diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
new file mode 100644
index 0000000..d72423a
--- /dev/null
+++ b/src/heap/incremental-marking.cc
@@ -0,0 +1,982 @@
+// 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/v8.h"
+
+#include "src/heap/incremental-marking.h"
+
+#include "src/code-stubs.h"
+#include "src/compilation-cache.h"
+#include "src/conversions.h"
+#include "src/heap/objects-visiting.h"
+#include "src/heap/objects-visiting-inl.h"
+
+namespace v8 {
+namespace internal {
+
+
+IncrementalMarking::IncrementalMarking(Heap* heap)
+    : heap_(heap),
+      state_(STOPPED),
+      marking_deque_memory_(NULL),
+      marking_deque_memory_committed_(false),
+      steps_count_(0),
+      old_generation_space_available_at_start_of_incremental_(0),
+      old_generation_space_used_at_start_of_incremental_(0),
+      should_hurry_(false),
+      marking_speed_(0),
+      allocated_(0),
+      no_marking_scope_depth_(0),
+      unscanned_bytes_of_large_object_(0) {}
+
+
+void IncrementalMarking::TearDown() { delete marking_deque_memory_; }
+
+
+void IncrementalMarking::RecordWriteSlow(HeapObject* obj, Object** slot,
+                                         Object* value) {
+  if (BaseRecordWrite(obj, slot, value) && slot != NULL) {
+    MarkBit obj_bit = Marking::MarkBitFrom(obj);
+    if (Marking::IsBlack(obj_bit)) {
+      // Object is not going to be rescanned we need to record the slot.
+      heap_->mark_compact_collector()->RecordSlot(HeapObject::RawField(obj, 0),
+                                                  slot, value);
+    }
+  }
+}
+
+
+void IncrementalMarking::RecordWriteFromCode(HeapObject* obj, Object** slot,
+                                             Isolate* isolate) {
+  DCHECK(obj->IsHeapObject());
+  IncrementalMarking* marking = isolate->heap()->incremental_marking();
+
+  MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
+  int counter = chunk->write_barrier_counter();
+  if (counter < (MemoryChunk::kWriteBarrierCounterGranularity / 2)) {
+    marking->write_barriers_invoked_since_last_step_ +=
+        MemoryChunk::kWriteBarrierCounterGranularity -
+        chunk->write_barrier_counter();
+    chunk->set_write_barrier_counter(
+        MemoryChunk::kWriteBarrierCounterGranularity);
+  }
+
+  marking->RecordWrite(obj, slot, *slot);
+}
+
+
+void IncrementalMarking::RecordCodeTargetPatch(Code* host, Address pc,
+                                               HeapObject* value) {
+  if (IsMarking()) {
+    RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
+    RecordWriteIntoCode(host, &rinfo, value);
+  }
+}
+
+
+void IncrementalMarking::RecordCodeTargetPatch(Address pc, HeapObject* value) {
+  if (IsMarking()) {
+    Code* host = heap_->isolate()
+                     ->inner_pointer_to_code_cache()
+                     ->GcSafeFindCodeForInnerPointer(pc);
+    RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
+    RecordWriteIntoCode(host, &rinfo, value);
+  }
+}
+
+
+void IncrementalMarking::RecordWriteOfCodeEntrySlow(JSFunction* host,
+                                                    Object** slot,
+                                                    Code* value) {
+  if (BaseRecordWrite(host, slot, value)) {
+    DCHECK(slot != NULL);
+    heap_->mark_compact_collector()->RecordCodeEntrySlot(
+        reinterpret_cast<Address>(slot), value);
+  }
+}
+
+
+void IncrementalMarking::RecordWriteIntoCodeSlow(HeapObject* obj,
+                                                 RelocInfo* rinfo,
+                                                 Object* value) {
+  MarkBit value_bit = Marking::MarkBitFrom(HeapObject::cast(value));
+  if (Marking::IsWhite(value_bit)) {
+    MarkBit obj_bit = Marking::MarkBitFrom(obj);
+    if (Marking::IsBlack(obj_bit)) {
+      BlackToGreyAndUnshift(obj, obj_bit);
+      RestartIfNotMarking();
+    }
+    // Object is either grey or white.  It will be scanned if survives.
+    return;
+  }
+
+  if (is_compacting_) {
+    MarkBit obj_bit = Marking::MarkBitFrom(obj);
+    if (Marking::IsBlack(obj_bit)) {
+      // Object is not going to be rescanned.  We need to record the slot.
+      heap_->mark_compact_collector()->RecordRelocSlot(rinfo,
+                                                       Code::cast(value));
+    }
+  }
+}
+
+
+static void MarkObjectGreyDoNotEnqueue(Object* obj) {
+  if (obj->IsHeapObject()) {
+    HeapObject* heap_obj = HeapObject::cast(obj);
+    MarkBit mark_bit = Marking::MarkBitFrom(HeapObject::cast(obj));
+    if (Marking::IsBlack(mark_bit)) {
+      MemoryChunk::IncrementLiveBytesFromGC(heap_obj->address(),
+                                            -heap_obj->Size());
+    }
+    Marking::AnyToGrey(mark_bit);
+  }
+}
+
+
+static inline void MarkBlackOrKeepGrey(HeapObject* heap_object,
+                                       MarkBit mark_bit, int size) {
+  DCHECK(!Marking::IsImpossible(mark_bit));
+  if (mark_bit.Get()) return;
+  mark_bit.Set();
+  MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(), size);
+  DCHECK(Marking::IsBlack(mark_bit));
+}
+
+
+static inline void MarkBlackOrKeepBlack(HeapObject* heap_object,
+                                        MarkBit mark_bit, int size) {
+  DCHECK(!Marking::IsImpossible(mark_bit));
+  if (Marking::IsBlack(mark_bit)) return;
+  Marking::MarkBlack(mark_bit);
+  MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(), size);
+  DCHECK(Marking::IsBlack(mark_bit));
+}
+
+
+class IncrementalMarkingMarkingVisitor
+    : public StaticMarkingVisitor<IncrementalMarkingMarkingVisitor> {
+ public:
+  static void Initialize() {
+    StaticMarkingVisitor<IncrementalMarkingMarkingVisitor>::Initialize();
+    table_.Register(kVisitFixedArray, &VisitFixedArrayIncremental);
+    table_.Register(kVisitNativeContext, &VisitNativeContextIncremental);
+    table_.Register(kVisitJSRegExp, &VisitJSRegExp);
+  }
+
+  static const int kProgressBarScanningChunk = 32 * 1024;
+
+  static void VisitFixedArrayIncremental(Map* map, HeapObject* object) {
+    MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());
+    // TODO(mstarzinger): Move setting of the flag to the allocation site of
+    // the array. The visitor should just check the flag.
+    if (FLAG_use_marking_progress_bar &&
+        chunk->owner()->identity() == LO_SPACE) {
+      chunk->SetFlag(MemoryChunk::HAS_PROGRESS_BAR);
+    }
+    if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
+      Heap* heap = map->GetHeap();
+      // When using a progress bar for large fixed arrays, scan only a chunk of
+      // the array and try to push it onto the marking deque again until it is
+      // fully scanned. Fall back to scanning it through to the end in case this
+      // fails because of a full deque.
+      int object_size = FixedArray::BodyDescriptor::SizeOf(map, object);
+      int start_offset =
+          Max(FixedArray::BodyDescriptor::kStartOffset, chunk->progress_bar());
+      int end_offset =
+          Min(object_size, start_offset + kProgressBarScanningChunk);
+      int already_scanned_offset = start_offset;
+      bool scan_until_end = false;
+      do {
+        VisitPointersWithAnchor(heap, HeapObject::RawField(object, 0),
+                                HeapObject::RawField(object, start_offset),
+                                HeapObject::RawField(object, end_offset));
+        start_offset = end_offset;
+        end_offset = Min(object_size, end_offset + kProgressBarScanningChunk);
+        scan_until_end = heap->incremental_marking()->marking_deque()->IsFull();
+      } while (scan_until_end && start_offset < object_size);
+      chunk->set_progress_bar(start_offset);
+      if (start_offset < object_size) {
+        heap->incremental_marking()->marking_deque()->UnshiftGrey(object);
+        heap->incremental_marking()->NotifyIncompleteScanOfObject(
+            object_size - (start_offset - already_scanned_offset));
+      }
+    } else {
+      FixedArrayVisitor::Visit(map, object);
+    }
+  }
+
+  static void VisitNativeContextIncremental(Map* map, HeapObject* object) {
+    Context* context = Context::cast(object);
+
+    // We will mark cache black with a separate pass when we finish marking.
+    // Note that GC can happen when the context is not fully initialized,
+    // so the cache can be undefined.
+    Object* cache = context->get(Context::NORMALIZED_MAP_CACHE_INDEX);
+    if (!cache->IsUndefined()) {
+      MarkObjectGreyDoNotEnqueue(cache);
+    }
+    VisitNativeContext(map, context);
+  }
+
+  INLINE(static void VisitPointer(Heap* heap, Object** p)) {
+    Object* obj = *p;
+    if (obj->IsHeapObject()) {
+      heap->mark_compact_collector()->RecordSlot(p, p, obj);
+      MarkObject(heap, obj);
+    }
+  }
+
+  INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {
+    for (Object** p = start; p < end; p++) {
+      Object* obj = *p;
+      if (obj->IsHeapObject()) {
+        heap->mark_compact_collector()->RecordSlot(start, p, obj);
+        MarkObject(heap, obj);
+      }
+    }
+  }
+
+  INLINE(static void VisitPointersWithAnchor(Heap* heap, Object** anchor,
+                                             Object** start, Object** end)) {
+    for (Object** p = start; p < end; p++) {
+      Object* obj = *p;
+      if (obj->IsHeapObject()) {
+        heap->mark_compact_collector()->RecordSlot(anchor, p, obj);
+        MarkObject(heap, obj);
+      }
+    }
+  }
+
+  // Marks the object grey and pushes it on the marking stack.
+  INLINE(static void MarkObject(Heap* heap, Object* obj)) {
+    HeapObject* heap_object = HeapObject::cast(obj);
+    MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
+    if (mark_bit.data_only()) {
+      MarkBlackOrKeepGrey(heap_object, mark_bit, heap_object->Size());
+    } else if (Marking::IsWhite(mark_bit)) {
+      heap->incremental_marking()->WhiteToGreyAndPush(heap_object, mark_bit);
+    }
+  }
+
+  // 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, Object* obj)) {
+    HeapObject* heap_object = HeapObject::cast(obj);
+    MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
+    if (Marking::IsWhite(mark_bit)) {
+      mark_bit.Set();
+      MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(),
+                                            heap_object->Size());
+      return true;
+    }
+    return false;
+  }
+};
+
+
+class IncrementalMarkingRootMarkingVisitor : public ObjectVisitor {
+ public:
+  explicit IncrementalMarkingRootMarkingVisitor(
+      IncrementalMarking* incremental_marking)
+      : incremental_marking_(incremental_marking) {}
+
+  void VisitPointer(Object** p) { MarkObjectByPointer(p); }
+
+  void VisitPointers(Object** start, Object** end) {
+    for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
+  }
+
+ private:
+  void MarkObjectByPointer(Object** p) {
+    Object* obj = *p;
+    if (!obj->IsHeapObject()) return;
+
+    HeapObject* heap_object = HeapObject::cast(obj);
+    MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
+    if (mark_bit.data_only()) {
+      MarkBlackOrKeepGrey(heap_object, mark_bit, heap_object->Size());
+    } else {
+      if (Marking::IsWhite(mark_bit)) {
+        incremental_marking_->WhiteToGreyAndPush(heap_object, mark_bit);
+      }
+    }
+  }
+
+  IncrementalMarking* incremental_marking_;
+};
+
+
+void IncrementalMarking::Initialize() {
+  IncrementalMarkingMarkingVisitor::Initialize();
+}
+
+
+void IncrementalMarking::SetOldSpacePageFlags(MemoryChunk* chunk,
+                                              bool is_marking,
+                                              bool is_compacting) {
+  if (is_marking) {
+    chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
+    chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
+
+    // It's difficult to filter out slots recorded for large objects.
+    if (chunk->owner()->identity() == LO_SPACE &&
+        chunk->size() > static_cast<size_t>(Page::kPageSize) && is_compacting) {
+      chunk->SetFlag(MemoryChunk::RESCAN_ON_EVACUATION);
+    }
+  } else if (chunk->owner()->identity() == CELL_SPACE ||
+             chunk->owner()->identity() == PROPERTY_CELL_SPACE ||
+             chunk->scan_on_scavenge()) {
+    chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
+    chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
+  } else {
+    chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
+    chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
+  }
+}
+
+
+void IncrementalMarking::SetNewSpacePageFlags(NewSpacePage* chunk,
+                                              bool is_marking) {
+  chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
+  if (is_marking) {
+    chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
+  } else {
+    chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
+  }
+  chunk->SetFlag(MemoryChunk::SCAN_ON_SCAVENGE);
+}
+
+
+void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
+    PagedSpace* space) {
+  PageIterator it(space);
+  while (it.has_next()) {
+    Page* p = it.next();
+    SetOldSpacePageFlags(p, false, false);
+  }
+}
+
+
+void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
+    NewSpace* space) {
+  NewSpacePageIterator it(space);
+  while (it.has_next()) {
+    NewSpacePage* p = it.next();
+    SetNewSpacePageFlags(p, false);
+  }
+}
+
+
+void IncrementalMarking::DeactivateIncrementalWriteBarrier() {
+  DeactivateIncrementalWriteBarrierForSpace(heap_->old_pointer_space());
+  DeactivateIncrementalWriteBarrierForSpace(heap_->old_data_space());
+  DeactivateIncrementalWriteBarrierForSpace(heap_->cell_space());
+  DeactivateIncrementalWriteBarrierForSpace(heap_->property_cell_space());
+  DeactivateIncrementalWriteBarrierForSpace(heap_->map_space());
+  DeactivateIncrementalWriteBarrierForSpace(heap_->code_space());
+  DeactivateIncrementalWriteBarrierForSpace(heap_->new_space());
+
+  LargePage* lop = heap_->lo_space()->first_page();
+  while (lop->is_valid()) {
+    SetOldSpacePageFlags(lop, false, false);
+    lop = lop->next_page();
+  }
+}
+
+
+void IncrementalMarking::ActivateIncrementalWriteBarrier(PagedSpace* space) {
+  PageIterator it(space);
+  while (it.has_next()) {
+    Page* p = it.next();
+    SetOldSpacePageFlags(p, true, is_compacting_);
+  }
+}
+
+
+void IncrementalMarking::ActivateIncrementalWriteBarrier(NewSpace* space) {
+  NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
+  while (it.has_next()) {
+    NewSpacePage* p = it.next();
+    SetNewSpacePageFlags(p, true);
+  }
+}
+
+
+void IncrementalMarking::ActivateIncrementalWriteBarrier() {
+  ActivateIncrementalWriteBarrier(heap_->old_pointer_space());
+  ActivateIncrementalWriteBarrier(heap_->old_data_space());
+  ActivateIncrementalWriteBarrier(heap_->cell_space());
+  ActivateIncrementalWriteBarrier(heap_->property_cell_space());
+  ActivateIncrementalWriteBarrier(heap_->map_space());
+  ActivateIncrementalWriteBarrier(heap_->code_space());
+  ActivateIncrementalWriteBarrier(heap_->new_space());
+
+  LargePage* lop = heap_->lo_space()->first_page();
+  while (lop->is_valid()) {
+    SetOldSpacePageFlags(lop, true, is_compacting_);
+    lop = lop->next_page();
+  }
+}
+
+
+bool IncrementalMarking::ShouldActivate() {
+  return WorthActivating() && heap_->NextGCIsLikelyToBeFull();
+}
+
+
+bool IncrementalMarking::WorthActivating() {
+#ifndef DEBUG
+  static const intptr_t kActivationThreshold = 8 * MB;
+#else
+  // TODO(gc) consider setting this to some low level so that some
+  // debug tests run with incremental marking and some without.
+  static const intptr_t kActivationThreshold = 0;
+#endif
+  // Only start incremental marking in a safe state: 1) when incremental
+  // marking is turned on, 2) when we are currently not in a GC, and
+  // 3) when we are currently not serializing or deserializing the heap.
+  return FLAG_incremental_marking && FLAG_incremental_marking_steps &&
+         heap_->gc_state() == Heap::NOT_IN_GC &&
+         !heap_->isolate()->serializer_enabled() &&
+         heap_->isolate()->IsInitialized() &&
+         heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
+}
+
+
+void IncrementalMarking::ActivateGeneratedStub(Code* stub) {
+  DCHECK(RecordWriteStub::GetMode(stub) == RecordWriteStub::STORE_BUFFER_ONLY);
+
+  if (!IsMarking()) {
+    // Initially stub is generated in STORE_BUFFER_ONLY mode thus
+    // we don't need to do anything if incremental marking is
+    // not active.
+  } else if (IsCompacting()) {
+    RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL_COMPACTION);
+  } else {
+    RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL);
+  }
+}
+
+
+static void PatchIncrementalMarkingRecordWriteStubs(
+    Heap* heap, RecordWriteStub::Mode mode) {
+  UnseededNumberDictionary* stubs = heap->code_stubs();
+
+  int capacity = stubs->Capacity();
+  for (int i = 0; i < capacity; i++) {
+    Object* k = stubs->KeyAt(i);
+    if (stubs->IsKey(k)) {
+      uint32_t key = NumberToUint32(k);
+
+      if (CodeStub::MajorKeyFromKey(key) == CodeStub::RecordWrite) {
+        Object* e = stubs->ValueAt(i);
+        if (e->IsCode()) {
+          RecordWriteStub::Patch(Code::cast(e), mode);
+        }
+      }
+    }
+  }
+}
+
+
+void IncrementalMarking::EnsureMarkingDequeIsCommitted() {
+  if (marking_deque_memory_ == NULL) {
+    marking_deque_memory_ = new base::VirtualMemory(4 * MB);
+  }
+  if (!marking_deque_memory_committed_) {
+    bool success = marking_deque_memory_->Commit(
+        reinterpret_cast<Address>(marking_deque_memory_->address()),
+        marking_deque_memory_->size(),
+        false);  // Not executable.
+    CHECK(success);
+    marking_deque_memory_committed_ = true;
+  }
+}
+
+
+void IncrementalMarking::UncommitMarkingDeque() {
+  if (state_ == STOPPED && marking_deque_memory_committed_) {
+    bool success = marking_deque_memory_->Uncommit(
+        reinterpret_cast<Address>(marking_deque_memory_->address()),
+        marking_deque_memory_->size());
+    CHECK(success);
+    marking_deque_memory_committed_ = false;
+  }
+}
+
+
+void IncrementalMarking::Start(CompactionFlag flag) {
+  if (FLAG_trace_incremental_marking) {
+    PrintF("[IncrementalMarking] Start\n");
+  }
+  DCHECK(FLAG_incremental_marking);
+  DCHECK(FLAG_incremental_marking_steps);
+  DCHECK(state_ == STOPPED);
+  DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
+  DCHECK(!heap_->isolate()->serializer_enabled());
+  DCHECK(heap_->isolate()->IsInitialized());
+
+  ResetStepCounters();
+
+  if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
+    StartMarking(flag);
+  } else {
+    if (FLAG_trace_incremental_marking) {
+      PrintF("[IncrementalMarking] Start sweeping.\n");
+    }
+    state_ = SWEEPING;
+  }
+
+  heap_->new_space()->LowerInlineAllocationLimit(kAllocatedThreshold);
+}
+
+
+void IncrementalMarking::StartMarking(CompactionFlag flag) {
+  if (FLAG_trace_incremental_marking) {
+    PrintF("[IncrementalMarking] Start marking\n");
+  }
+
+  is_compacting_ = !FLAG_never_compact && (flag == ALLOW_COMPACTION) &&
+                   heap_->mark_compact_collector()->StartCompaction(
+                       MarkCompactCollector::INCREMENTAL_COMPACTION);
+
+  state_ = MARKING;
+
+  RecordWriteStub::Mode mode = is_compacting_
+                                   ? RecordWriteStub::INCREMENTAL_COMPACTION
+                                   : RecordWriteStub::INCREMENTAL;
+
+  PatchIncrementalMarkingRecordWriteStubs(heap_, mode);
+
+  EnsureMarkingDequeIsCommitted();
+
+  // Initialize marking stack.
+  Address addr = static_cast<Address>(marking_deque_memory_->address());
+  size_t size = marking_deque_memory_->size();
+  if (FLAG_force_marking_deque_overflows) size = 64 * kPointerSize;
+  marking_deque_.Initialize(addr, addr + size);
+
+  ActivateIncrementalWriteBarrier();
+
+// Marking bits are cleared by the sweeper.
+#ifdef VERIFY_HEAP
+  if (FLAG_verify_heap) {
+    heap_->mark_compact_collector()->VerifyMarkbitsAreClean();
+  }
+#endif
+
+  heap_->CompletelyClearInstanceofCache();
+  heap_->isolate()->compilation_cache()->MarkCompactPrologue();
+
+  if (FLAG_cleanup_code_caches_at_gc) {
+    // We will mark cache black with a separate pass
+    // when we finish marking.
+    MarkObjectGreyDoNotEnqueue(heap_->polymorphic_code_cache());
+  }
+
+  // Mark strong roots grey.
+  IncrementalMarkingRootMarkingVisitor visitor(this);
+  heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
+
+  heap_->mark_compact_collector()->MarkWeakObjectToCodeTable();
+
+  // Ready to start incremental marking.
+  if (FLAG_trace_incremental_marking) {
+    PrintF("[IncrementalMarking] Running\n");
+  }
+}
+
+
+void IncrementalMarking::PrepareForScavenge() {
+  if (!IsMarking()) return;
+  NewSpacePageIterator it(heap_->new_space()->FromSpaceStart(),
+                          heap_->new_space()->FromSpaceEnd());
+  while (it.has_next()) {
+    Bitmap::Clear(it.next());
+  }
+}
+
+
+void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
+  if (!IsMarking()) return;
+
+  int current = marking_deque_.bottom();
+  int mask = marking_deque_.mask();
+  int limit = marking_deque_.top();
+  HeapObject** array = marking_deque_.array();
+  int new_top = current;
+
+  Map* filler_map = heap_->one_pointer_filler_map();
+
+  while (current != limit) {
+    HeapObject* obj = array[current];
+    DCHECK(obj->IsHeapObject());
+    current = ((current + 1) & mask);
+    if (heap_->InNewSpace(obj)) {
+      MapWord map_word = obj->map_word();
+      if (map_word.IsForwardingAddress()) {
+        HeapObject* dest = map_word.ToForwardingAddress();
+        array[new_top] = dest;
+        new_top = ((new_top + 1) & mask);
+        DCHECK(new_top != marking_deque_.bottom());
+#ifdef DEBUG
+        MarkBit mark_bit = Marking::MarkBitFrom(obj);
+        DCHECK(Marking::IsGrey(mark_bit) ||
+               (obj->IsFiller() && Marking::IsWhite(mark_bit)));
+#endif
+      }
+    } else if (obj->map() != filler_map) {
+      // Skip one word filler objects that appear on the
+      // stack when we perform in place array shift.
+      array[new_top] = obj;
+      new_top = ((new_top + 1) & mask);
+      DCHECK(new_top != marking_deque_.bottom());
+#ifdef DEBUG
+      MarkBit mark_bit = Marking::MarkBitFrom(obj);
+      MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
+      DCHECK(Marking::IsGrey(mark_bit) ||
+             (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||
+             (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
+              Marking::IsBlack(mark_bit)));
+#endif
+    }
+  }
+  marking_deque_.set_top(new_top);
+}
+
+
+void IncrementalMarking::VisitObject(Map* map, HeapObject* obj, int size) {
+  MarkBit map_mark_bit = Marking::MarkBitFrom(map);
+  if (Marking::IsWhite(map_mark_bit)) {
+    WhiteToGreyAndPush(map, map_mark_bit);
+  }
+
+  IncrementalMarkingMarkingVisitor::IterateBody(map, obj);
+
+  MarkBit mark_bit = Marking::MarkBitFrom(obj);
+#if ENABLE_SLOW_DCHECKS
+  MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
+  SLOW_DCHECK(Marking::IsGrey(mark_bit) ||
+              (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||
+              (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
+               Marking::IsBlack(mark_bit)));
+#endif
+  MarkBlackOrKeepBlack(obj, mark_bit, size);
+}
+
+
+intptr_t IncrementalMarking::ProcessMarkingDeque(intptr_t bytes_to_process) {
+  intptr_t bytes_processed = 0;
+  Map* filler_map = heap_->one_pointer_filler_map();
+  while (!marking_deque_.IsEmpty() && bytes_processed < bytes_to_process) {
+    HeapObject* obj = marking_deque_.Pop();
+
+    // Explicitly skip one word fillers. Incremental markbit patterns are
+    // correct only for objects that occupy at least two words.
+    Map* map = obj->map();
+    if (map == filler_map) continue;
+
+    int size = obj->SizeFromMap(map);
+    unscanned_bytes_of_large_object_ = 0;
+    VisitObject(map, obj, size);
+    int delta = (size - unscanned_bytes_of_large_object_);
+    // TODO(jochen): remove after http://crbug.com/381820 is resolved.
+    CHECK_LT(0, delta);
+    bytes_processed += delta;
+  }
+  return bytes_processed;
+}
+
+
+void IncrementalMarking::ProcessMarkingDeque() {
+  Map* filler_map = heap_->one_pointer_filler_map();
+  while (!marking_deque_.IsEmpty()) {
+    HeapObject* obj = marking_deque_.Pop();
+
+    // Explicitly skip one word fillers. Incremental markbit patterns are
+    // correct only for objects that occupy at least two words.
+    Map* map = obj->map();
+    if (map == filler_map) continue;
+
+    VisitObject(map, obj, obj->SizeFromMap(map));
+  }
+}
+
+
+void IncrementalMarking::Hurry() {
+  if (state() == MARKING) {
+    double start = 0.0;
+    if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
+      start = base::OS::TimeCurrentMillis();
+      if (FLAG_trace_incremental_marking) {
+        PrintF("[IncrementalMarking] Hurry\n");
+      }
+    }
+    // TODO(gc) hurry can mark objects it encounters black as mutator
+    // was stopped.
+    ProcessMarkingDeque();
+    state_ = COMPLETE;
+    if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
+      double end = base::OS::TimeCurrentMillis();
+      double delta = end - start;
+      heap_->tracer()->AddMarkingTime(delta);
+      if (FLAG_trace_incremental_marking) {
+        PrintF("[IncrementalMarking] Complete (hurry), spent %d ms.\n",
+               static_cast<int>(delta));
+      }
+    }
+  }
+
+  if (FLAG_cleanup_code_caches_at_gc) {
+    PolymorphicCodeCache* poly_cache = heap_->polymorphic_code_cache();
+    Marking::GreyToBlack(Marking::MarkBitFrom(poly_cache));
+    MemoryChunk::IncrementLiveBytesFromGC(poly_cache->address(),
+                                          PolymorphicCodeCache::kSize);
+  }
+
+  Object* context = heap_->native_contexts_list();
+  while (!context->IsUndefined()) {
+    // GC can happen when the context is not fully initialized,
+    // so the cache can be undefined.
+    HeapObject* cache = HeapObject::cast(
+        Context::cast(context)->get(Context::NORMALIZED_MAP_CACHE_INDEX));
+    if (!cache->IsUndefined()) {
+      MarkBit mark_bit = Marking::MarkBitFrom(cache);
+      if (Marking::IsGrey(mark_bit)) {
+        Marking::GreyToBlack(mark_bit);
+        MemoryChunk::IncrementLiveBytesFromGC(cache->address(), cache->Size());
+      }
+    }
+    context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
+  }
+}
+
+
+void IncrementalMarking::Abort() {
+  if (IsStopped()) return;
+  if (FLAG_trace_incremental_marking) {
+    PrintF("[IncrementalMarking] Aborting.\n");
+  }
+  heap_->new_space()->LowerInlineAllocationLimit(0);
+  IncrementalMarking::set_should_hurry(false);
+  ResetStepCounters();
+  if (IsMarking()) {
+    PatchIncrementalMarkingRecordWriteStubs(heap_,
+                                            RecordWriteStub::STORE_BUFFER_ONLY);
+    DeactivateIncrementalWriteBarrier();
+
+    if (is_compacting_) {
+      LargeObjectIterator it(heap_->lo_space());
+      for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
+        Page* p = Page::FromAddress(obj->address());
+        if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
+          p->ClearFlag(Page::RESCAN_ON_EVACUATION);
+        }
+      }
+    }
+  }
+  heap_->isolate()->stack_guard()->ClearGC();
+  state_ = STOPPED;
+  is_compacting_ = false;
+}
+
+
+void IncrementalMarking::Finalize() {
+  Hurry();
+  state_ = STOPPED;
+  is_compacting_ = false;
+  heap_->new_space()->LowerInlineAllocationLimit(0);
+  IncrementalMarking::set_should_hurry(false);
+  ResetStepCounters();
+  PatchIncrementalMarkingRecordWriteStubs(heap_,
+                                          RecordWriteStub::STORE_BUFFER_ONLY);
+  DeactivateIncrementalWriteBarrier();
+  DCHECK(marking_deque_.IsEmpty());
+  heap_->isolate()->stack_guard()->ClearGC();
+}
+
+
+void IncrementalMarking::MarkingComplete(CompletionAction action) {
+  state_ = COMPLETE;
+  // We will set the stack guard to request a GC now.  This will mean the rest
+  // of the GC gets performed as soon as possible (we can't do a GC here in a
+  // record-write context).  If a few things get allocated between now and then
+  // that shouldn't make us do a scavenge and keep being incremental, so we set
+  // the should-hurry flag to indicate that there can't be much work left to do.
+  set_should_hurry(true);
+  if (FLAG_trace_incremental_marking) {
+    PrintF("[IncrementalMarking] Complete (normal).\n");
+  }
+  if (action == GC_VIA_STACK_GUARD) {
+    heap_->isolate()->stack_guard()->RequestGC();
+  }
+}
+
+
+void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
+  if (IsStopped() && ShouldActivate()) {
+    // TODO(hpayer): Let's play safe for now, but compaction should be
+    // in principle possible.
+    Start(PREVENT_COMPACTION);
+  } else {
+    Step(allocated * kFastMarking / kInitialMarkingSpeed, GC_VIA_STACK_GUARD);
+  }
+}
+
+
+void IncrementalMarking::SpeedUp() {
+  bool speed_up = false;
+
+  if ((steps_count_ % kMarkingSpeedAccellerationInterval) == 0) {
+    if (FLAG_trace_gc) {
+      PrintPID("Speed up marking after %d steps\n",
+               static_cast<int>(kMarkingSpeedAccellerationInterval));
+    }
+    speed_up = true;
+  }
+
+  bool space_left_is_very_small =
+      (old_generation_space_available_at_start_of_incremental_ < 10 * MB);
+
+  bool only_1_nth_of_space_that_was_available_still_left =
+      (SpaceLeftInOldSpace() * (marking_speed_ + 1) <
+       old_generation_space_available_at_start_of_incremental_);
+
+  if (space_left_is_very_small ||
+      only_1_nth_of_space_that_was_available_still_left) {
+    if (FLAG_trace_gc) PrintPID("Speed up marking because of low space left\n");
+    speed_up = true;
+  }
+
+  bool size_of_old_space_multiplied_by_n_during_marking =
+      (heap_->PromotedTotalSize() >
+       (marking_speed_ + 1) *
+           old_generation_space_used_at_start_of_incremental_);
+  if (size_of_old_space_multiplied_by_n_during_marking) {
+    speed_up = true;
+    if (FLAG_trace_gc) {
+      PrintPID("Speed up marking because of heap size increase\n");
+    }
+  }
+
+  int64_t promoted_during_marking =
+      heap_->PromotedTotalSize() -
+      old_generation_space_used_at_start_of_incremental_;
+  intptr_t delay = marking_speed_ * MB;
+  intptr_t scavenge_slack = heap_->MaxSemiSpaceSize();
+
+  // We try to scan at at least twice the speed that we are allocating.
+  if (promoted_during_marking > bytes_scanned_ / 2 + scavenge_slack + delay) {
+    if (FLAG_trace_gc) {
+      PrintPID("Speed up marking because marker was not keeping up\n");
+    }
+    speed_up = true;
+  }
+
+  if (speed_up) {
+    if (state_ != MARKING) {
+      if (FLAG_trace_gc) {
+        PrintPID("Postponing speeding up marking until marking starts\n");
+      }
+    } else {
+      marking_speed_ += kMarkingSpeedAccelleration;
+      marking_speed_ = static_cast<int>(
+          Min(kMaxMarkingSpeed, static_cast<intptr_t>(marking_speed_ * 1.3)));
+      if (FLAG_trace_gc) {
+        PrintPID("Marking speed increased to %d\n", marking_speed_);
+      }
+    }
+  }
+}
+
+
+void IncrementalMarking::Step(intptr_t allocated_bytes, CompletionAction action,
+                              bool force_marking) {
+  if (heap_->gc_state() != Heap::NOT_IN_GC || !FLAG_incremental_marking ||
+      !FLAG_incremental_marking_steps ||
+      (state_ != SWEEPING && state_ != MARKING)) {
+    return;
+  }
+
+  allocated_ += allocated_bytes;
+
+  if (!force_marking && allocated_ < kAllocatedThreshold &&
+      write_barriers_invoked_since_last_step_ <
+          kWriteBarriersInvokedThreshold) {
+    return;
+  }
+
+  if (state_ == MARKING && no_marking_scope_depth_ > 0) return;
+
+  {
+    HistogramTimerScope incremental_marking_scope(
+        heap_->isolate()->counters()->gc_incremental_marking());
+    double start = base::OS::TimeCurrentMillis();
+
+    // The marking speed is driven either by the allocation rate or by the rate
+    // at which we are having to check the color of objects in the write
+    // barrier.
+    // It is possible for a tight non-allocating loop to run a lot of write
+    // barriers before we get here and check them (marking can only take place
+    // on
+    // allocation), so to reduce the lumpiness we don't use the write barriers
+    // invoked since last step directly to determine the amount of work to do.
+    intptr_t bytes_to_process =
+        marking_speed_ *
+        Max(allocated_, write_barriers_invoked_since_last_step_);
+    allocated_ = 0;
+    write_barriers_invoked_since_last_step_ = 0;
+
+    bytes_scanned_ += bytes_to_process;
+    intptr_t bytes_processed = 0;
+
+    if (state_ == SWEEPING) {
+      if (heap_->mark_compact_collector()->sweeping_in_progress() &&
+          heap_->mark_compact_collector()->IsSweepingCompleted()) {
+        heap_->mark_compact_collector()->EnsureSweepingCompleted();
+      }
+      if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
+        bytes_scanned_ = 0;
+        StartMarking(PREVENT_COMPACTION);
+      }
+    } else if (state_ == MARKING) {
+      bytes_processed = ProcessMarkingDeque(bytes_to_process);
+      if (marking_deque_.IsEmpty()) MarkingComplete(action);
+    }
+
+    steps_count_++;
+
+    // Speed up marking if we are marking too slow or if we are almost done
+    // with marking.
+    SpeedUp();
+
+    double end = base::OS::TimeCurrentMillis();
+    double duration = (end - start);
+    // Note that we report zero bytes here when sweeping was in progress or
+    // when we just started incremental marking. In these cases we did not
+    // process the marking deque.
+    heap_->tracer()->AddIncrementalMarkingStep(duration, bytes_processed);
+  }
+}
+
+
+void IncrementalMarking::ResetStepCounters() {
+  steps_count_ = 0;
+  old_generation_space_available_at_start_of_incremental_ =
+      SpaceLeftInOldSpace();
+  old_generation_space_used_at_start_of_incremental_ =
+      heap_->PromotedTotalSize();
+  bytes_rescanned_ = 0;
+  marking_speed_ = kInitialMarkingSpeed;
+  bytes_scanned_ = 0;
+  write_barriers_invoked_since_last_step_ = 0;
+}
+
+
+int64_t IncrementalMarking::SpaceLeftInOldSpace() {
+  return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();
+}
+}
+}  // namespace v8::internal