space_used_at_start_of_incremental_;
   1100   intptr_t delay = marking_speed_ * MB;
   1101   intptr_t scavenge_slack = heap_->MaxSemiSpaceSize();
   1102 
   1103   // We try to scan at at least twice the speed that we are allocating.
   1104   if (promoted_during_marking > bytes_scanned_ / 2 + scavenge_slack + delay) {
   1105     if (FLAG_trace_incremental_marking) {
   1106       PrintIsolate(heap()->isolate(),
   1107                    "Speed up marking because marker was not keeping up\n");
   1108     }
   1109     speed_up = true;
   1110   }
   1111 
   1112   if (speed_up) {
   1113     if (state_ != MARKING) {
   1114       if (FLAG_trace_incremental_marking) {
   1115         PrintIsolate(heap()->isolate(),
   1116                      "Postponing speeding up marking until marking starts\n");
   1117       }
   1118     } else {
   1119       marking_speed_ += kMarkingSpeedAccelleration;
   1120       marking_speed_ = static_cast<int>(
   1121           Min(kMaxMarkingSpeed, static_cast<intptr_t>(marking_speed_ * 1.3)));
   1122       if (FLAG_trace_incremental_marking) {
   1123         PrintIsolate(heap()->isolate(), "Marking speed increased to %d\n",
   1124                      marking_speed_);
   1125       }
   1126     }
   1127   }
   1128 }
   1129 
   1130 
   1131 intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
   1132                                   CompletionAction action,
   1133                                   ForceMarkingAction marking,
   1134                                   ForceCompletionAction completion) {
   1135   DCHECK(allocated_bytes >= 0);
   1136 
   1137   if (heap_->gc_state() != Heap::NOT_IN_GC || !FLAG_incremental_marking ||
   1138       (state_ != SWEEPING && state_ != MARKING)) {
   1139     return 0;
   1140   }
   1141 
   1142   allocated_ += allocated_bytes;
   1143 
   1144   if (marking == DO_NOT_FORCE_MARKING && allocated_ < kAllocatedThreshold &&
   1145       write_barriers_invoked_since_last_step_ <
   1146           kWriteBarriersInvokedThreshold) {
   1147     return 0;
   1148   }
   1149 
   1150   // If an idle notification happened recently, we delay marking steps.
   1151   if (marking == DO_NOT_FORCE_MARKING &&
   1152       heap_->RecentIdleNotificationHappened()) {
   1153     return 0;
   1154   }
   1155 
   1156   if (state_ == MARKING && no_marking_scope_depth_ > 0) return 0;
   1157 
   1158   intptr_t bytes_processed = 0;
   1159   {
   1160     HistogramTimerScope incremental_marking_scope(
   1161         heap_->isolate()->counters()->gc_incremental_marking());
   1162     double start = heap_->MonotonicallyIncreasingTimeInMs();
   1163 
   1164     // The marking speed is driven either by the allocation rate or by the rate
   1165     // at which we are having to check the color of objects in the write
   1166     // barrier.
   1167     // It is possible for a tight non-allocating loop to run a lot of write
   1168     // barriers before we get here and check them (marking can only take place
   1169     // on
   1170     // allocation), so to reduce the lumpiness we don't use the write barriers
   1171     // invoked since last step directly to determine the amount of work to do.
   1172     intptr_t bytes_to_process =
   1173         marking_speed_ *
   1174         Max(allocated_, write_barriers_invoked_since_last_step_);
   1175     allocated_ = 0;
   1176     write_barriers_invoked_since_last_step_ = 0;
   1177 
   1178     bytes_scanned_ += bytes_to_process;
   1179 
   1180     if (state_ == SWEEPING) {
   1181       if (heap_->mark_compact_collector()->sweeping_in_progress() &&
   1182           (heap_->mark_compact_collector()->IsSweepingCompleted() ||
   1183            !FLAG_concurrent_sweeping)) {
   1184         heap_->mark_compact_collector()->EnsureSweepingCompleted();
   1185       }
   1186       if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
   1187         bytes_scanned_ = 0;
   1188         StartMarking();
   1189       }
   1190     } else if (state_ == MARKING) {
   1191       bytes_processed = ProcessMarkingDeque(bytes_to_process);
   1192       if (heap_->mark_compact_collector()->marking_deque()->IsEmpty()) {
   1193         if (completion == FORCE_COMPLETION ||
   1194             IsIdleMarkingDelayCounterLimitReached()) {
   1195           if (!finalize_marking_completed_) {
   1196             FinalizeMarking(action);
   1197           } else {
   1198             MarkingComplete(action);
   1199           }
   1200         } else {
   1201           IncrementIdleMarkingDelayCounter();
   1202         }
   1203       }
   1204     }
   1205 
   1206     steps_count_++;
   1207 
   1208     // Speed up marking if we are marking too slow or if we are almost done
   1209     // with marking.
   1210     SpeedUp();
   1211 
   1212     double end = heap_->MonotonicallyIncreasingTimeInMs();
   1213     double duration = (end - start);
   1214     // Note that we report zero bytes here when sweeping was in progress or
   1215     // when we just started incremental marking. In these cases we did not
   1216     // process the marking deque.
   1217     heap_->tracer()->AddIncrementalMarkingStep(duration, bytes_processed);
   1218   }
   1219   return bytes_processed;
   1220 }
   1221 
   1222 
   1223 void IncrementalMarking::ResetStepCounters() {
   1224   steps_count_ = 0;
   1225   old_generation_space_available_at_start_of_incremental_ =
   1226       SpaceLeftInOldSpace();
   1227   old_generation_space_used_at_start_of_incremental_ =
   1228       heap_->PromotedTotalSize();
   1229   bytes_rescanned_ = 0;
   1230   marking_speed_ = kInitialMarkingSpeed;
   1231   bytes_scanned_ = 0;
   1232   write_barriers_invoked_since_last_step_ = 0;
   1233 }
   1234 
   1235 
   1236 int64_t IncrementalMarking::SpaceLeftInOldSpace() {
   1237   return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();
   1238 }
   1239 
   1240 
   1241 bool IncrementalMarking::IsIdleMarkingDelayCounterLimitReached() {
   1242   return idle_marking_delay_counter_ > kMaxIdleMarkingDelayCounter;
   1243 }
   1244 
   1245 
   1246 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   1247   idle_marking_delay_counter_++;
   1248 }
   1249 
   1250 
   1251 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   1252   idle_marking_delay_counter_ = 0;
   1253 }
   1254 }  // namespace internal
   1255 }  // namespace v8
   1256