[heap] Fine-grained JSArrayBuffer tracking

Track based on JSArrayBuffer addresses instead of the attached backing store.
This way we can later on iterate buffers on a single page. The reland also
switches to a page-based implementation where a page contains the set of its
contained (live and dead) buffers.

Details of tracking:
- Scavenge: New space pages are processes in bulk on the main thread
- MC: Unswept pages are processed in bulk in parallel. All other pages
  are processed by the sweeper concurrently.

BUG=chromium:611688
LOG=N
CQ_EXTRA_TRYBOTS=tryserver.v8:v8_linux_arm64_gc_stress_dbg,v8_linux_gc_stress_dbg,v8_mac_gc_stress_dbg,v8_linux64_tsan_rel,v8_mac64_asan_rel

Review-Url: https://codereview.chromium.org/1964023002
Cr-Commit-Position: refs/heads/master@{#36437}

BUILD.gn

@@ -1170,6 +1170,7 @@ v8_source_set("v8_base") {
     "src/handles.h",
     "src/hashmap.h",
     "src/heap-symbols.h",
+    "src/heap/array-buffer-tracker-inl.h",
     "src/heap/array-buffer-tracker.cc",
     "src/heap/array-buffer-tracker.h",
     "src/heap/gc-idle-time-handler.cc",

include/v8.h

@@ -7392,7 +7392,7 @@ class Internals {
       kAmountOfExternalAllocatedMemoryOffset + kApiInt64Size;
   static const int kIsolateRootsOffset =
       kAmountOfExternalAllocatedMemoryAtLastGlobalGCOffset + kApiInt64Size +
-      kApiPointerSize;
+      kApiPointerSize + kApiPointerSize;
   static const int kUndefinedValueRootIndex = 4;
   static const int kTheHoleValueRootIndex = 5;
   static const int kNullValueRootIndex = 6;

src/heap/array-buffer-tracker-inl.h

+// Copyright 2016 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/array-buffer-tracker.h"
+#include "src/heap/heap.h"
+#include "src/heap/mark-compact.h"
+#include "src/isolate.h"
+
+namespace v8 {
+namespace internal {
+
+template <typename Callback>
+void LocalArrayBufferTracker::Process(Callback callback) {
+  JSArrayBuffer* new_buffer = nullptr;
+  size_t freed_memory = 0;
+  for (TrackingMap::iterator it = live_.begin(); it != live_.end();) {
+    switch (callback(it->first, &new_buffer)) {
+      case kKeepEntry:
+        it++;
+        break;
+      case kKeepAndUpdateEntry:
+        DCHECK_NOT_NULL(new_buffer);
+        Page::FromAddress(new_buffer->address())
+            ->local_tracker()
+            ->AddLive(new_buffer, it->second);
+        live_.erase(it++);
+        break;
+      case kRemoveEntry:
+        heap_->isolate()->array_buffer_allocator()->Free(it->second.first,
+                                                         it->second.second);
+        freed_memory += it->second.second;
+        live_.erase(it++);
+        break;
+      default:
+        UNREACHABLE();
+    }
+  }
+  if (freed_memory > 0) {
+    heap_->update_amount_of_external_allocated_freed_memory(
+        static_cast<intptr_t>(freed_memory));
+  }
+  not_yet_discovered_.clear();
+  started_ = false;
+}
+
+template <LocalArrayBufferTracker::LivenessIndicator liveness_indicator>
+void LocalArrayBufferTracker::ScanAndFreeDead() {
+  switch (liveness_indicator) {
+    case kForwardingPointer:
+      Process([](JSArrayBuffer* old_buffer, JSArrayBuffer** new_buffer) {
+        MapWord map_word = old_buffer->map_word();
+        if (map_word.IsForwardingAddress()) {
+          *new_buffer = JSArrayBuffer::cast(map_word.ToForwardingAddress());
+          return LocalArrayBufferTracker::kKeepAndUpdateEntry;
+        }
+        return LocalArrayBufferTracker::kRemoveEntry;
+      });
+      break;
+    case kMarkBit:
+      Process([](JSArrayBuffer* old_buffer, JSArrayBuffer**) {
+        if (Marking::IsBlackOrGrey(Marking::MarkBitFrom(old_buffer))) {
+          return LocalArrayBufferTracker::kKeepEntry;
+        }
+        return LocalArrayBufferTracker::kRemoveEntry;
+      });
+      break;
+    default:
+      UNREACHABLE();
+  }
+}
+
+}  // namespace internal
+}  // namespace v8

src/heap/array-buffer-tracker.cc

@@ -3,53 +3,98 @@
 // found in the LICENSE file.
 
 #include "src/heap/array-buffer-tracker.h"
+#include "src/heap/array-buffer-tracker-inl.h"
 #include "src/heap/heap.h"
 #include "src/isolate.h"
-#include "src/objects.h"
 #include "src/objects-inl.h"
+#include "src/objects.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace internal {
 
-ArrayBufferTracker::~ArrayBufferTracker() {
-  Isolate* isolate = heap()->isolate();
+LocalArrayBufferTracker::~LocalArrayBufferTracker() {
   size_t freed_memory = 0;
-  for (auto& buffer : live_array_buffers_) {
-    isolate->array_buffer_allocator()->Free(buffer.first, buffer.second);
-    freed_memory += buffer.second;
+  for (auto& buffer : live_) {
+    heap_->isolate()->array_buffer_allocator()->Free(buffer.second.first,
+                                                     buffer.second.second);
+    freed_memory += buffer.second.second;
   }
-  for (auto& buffer : live_array_buffers_for_scavenge_) {
-    isolate->array_buffer_allocator()->Free(buffer.first, buffer.second);
-    freed_memory += buffer.second;
+  if (freed_memory > 0) {
+    heap_->update_amount_of_external_allocated_freed_memory(
+        static_cast<intptr_t>(freed_memory));
   }
-  live_array_buffers_.clear();
-  live_array_buffers_for_scavenge_.clear();
-  not_yet_discovered_array_buffers_.clear();
-  not_yet_discovered_array_buffers_for_scavenge_.clear();
+  live_.clear();
+  not_yet_discovered_.clear();
+}
+
+void LocalArrayBufferTracker::Add(Key key, const Value& value) {
+  live_[key] = value;
+  not_yet_discovered_[key] = value;
+}
+
+void LocalArrayBufferTracker::AddLive(Key key, const Value& value) {
+  DCHECK_EQ(not_yet_discovered_.count(key), 0);
+  live_[key] = value;
+}
+
+void LocalArrayBufferTracker::MarkLive(Key key) {
+  DCHECK_EQ(live_.count(key), 1);
+  not_yet_discovered_.erase(key);
+}
+
+LocalArrayBufferTracker::Value LocalArrayBufferTracker::Remove(Key key) {
+  DCHECK_EQ(live_.count(key), 1);
+  Value value = live_[key];
+  live_.erase(key);
+  not_yet_discovered_.erase(key);
+  return value;
+}
 
+void LocalArrayBufferTracker::FreeDead() {
+  size_t freed_memory = 0;
+  for (TrackingMap::iterator it = not_yet_discovered_.begin();
+       it != not_yet_discovered_.end();) {
+    heap_->isolate()->array_buffer_allocator()->Free(it->second.first,
+                                                     it->second.second);
+    freed_memory += it->second.second;
+    live_.erase(it->first);
+    not_yet_discovered_.erase(it++);
+  }
   if (freed_memory > 0) {
-    heap()->update_amount_of_external_allocated_memory(
-        -static_cast<int64_t>(freed_memory));
+    heap_->update_amount_of_external_allocated_freed_memory(
+        static_cast<intptr_t>(freed_memory));
   }
+  started_ = false;
 }
 
+void LocalArrayBufferTracker::Reset() {
+  if (!started_) {
+    not_yet_discovered_ = live_;
+    started_ = true;
+  }
+}
 
-void ArrayBufferTracker::RegisterNew(JSArrayBuffer* buffer) {
+bool LocalArrayBufferTracker::IsEmpty() {
+  return live_.empty() && not_yet_discovered_.empty();
+}
+
+ArrayBufferTracker::~ArrayBufferTracker() {}
+
+void ArrayBufferTracker::RegisterNew(JSArrayBuffer* buffer, bool track_live) {
   void* data = buffer->backing_store();
   if (!data) return;
 
-  bool in_new_space = heap()->InNewSpace(buffer);
-  size_t length = NumberToSize(heap()->isolate(), buffer->byte_length());
-  if (in_new_space) {
-    live_array_buffers_for_scavenge_[data] = length;
+  size_t length = NumberToSize(heap_->isolate(), buffer->byte_length());
+  Page* page = Page::FromAddress(buffer->address());
+  if (track_live) {
+    page->local_tracker()->AddLive(buffer, std::make_pair(data, length));
   } else {
-    live_array_buffers_[data] = length;
+    page->local_tracker()->Add(buffer, std::make_pair(data, length));
   }
-
   // We may go over the limit of externally allocated memory here. We call the
   // api function to trigger a GC in this case.
-  reinterpret_cast<v8::Isolate*>(heap()->isolate())
+  reinterpret_cast<v8::Isolate*>(heap_->isolate())
       ->AdjustAmountOfExternalAllocatedMemory(length);
 }
 
@@ -58,84 +103,49 @@ void ArrayBufferTracker::Unregister(JSArrayBuffer* buffer) {
   void* data = buffer->backing_store();
   if (!data) return;
 
-  bool in_new_space = heap()->InNewSpace(buffer);
-  std::map<void*, size_t>* live_buffers =
-      in_new_space ? &live_array_buffers_for_scavenge_ : &live_array_buffers_;
-  std::map<void*, size_t>* not_yet_discovered_buffers =
-      in_new_space ? &not_yet_discovered_array_buffers_for_scavenge_
-                   : &not_yet_discovered_array_buffers_;
-
-  DCHECK(live_buffers->count(data) > 0);
+  size_t length = Page::FromAddress(buffer->address())
+                      ->local_tracker()
+                      ->Remove(buffer)
+                      .second;
+  heap_->update_amount_of_external_allocated_memory(
+      -static_cast<intptr_t>(length));
+}
 
-  size_t length = (*live_buffers)[data];
-  live_buffers->erase(data);
-  not_yet_discovered_buffers->erase(data);
+void ArrayBufferTracker::FreeDeadInNewSpace() {
+  NewSpacePageIterator from_it(heap_->new_space()->FromSpaceStart(),
+                               heap_->new_space()->FromSpaceEnd());
+  while (from_it.has_next()) {
+    Page* p = from_it.next();
+    p->ScanAndFreeDeadArrayBuffers<
+        LocalArrayBufferTracker::kForwardingPointer>();
+  }
+  heap_->account_amount_of_external_allocated_freed_memory();
+}
 
-  heap()->update_amount_of_external_allocated_memory(
-      -static_cast<int64_t>(length));
+void ArrayBufferTracker::ResetTrackersInOldSpace() {
+  heap_->old_space()->ForAllPages([](Page* p) { p->ResetTracker(); });
 }
 
+#define UPDATE_GUARD(buffer, data)   \
+  if (buffer->is_external()) return; \
+  data = buffer->backing_store();    \
+  if (data == nullptr) return;       \
+  if (data == heap_->undefined_value()) return;
 
 void ArrayBufferTracker::MarkLive(JSArrayBuffer* buffer) {
-  base::LockGuard<base::Mutex> guard(&mutex_);
-  void* data = buffer->backing_store();
+  void* data = nullptr;
+  UPDATE_GUARD(buffer, data);
 
-  // ArrayBuffer might be in the middle of being constructed.
-  if (data == heap()->undefined_value()) return;
-  if (heap()->InNewSpace(buffer)) {
-    not_yet_discovered_array_buffers_for_scavenge_.erase(data);
+  LocalArrayBufferTracker* tracker =
+      Page::FromAddress(buffer->address())->local_tracker();
+  if (tracker->IsTracked(buffer)) {
+    tracker->MarkLive((buffer));
   } else {
-    not_yet_discovered_array_buffers_.erase(data);
+    heap_->RegisterNewArrayBuffer(buffer);
   }
 }
 
-
-void ArrayBufferTracker::FreeDead(bool from_scavenge) {
-  size_t freed_memory = 0;
-  Isolate* isolate = heap()->isolate();
-  for (auto& buffer : not_yet_discovered_array_buffers_for_scavenge_) {
-    isolate->array_buffer_allocator()->Free(buffer.first, buffer.second);
-    freed_memory += buffer.second;
-    live_array_buffers_for_scavenge_.erase(buffer.first);
-  }
-
-  if (!from_scavenge) {
-    for (auto& buffer : not_yet_discovered_array_buffers_) {
-      isolate->array_buffer_allocator()->Free(buffer.first, buffer.second);
-      freed_memory += buffer.second;
-      live_array_buffers_.erase(buffer.first);
-    }
-  }
-
-  not_yet_discovered_array_buffers_for_scavenge_ =
-      live_array_buffers_for_scavenge_;
-  if (!from_scavenge) not_yet_discovered_array_buffers_ = live_array_buffers_;
-
-  // Do not call through the api as this code is triggered while doing a GC.
-  heap()->update_amount_of_external_allocated_memory(
-      -static_cast<int64_t>(freed_memory));
-}
-
-
-void ArrayBufferTracker::PrepareDiscoveryInNewSpace() {
-  not_yet_discovered_array_buffers_for_scavenge_ =
-      live_array_buffers_for_scavenge_;
-}
-
-
-void ArrayBufferTracker::Promote(JSArrayBuffer* buffer) {
-  base::LockGuard<base::Mutex> guard(&mutex_);
-
-  if (buffer->is_external()) return;
-  void* data = buffer->backing_store();
-  if (!data) return;
-  // ArrayBuffer might be in the middle of being constructed.
-  if (data == heap()->undefined_value()) return;
-  DCHECK(live_array_buffers_for_scavenge_.count(data) > 0);
-  live_array_buffers_[data] = live_array_buffers_for_scavenge_[data];
-  live_array_buffers_for_scavenge_.erase(data);
-  not_yet_discovered_array_buffers_for_scavenge_.erase(data);
-}
+#undef UPDATE_GUARD
 
 }  // namespace internal
 }  // namespace v8

src/heap/array-buffer-tracker.h

@@ -15,61 +15,105 @@ namespace internal {
 
 // Forward declarations.
 class Heap;
+class Page;
 class JSArrayBuffer;
 
+// LocalArrayBufferTracker is tracker for live and dead JSArrayBuffer objects.
+//
+// It consists of two sets, a live, and a not yet discovered set of buffers.
+// Upon registration (in the ArrayBufferTracker) the buffers are added to both
+// sets. When a buffer is encountered as live (or added is live) it is removed
+// from the not yet discovered set. Finally, after each round (sometime during
+// GC) the left over not yet discovered buffers are cleaned up. Upon starting
+// a new round the not yet discovered buffers are initialized from the live set.
+//
+// Caveats:
+// - Between cleaning up the buffers using |Free| we always need a |Reset| and
+//   thus another marking phase.
+class LocalArrayBufferTracker {
+ public:
+  typedef std::pair<void*, size_t> Value;
+  typedef JSArrayBuffer* Key;
+
+  enum LivenessIndicator { kForwardingPointer, kMarkBit };
+  enum CallbackResult { kKeepEntry, kKeepAndUpdateEntry, kRemoveEntry };
+
+  explicit LocalArrayBufferTracker(Heap* heap) : heap_(heap), started_(false) {}
+  ~LocalArrayBufferTracker();
+
+  void Add(Key key, const Value& value);
+  void AddLive(Key key, const Value& value);
+  Value Remove(Key key);
+  void MarkLive(Key key);
+  bool IsEmpty();
+
+  // Resets the tracking set, i.e., not yet discovered buffers are initialized
+  // from the remaining live set of buffers.
+  void Reset();
+
+  // Frees up any dead backing stores of not yet discovered array buffers.
+  // Requires that the buffers have been properly marked using MarkLive.
+  void FreeDead();
+
+  // Scans the whole tracker and decides based on liveness_indicator whether
+  // a JSArrayBuffer is still considered live.
+  template <LivenessIndicator liveness_indicator>
+  inline void ScanAndFreeDead();
+
+  bool IsTracked(Key key) { return live_.find(key) != live_.end(); }
+
+ private:
+  // TODO(mlippautz): Switch to unordered_map once it is supported on all
+  // platforms.
+  typedef std::map<Key, Value> TrackingMap;
+
+  // Processes buffers one by one. The CallbackResult decides whether the buffer
+  // will be dropped or not.
+  //
+  // Callback should be of type:
+  //   CallbackResult fn(JSArrayBuffer*, JSArrayBuffer**);
+  template <typename Callback>
+  inline void Process(Callback callback);
+
+  Heap* heap_;
+
+  // |live_| maps tracked JSArrayBuffers to the internally allocated backing
+  // store and length. For each GC round |not_yet_discovered_| is initialized
+  // as a copy of |live_|. Upon finding a JSArrayBuffer during GC, the buffer
+  // is removed from |not_yet_discovered_|. At the end of a GC, we free up the
+  // remaining JSArrayBuffers in |not_yet_discovered_|.
+  TrackingMap live_;
+  TrackingMap not_yet_discovered_;
+
+  bool started_;
+};
+
 class ArrayBufferTracker {
  public:
   explicit ArrayBufferTracker(Heap* heap) : heap_(heap) {}
   ~ArrayBufferTracker();
 
-  inline Heap* heap() { return heap_; }
-
   // The following methods are used to track raw C++ pointers to externally
   // allocated memory used as backing store in live array buffers.
 
-  // A new ArrayBuffer was created with |data| as backing store.
-  void RegisterNew(JSArrayBuffer* buffer);
-
-  // The backing store |data| is no longer owned by V8.
+  // Register/unregister a new JSArrayBuffer |buffer| for tracking.
+  // |track_live| indicates whether marking will still visit the buffer and we
+  // can delay marking it as live.
+  void RegisterNew(JSArrayBuffer* buffer, bool track_live);
   void Unregister(JSArrayBuffer* buffer);
 
-  // A live ArrayBuffer was discovered during marking/scavenge.
-  void MarkLive(JSArrayBuffer* buffer);
+  // Frees all backing store pointers for dead JSArrayBuffers in new space.
+  void FreeDeadInNewSpace();
 
-  // Frees all backing store pointers that weren't discovered in the previous
-  // marking or scavenge phase.
-  void FreeDead(bool from_scavenge);
+  void ResetTrackersInOldSpace();
 
-  // Prepare for a new scavenge phase. A new marking phase is implicitly
-  // prepared by finishing the previous one.
-  void PrepareDiscoveryInNewSpace();
-
-  // An ArrayBuffer moved from new space to old space.
-  void Promote(JSArrayBuffer* buffer);
+  // A live JSArrayBuffer was discovered during marking.
+  void MarkLive(JSArrayBuffer* buffer);
 
  private:
-  base::Mutex mutex_;
   Heap* heap_;
-
-  // |live_array_buffers_| maps externally allocated memory used as backing
-  // store for ArrayBuffers to the length of the respective memory blocks.
-  //
-  // At the beginning of mark/compact, |not_yet_discovered_array_buffers_| is
-  // a copy of |live_array_buffers_| and we remove pointers as we discover live
-  // ArrayBuffer objects during marking. At the end of mark/compact, the
-  // remaining memory blocks can be freed.
-  std::map<void*, size_t> live_array_buffers_;
-  std::map<void*, size_t> not_yet_discovered_array_buffers_;
-
-  // To be able to free memory held by ArrayBuffers during scavenge as well, we
-  // have a separate list of allocated memory held by ArrayBuffers in new space.
-  //
-  // Since mark/compact also evacuates the new space, all pointers in the
-  // |live_array_buffers_for_scavenge_| list are also in the
-  // |live_array_buffers_| list.
-  std::map<void*, size_t> live_array_buffers_for_scavenge_;
-  std::map<void*, size_t> not_yet_discovered_array_buffers_for_scavenge_;
 };
+
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_HEAP_ARRAY_BUFFER_TRACKER_H_

src/heap/heap.cc

@@ -1626,8 +1626,6 @@ void Heap::Scavenge() {
 
   scavenge_collector_->SelectScavengingVisitorsTable();
 
-  array_buffer_tracker()->PrepareDiscoveryInNewSpace();
-
   // Flip the semispaces.  After flipping, to space is empty, from space has
   // live objects.
   new_space_.Flip();
@@ -1744,7 +1742,7 @@ void Heap::Scavenge() {
   // Set age mark.
   new_space_.set_age_mark(new_space_.top());
 
-  array_buffer_tracker()->FreeDead(true);
+  array_buffer_tracker()->FreeDeadInNewSpace();
 
   // Update how much has survived scavenge.
   IncrementYoungSurvivorsCounter(static_cast<int>(
@@ -2024,7 +2022,8 @@ HeapObject* Heap::DoubleAlignForDeserialization(HeapObject* object, int size) {
 
 
 void Heap::RegisterNewArrayBuffer(JSArrayBuffer* buffer) {
-  return array_buffer_tracker()->RegisterNew(buffer);
+  const bool track_live = Marking::IsBlack(Marking::MarkBitFrom(buffer));
+  return array_buffer_tracker()->RegisterNew(buffer, track_live);
 }
 
 

src/heap/heap.h

@@ -815,6 +815,16 @@ class Heap {
     amount_of_external_allocated_memory_ += delta;
   }
 
+  void update_amount_of_external_allocated_freed_memory(intptr_t freed) {
+    amount_of_external_allocated_memory_freed_.Increment(freed);
+  }
+
+  void account_amount_of_external_allocated_freed_memory() {
+    amount_of_external_allocated_memory_ -=
+        amount_of_external_allocated_memory_freed_.Value();
+    amount_of_external_allocated_memory_freed_.SetValue(0);
+  }
+
   void DeoptMarkedAllocationSites();
 
   bool DeoptMaybeTenuredAllocationSites() {
@@ -1982,6 +1992,8 @@ class Heap {
   // Caches the amount of external memory registered at the last global gc.
   int64_t amount_of_external_allocated_memory_at_last_global_gc_;
 
+  base::AtomicNumber<intptr_t> amount_of_external_allocated_memory_freed_;
+
   // This can be calculated directly from a pointer to the heap; however, it is
   // more expedient to get at the isolate directly from within Heap methods.
   Isolate* isolate_;

src/heap/incremental-marking.cc

@@ -547,6 +547,7 @@ void IncrementalMarking::StartMarking() {
       MarkCompactCollector::kMaxMarkingDequeSize);
 
   ActivateIncrementalWriteBarrier();
+  heap_->array_buffer_tracker()->ResetTrackersInOldSpace();
 
 // Marking bits are cleared by the sweeper.
 #ifdef VERIFY_HEAP

src/heap/mark-compact.cc

@@ -14,7 +14,7 @@
 #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/array-buffer-tracker-inl.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/incremental-marking.h"
 #include "src/heap/mark-compact-inl.h"
@@ -872,6 +872,10 @@ void MarkCompactCollector::Prepare() {
        space = spaces.next()) {
     space->PrepareForMarkCompact();
   }
+  if (!was_marked_incrementally_) {
+    heap_->array_buffer_tracker()->ResetTrackersInOldSpace();
+  }
+  heap()->account_amount_of_external_allocated_freed_memory();
 
 #ifdef VERIFY_HEAP
   if (!was_marked_incrementally_ && FLAG_verify_heap) {
@@ -1727,20 +1731,12 @@ class MarkCompactCollector::EvacuateNewSpaceVisitor final
     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;
   }
@@ -1865,10 +1861,6 @@ class MarkCompactCollector::EvacuateNewSpacePageVisitor final
   }
 
   inline bool Visit(HeapObject* object) {
-    if (V8_UNLIKELY(object->IsJSArrayBuffer())) {
-      object->GetHeap()->array_buffer_tracker()->Promote(
-          JSArrayBuffer::cast(object));
-    }
     RecordMigratedSlotVisitor visitor(heap_->mark_compact_collector());
     object->IterateBodyFast(&visitor);
     promoted_size_ += object->Size();
@@ -1909,6 +1901,9 @@ class MarkCompactCollector::EvacuateRecordOnlyVisitor final
   inline bool Visit(HeapObject* object) {
     RecordMigratedSlotVisitor visitor(heap_->mark_compact_collector());
     object->IterateBody(&visitor);
+    if (V8_UNLIKELY(object->IsJSArrayBuffer())) {
+      heap_->array_buffer_tracker()->MarkLive(JSArrayBuffer::cast(object));
+    }
     return true;
   }
 
@@ -3126,21 +3121,27 @@ bool MarkCompactCollector::Evacuator::EvacuatePage(Page* page) {
   switch (ComputeEvacuationMode(page)) {
     case kObjectsNewToOld:
       result = EvacuateSinglePage<kClearMarkbits>(page, &new_space_visitor_);
+      page->ScanAndFreeDeadArrayBuffers<
+          LocalArrayBufferTracker::kForwardingPointer>();
       DCHECK(result);
       USE(result);
       break;
     case kPageNewToOld:
       result = EvacuateSinglePage<kKeepMarking>(page, &new_space_page_visitor);
+      // ArrayBufferTracker will be updated during sweeping.
       DCHECK(result);
       USE(result);
       break;
     case kObjectsOldToOld:
       result = EvacuateSinglePage<kClearMarkbits>(page, &old_space_visitor_);
+      page->ScanAndFreeDeadArrayBuffers<
+          LocalArrayBufferTracker::kForwardingPointer>();
       if (!result) {
         // Aborted compaction page. We can record slots here to have them
         // processed in parallel later on.
         EvacuateRecordOnlyVisitor record_visitor(collector_->heap());
         result = EvacuateSinglePage<kKeepMarking>(page, &record_visitor);
+        page->ScanAndFreeDeadArrayBuffers<LocalArrayBufferTracker::kMarkBit>();
         DCHECK(result);
         USE(result);
         // We need to return failure here to indicate that we want this page
@@ -3383,6 +3384,7 @@ int MarkCompactCollector::Sweeper::RawSweep(PagedSpace* space, Page* p,
     freed_bytes = space->UnaccountedFree(free_start, size);
     max_freed_bytes = Max(freed_bytes, max_freed_bytes);
   }
+  p->FreeDeadArrayBuffers();
   p->concurrent_sweeping_state().SetValue(Page::kSweepingDone);
   return FreeList::GuaranteedAllocatable(static_cast<int>(max_freed_bytes));
 }
@@ -3526,11 +3528,6 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
       }
     }
 
-    // EvacuateNewSpaceAndCandidates iterates over new space objects and for
-    // ArrayBuffers either re-registers them as live or promotes them. This is
-    // needed to properly free them.
-    heap()->array_buffer_tracker()->FreeDead(false);
-
     // Deallocate evacuated candidate pages.
     ReleaseEvacuationCandidates();
   }

src/heap/objects-visiting-inl.h

@@ -105,11 +105,6 @@ int StaticNewSpaceVisitor<StaticVisitor>::VisitJSArrayBuffer(
     Map* map, HeapObject* object) {
   typedef FlexibleBodyVisitor<StaticVisitor, JSArrayBuffer::BodyDescriptor, int>
       JSArrayBufferBodyVisitor;
-
-  if (!JSArrayBuffer::cast(object)->is_external()) {
-    Heap* heap = map->GetHeap();
-    heap->array_buffer_tracker()->MarkLive(JSArrayBuffer::cast(object));
-  }
   return JSArrayBufferBodyVisitor::Visit(map, object);
 }
 

src/heap/scavenger.cc

@@ -289,14 +289,6 @@ class ScavengingVisitor : public StaticVisitorBase {
   static inline void EvacuateJSArrayBuffer(Map* map, HeapObject** slot,
                                            HeapObject* object) {
     ObjectEvacuationStrategy<POINTER_OBJECT>::Visit(map, slot, object);
-
-    Heap* heap = map->GetHeap();
-    MapWord map_word = object->map_word();
-    DCHECK(map_word.IsForwardingAddress());
-    HeapObject* target = map_word.ToForwardingAddress();
-    if (!heap->InNewSpace(target)) {
-      heap->array_buffer_tracker()->Promote(JSArrayBuffer::cast(target));
-    }
   }
 
 

src/heap/spaces.cc

@@ -518,6 +518,7 @@ MemoryChunk* MemoryChunk::Initialize(Heap* heap, Address base, size_t size,
   Bitmap::Clear(chunk);
   chunk->set_next_chunk(nullptr);
   chunk->set_prev_chunk(nullptr);
+  chunk->local_tracker_ = nullptr;
 
   DCHECK(OFFSET_OF(MemoryChunk, flags_) == kFlagsOffset);
   DCHECK(OFFSET_OF(MemoryChunk, live_byte_count_) == kLiveBytesOffset);
@@ -1039,6 +1040,11 @@ void MemoryChunk::ReleaseAllocatedMemory() {
   if (old_to_old_slots_ != nullptr) ReleaseOldToOldSlots();
   if (typed_old_to_new_slots_ != nullptr) ReleaseTypedOldToNewSlots();
   if (typed_old_to_old_slots_ != nullptr) ReleaseTypedOldToOldSlots();
+
+  if (local_tracker_ != nullptr) {
+    delete local_tracker_;
+    local_tracker_ = nullptr;
+  }
 }
 
 static SlotSet* AllocateSlotSet(size_t size, Address page_start) {

src/heap/spaces.h

@@ -14,6 +14,7 @@
 #include "src/base/platform/mutex.h"
 #include "src/flags.h"
 #include "src/hashmap.h"
+#include "src/heap/array-buffer-tracker.h"
 #include "src/list.h"
 #include "src/objects.h"
 #include "src/utils.h"
@@ -523,7 +524,8 @@ class MemoryChunk {
       + kPointerSize      // AtomicValue next_chunk_
       + kPointerSize      // AtomicValue prev_chunk_
       // FreeListCategory categories_[kNumberOfCategories]
-      + FreeListCategory::kSize * kNumberOfCategories;
+      + FreeListCategory::kSize * kNumberOfCategories +
+      kPointerSize;  // LocalArrayBufferTracker tracker_
 
   // We add some more space to the computed header size to amount for missing
   // alignment requirements in our computation.
@@ -824,6 +826,8 @@ class MemoryChunk {
 
   FreeListCategory categories_[kNumberOfCategories];
 
+  LocalArrayBufferTracker* local_tracker_;
+
  private:
   void InitializeReservedMemory() { reservation_.Reset(); }
 
@@ -954,6 +958,40 @@ class Page : public MemoryChunk {
     available_in_free_list_.Increment(available);
   }
 
+  LocalArrayBufferTracker* local_tracker() {
+    if (local_tracker_ == nullptr) {
+      local_tracker_ = new LocalArrayBufferTracker(heap_);
+    }
+    return local_tracker_;
+  }
+
+  void FreeDeadArrayBuffers() {
+    if (local_tracker_ != nullptr) {
+      local_tracker_->FreeDead();
+      if (local_tracker_->IsEmpty()) {
+        delete local_tracker_;
+        local_tracker_ = nullptr;
+      }
+    }
+  }
+
+  template <LocalArrayBufferTracker::LivenessIndicator liveness_indicator>
+  void ScanAndFreeDeadArrayBuffers() {
+    if (local_tracker_ != nullptr) {
+      local_tracker_->ScanAndFreeDead<liveness_indicator>();
+      if (local_tracker_->IsEmpty()) {
+        delete local_tracker_;
+        local_tracker_ = nullptr;
+      }
+    }
+  }
+
+  void ResetTracker() {
+    if (local_tracker_ != nullptr) {
+      local_tracker_->Reset();
+    }
+  }
+
 #ifdef DEBUG
   void Print();
 #endif  // DEBUG
@@ -2295,6 +2333,16 @@ class PagedSpace : public Space {
   inline void UnlinkFreeListCategories(Page* page);
   inline intptr_t RelinkFreeListCategories(Page* page);
 
+  // Callback signature:
+  //   void Callback(Page*);
+  template <typename Callback>
+  void ForAllPages(Callback callback) {
+    PageIterator it(this);
+    while (it.has_next()) {
+      callback(it.next());
+    }
+  }
+
  protected:
   // PagedSpaces that should be included in snapshots have different, i.e.,
   // smaller, initial pages.

src/v8.gyp

@@ -830,6 +830,7 @@
         'handles.h',
         'hashmap.h',
         'heap-symbols.h',
+        'heap/array-buffer-tracker-inl.h',
         'heap/array-buffer-tracker.cc',
         'heap/array-buffer-tracker.h',
         'heap/memory-reducer.cc',

test/cctest/cctest.gyp

@@ -102,6 +102,7 @@
         'heap/heap-utils.cc',
         'heap/heap-utils.h',
         'heap/test-alloc.cc',
+        'heap/test-array-buffer-tracker.cc',
         'heap/test-compaction.cc',
         'heap/test-heap.cc',
         'heap/test-incremental-marking.cc',

test/cctest/heap/heap-utils.cc

@@ -141,6 +141,21 @@ void SimulateFullSpace(v8::internal::PagedSpace* space) {
   space->ClearStats();
 }
 
+void AbandonCurrentlyFreeMemory(PagedSpace* space) {
+  space->EmptyAllocationInfo();
+  PageIterator pit(space);
+  while (pit.has_next()) {
+    pit.next()->MarkNeverAllocateForTesting();
+  }
+}
+
+void GcAndSweep(Heap* heap, AllocationSpace space) {
+  heap->CollectGarbage(space);
+  if (heap->mark_compact_collector()->sweeping_in_progress()) {
+    heap->mark_compact_collector()->EnsureSweepingCompleted();
+  }
+}
+
 }  // namespace heap
 }  // namespace internal
 }  // namespace v8

test/cctest/heap/heap-utils.h

@@ -40,6 +40,10 @@ void SimulateIncrementalMarking(i::Heap* heap, bool force_completion = true);
 // Helper function that simulates a full old-space in the heap.
 void SimulateFullSpace(v8::internal::PagedSpace* space);
 
+void AbandonCurrentlyFreeMemory(PagedSpace* space);
+
+void GcAndSweep(Heap* heap, AllocationSpace space);
+
 }  // namespace heap
 }  // namespace internal
 }  // namespace v8

test/cctest/heap/test-array-buffer-tracker.cc

+// Copyright 2016 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/array-buffer-tracker-inl.h"
+#include "src/heap/array-buffer-tracker.h"
+#include "test/cctest/cctest.h"
+#include "test/cctest/heap/heap-utils.h"
+
+namespace {
+
+typedef i::LocalArrayBufferTracker LocalTracker;
+
+void VerifyTrackedInNewSpace(i::JSArrayBuffer* buf) {
+  CHECK(i::Page::FromAddress(buf->address())->InNewSpace());
+  CHECK(i::Page::FromAddress(buf->address())->local_tracker()->IsTracked(buf));
+}
+
+void VerifyTrackedInOldSpace(i::JSArrayBuffer* buf) {
+  CHECK(!i::Page::FromAddress(buf->address())->InNewSpace());
+  CHECK(i::Page::FromAddress(buf->address())->local_tracker()->IsTracked(buf));
+}
+
+void VerifyUntracked(i::JSArrayBuffer* buf) {
+  CHECK(!i::Page::FromAddress(buf->address())->local_tracker()->IsTracked(buf));
+}
+
+}  // namespace
+
+namespace v8 {
+namespace internal {
+
+// The following tests make sure that JSArrayBuffer tracking works expected when
+// moving the objects through various spaces during GC phases.
+
+TEST(ArrayBuffer_OnlyMC) {
+  CcTest::InitializeVM();
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  Heap* heap = reinterpret_cast<Isolate*>(isolate)->heap();
+
+  JSArrayBuffer* raw_ab = nullptr;
+  {
+    v8::HandleScope handle_scope(isolate);
+    Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, 100);
+    Handle<JSArrayBuffer> buf = v8::Utils::OpenHandle(*ab);
+    VerifyTrackedInNewSpace(*buf);
+    heap::GcAndSweep(heap, OLD_SPACE);
+    VerifyTrackedInNewSpace(*buf);
+    heap::GcAndSweep(heap, OLD_SPACE);
+    VerifyTrackedInOldSpace(*buf);
+    raw_ab = *buf;
+  }
+  // 2 GCs are needed because we promote to old space as live, meaining that
+  // we will survive one GC.
+  heap::GcAndSweep(heap, OLD_SPACE);
+  heap::GcAndSweep(heap, OLD_SPACE);
+  VerifyUntracked(raw_ab);
+}
+
+TEST(ArrayBuffer_OnlyScavenge) {
+  CcTest::InitializeVM();
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  Heap* heap = reinterpret_cast<Isolate*>(isolate)->heap();
+
+  JSArrayBuffer* raw_ab = nullptr;
+  {
+    v8::HandleScope handle_scope(isolate);
+    Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, 100);
+    Handle<JSArrayBuffer> buf = v8::Utils::OpenHandle(*ab);
+    VerifyTrackedInNewSpace(*buf);
+    heap::GcAndSweep(heap, NEW_SPACE);
+    VerifyTrackedInNewSpace(*buf);
+    heap::GcAndSweep(heap, NEW_SPACE);
+    VerifyTrackedInOldSpace(*buf);
+    heap::GcAndSweep(heap, NEW_SPACE);
+    VerifyTrackedInOldSpace(*buf);
+    raw_ab = *buf;
+  }
+  // 2 GCs are needed because we promote to old space as live, meaning that
+  // we will survive one GC.
+  heap::GcAndSweep(heap, OLD_SPACE);
+  heap::GcAndSweep(heap, OLD_SPACE);
+  VerifyUntracked(raw_ab);
+}
+
+TEST(ArrayBuffer_ScavengeAndMC) {
+  CcTest::InitializeVM();
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  Heap* heap = reinterpret_cast<Isolate*>(isolate)->heap();
+
+  JSArrayBuffer* raw_ab = nullptr;
+  {
+    v8::HandleScope handle_scope(isolate);
+    Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, 100);
+    Handle<JSArrayBuffer> buf = v8::Utils::OpenHandle(*ab);
+    VerifyTrackedInNewSpace(*buf);
+    heap::GcAndSweep(heap, NEW_SPACE);
+    VerifyTrackedInNewSpace(*buf);
+    heap::GcAndSweep(heap, NEW_SPACE);
+    VerifyTrackedInOldSpace(*buf);
+    heap::GcAndSweep(heap, OLD_SPACE);
+    VerifyTrackedInOldSpace(*buf);
+    heap::GcAndSweep(heap, NEW_SPACE);
+    VerifyTrackedInOldSpace(*buf);
+    raw_ab = *buf;
+  }
+  // 2 GCs are needed because we promote to old space as live, meaning that
+  // we will survive one GC.
+  heap::GcAndSweep(heap, OLD_SPACE);
+  heap::GcAndSweep(heap, OLD_SPACE);
+  VerifyUntracked(raw_ab);
+}
+
+TEST(ArrayBuffer_Compaction) {
+  FLAG_manual_evacuation_candidates_selection = true;
+  CcTest::InitializeVM();
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  Heap* heap = reinterpret_cast<Isolate*>(isolate)->heap();
+  heap::AbandonCurrentlyFreeMemory(heap->old_space());
+
+  v8::HandleScope handle_scope(isolate);
+  Local<v8::ArrayBuffer> ab1 = v8::ArrayBuffer::New(isolate, 100);
+  Handle<JSArrayBuffer> buf1 = v8::Utils::OpenHandle(*ab1);
+  VerifyTrackedInNewSpace(*buf1);
+  heap::GcAndSweep(heap, NEW_SPACE);
+  heap::GcAndSweep(heap, NEW_SPACE);
+
+  Page* page_before_gc = Page::FromAddress(buf1->address());
+  page_before_gc->SetFlag(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING);
+  VerifyTrackedInOldSpace(*buf1);
+
+  heap->CollectAllGarbage();
+
+  Page* page_after_gc = Page::FromAddress(buf1->address());
+  VerifyTrackedInOldSpace(*buf1);
+
+  CHECK_NE(page_before_gc, page_after_gc);
+}
+
+}  // namespace internal
+}  // namespace v8