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      1 // Copyright 2011 the V8 project authors. All rights reserved.
      2 // Redistribution and use in source and binary forms, with or without
      3 // modification, are permitted provided that the following conditions are
      4 // met:
      5 //
      6 //     * Redistributions of source code must retain the above copyright
      7 //       notice, this list of conditions and the following disclaimer.
      8 //     * Redistributions in binary form must reproduce the above
      9 //       copyright notice, this list of conditions and the following
     10 //       disclaimer in the documentation and/or other materials provided
     11 //       with the distribution.
     12 //     * Neither the name of Google Inc. nor the names of its
     13 //       contributors may be used to endorse or promote products derived
     14 //       from this software without specific prior written permission.
     15 //
     16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27 
     28 #include "v8.h"
     29 
     30 #include "incremental-marking.h"
     31 
     32 #include "code-stubs.h"
     33 #include "compilation-cache.h"
     34 #include "v8conversions.h"
     35 
     36 namespace v8 {
     37 namespace internal {
     38 
     39 
     40 IncrementalMarking::IncrementalMarking(Heap* heap)
     41     : heap_(heap),
     42       state_(STOPPED),
     43       marking_deque_memory_(NULL),
     44       marking_deque_memory_committed_(false),
     45       steps_count_(0),
     46       steps_took_(0),
     47       longest_step_(0.0),
     48       old_generation_space_available_at_start_of_incremental_(0),
     49       old_generation_space_used_at_start_of_incremental_(0),
     50       steps_count_since_last_gc_(0),
     51       steps_took_since_last_gc_(0),
     52       should_hurry_(false),
     53       allocation_marking_factor_(0),
     54       allocated_(0),
     55       no_marking_scope_depth_(0) {
     56 }
     57 
     58 
     59 void IncrementalMarking::TearDown() {
     60   delete marking_deque_memory_;
     61 }
     62 
     63 
     64 void IncrementalMarking::RecordWriteSlow(HeapObject* obj,
     65                                          Object** slot,
     66                                          Object* value) {
     67   if (BaseRecordWrite(obj, slot, value) && is_compacting_ && slot != NULL) {
     68     MarkBit obj_bit = Marking::MarkBitFrom(obj);
     69     if (Marking::IsBlack(obj_bit)) {
     70       // Object is not going to be rescanned we need to record the slot.
     71       heap_->mark_compact_collector()->RecordSlot(
     72           HeapObject::RawField(obj, 0), slot, value);
     73     }
     74   }
     75 }
     76 
     77 
     78 void IncrementalMarking::RecordWriteFromCode(HeapObject* obj,
     79                                              Object* value,
     80                                              Isolate* isolate) {
     81   ASSERT(obj->IsHeapObject());
     82 
     83   // Fast cases should already be covered by RecordWriteStub.
     84   ASSERT(value->IsHeapObject());
     85   ASSERT(!value->IsHeapNumber());
     86   ASSERT(!value->IsString() ||
     87          value->IsConsString() ||
     88          value->IsSlicedString());
     89   ASSERT(Marking::IsWhite(Marking::MarkBitFrom(HeapObject::cast(value))));
     90 
     91   IncrementalMarking* marking = isolate->heap()->incremental_marking();
     92   ASSERT(!marking->is_compacting_);
     93   marking->RecordWrite(obj, NULL, value);
     94 }
     95 
     96 
     97 void IncrementalMarking::RecordWriteForEvacuationFromCode(HeapObject* obj,
     98                                                           Object** slot,
     99                                                           Isolate* isolate) {
    100   IncrementalMarking* marking = isolate->heap()->incremental_marking();
    101   ASSERT(marking->is_compacting_);
    102   marking->RecordWrite(obj, slot, *slot);
    103 }
    104 
    105 
    106 void IncrementalMarking::RecordCodeTargetPatch(Code* host,
    107                                                Address pc,
    108                                                HeapObject* value) {
    109   if (IsMarking()) {
    110     RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
    111     RecordWriteIntoCode(host, &rinfo, value);
    112   }
    113 }
    114 
    115 
    116 void IncrementalMarking::RecordCodeTargetPatch(Address pc, HeapObject* value) {
    117   if (IsMarking()) {
    118     Code* host = heap_->isolate()->inner_pointer_to_code_cache()->
    119         GcSafeFindCodeForInnerPointer(pc);
    120     RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
    121     RecordWriteIntoCode(host, &rinfo, value);
    122   }
    123 }
    124 
    125 
    126 void IncrementalMarking::RecordWriteOfCodeEntrySlow(JSFunction* host,
    127                                                 Object** slot,
    128                                                 Code* value) {
    129   if (BaseRecordWrite(host, slot, value) && is_compacting_) {
    130     ASSERT(slot != NULL);
    131     heap_->mark_compact_collector()->
    132         RecordCodeEntrySlot(reinterpret_cast<Address>(slot), value);
    133   }
    134 }
    135 
    136 
    137 void IncrementalMarking::RecordWriteIntoCodeSlow(HeapObject* obj,
    138                                                  RelocInfo* rinfo,
    139                                                  Object* value) {
    140   MarkBit value_bit = Marking::MarkBitFrom(HeapObject::cast(value));
    141   if (Marking::IsWhite(value_bit)) {
    142     MarkBit obj_bit = Marking::MarkBitFrom(obj);
    143     if (Marking::IsBlack(obj_bit)) {
    144       BlackToGreyAndUnshift(obj, obj_bit);
    145       RestartIfNotMarking();
    146     }
    147     // Object is either grey or white.  It will be scanned if survives.
    148     return;
    149   }
    150 
    151   if (is_compacting_) {
    152     MarkBit obj_bit = Marking::MarkBitFrom(obj);
    153     if (Marking::IsBlack(obj_bit)) {
    154       // Object is not going to be rescanned.  We need to record the slot.
    155       heap_->mark_compact_collector()->RecordRelocSlot(rinfo,
    156                                                        Code::cast(value));
    157     }
    158   }
    159 }
    160 
    161 
    162 class IncrementalMarkingMarkingVisitor : public ObjectVisitor {
    163  public:
    164   IncrementalMarkingMarkingVisitor(Heap* heap,
    165                                    IncrementalMarking* incremental_marking)
    166       : heap_(heap),
    167         incremental_marking_(incremental_marking) {
    168   }
    169 
    170   void VisitEmbeddedPointer(RelocInfo* rinfo) {
    171     ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
    172     Object* target = rinfo->target_object();
    173     if (target->NonFailureIsHeapObject()) {
    174       heap_->mark_compact_collector()->RecordRelocSlot(rinfo, target);
    175       MarkObject(target);
    176     }
    177   }
    178 
    179   void VisitCodeTarget(RelocInfo* rinfo) {
    180     ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode()));
    181     Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
    182     if (FLAG_cleanup_code_caches_at_gc && target->is_inline_cache_stub()
    183         && (target->ic_age() != heap_->global_ic_age())) {
    184       IC::Clear(rinfo->pc());
    185       target = Code::GetCodeFromTargetAddress(rinfo->target_address());
    186     }
    187     heap_->mark_compact_collector()->RecordRelocSlot(rinfo, Code::cast(target));
    188     MarkObject(target);
    189   }
    190 
    191   void VisitDebugTarget(RelocInfo* rinfo) {
    192     ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) &&
    193             rinfo->IsPatchedReturnSequence()) ||
    194            (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
    195             rinfo->IsPatchedDebugBreakSlotSequence()));
    196     Object* target = Code::GetCodeFromTargetAddress(rinfo->call_address());
    197     heap_->mark_compact_collector()->RecordRelocSlot(rinfo, Code::cast(target));
    198     MarkObject(target);
    199   }
    200 
    201   void VisitCodeEntry(Address entry_address) {
    202     Object* target = Code::GetObjectFromEntryAddress(entry_address);
    203     heap_->mark_compact_collector()->
    204         RecordCodeEntrySlot(entry_address, Code::cast(target));
    205     MarkObject(target);
    206   }
    207 
    208   void VisitSharedFunctionInfo(SharedFunctionInfo* shared) {
    209     if (shared->ic_age() != heap_->global_ic_age()) {
    210       shared->ResetForNewContext(heap_->global_ic_age());
    211     }
    212   }
    213 
    214   void VisitPointer(Object** p) {
    215     Object* obj = *p;
    216     if (obj->NonFailureIsHeapObject()) {
    217       heap_->mark_compact_collector()->RecordSlot(p, p, obj);
    218       MarkObject(obj);
    219     }
    220   }
    221 
    222   void VisitPointers(Object** start, Object** end) {
    223     for (Object** p = start; p < end; p++) {
    224       Object* obj = *p;
    225       if (obj->NonFailureIsHeapObject()) {
    226         heap_->mark_compact_collector()->RecordSlot(start, p, obj);
    227         MarkObject(obj);
    228       }
    229     }
    230   }
    231 
    232  private:
    233   // Mark object pointed to by p.
    234   INLINE(void MarkObject(Object* obj)) {
    235     HeapObject* heap_object = HeapObject::cast(obj);
    236     MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
    237     if (mark_bit.data_only()) {
    238       if (incremental_marking_->MarkBlackOrKeepGrey(mark_bit)) {
    239         MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(),
    240                                               heap_object->Size());
    241       }
    242     } else if (Marking::IsWhite(mark_bit)) {
    243       incremental_marking_->WhiteToGreyAndPush(heap_object, mark_bit);
    244     }
    245   }
    246 
    247   Heap* heap_;
    248   IncrementalMarking* incremental_marking_;
    249 };
    250 
    251 
    252 class IncrementalMarkingRootMarkingVisitor : public ObjectVisitor {
    253  public:
    254   IncrementalMarkingRootMarkingVisitor(Heap* heap,
    255                                        IncrementalMarking* incremental_marking)
    256       : heap_(heap),
    257         incremental_marking_(incremental_marking) {
    258   }
    259 
    260   void VisitPointer(Object** p) {
    261     MarkObjectByPointer(p);
    262   }
    263 
    264   void VisitPointers(Object** start, Object** end) {
    265     for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
    266   }
    267 
    268  private:
    269   void MarkObjectByPointer(Object** p) {
    270     Object* obj = *p;
    271     if (!obj->IsHeapObject()) return;
    272 
    273     HeapObject* heap_object = HeapObject::cast(obj);
    274     MarkBit mark_bit = Marking::MarkBitFrom(heap_object);
    275     if (mark_bit.data_only()) {
    276       if (incremental_marking_->MarkBlackOrKeepGrey(mark_bit)) {
    277           MemoryChunk::IncrementLiveBytesFromGC(heap_object->address(),
    278                                                 heap_object->Size());
    279       }
    280     } else {
    281       if (Marking::IsWhite(mark_bit)) {
    282         incremental_marking_->WhiteToGreyAndPush(heap_object, mark_bit);
    283       }
    284     }
    285   }
    286 
    287   Heap* heap_;
    288   IncrementalMarking* incremental_marking_;
    289 };
    290 
    291 
    292 void IncrementalMarking::SetOldSpacePageFlags(MemoryChunk* chunk,
    293                                               bool is_marking,
    294                                               bool is_compacting) {
    295   if (is_marking) {
    296     chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    297     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    298 
    299     // It's difficult to filter out slots recorded for large objects.
    300     if (chunk->owner()->identity() == LO_SPACE &&
    301         chunk->size() > static_cast<size_t>(Page::kPageSize) &&
    302         is_compacting) {
    303       chunk->SetFlag(MemoryChunk::RESCAN_ON_EVACUATION);
    304     }
    305   } else if (chunk->owner()->identity() == CELL_SPACE ||
    306              chunk->scan_on_scavenge()) {
    307     chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    308     chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    309   } else {
    310     chunk->ClearFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    311     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    312   }
    313 }
    314 
    315 
    316 void IncrementalMarking::SetNewSpacePageFlags(NewSpacePage* chunk,
    317                                               bool is_marking) {
    318   chunk->SetFlag(MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING);
    319   if (is_marking) {
    320     chunk->SetFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    321   } else {
    322     chunk->ClearFlag(MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING);
    323   }
    324   chunk->SetFlag(MemoryChunk::SCAN_ON_SCAVENGE);
    325 }
    326 
    327 
    328 void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
    329     PagedSpace* space) {
    330   PageIterator it(space);
    331   while (it.has_next()) {
    332     Page* p = it.next();
    333     SetOldSpacePageFlags(p, false, false);
    334   }
    335 }
    336 
    337 
    338 void IncrementalMarking::DeactivateIncrementalWriteBarrierForSpace(
    339     NewSpace* space) {
    340   NewSpacePageIterator it(space);
    341   while (it.has_next()) {
    342     NewSpacePage* p = it.next();
    343     SetNewSpacePageFlags(p, false);
    344   }
    345 }
    346 
    347 
    348 void IncrementalMarking::DeactivateIncrementalWriteBarrier() {
    349   DeactivateIncrementalWriteBarrierForSpace(heap_->old_pointer_space());
    350   DeactivateIncrementalWriteBarrierForSpace(heap_->old_data_space());
    351   DeactivateIncrementalWriteBarrierForSpace(heap_->cell_space());
    352   DeactivateIncrementalWriteBarrierForSpace(heap_->map_space());
    353   DeactivateIncrementalWriteBarrierForSpace(heap_->code_space());
    354   DeactivateIncrementalWriteBarrierForSpace(heap_->new_space());
    355 
    356   LargePage* lop = heap_->lo_space()->first_page();
    357   while (lop->is_valid()) {
    358     SetOldSpacePageFlags(lop, false, false);
    359     lop = lop->next_page();
    360   }
    361 }
    362 
    363 
    364 void IncrementalMarking::ActivateIncrementalWriteBarrier(PagedSpace* space) {
    365   PageIterator it(space);
    366   while (it.has_next()) {
    367     Page* p = it.next();
    368     SetOldSpacePageFlags(p, true, is_compacting_);
    369   }
    370 }
    371 
    372 
    373 void IncrementalMarking::ActivateIncrementalWriteBarrier(NewSpace* space) {
    374   NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
    375   while (it.has_next()) {
    376     NewSpacePage* p = it.next();
    377     SetNewSpacePageFlags(p, true);
    378   }
    379 }
    380 
    381 
    382 void IncrementalMarking::ActivateIncrementalWriteBarrier() {
    383   ActivateIncrementalWriteBarrier(heap_->old_pointer_space());
    384   ActivateIncrementalWriteBarrier(heap_->old_data_space());
    385   ActivateIncrementalWriteBarrier(heap_->cell_space());
    386   ActivateIncrementalWriteBarrier(heap_->map_space());
    387   ActivateIncrementalWriteBarrier(heap_->code_space());
    388   ActivateIncrementalWriteBarrier(heap_->new_space());
    389 
    390   LargePage* lop = heap_->lo_space()->first_page();
    391   while (lop->is_valid()) {
    392     SetOldSpacePageFlags(lop, true, is_compacting_);
    393     lop = lop->next_page();
    394   }
    395 }
    396 
    397 
    398 bool IncrementalMarking::WorthActivating() {
    399 #ifndef DEBUG
    400   static const intptr_t kActivationThreshold = 8 * MB;
    401 #else
    402   // TODO(gc) consider setting this to some low level so that some
    403   // debug tests run with incremental marking and some without.
    404   static const intptr_t kActivationThreshold = 0;
    405 #endif
    406 
    407   return !FLAG_expose_gc &&
    408       FLAG_incremental_marking &&
    409       !Serializer::enabled() &&
    410       heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
    411 }
    412 
    413 
    414 void IncrementalMarking::ActivateGeneratedStub(Code* stub) {
    415   ASSERT(RecordWriteStub::GetMode(stub) ==
    416          RecordWriteStub::STORE_BUFFER_ONLY);
    417 
    418   if (!IsMarking()) {
    419     // Initially stub is generated in STORE_BUFFER_ONLY mode thus
    420     // we don't need to do anything if incremental marking is
    421     // not active.
    422   } else if (IsCompacting()) {
    423     RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL_COMPACTION);
    424   } else {
    425     RecordWriteStub::Patch(stub, RecordWriteStub::INCREMENTAL);
    426   }
    427 }
    428 
    429 
    430 static void PatchIncrementalMarkingRecordWriteStubs(
    431     Heap* heap, RecordWriteStub::Mode mode) {
    432   UnseededNumberDictionary* stubs = heap->code_stubs();
    433 
    434   int capacity = stubs->Capacity();
    435   for (int i = 0; i < capacity; i++) {
    436     Object* k = stubs->KeyAt(i);
    437     if (stubs->IsKey(k)) {
    438       uint32_t key = NumberToUint32(k);
    439 
    440       if (CodeStub::MajorKeyFromKey(key) ==
    441           CodeStub::RecordWrite) {
    442         Object* e = stubs->ValueAt(i);
    443         if (e->IsCode()) {
    444           RecordWriteStub::Patch(Code::cast(e), mode);
    445         }
    446       }
    447     }
    448   }
    449 }
    450 
    451 
    452 void IncrementalMarking::EnsureMarkingDequeIsCommitted() {
    453   if (marking_deque_memory_ == NULL) {
    454     marking_deque_memory_ = new VirtualMemory(4 * MB);
    455   }
    456   if (!marking_deque_memory_committed_) {
    457     bool success = marking_deque_memory_->Commit(
    458         reinterpret_cast<Address>(marking_deque_memory_->address()),
    459         marking_deque_memory_->size(),
    460         false);  // Not executable.
    461     CHECK(success);
    462     marking_deque_memory_committed_ = true;
    463   }
    464 }
    465 
    466 void IncrementalMarking::UncommitMarkingDeque() {
    467   if (state_ == STOPPED && marking_deque_memory_committed_) {
    468     bool success = marking_deque_memory_->Uncommit(
    469         reinterpret_cast<Address>(marking_deque_memory_->address()),
    470         marking_deque_memory_->size());
    471     CHECK(success);
    472     marking_deque_memory_committed_ = false;
    473   }
    474 }
    475 
    476 
    477 void IncrementalMarking::Start() {
    478   if (FLAG_trace_incremental_marking) {
    479     PrintF("[IncrementalMarking] Start\n");
    480   }
    481   ASSERT(FLAG_incremental_marking);
    482   ASSERT(state_ == STOPPED);
    483 
    484   ResetStepCounters();
    485 
    486   if (heap_->old_pointer_space()->IsSweepingComplete() &&
    487       heap_->old_data_space()->IsSweepingComplete()) {
    488     StartMarking(ALLOW_COMPACTION);
    489   } else {
    490     if (FLAG_trace_incremental_marking) {
    491       PrintF("[IncrementalMarking] Start sweeping.\n");
    492     }
    493     state_ = SWEEPING;
    494   }
    495 
    496   heap_->new_space()->LowerInlineAllocationLimit(kAllocatedThreshold);
    497 }
    498 
    499 
    500 static void MarkObjectGreyDoNotEnqueue(Object* obj) {
    501   if (obj->IsHeapObject()) {
    502     HeapObject* heap_obj = HeapObject::cast(obj);
    503     MarkBit mark_bit = Marking::MarkBitFrom(HeapObject::cast(obj));
    504     if (Marking::IsBlack(mark_bit)) {
    505       MemoryChunk::IncrementLiveBytesFromGC(heap_obj->address(),
    506                                             -heap_obj->Size());
    507     }
    508     Marking::AnyToGrey(mark_bit);
    509   }
    510 }
    511 
    512 
    513 void IncrementalMarking::StartMarking(CompactionFlag flag) {
    514   if (FLAG_trace_incremental_marking) {
    515     PrintF("[IncrementalMarking] Start marking\n");
    516   }
    517 
    518   is_compacting_ = !FLAG_never_compact && (flag == ALLOW_COMPACTION) &&
    519       heap_->mark_compact_collector()->StartCompaction(
    520           MarkCompactCollector::INCREMENTAL_COMPACTION);
    521 
    522   state_ = MARKING;
    523 
    524   RecordWriteStub::Mode mode = is_compacting_ ?
    525       RecordWriteStub::INCREMENTAL_COMPACTION : RecordWriteStub::INCREMENTAL;
    526 
    527   PatchIncrementalMarkingRecordWriteStubs(heap_, mode);
    528 
    529   EnsureMarkingDequeIsCommitted();
    530 
    531   // Initialize marking stack.
    532   Address addr = static_cast<Address>(marking_deque_memory_->address());
    533   size_t size = marking_deque_memory_->size();
    534   if (FLAG_force_marking_deque_overflows) size = 64 * kPointerSize;
    535   marking_deque_.Initialize(addr, addr + size);
    536 
    537   ActivateIncrementalWriteBarrier();
    538 
    539 #ifdef DEBUG
    540   // Marking bits are cleared by the sweeper.
    541   if (FLAG_verify_heap) {
    542     heap_->mark_compact_collector()->VerifyMarkbitsAreClean();
    543   }
    544 #endif
    545 
    546   heap_->CompletelyClearInstanceofCache();
    547   heap_->isolate()->compilation_cache()->MarkCompactPrologue();
    548 
    549   if (FLAG_cleanup_code_caches_at_gc) {
    550     // We will mark cache black with a separate pass
    551     // when we finish marking.
    552     MarkObjectGreyDoNotEnqueue(heap_->polymorphic_code_cache());
    553   }
    554 
    555   // Mark strong roots grey.
    556   IncrementalMarkingRootMarkingVisitor visitor(heap_, this);
    557   heap_->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
    558 
    559   // Ready to start incremental marking.
    560   if (FLAG_trace_incremental_marking) {
    561     PrintF("[IncrementalMarking] Running\n");
    562   }
    563 }
    564 
    565 
    566 void IncrementalMarking::PrepareForScavenge() {
    567   if (!IsMarking()) return;
    568   NewSpacePageIterator it(heap_->new_space()->FromSpaceStart(),
    569                           heap_->new_space()->FromSpaceEnd());
    570   while (it.has_next()) {
    571     Bitmap::Clear(it.next());
    572   }
    573 }
    574 
    575 
    576 void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
    577   if (!IsMarking()) return;
    578 
    579   int current = marking_deque_.bottom();
    580   int mask = marking_deque_.mask();
    581   int limit = marking_deque_.top();
    582   HeapObject** array = marking_deque_.array();
    583   int new_top = current;
    584 
    585   Map* filler_map = heap_->one_pointer_filler_map();
    586 
    587   while (current != limit) {
    588     HeapObject* obj = array[current];
    589     ASSERT(obj->IsHeapObject());
    590     current = ((current + 1) & mask);
    591     if (heap_->InNewSpace(obj)) {
    592       MapWord map_word = obj->map_word();
    593       if (map_word.IsForwardingAddress()) {
    594         HeapObject* dest = map_word.ToForwardingAddress();
    595         array[new_top] = dest;
    596         new_top = ((new_top + 1) & mask);
    597         ASSERT(new_top != marking_deque_.bottom());
    598 #ifdef DEBUG
    599         MarkBit mark_bit = Marking::MarkBitFrom(obj);
    600         ASSERT(Marking::IsGrey(mark_bit) ||
    601                (obj->IsFiller() && Marking::IsWhite(mark_bit)));
    602 #endif
    603       }
    604     } else if (obj->map() != filler_map) {
    605       // Skip one word filler objects that appear on the
    606       // stack when we perform in place array shift.
    607       array[new_top] = obj;
    608       new_top = ((new_top + 1) & mask);
    609       ASSERT(new_top != marking_deque_.bottom());
    610 #ifdef DEBUG
    611         MarkBit mark_bit = Marking::MarkBitFrom(obj);
    612         ASSERT(Marking::IsGrey(mark_bit) ||
    613                (obj->IsFiller() && Marking::IsWhite(mark_bit)));
    614 #endif
    615     }
    616   }
    617   marking_deque_.set_top(new_top);
    618 
    619   steps_took_since_last_gc_ = 0;
    620   steps_count_since_last_gc_ = 0;
    621   longest_step_ = 0.0;
    622 }
    623 
    624 
    625 void IncrementalMarking::VisitGlobalContext(Context* ctx, ObjectVisitor* v) {
    626   v->VisitPointers(
    627       HeapObject::RawField(
    628           ctx, Context::MarkCompactBodyDescriptor::kStartOffset),
    629       HeapObject::RawField(
    630           ctx, Context::MarkCompactBodyDescriptor::kEndOffset));
    631 
    632   MarkCompactCollector* collector = heap_->mark_compact_collector();
    633   for (int idx = Context::FIRST_WEAK_SLOT;
    634        idx < Context::GLOBAL_CONTEXT_SLOTS;
    635        ++idx) {
    636     Object** slot =
    637         HeapObject::RawField(ctx, FixedArray::OffsetOfElementAt(idx));
    638     collector->RecordSlot(slot, slot, *slot);
    639   }
    640 }
    641 
    642 
    643 void IncrementalMarking::Hurry() {
    644   if (state() == MARKING) {
    645     double start = 0.0;
    646     if (FLAG_trace_incremental_marking) {
    647       PrintF("[IncrementalMarking] Hurry\n");
    648       start = OS::TimeCurrentMillis();
    649     }
    650     // TODO(gc) hurry can mark objects it encounters black as mutator
    651     // was stopped.
    652     Map* filler_map = heap_->one_pointer_filler_map();
    653     Map* global_context_map = heap_->global_context_map();
    654     IncrementalMarkingMarkingVisitor marking_visitor(heap_, this);
    655     while (!marking_deque_.IsEmpty()) {
    656       HeapObject* obj = marking_deque_.Pop();
    657 
    658       // Explicitly skip one word fillers. Incremental markbit patterns are
    659       // correct only for objects that occupy at least two words.
    660       Map* map = obj->map();
    661       if (map == filler_map) {
    662         continue;
    663       } else if (map == global_context_map) {
    664         // Global contexts have weak fields.
    665         VisitGlobalContext(Context::cast(obj), &marking_visitor);
    666       } else {
    667         obj->Iterate(&marking_visitor);
    668       }
    669 
    670       MarkBit mark_bit = Marking::MarkBitFrom(obj);
    671       ASSERT(!Marking::IsBlack(mark_bit));
    672       Marking::MarkBlack(mark_bit);
    673       MemoryChunk::IncrementLiveBytesFromGC(obj->address(), obj->Size());
    674     }
    675     state_ = COMPLETE;
    676     if (FLAG_trace_incremental_marking) {
    677       double end = OS::TimeCurrentMillis();
    678       PrintF("[IncrementalMarking] Complete (hurry), spent %d ms.\n",
    679              static_cast<int>(end - start));
    680     }
    681   }
    682 
    683   if (FLAG_cleanup_code_caches_at_gc) {
    684     PolymorphicCodeCache* poly_cache = heap_->polymorphic_code_cache();
    685     Marking::GreyToBlack(Marking::MarkBitFrom(poly_cache));
    686     MemoryChunk::IncrementLiveBytesFromGC(poly_cache->address(),
    687                                           PolymorphicCodeCache::kSize);
    688   }
    689 
    690   Object* context = heap_->global_contexts_list();
    691   while (!context->IsUndefined()) {
    692     // GC can happen when the context is not fully initialized,
    693     // so the cache can be undefined.
    694     HeapObject* cache = HeapObject::cast(
    695         Context::cast(context)->get(Context::NORMALIZED_MAP_CACHE_INDEX));
    696     if (!cache->IsUndefined()) {
    697       MarkBit mark_bit = Marking::MarkBitFrom(cache);
    698       if (Marking::IsGrey(mark_bit)) {
    699         Marking::GreyToBlack(mark_bit);
    700         MemoryChunk::IncrementLiveBytesFromGC(cache->address(), cache->Size());
    701       }
    702     }
    703     context = Context::cast(context)->get(Context::NEXT_CONTEXT_LINK);
    704   }
    705 }
    706 
    707 
    708 void IncrementalMarking::Abort() {
    709   if (IsStopped()) return;
    710   if (FLAG_trace_incremental_marking) {
    711     PrintF("[IncrementalMarking] Aborting.\n");
    712   }
    713   heap_->new_space()->LowerInlineAllocationLimit(0);
    714   IncrementalMarking::set_should_hurry(false);
    715   ResetStepCounters();
    716   if (IsMarking()) {
    717     PatchIncrementalMarkingRecordWriteStubs(heap_,
    718                                             RecordWriteStub::STORE_BUFFER_ONLY);
    719     DeactivateIncrementalWriteBarrier();
    720 
    721     if (is_compacting_) {
    722       LargeObjectIterator it(heap_->lo_space());
    723       for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
    724         Page* p = Page::FromAddress(obj->address());
    725         if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
    726           p->ClearFlag(Page::RESCAN_ON_EVACUATION);
    727         }
    728       }
    729     }
    730   }
    731   heap_->isolate()->stack_guard()->Continue(GC_REQUEST);
    732   state_ = STOPPED;
    733   is_compacting_ = false;
    734 }
    735 
    736 
    737 void IncrementalMarking::Finalize() {
    738   Hurry();
    739   state_ = STOPPED;
    740   is_compacting_ = false;
    741   heap_->new_space()->LowerInlineAllocationLimit(0);
    742   IncrementalMarking::set_should_hurry(false);
    743   ResetStepCounters();
    744   PatchIncrementalMarkingRecordWriteStubs(heap_,
    745                                           RecordWriteStub::STORE_BUFFER_ONLY);
    746   DeactivateIncrementalWriteBarrier();
    747   ASSERT(marking_deque_.IsEmpty());
    748   heap_->isolate()->stack_guard()->Continue(GC_REQUEST);
    749 }
    750 
    751 
    752 void IncrementalMarking::MarkingComplete(CompletionAction action) {
    753   state_ = COMPLETE;
    754   // We will set the stack guard to request a GC now.  This will mean the rest
    755   // of the GC gets performed as soon as possible (we can't do a GC here in a
    756   // record-write context).  If a few things get allocated between now and then
    757   // that shouldn't make us do a scavenge and keep being incremental, so we set
    758   // the should-hurry flag to indicate that there can't be much work left to do.
    759   set_should_hurry(true);
    760   if (FLAG_trace_incremental_marking) {
    761     PrintF("[IncrementalMarking] Complete (normal).\n");
    762   }
    763   if (action == GC_VIA_STACK_GUARD) {
    764     heap_->isolate()->stack_guard()->RequestGC();
    765   }
    766 }
    767 
    768 
    769 void IncrementalMarking::Step(intptr_t allocated_bytes,
    770                               CompletionAction action) {
    771   if (heap_->gc_state() != Heap::NOT_IN_GC ||
    772       !FLAG_incremental_marking ||
    773       !FLAG_incremental_marking_steps ||
    774       (state_ != SWEEPING && state_ != MARKING)) {
    775     return;
    776   }
    777 
    778   allocated_ += allocated_bytes;
    779 
    780   if (allocated_ < kAllocatedThreshold) return;
    781 
    782   if (state_ == MARKING && no_marking_scope_depth_ > 0) return;
    783 
    784   intptr_t bytes_to_process = allocated_ * allocation_marking_factor_;
    785   bytes_scanned_ += bytes_to_process;
    786 
    787   double start = 0;
    788 
    789   if (FLAG_trace_incremental_marking || FLAG_trace_gc) {
    790     start = OS::TimeCurrentMillis();
    791   }
    792 
    793   if (state_ == SWEEPING) {
    794     if (heap_->AdvanceSweepers(static_cast<int>(bytes_to_process))) {
    795       bytes_scanned_ = 0;
    796       StartMarking(PREVENT_COMPACTION);
    797     }
    798   } else if (state_ == MARKING) {
    799     Map* filler_map = heap_->one_pointer_filler_map();
    800     Map* global_context_map = heap_->global_context_map();
    801     IncrementalMarkingMarkingVisitor marking_visitor(heap_, this);
    802     while (!marking_deque_.IsEmpty() && bytes_to_process > 0) {
    803       HeapObject* obj = marking_deque_.Pop();
    804 
    805       // Explicitly skip one word fillers. Incremental markbit patterns are
    806       // correct only for objects that occupy at least two words.
    807       Map* map = obj->map();
    808       if (map == filler_map) continue;
    809 
    810       if (obj->IsMap()) {
    811         Map* map = Map::cast(obj);
    812         heap_->ClearCacheOnMap(map);
    813       }
    814 
    815 
    816       int size = obj->SizeFromMap(map);
    817       bytes_to_process -= size;
    818       MarkBit map_mark_bit = Marking::MarkBitFrom(map);
    819       if (Marking::IsWhite(map_mark_bit)) {
    820         WhiteToGreyAndPush(map, map_mark_bit);
    821       }
    822 
    823       // TODO(gc) switch to static visitor instead of normal visitor.
    824       if (map == global_context_map) {
    825         // Global contexts have weak fields.
    826         Context* ctx = Context::cast(obj);
    827 
    828         // We will mark cache black with a separate pass
    829         // when we finish marking.
    830         MarkObjectGreyDoNotEnqueue(ctx->normalized_map_cache());
    831 
    832         VisitGlobalContext(ctx, &marking_visitor);
    833       } else {
    834         obj->IterateBody(map->instance_type(), size, &marking_visitor);
    835       }
    836 
    837       MarkBit obj_mark_bit = Marking::MarkBitFrom(obj);
    838       SLOW_ASSERT(Marking::IsGrey(obj_mark_bit) ||
    839                   (obj->IsFiller() && Marking::IsWhite(obj_mark_bit)));
    840       Marking::MarkBlack(obj_mark_bit);
    841       MemoryChunk::IncrementLiveBytesFromGC(obj->address(), size);
    842     }
    843     if (marking_deque_.IsEmpty()) MarkingComplete(action);
    844   }
    845 
    846   allocated_ = 0;
    847 
    848   steps_count_++;
    849   steps_count_since_last_gc_++;
    850 
    851   bool speed_up = false;
    852 
    853   if ((steps_count_ % kAllocationMarkingFactorSpeedupInterval) == 0) {
    854     if (FLAG_trace_gc) {
    855       PrintF("Speed up marking after %d steps\n",
    856              static_cast<int>(kAllocationMarkingFactorSpeedupInterval));
    857     }
    858     speed_up = true;
    859   }
    860 
    861   bool space_left_is_very_small =
    862       (old_generation_space_available_at_start_of_incremental_ < 10 * MB);
    863 
    864   bool only_1_nth_of_space_that_was_available_still_left =
    865       (SpaceLeftInOldSpace() * (allocation_marking_factor_ + 1) <
    866           old_generation_space_available_at_start_of_incremental_);
    867 
    868   if (space_left_is_very_small ||
    869       only_1_nth_of_space_that_was_available_still_left) {
    870     if (FLAG_trace_gc) PrintF("Speed up marking because of low space left\n");
    871     speed_up = true;
    872   }
    873 
    874   bool size_of_old_space_multiplied_by_n_during_marking =
    875       (heap_->PromotedTotalSize() >
    876        (allocation_marking_factor_ + 1) *
    877            old_generation_space_used_at_start_of_incremental_);
    878   if (size_of_old_space_multiplied_by_n_during_marking) {
    879     speed_up = true;
    880     if (FLAG_trace_gc) {
    881       PrintF("Speed up marking because of heap size increase\n");
    882     }
    883   }
    884 
    885   int64_t promoted_during_marking = heap_->PromotedTotalSize()
    886       - old_generation_space_used_at_start_of_incremental_;
    887   intptr_t delay = allocation_marking_factor_ * MB;
    888   intptr_t scavenge_slack = heap_->MaxSemiSpaceSize();
    889 
    890   // We try to scan at at least twice the speed that we are allocating.
    891   if (promoted_during_marking > bytes_scanned_ / 2 + scavenge_slack + delay) {
    892     if (FLAG_trace_gc) {
    893       PrintF("Speed up marking because marker was not keeping up\n");
    894     }
    895     speed_up = true;
    896   }
    897 
    898   if (speed_up) {
    899     if (state_ != MARKING) {
    900       if (FLAG_trace_gc) {
    901         PrintF("Postponing speeding up marking until marking starts\n");
    902       }
    903     } else {
    904       allocation_marking_factor_ += kAllocationMarkingFactorSpeedup;
    905       allocation_marking_factor_ = static_cast<int>(
    906           Min(kMaxAllocationMarkingFactor,
    907               static_cast<intptr_t>(allocation_marking_factor_ * 1.3)));
    908       if (FLAG_trace_gc) {
    909         PrintF("Marking speed increased to %d\n", allocation_marking_factor_);
    910       }
    911     }
    912   }
    913 
    914   if (FLAG_trace_incremental_marking || FLAG_trace_gc) {
    915     double end = OS::TimeCurrentMillis();
    916     double delta = (end - start);
    917     longest_step_ = Max(longest_step_, delta);
    918     steps_took_ += delta;
    919     steps_took_since_last_gc_ += delta;
    920   }
    921 }
    922 
    923 
    924 void IncrementalMarking::ResetStepCounters() {
    925   steps_count_ = 0;
    926   steps_took_ = 0;
    927   longest_step_ = 0.0;
    928   old_generation_space_available_at_start_of_incremental_ =
    929       SpaceLeftInOldSpace();
    930   old_generation_space_used_at_start_of_incremental_ =
    931       heap_->PromotedTotalSize();
    932   steps_count_since_last_gc_ = 0;
    933   steps_took_since_last_gc_ = 0;
    934   bytes_rescanned_ = 0;
    935   allocation_marking_factor_ = kInitialAllocationMarkingFactor;
    936   bytes_scanned_ = 0;
    937 }
    938 
    939 
    940 int64_t IncrementalMarking::SpaceLeftInOldSpace() {
    941   return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSize();
    942 }
    943 
    944 } }  // namespace v8::internal
    945