deps/v8/src/heap/incremental-marking.cc

   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/v8.h"
   6
   7 #include "src/heap/incremental-marking.h"
   8
   9 #include "src/code-stubs.h"
  10 #include "src/compilation-cache.h"
  11 #include "src/conversions.h"
  12 #include "src/heap/objects-visiting.h"
  13 #include "src/heap/objects-visiting-inl.h"
  14
  15 namespace v8 {
  16 namespace internal {
  17
  18
  19 IncrementalMarking::StepActions IncrementalMarking::IdleStepActions() {
  20   return StepActions(IncrementalMarking::NO_GC_VIA_STACK_GUARD,
  21                      IncrementalMarking::FORCE_MARKING,
  22                      IncrementalMarking::DO_NOT_FORCE_COMPLETION);
  23 }
  24
  25
  26 IncrementalMarking::IncrementalMarking(Heap* heap)
  27     : heap_(heap),
  28       state_(STOPPED),
  29       is_compacting_(false),
  30       steps_count_(0),
  31       old_generation_space_available_at_start_of_incremental_(0),
  32       old_generation_space_used_at_start_of_incremental_(0),
  33       bytes_rescanned_(0),
  34       should_hurry_(false),
  35       marking_speed_(0),
  36       bytes_scanned_(0),
  37       allocated_(0),
  38       write_barriers_invoked_since_last_step_(0),
  39       idle_marking_delay_counter_(0),
  40       no_marking_scope_depth_(0),
  41       unscanned_bytes_of_large_object_(0),
  42       was_activated_(false),
  43       weak_closure_was_overapproximated_(false),
  44       weak_closure_approximation_rounds_(0),
  45       request_type_(COMPLETE_MARKING),
  46       gc_callback_flags_(kNoGCCallbackFlags) {}
  47
  48
  49 void IncrementalMarking::RecordWriteSlow(HeapObject* obj, Object** slot,
  50                                          Object* value) {
  51   if (BaseRecordWrite(obj, slot, value) && slot != NULL) {
  52     MarkBit obj_bit = Marking::MarkBitFrom(obj);
  53     if (Marking::IsBlack(obj_bit)) {
  54       // Object is not going to be rescanned we need to record the slot.
  55       heap_->mark_compact_collector()->RecordSlot(HeapObject::RawField(obj, 0),
  56                                                   slot, value);
  57     }
  58   }
  59 }
  60
  61
  62 void IncrementalMarking::RecordWriteFromCode(HeapObject* obj, Object** slot,
  63                                              Isolate* isolate) {
  64   DCHECK(obj->IsHeapObject());
  65   IncrementalMarking* marking = isolate->heap()->incremental_marking();
  66
  67   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
  68   int counter = chunk->write_barrier_counter();
  69   if (counter < (MemoryChunk::kWriteBarrierCounterGranularity / 2)) {
  70     marking->write_barriers_invoked_since_last_step_ +=
  71         MemoryChunk::kWriteBarrierCounterGranularity -
  72         chunk->write_barrier_counter();
  73     chunk->set_write_barrier_counter(
  74         MemoryChunk::kWriteBarrierCounterGranularity);
  75   }
  76
  77   marking->RecordWrite(obj, slot, *slot);
  78 }
  79
  80
  81 void IncrementalMarking::RecordCodeTargetPatch(Code* host, Address pc,
  82                                                HeapObject* value) {
  83   if (IsMarking()) {
  84     RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
  85     RecordWriteIntoCode(host, &rinfo, value);
  86   }
  87 }
  88
  89
  90 void IncrementalMarking::RecordCodeTargetPatch(Address pc, HeapObject* value) {
  91   if (IsMarking()) {
  92     Code* host = heap_->isolate()
  93                      ->inner_pointer_to_code_cache()
  94                      ->GcSafeFindCodeForInnerPointer(pc);
  95     RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
  96     RecordWriteIntoCode(host, &rinfo, value);
  97   }
  98 }
  99
 100
 101 void IncrementalMarking::RecordWriteOfCodeEntrySlow(JSFunction* host,
 102                                                     Object** slot,
 103                                                     Code* value) {
 104   if (BaseRecordWrite(host, slot, value)) {
 105     DCHECK(slot != NULL);
 106     heap_->mark_compact_collector()->RecordCodeEntrySlot(
 107         reinterpret_cast<Address>(slot), value);
 108   }
 109 }
 110
 111
 112 void IncrementalMarking::RecordWriteIntoCodeSlow(HeapObject* obj,
 113                                                  RelocInfo* rinfo,
 114                                                  Object* value) {
 115   MarkBit value_bit = Marking::MarkBitFrom(HeapObject::cast(value));
 116   if (Marking::IsWhite(value_bit)) {
 117     MarkBit obj_bit = Marking::MarkBitFrom(obj);
 118     if (Marking::IsBlack(obj_bit)) {
 119       BlackToGreyAndUnshift(obj, obj_bit);
 120       RestartIfNotMarking();
 121     }
 122     // Object is either grey or white.  It will be scanned if survives.
 123     return;
 124   }
 125
 126   if (is_compacting_) {
 127     MarkBit obj_bit = Marking::MarkBitFrom(obj);
 128     if (Marking::IsBlack(obj_bit)) {
 129       // Object is not going to be rescanned.  We need to record the slot.
 130       heap_->mark_compact_collector()->RecordRelocSlot(rinfo,
 131                                                        Code::cast(value));
 132     }
 133   }
 134 }
 135
 136
 137 static void MarkObjectGreyDoNotEnqueue(Object* obj) {
 138   if (obj->IsHeapObject()) {
 139     HeapObject* heap_obj = HeapObject::cast(obj);
 140     MarkBit mark_bit = Marking::MarkBitFrom(HeapObject::cast(obj));
 141     if (Marking::IsBlack(mark_bit)) {
 142       MemoryChunk::IncrementLiveBytesFromGC(heap_obj->address(),
 143                                             -heap_obj->Size());
 144     }
 145     Marking::AnyToGrey(mark_bit);
 146   }
 147 }
 148
 149
 150 static inline void MarkBlackOrKeepBlack(HeapObject* heap_object,
 151                                         MarkBit mark_bit, int size) {
 152   DCHECK(!Marking::IsImpossible(mark_bit));
 153   if (Marking::IsBlack(mark_bit)) return;
 154   Marking::MarkBlack(mark_bit);
 155   MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(), size);
 156 }
 157
 158
 159 class IncrementalMarkingMarkingVisitor
 160     : public StaticMarkingVisitor<IncrementalMarkingMarkingVisitor> {
 161  public:
 162   static void Initialize() {
 163     StaticMarkingVisitor<IncrementalMarkingMarkingVisitor>::Initialize();
 164     table_.Register(kVisitFixedArray, &VisitFixedArrayIncremental);
 165     table_.Register(kVisitNativeContext, &VisitNativeContextIncremental);
 166     table_.Register(kVisitJSRegExp, &VisitJSRegExp);
 167   }
 168
 169   static const int kProgressBarScanningChunk = 32 * 1024;
 170
 171   static void VisitFixedArrayIncremental(Map* map, HeapObject* object) {
 172     MemoryChunk* chunk = MemoryChunk::FromAddress(object->address());
 173     // TODO(mstarzinger): Move setting of the flag to the allocation site of
 174     // the array. The visitor should just check the flag.
 175     if (FLAG_use_marking_progress_bar &&
 176         chunk->owner()->identity() == LO_SPACE) {
 177       chunk->SetFlag(MemoryChunk::HAS_PROGRESS_BAR);
 178     }
 179     if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
 180       Heap* heap = map->GetHeap();
 181       // When using a progress bar for large fixed arrays, scan only a chunk of
 182       // the array and try to push it onto the marking deque again until it is
 183       // fully scanned. Fall back to scanning it through to the end in case this
 184       // fails because of a full deque.
 185       int object_size = FixedArray::BodyDescriptor::SizeOf(map, object);
 186       int start_offset =
 187           Max(FixedArray::BodyDescriptor::kStartOffset, chunk->progress_bar());
 188       int end_offset =
 189           Min(object_size, start_offset + kProgressBarScanningChunk);
 190       int already_scanned_offset = start_offset;
 191       bool scan_until_end = false;
 192       do {
 193         VisitPointersWithAnchor(heap, HeapObject::RawField(object, 0),
 194                                 HeapObject::RawField(object, start_offset),
 195                                 HeapObject::RawField(object, end_offset));
 196         start_offset = end_offset;
 197         end_offset = Min(object_size, end_offset + kProgressBarScanningChunk);
 198         scan_until_end =
 199             heap->mark_compact_collector()->marking_deque()->IsFull();
 200       } while (scan_until_end && start_offset < object_size);
 201       chunk->set_progress_bar(start_offset);
 202       if (start_offset < object_size) {
 203         if (Marking::IsGrey(Marking::MarkBitFrom(object))) {
 204           heap->mark_compact_collector()->marking_deque()->UnshiftGrey(object);
 205         } else {
 206           DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
 207           heap->mark_compact_collector()->marking_deque()->UnshiftBlack(object);
 208         }
 209         heap->incremental_marking()->NotifyIncompleteScanOfObject(
 210             object_size - (start_offset - already_scanned_offset));
 211       }
 212     } else {
 213       FixedArrayVisitor::Visit(map, object);
 214     }
 215   }
 216
 217   static void VisitNativeContextIncremental(Map* map, HeapObject* object) {
 218     Context* context = Context::cast(object);
 219
 220     // We will mark cache black with a separate pass when we finish marking.
 221     // Note that GC can happen when the context is not fully initialized,
 222     // so the cache can be undefined.
 223     Object* cache = context->get(Context::NORMALIZED_MAP_CACHE_INDEX);
 224     if (!cache->IsUndefined()) {
 225       MarkObjectGreyDoNotEnqueue(cache);
 226     }
 227     VisitNativeContext(map, context);
 228   }
 229
 230   INLINE(static void VisitPointer(Heap* heap, Object** p)) {
 231     Object* obj = *p;
 232     if (obj->IsHeapObject()) {
 233       heap->mark_compact_collector()->RecordSlot(p, p, obj);
 234       MarkObject(heap, obj);
 235     }
 236   }
 237
 238   INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {
 239     for (Object** p = start; p < end; p++) {
 240       Object* obj = *p;
 241       if (obj->IsHeapObject()) {
 242         heap->mark_compact_collector()->RecordSlot(start, p, obj);
 243         MarkObject(heap, obj);
 244       }
 245     }
 246   }
 247
 248   INLINE(static void VisitPointersWithAnchor(Heap* heap, Object** anchor,
 249                                              Object** start, Object** end)) {
 250     for (Object** p = start; p < end; p++) {
 251       Object* obj = *p;
 252       if (obj->IsHeapObject()) {
 253         heap->mark_compact_collector()->RecordSlot(anchor, p, obj);
 254         MarkObject(heap, obj);
 255       }
 256     }
 257   }
 258
 259   // Marks the object grey and pushes it on the marking stack.
 260   INLINE(static void MarkObject(Heap* heap, Object* obj)) {
 261     IncrementalMarking::MarkObject(heap, HeapObject::cast(obj));
 262   }
 263
 264   // Marks the object black without pushing it on the marking stack.
 265   // Returns true if object needed marking and false otherwise.
 266   INLINE(static bool MarkObjectWithoutPush(Heap* heap, Object* obj)) {
 267     HeapObject* heap_object = HeapObject::cast(obj);
 268     MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
 269     if (Marking::IsWhite(mark_bit)) {
 270       Marking::MarkBlack(mark_bit);
 271       MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(),
 272                                             heap_object->Size());
 273       return true;
 274     }
 275     return false;
 276   }
 277 };
 278
 279
 280 class IncrementalMarkingRootMarkingVisitor : public ObjectVisitor {
 281  public:
 282   explicit IncrementalMarkingRootMarkingVisitor(
 283       IncrementalMarking* incremental_marking)
 284       : heap_(incremental_marking->heap()) {}
 285
 286   void VisitPointer(Object** p) { MarkObjectByPointer(p); }
 287
 288   void VisitPointers(Object** start, Object** end) {
 289     for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
 290   }
 291
 292  private:
 293   void MarkObjectByPointer(Object** p) {
 294     Object* obj = *p;
 295     if (!obj->IsHeapObject()) return;
 296
 297     IncrementalMarking::MarkObject(heap_, HeapObject::cast(obj));
 298   }
 299
 300   Heap* heap_;
 301 };
 302
 303
 304 void IncrementalMarking::Initialize() {
 305   IncrementalMarkingMarkingVisitor::Initialize();
 306 }
 307
 308
 309 void IncrementalMarking::SetOldSpacePageFlags(MemoryChunk* chunk,
 310                                               bool is_marking,
 311                                               bool is_compacting) {
 312   if (is_marking) {
 313     chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
 314     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
 315
 316     // It's difficult to filter out slots recorded for large objects.
 317     if (chunk->owner()->identity() == LO_SPACE &&
 318         chunk->size() > static_cast<size_t>(Page::kPageSize) && is_compacting) {
 319       chunk->SetFlag(MemoryChunk::RESCAN_ON_EVACUATION);
 320     }
 321   } else {
 322     chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
 323     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
 324   }
 325 }
 326
 327
 328 void IncrementalMarking::SetNewSpacePageFlags(NewSpacePage* chunk,
 329                                               bool is_marking) {
 330   chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
 331   if (is_marking) {
 332     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
 333   } else {
 334     chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
 335   }
 336   chunk->SetFlag(MemoryChunk::SCAN_ON_SCAVENGE);
 337 }
 338
 339
 340 void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
 341     PagedSpace* space) {
 342   PageIterator it(space);
 343   while (it.has_next()) {
 344     Page* p = it.next();
 345     SetOldSpacePageFlags(p, false, false);
 346   }
 347 }
 348
 349
 350 void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
 351     NewSpace* space) {
 352   NewSpacePageIterator it(space);
 353   while (it.has_next()) {
 354     NewSpacePage* p = it.next();
 355     SetNewSpacePageFlags(p, false);
 356   }
 357 }
 358
 359
 360 void IncrementalMarking::DeactivateIncrementalWriteBarrier() {
 361   DeactivateIncrementalWriteBarrierForSpace(heap_->old_space());
 362   DeactivateIncrementalWriteBarrierForSpace(heap_->map_space());
 363   DeactivateIncrementalWriteBarrierForSpace(heap_->code_space());
 364   DeactivateIncrementalWriteBarrierForSpace(heap_->new_space());
 365
 366   LargePage* lop = heap_->lo_space()->first_page();
 367   while (LargePage::IsValid(lop)) {
 368     SetOldSpacePageFlags(lop, false, false);
 369     lop = lop->next_page();
 370   }
 371 }
 372
 373
 374 void IncrementalMarking::ActivateIncrementalWriteBarrier(PagedSpace* space) {
 375   PageIterator it(space);
 376   while (it.has_next()) {
 377     Page* p = it.next();
 378     SetOldSpacePageFlags(p, true, is_compacting_);
 379   }
 380 }
 381
 382
 383 void IncrementalMarking::ActivateIncrementalWriteBarrier(NewSpace* space) {
 384   NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
 385   while (it.has_next()) {
 386     NewSpacePage* p = it.next();
 387     SetNewSpacePageFlags(p, true);
 388   }
 389 }
 390
 391
 392 void IncrementalMarking::ActivateIncrementalWriteBarrier() {
 393   ActivateIncrementalWriteBarrier(heap_->old_space());
 394   ActivateIncrementalWriteBarrier(heap_->map_space());
 395   ActivateIncrementalWriteBarrier(heap_->code_space());
 396   ActivateIncrementalWriteBarrier(heap_->new_space());
 397
 398   LargePage* lop = heap_->lo_space()->first_page();
 399   while (LargePage::IsValid(lop)) {
 400     SetOldSpacePageFlags(lop, true, is_compacting_);
 401     lop = lop->next_page();
 402   }
 403 }
 404
 405
 406 bool IncrementalMarking::ShouldActivateEvenWithoutIdleNotification() {
 407   return CanBeActivated() &&
 408          heap_->HeapIsFullEnoughToStartIncrementalMarking(
 409              heap_->old_generation_allocation_limit());
 410 }
 411
 412
 413 bool IncrementalMarking::WasActivated() { return was_activated_; }
 414
 415
 416 bool IncrementalMarking::CanBeActivated() {
 417 #ifndef DEBUG
 418   static const intptr_t kActivationThreshold = 8 * MB;
 419 #else
 420   // TODO(gc) consider setting this to some low level so that some
 421   // debug tests run with incremental marking and some without.
 422   static const intptr_t kActivationThreshold = 0;
 423 #endif
 424   // Only start incremental marking in a safe state: 1) when incremental
 425   // marking is turned on, 2) when we are currently not in a GC, and
 426   // 3) when we are currently not serializing or deserializing the heap.
 427   // Don't switch on for very small heaps.
 428   return FLAG_incremental_marking && FLAG_incremental_marking_steps &&
 429          heap_->gc_state() == Heap::NOT_IN_GC &&
 430          heap_->deserialization_complete() &&
 431          !heap_->isolate()->serializer_enabled() &&
 432          heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
 433 }
 434
 435
 436 void IncrementalMarking::ActivateGeneratedStub(Code* stub) {
 437   DCHECK(RecordWriteStub::GetMode(stub) == RecordWriteStub::STORE_BUFFER_ONLY);
 438
 439   if (!IsMarking()) {
 440     // Initially stub is generated in STORE_BUFFER_ONLY mode thus
 441     // we don't need to do anything if incremental marking is
 442     // not active.
 443   } else if (IsCompacting()) {
 444     RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL_COMPACTION);
 445   } else {
 446     RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL);
 447   }
 448 }
 449
 450
 451 void IncrementalMarking::NotifyOfHighPromotionRate() {
 452   if (IsMarking()) {
 453     if (marking_speed_ < kFastMarking) {
 454       if (FLAG_trace_gc) {
 455         PrintIsolate(heap()->isolate(),
 456                      "Increasing marking speed to %d "
 457                      "due to high promotion rate\n",
 458                      static_cast<int>(kFastMarking));
 459       }
 460       marking_speed_ = kFastMarking;
 461     }
 462   }
 463 }
 464
 465
 466 static void PatchIncrementalMarkingRecordWriteStubs(
 467     Heap* heap, RecordWriteStub::Mode mode) {
 468   UnseededNumberDictionary* stubs = heap->code_stubs();
 469
 470   int capacity = stubs->Capacity();
 471   for (int i = 0; i < capacity; i++) {
 472     Object* k = stubs->KeyAt(i);
 473     if (stubs->IsKey(k)) {
 474       uint32_t key = NumberToUint32(k);
 475
 476       if (CodeStub::MajorKeyFromKey(key) == CodeStub::RecordWrite) {
 477         Object* e = stubs->ValueAt(i);
 478         if (e->IsCode()) {
 479           RecordWriteStub::Patch(Code::cast(e), mode);
 480         }
 481       }
 482     }
 483   }
 484 }
 485
 486
 487 void IncrementalMarking::Start(int mark_compact_flags,
 488                                const GCCallbackFlags gc_callback_flags,
 489                                const char* reason) {
 490   if (FLAG_trace_incremental_marking) {
 491     PrintF("[IncrementalMarking] Start (%s)\n",
 492            (reason == nullptr) ? "unknown reason" : reason);
 493   }
 494   DCHECK(FLAG_incremental_marking);
 495   DCHECK(FLAG_incremental_marking_steps);
 496   DCHECK(state_ == STOPPED);
 497   DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
 498   DCHECK(!heap_->isolate()->serializer_enabled());
 499
 500   ResetStepCounters();
 501
 502   gc_callback_flags_ = gc_callback_flags;
 503   was_activated_ = true;
 504
 505   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
 506     heap_->mark_compact_collector()->SetFlags(mark_compact_flags);
 507     StartMarking();
 508     heap_->mark_compact_collector()->SetFlags(Heap::kNoGCFlags);
 509   } else {
 510     if (FLAG_trace_incremental_marking) {
 511       PrintF("[IncrementalMarking] Start sweeping.\n");
 512     }
 513     state_ = SWEEPING;
 514   }
 515
 516   heap_->new_space()->LowerInlineAllocationLimit(kAllocatedThreshold);
 517 }
 518
 519
 520 void IncrementalMarking::StartMarking() {
 521   if (FLAG_trace_incremental_marking) {
 522     PrintF("[IncrementalMarking] Start marking\n");
 523   }
 524
 525   is_compacting_ = !FLAG_never_compact &&
 526                    heap_->mark_compact_collector()->StartCompaction(
 527                        MarkCompactCollector::INCREMENTAL_COMPACTION);
 528
 529   state_ = MARKING;
 530
 531   RecordWriteStub::Mode mode = is_compacting_
 532                                    ? RecordWriteStub::INCREMENTAL_COMPACTION
 533                                    : RecordWriteStub::INCREMENTAL;
 534
 535   PatchIncrementalMarkingRecordWriteStubs(heap_, mode);
 536
 537   heap_->mark_compact_collector()->EnsureMarkingDequeIsCommittedAndInitialize(
 538       MarkCompactCollector::kMaxMarkingDequeSize);
 539
 540   ActivateIncrementalWriteBarrier();
 541
 542 // Marking bits are cleared by the sweeper.
 543 #ifdef VERIFY_HEAP
 544   if (FLAG_verify_heap) {
 545     heap_->mark_compact_collector()->VerifyMarkbitsAreClean();
 546   }
 547 #endif
 548
 549   heap_->CompletelyClearInstanceofCache();
 550   heap_->isolate()->compilation_cache()->MarkCompactPrologue();
 551
 552   if (FLAG_cleanup_code_caches_at_gc) {
 553     // We will mark cache black with a separate pass
 554     // when we finish marking.
 555     MarkObjectGreyDoNotEnqueue(heap_->polymorphic_code_cache());
 556   }
 557
 558   // Mark strong roots grey.
 559   IncrementalMarkingRootMarkingVisitor visitor(this);
 560   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
 561
 562   // Ready to start incremental marking.
 563   if (FLAG_trace_incremental_marking) {
 564     PrintF("[IncrementalMarking] Running\n");
 565   }
 566 }
 567
 568
 569 void IncrementalMarking::MarkObjectGroups() {
 570   DCHECK(FLAG_overapproximate_weak_closure);
 571   DCHECK(!weak_closure_was_overapproximated_);
 572
 573   int old_marking_deque_top =
 574       heap_->mark_compact_collector()->marking_deque()->top();
 575
 576   heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
 577
 578   IncrementalMarkingRootMarkingVisitor visitor(this);
 579   heap_->isolate()->global_handles()->IterateObjectGroups(
 580       &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
 581
 582   int marking_progress =
 583       abs(old_marking_deque_top -
 584           heap_->mark_compact_collector()->marking_deque()->top());
 585
 586   ++weak_closure_approximation_rounds_;
 587   if ((weak_closure_approximation_rounds_ >=
 588        FLAG_max_object_groups_marking_rounds) ||
 589       (marking_progress < FLAG_min_progress_during_object_groups_marking)) {
 590     weak_closure_was_overapproximated_ = true;
 591   }
 592
 593   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
 594   heap_->isolate()->global_handles()->RemoveObjectGroups();
 595 }
 596
 597
 598 void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
 599   if (!IsMarking()) return;
 600
 601   MarkingDeque* marking_deque =
 602       heap_->mark_compact_collector()->marking_deque();
 603   int current = marking_deque->bottom();
 604   int mask = marking_deque->mask();
 605   int limit = marking_deque->top();
 606   HeapObject** array = marking_deque->array();
 607   int new_top = current;
 608
 609   Map* filler_map = heap_->one_pointer_filler_map();
 610
 611   while (current != limit) {
 612     HeapObject* obj = array[current];
 613     DCHECK(obj->IsHeapObject());
 614     current = ((current + 1) & mask);
 615     if (heap_->InNewSpace(obj)) {
 616       MapWord map_word = obj->map_word();
 617       if (map_word.IsForwardingAddress()) {
 618         HeapObject* dest = map_word.ToForwardingAddress();
 619         array[new_top] = dest;
 620         new_top = ((new_top + 1) & mask);
 621         DCHECK(new_top != marking_deque->bottom());
 622 #ifdef DEBUG
 623         MarkBit mark_bit = Marking::MarkBitFrom(obj);
 624         DCHECK(Marking::IsGrey(mark_bit) ||
 625                (obj->IsFiller() && Marking::IsWhite(mark_bit)));
 626 #endif
 627       }
 628     } else if (obj->map() != filler_map) {
 629       // Skip one word filler objects that appear on the
 630       // stack when we perform in place array shift.
 631       array[new_top] = obj;
 632       new_top = ((new_top + 1) & mask);
 633       DCHECK(new_top != marking_deque->bottom());
 634 #ifdef DEBUG
 635       MarkBit mark_bit = Marking::MarkBitFrom(obj);
 636       MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
 637       DCHECK(Marking::IsGrey(mark_bit) ||
 638              (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||
 639              (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
 640               Marking::IsBlack(mark_bit)));
 641 #endif
 642     }
 643   }
 644   marking_deque->set_top(new_top);
 645 }
 646
 647
 648 void IncrementalMarking::VisitObject(Map* map, HeapObject* obj, int size) {
 649   MarkObject(heap_, map);
 650
 651   IncrementalMarkingMarkingVisitor::IterateBody(map, obj);
 652
 653   MarkBit mark_bit = Marking::MarkBitFrom(obj);
 654 #if ENABLE_SLOW_DCHECKS
 655   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
 656   SLOW_DCHECK(Marking::IsGrey(mark_bit) ||
 657               (obj->IsFiller() && Marking::IsWhite(mark_bit)) ||
 658               (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR) &&
 659                Marking::IsBlack(mark_bit)));
 660 #endif
 661   MarkBlackOrKeepBlack(obj, mark_bit, size);
 662 }
 663
 664
 665 void IncrementalMarking::MarkObject(Heap* heap, HeapObject* obj) {
 666   MarkBit mark_bit = Marking::MarkBitFrom(obj);
 667   if (Marking::IsWhite(mark_bit)) {
 668     heap->incremental_marking()->WhiteToGreyAndPush(obj, mark_bit);
 669   }
 670 }
 671
 672
 673 intptr_t IncrementalMarking::ProcessMarkingDeque(intptr_t bytes_to_process) {
 674   intptr_t bytes_processed = 0;
 675   Map* filler_map = heap_->one_pointer_filler_map();
 676   MarkingDeque* marking_deque =
 677       heap_->mark_compact_collector()->marking_deque();
 678   while (!marking_deque->IsEmpty() && bytes_processed < bytes_to_process) {
 679     HeapObject* obj = marking_deque->Pop();
 680
 681     // Explicitly skip one word fillers. Incremental markbit patterns are
 682     // correct only for objects that occupy at least two words.
 683     Map* map = obj->map();
 684     if (map == filler_map) continue;
 685
 686     int size = obj->SizeFromMap(map);
 687     unscanned_bytes_of_large_object_ = 0;
 688     VisitObject(map, obj, size);
 689     bytes_processed += size - unscanned_bytes_of_large_object_;
 690   }
 691   return bytes_processed;
 692 }
 693
 694
 695 void IncrementalMarking::ProcessMarkingDeque() {
 696   Map* filler_map = heap_->one_pointer_filler_map();
 697   MarkingDeque* marking_deque =
 698       heap_->mark_compact_collector()->marking_deque();
 699   while (!marking_deque->IsEmpty()) {
 700     HeapObject* obj = marking_deque->Pop();
 701
 702     // Explicitly skip one word fillers. Incremental markbit patterns are
 703     // correct only for objects that occupy at least two words.
 704     Map* map = obj->map();
 705     if (map == filler_map) continue;
 706
 707     VisitObject(map, obj, obj->SizeFromMap(map));
 708   }
 709 }
 710
 711
 712 void IncrementalMarking::Hurry() {
 713   if (state() == MARKING) {
 714     double start = 0.0;
 715     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
 716       start = base::OS::TimeCurrentMillis();
 717       if (FLAG_trace_incremental_marking) {
 718         PrintF("[IncrementalMarking] Hurry\n");
 719       }
 720     }
 721     // TODO(gc) hurry can mark objects it encounters black as mutator
 722     // was stopped.
 723     ProcessMarkingDeque();
 724     state_ = COMPLETE;
 725     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
 726       double end = base::OS::TimeCurrentMillis();
 727       double delta = end - start;
 728       heap_->tracer()->AddMarkingTime(delta);
 729       if (FLAG_trace_incremental_marking) {
 730         PrintF("[IncrementalMarking] Complete (hurry), spent %d ms.\n",
 731                static_cast<int>(delta));
 732       }
 733     }
 734   }
 735
 736   if (FLAG_cleanup_code_caches_at_gc) {
 737     PolymorphicCodeCache* poly_cache = heap_->polymorphic_code_cache();
 738     Marking::GreyToBlack(Marking::MarkBitFrom(poly_cache));
 739     MemoryChunk::IncrementLiveBytesFromGC(poly_cache->address(),
 740                                           PolymorphicCodeCache::kSize);
 741   }
 742
 743   Object* context = heap_->native_contexts_list();
 744   while (!context->IsUndefined()) {
 745     // GC can happen when the context is not fully initialized,
 746     // so the cache can be undefined.
 747     HeapObject* cache = HeapObject::cast(
 748         Context::cast(context)->get(Context::NORMALIZED_MAP_CACHE_INDEX));
 749     if (!cache->IsUndefined()) {
 750       MarkBit mark_bit = Marking::MarkBitFrom(cache);
 751       if (Marking::IsGrey(mark_bit)) {
 752         Marking::GreyToBlack(mark_bit);
 753         MemoryChunk::IncrementLiveBytesFromGC(cache->address(), cache->Size());
 754       }
 755     }
 756     context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
 757   }
 758 }
 759
 760
 761 void IncrementalMarking::Abort() {
 762   if (IsStopped()) return;
 763   if (FLAG_trace_incremental_marking) {
 764     PrintF("[IncrementalMarking] Aborting.\n");
 765   }
 766   heap_->new_space()->LowerInlineAllocationLimit(0);
 767   IncrementalMarking::set_should_hurry(false);
 768   ResetStepCounters();
 769   if (IsMarking()) {
 770     PatchIncrementalMarkingRecordWriteStubs(heap_,
 771                                             RecordWriteStub::STORE_BUFFER_ONLY);
 772     DeactivateIncrementalWriteBarrier();
 773
 774     if (is_compacting_) {
 775       LargeObjectIterator it(heap_->lo_space());
 776       for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
 777         Page* p = Page::FromAddress(obj->address());
 778         if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
 779           p->ClearFlag(Page::RESCAN_ON_EVACUATION);
 780         }
 781       }
 782     }
 783   }
 784   heap_->isolate()->stack_guard()->ClearGC();
 785   state_ = STOPPED;
 786   is_compacting_ = false;
 787 }
 788
 789
 790 void IncrementalMarking::Finalize() {
 791   Hurry();
 792   state_ = STOPPED;
 793   is_compacting_ = false;
 794   heap_->new_space()->LowerInlineAllocationLimit(0);
 795   IncrementalMarking::set_should_hurry(false);
 796   ResetStepCounters();
 797   PatchIncrementalMarkingRecordWriteStubs(heap_,
 798                                           RecordWriteStub::STORE_BUFFER_ONLY);
 799   DeactivateIncrementalWriteBarrier();
 800   DCHECK(heap_->mark_compact_collector()->marking_deque()->IsEmpty());
 801   heap_->isolate()->stack_guard()->ClearGC();
 802 }
 803
 804
 805 void IncrementalMarking::OverApproximateWeakClosure(CompletionAction action) {
 806   DCHECK(FLAG_overapproximate_weak_closure);
 807   DCHECK(!weak_closure_was_overapproximated_);
 808   if (FLAG_trace_incremental_marking) {
 809     PrintF("[IncrementalMarking] requesting weak closure overapproximation.\n");
 810   }
 811   request_type_ = OVERAPPROXIMATION;
 812   if (action == GC_VIA_STACK_GUARD) {
 813     heap_->isolate()->stack_guard()->RequestGC();
 814   }
 815 }
 816
 817
 818 void IncrementalMarking::MarkingComplete(CompletionAction action) {
 819   state_ = COMPLETE;
 820   // We will set the stack guard to request a GC now.  This will mean the rest
 821   // of the GC gets performed as soon as possible (we can't do a GC here in a
 822   // record-write context).  If a few things get allocated between now and then
 823   // that shouldn't make us do a scavenge and keep being incremental, so we set
 824   // the should-hurry flag to indicate that there can't be much work left to do.
 825   set_should_hurry(true);
 826   if (FLAG_trace_incremental_marking) {
 827     PrintF("[IncrementalMarking] Complete (normal).\n");
 828   }
 829   request_type_ = COMPLETE_MARKING;
 830   if (action == GC_VIA_STACK_GUARD) {
 831     heap_->isolate()->stack_guard()->RequestGC();
 832   }
 833 }
 834
 835
 836 void IncrementalMarking::Epilogue() {
 837   was_activated_ = false;
 838   weak_closure_was_overapproximated_ = false;
 839   weak_closure_approximation_rounds_ = 0;
 840 }
 841
 842
 843 void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
 844   if (IsStopped() && ShouldActivateEvenWithoutIdleNotification()) {
 845     Start(Heap::kNoGCFlags, kNoGCCallbackFlags, "old space step");
 846   } else {
 847     Step(allocated * kFastMarking / kInitialMarkingSpeed, GC_VIA_STACK_GUARD);
 848   }
 849 }
 850
 851
 852 void IncrementalMarking::SpeedUp() {
 853   bool speed_up = false;
 854
 855   if ((steps_count_ % kMarkingSpeedAccellerationInterval) == 0) {
 856     if (FLAG_trace_incremental_marking) {
 857       PrintIsolate(heap()->isolate(), "Speed up marking after %d steps\n",
 858                    static_cast<int>(kMarkingSpeedAccellerationInterval));
 859     }
 860     speed_up = true;
 861   }
 862
 863   bool space_left_is_very_small =
 864       (old_generation_space_available_at_start_of_incremental_ < 10 * MB);
 865
 866   bool only_1_nth_of_space_that_was_available_still_left =
 867       (SpaceLeftInOldSpace() * (marking_speed_ + 1) <
 868        old_generation_space_available_at_start_of_incremental_);
 869
 870   if (space_left_is_very_small ||
 871       only_1_nth_of_space_that_was_available_still_left) {
 872     if (FLAG_trace_incremental_marking)
 873       PrintIsolate(heap()->isolate(),
 874                    "Speed up marking because of low space left\n");
 875     speed_up = true;
 876   }
 877
 878   bool size_of_old_space_multiplied_by_n_during_marking =
 879       (heap_->PromotedTotalSize() >
 880        (marking_speed_ + 1) *
 881            old_generation_space_used_at_start_of_incremental_);
 882   if (size_of_old_space_multiplied_by_n_during_marking) {
 883     speed_up = true;
 884     if (FLAG_trace_incremental_marking) {
 885       PrintIsolate(heap()->isolate(),
 886                    "Speed up marking because of heap size increase\n");
 887     }
 888   }
 889
 890   int64_t promoted_during_marking =
 891       heap_->PromotedTotalSize() -
 892       old_generation_space_used_at_start_of_incremental_;
 893   intptr_t delay = marking_speed_ * MB;
 894   intptr_t scavenge_slack = heap_->MaxSemiSpaceSize();
 895
 896   // We try to scan at at least twice the speed that we are allocating.
 897   if (promoted_during_marking > bytes_scanned_ / 2 + scavenge_slack + delay) {
 898     if (FLAG_trace_incremental_marking) {
 899       PrintIsolate(heap()->isolate(),
 900                    "Speed up marking because marker was not keeping up\n");
 901     }
 902     speed_up = true;
 903   }
 904
 905   if (speed_up) {
 906     if (state_ != MARKING) {
 907       if (FLAG_trace_incremental_marking) {
 908         PrintIsolate(heap()->isolate(),
 909                      "Postponing speeding up marking until marking starts\n");
 910       }
 911     } else {
 912       marking_speed_ += kMarkingSpeedAccelleration;
 913       marking_speed_ = static_cast<int>(
 914           Min(kMaxMarkingSpeed, static_cast<intptr_t>(marking_speed_ * 1.3)));
 915       if (FLAG_trace_incremental_marking) {
 916         PrintIsolate(heap()->isolate(), "Marking speed increased to %d\n",
 917                      marking_speed_);
 918       }
 919     }
 920   }
 921 }
 922
 923
 924 intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
 925                                   CompletionAction action,
 926                                   ForceMarkingAction marking,
 927                                   ForceCompletionAction completion) {
 928   if (heap_->gc_state() != Heap::NOT_IN_GC || !FLAG_incremental_marking ||
 929       !FLAG_incremental_marking_steps ||
 930       (state_ != SWEEPING && state_ != MARKING)) {
 931     return 0;
 932   }
 933
 934   allocated_ += allocated_bytes;
 935
 936   if (marking == DO_NOT_FORCE_MARKING && allocated_ < kAllocatedThreshold &&
 937       write_barriers_invoked_since_last_step_ <
 938           kWriteBarriersInvokedThreshold) {
 939     return 0;
 940   }
 941
 942   // If an idle notification happened recently, we delay marking steps.
 943   if (marking == DO_NOT_FORCE_MARKING &&
 944       heap_->RecentIdleNotificationHappened()) {
 945     return 0;
 946   }
 947
 948   if (state_ == MARKING && no_marking_scope_depth_ > 0) return 0;
 949
 950   intptr_t bytes_processed = 0;
 951   {
 952     HistogramTimerScope incremental_marking_scope(
 953         heap_->isolate()->counters()->gc_incremental_marking());
 954     double start = base::OS::TimeCurrentMillis();
 955
 956     // The marking speed is driven either by the allocation rate or by the rate
 957     // at which we are having to check the color of objects in the write
 958     // barrier.
 959     // It is possible for a tight non-allocating loop to run a lot of write
 960     // barriers before we get here and check them (marking can only take place
 961     // on
 962     // allocation), so to reduce the lumpiness we don't use the write barriers
 963     // invoked since last step directly to determine the amount of work to do.
 964     intptr_t bytes_to_process =
 965         marking_speed_ *
 966         Max(allocated_, write_barriers_invoked_since_last_step_);
 967     allocated_ = 0;
 968     write_barriers_invoked_since_last_step_ = 0;
 969
 970     bytes_scanned_ += bytes_to_process;
 971
 972     if (state_ == SWEEPING) {
 973       if (heap_->mark_compact_collector()->sweeping_in_progress() &&
 974           (heap_->mark_compact_collector()->IsSweepingCompleted() ||
 975            !heap_->concurrent_sweeping_enabled())) {
 976         heap_->mark_compact_collector()->EnsureSweepingCompleted();
 977       }
 978       if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
 979         bytes_scanned_ = 0;
 980         StartMarking();
 981       }
 982     } else if (state_ == MARKING) {
 983       bytes_processed = ProcessMarkingDeque(bytes_to_process);
 984       if (heap_->mark_compact_collector()->marking_deque()->IsEmpty()) {
 985         if (completion == FORCE_COMPLETION ||
 986             IsIdleMarkingDelayCounterLimitReached()) {
 987           if (FLAG_overapproximate_weak_closure &&
 988               !weak_closure_was_overapproximated_) {
 989             OverApproximateWeakClosure(action);
 990           } else {
 991             MarkingComplete(action);
 992           }
 993         } else {
 994           IncrementIdleMarkingDelayCounter();
 995         }
 996       }
 997     }
 998
 999     steps_count_++;
1000
1001     // Speed up marking if we are marking too slow or if we are almost done
1002     // with marking.
1003     SpeedUp();
1004
1005     double end = base::OS::TimeCurrentMillis();
1006     double duration = (end - start);
1007     // Note that we report zero bytes here when sweeping was in progress or
1008     // when we just started incremental marking. In these cases we did not
1009     // process the marking deque.
1010     heap_->tracer()->AddIncrementalMarkingStep(duration, bytes_processed);
1011   }
1012   return bytes_processed;
1013 }
1014
1015
1016 void IncrementalMarking::ResetStepCounters() {
1017   steps_count_ = 0;
1018   old_generation_space_available_at_start_of_incremental_ =
1019       SpaceLeftInOldSpace();
1020   old_generation_space_used_at_start_of_incremental_ =
1021       heap_->PromotedTotalSize();
1022   bytes_rescanned_ = 0;
1023   marking_speed_ = kInitialMarkingSpeed;
1024   bytes_scanned_ = 0;
1025   write_barriers_invoked_since_last_step_ = 0;
1026 }
1027
1028
1029 int64_t IncrementalMarking::SpaceLeftInOldSpace() {
1030   return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();
1031 }
1032
1033
1034 bool IncrementalMarking::IsIdleMarkingDelayCounterLimitReached() {
1035   return idle_marking_delay_counter_ > kMaxIdleMarkingDelayCounter;
1036 }
1037
1038
1039 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
1040   idle_marking_delay_counter_++;
1041 }
1042
1043
1044 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
1045   idle_marking_delay_counter_ = 0;
1046 }
1047 }  // namespace internal
1048 }  // namespace v8