[heap] Evacuation for young generation

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 281 matching lines @@
   void VerifyPointers(Object** start, Object** end) override {
     for (Object** current = start; current < end; current++) {
       if ((*current)->IsHeapObject()) {
         HeapObject* object = HeapObject::cast(*current);
         CHECK(!MarkCompactCollector::IsOnEvacuationCandidate(object));
       }
     }
   }
 };
 
+class YoungGenerationEvacuationVerifier : public EvacuationVerifier {
+ public:
+  explicit YoungGenerationEvacuationVerifier(Heap* heap)
+      : EvacuationVerifier(heap) {}
+
+  void Run() override {
+    VerifyRoots(VISIT_ALL_IN_SCAVENGE);
+    VerifyEvacuation(heap_->new_space());

[ulan, 2017/04/26 09:51:28]

Verification should be done for the whole heap.

[Michael Lippautz, 2017/05/02 11:22:00]

Done.

+  }
+
+ protected:
+  void VerifyPointers(Object** start, Object** end) override {
+    for (Object** current = start; current < end; current++) {
+      if ((*current)->IsHeapObject()) {
+        HeapObject* object = HeapObject::cast(*current);
+        if (!heap_->InNewSpace(object)) return;

[ulan, 2017/04/26 09:51:28]

Let's instead do a check that object is not in from space.

[Michael Lippautz, 2017/05/02 11:22:00]

Done.

+        CHECK(!MarkCompactCollector::IsOnEvacuationCandidate(object));
+      }
+    }
+  }
+};
+
 }  // namespace
 #endif  // VERIFY_HEAP
 
 // =============================================================================
 // MarkCompactCollectorBase, MinorMarkCompactCollector, MarkCompactCollector
 // =============================================================================
 
 int MarkCompactCollectorBase::NumberOfParallelCompactionTasks(
     int pages, intptr_t live_bytes) {
   if (!FLAG_parallel_compaction) return 1;
@@ skipping 1276 matching lines @@
           *p = the_hole;
         }
       }
     }
   }
 
  private:
   Heap* heap_;
 };
 
+// Helper class for pruning the string table.
+class YoungGenerationExternalStringTableCleaner : public RootVisitor {
+ public:
+  YoungGenerationExternalStringTableCleaner(
+      const MinorMarkCompactCollector& collector)
+      : heap_(collector.heap()), collector_(collector) {}
+
+  void VisitRootPointers(Root root, Object** start, Object** end) override {
+    DCHECK_EQ(root, Root::kExternalStringsTable);
+    // Visit all HeapObject pointers in [start, end).
+    for (Object** p = start; p < end; p++) {
+      Object* o = *p;
+      if (o->IsHeapObject()) {
+        HeapObject* heap_object = HeapObject::cast(o);
+        if (ObjectMarking::IsWhite(heap_object,
+                                   collector_.marking_state(heap_object))) {
+          if (o->IsExternalString()) {
+            heap_->FinalizeExternalString(String::cast(*p));
+          } else {
+            // The original external string may have been internalized.
+            DCHECK(o->IsThinString());
+          }
+          // Set the entry to the_hole_value (as deleted).
+          *p = heap_->the_hole_value();
+        }
+      }
+    }
+  }
+
+ private:
+  Heap* heap_;
+  const MinorMarkCompactCollector& collector_;
+};
+
+// Marked young generation objects and all old generation objects will be
+// retained.
+class MinorMarkCompactWeakObjectRetainer : public WeakObjectRetainer {
+ public:
+  explicit MinorMarkCompactWeakObjectRetainer(
+      const MinorMarkCompactCollector& collector)
+      : collector_(collector) {}
+
+  virtual Object* RetainAs(Object* object) {
+    HeapObject* heap_object = HeapObject::cast(object);
+    if (!collector_.heap()->InNewSpace(heap_object)) return object;
+
+    DCHECK(!ObjectMarking::IsGrey(heap_object,
+                                  MarkingState::External(heap_object)));

[ulan, 2017/04/26 09:51:28]

Did you mean collector_.marking_state(heap_object) ?

[Michael Lippautz, 2017/05/02 11:22:00]

Done.

+    if (ObjectMarking::IsBlack(heap_object,
+                               collector_.marking_state(heap_object))) {
+      return object;
+    }
+    return nullptr;
+  }
+
+ private:
+  const MinorMarkCompactCollector& collector_;
+};
+
 // Implementation of WeakObjectRetainer for mark compact GCs. All marked objects
 // are retained.
 class MarkCompactWeakObjectRetainer : public WeakObjectRetainer {
  public:
   virtual Object* RetainAs(Object* object) {
     HeapObject* heap_object = HeapObject::cast(object);
     DCHECK(!ObjectMarking::IsGrey(heap_object,
                                   MarkingState::Internal(heap_object)));
     if (ObjectMarking::IsBlack(heap_object,
                                MarkingState::Internal(heap_object))) {
@@ skipping 104 matching lines @@
   inline void VisitCellPointer(Code* host, RelocInfo* rinfo) override {
     DCHECK_EQ(host, rinfo->host());
     DCHECK(rinfo->rmode() == RelocInfo::CELL);
     Cell* cell = rinfo->target_cell();
     // The cell is always in old space, we don't have to record the slot in
     // the old-to-new remembered set.
     DCHECK(!collector_->heap()->InNewSpace(cell));
     collector_->RecordRelocSlot(host, rinfo, cell);
   }
 
-  // Entries that will never move.
   inline void VisitCodeAgeSequence(Code* host, RelocInfo* rinfo) override {
     DCHECK_EQ(host, rinfo->host());
     DCHECK(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
     Code* stub = rinfo->code_age_stub();
     USE(stub);
     DCHECK(!Page::FromAddress(stub->address())->IsEvacuationCandidate());
   }
 
   // Entries that are skipped for recording.
   inline void VisitExternalReference(Code* host, RelocInfo* rinfo) final {}
@@ skipping 10 matching lines @@
         RememberedSet<OLD_TO_NEW>::Insert(Page::FromAddress(slot), slot);
       } else if (p->IsEvacuationCandidate()) {
         RememberedSet<OLD_TO_OLD>::Insert(Page::FromAddress(slot), slot);
       }
     }
   }
 
   MarkCompactCollector* collector_;
 };
 
+class YoungGenerationRecordMigratedSlotVisitor final
+    : public RecordMigratedSlotVisitor {
+ public:
+  explicit YoungGenerationRecordMigratedSlotVisitor(
+      MarkCompactCollector* collector)
+      : RecordMigratedSlotVisitor(collector) {}
+
+  inline void VisitCodeEntry(JSFunction* host, Address code_entry_slot) final {
+    Address code_entry = Memory::Address_at(code_entry_slot);
+    if (Page::FromAddress(code_entry)->IsEvacuationCandidate() &&
+        IsLive(host)) {
+      RememberedSet<OLD_TO_OLD>::InsertTyped(Page::FromAddress(code_entry_slot),
+                                             nullptr, CODE_ENTRY_SLOT,
+                                             code_entry_slot);
+    }
+  }
+
+  void VisitCodeTarget(Code* host, RelocInfo* rinfo) final { UNREACHABLE(); }
+  void VisitDebugTarget(Code* host, RelocInfo* rinfo) final { UNREACHABLE(); }
+  void VisitEmbeddedPointer(Code* host, RelocInfo* rinfo) final {
+    UNREACHABLE();
+  }
+  void VisitCellPointer(Code* host, RelocInfo* rinfo) final { UNREACHABLE(); }
+  void VisitCodeAgeSequence(Code* host, RelocInfo* rinfo) final {
+    UNREACHABLE();
+  }
+
+ private:
+  // Only record slots for host objects that are considered as live by the full
+  // collector.
+  inline bool IsLive(HeapObject* object) {
+    return ObjectMarking::IsBlack(object, collector_->marking_state(object));
+  }
+
+  inline void RecordMigratedSlot(HeapObject* host, Object* value,
+                                 Address slot) final {
+    if (value->IsHeapObject()) {
+      Page* p = Page::FromAddress(reinterpret_cast<Address>(value));
+      if (p->InNewSpace()) {
+        RememberedSet<OLD_TO_NEW>::Insert(Page::FromAddress(slot), slot);
+      } else if (p->IsEvacuationCandidate() && IsLive(host)) {
+        RememberedSet<OLD_TO_OLD>::Insert(Page::FromAddress(slot), slot);
+      }
+    }
+  }
+};
+
 class HeapObjectVisitor {
  public:
   virtual ~HeapObjectVisitor() {}
   virtual bool Visit(HeapObject* object) = 0;
 };
 
+class MigrationObserver {
+ public:
+  explicit MigrationObserver(Heap* heap) : heap_(heap) {}
+
+  virtual ~MigrationObserver() {}
+  virtual inline void Move(HeapObject* src, HeapObject* dst) {}
+
+ protected:
+  Heap* heap_;
+};
+
+class YoungGenerationMigrationObserver : public MigrationObserver {
+ public:
+  YoungGenerationMigrationObserver(
+      Heap* heap, MarkCompactCollector* mark_compact_collector,
+      std::vector<HeapObject*>* black_allocation_objects)
+      : MigrationObserver(heap),
+        mark_compact_collector_(mark_compact_collector),
+        black_allocation_objects_(black_allocation_objects) {}
+
+  inline void Move(HeapObject* src, HeapObject* dst) final {
+    // Migrate color to old generation marking in case the object survived young
+    // generation garbage collection.
+    if (heap_->incremental_marking()->IsMarking()) {
+      const MarkingState state = mark_compact_collector_->marking_state(dst);
+      if (heap_->incremental_marking()->black_allocation() &&
+          ObjectMarking::IsBlack(dst, state)) {

[ulan, 2017/04/26 09:51:28]

if (ObjectMarking::IsBlack(dst, state)) {
  DCHECK(heap_->incremental_marking()->black_allocation());
  ...
} else {
  IncrementalMarking::TransferColor();
}

[Michael Lippautz, 2017/05/02 11:22:00]

Done.

+        base::LockGuard<base::Mutex> guard(&mutex_);
+        black_allocation_objects_->push_back(dst);
+      }
+
+      // Transfer old generation marking state.
+      if (!ObjectMarking::IsBlack(dst, state)) {
+        IncrementalMarking::TransferColor<MarkBit::ATOMIC>(src, dst);
+      }
+    }
+  }
+
+ protected:
+  base::Mutex mutex_;
+  MarkCompactCollector* mark_compact_collector_;
+  std::vector<HeapObject*>* black_allocation_objects_;
+};
+
 class EvacuateVisitorBase : public HeapObjectVisitor {
  protected:
   enum MigrationMode { kFast, kProfiled };
 
   EvacuateVisitorBase(Heap* heap, CompactionSpaceCollection* compaction_spaces,
-                      RecordMigratedSlotVisitor* record_visitor)
+                      RecordMigratedSlotVisitor* record_visitor,
+                      MigrationObserver* migration_observer)
       : heap_(heap),
         compaction_spaces_(compaction_spaces),
         record_visitor_(record_visitor),
+        migration_observer_(migration_observer),
         profiling_(
             heap->isolate()->is_profiling() ||
             heap->isolate()->logger()->is_logging_code_events() ||
             heap->isolate()->heap_profiler()->is_tracking_object_moves()) {}
 
   inline bool TryEvacuateObject(PagedSpace* target_space, HeapObject* object,
                                 HeapObject** target_object) {
 #ifdef VERIFY_HEAP
     if (AbortCompactionForTesting(object)) return false;
 #endif  // VERIFY_HEAP
@@ skipping 24 matching lines @@
     DCHECK(heap_->AllowedToBeMigrated(src, dest));
     DCHECK(dest != LO_SPACE);
     if (dest == OLD_SPACE) {
       DCHECK_OBJECT_SIZE(size);
       DCHECK(IsAligned(size, kPointerSize));
       heap_->CopyBlock(dst_addr, src_addr, size);
       if ((mode == kProfiled) && dst->IsBytecodeArray()) {
         PROFILE(heap_->isolate(),
                 CodeMoveEvent(AbstractCode::cast(src), dst_addr));
       }
+      migration_observer_->Move(src, dst);
       dst->IterateBodyFast(dst->map()->instance_type(), size, record_visitor_);
     } else if (dest == CODE_SPACE) {
       DCHECK_CODEOBJECT_SIZE(size, heap_->code_space());
       if (mode == kProfiled) {
         PROFILE(heap_->isolate(),
                 CodeMoveEvent(AbstractCode::cast(src), dst_addr));
       }
       heap_->CopyBlock(dst_addr, src_addr, size);
       Code::cast(dst)->Relocate(dst_addr - src_addr);
-      RecordMigratedSlotVisitor visitor(heap_->mark_compact_collector());
+      migration_observer_->Move(src, dst);
       dst->IterateBodyFast(dst->map()->instance_type(), size, record_visitor_);
     } else {
       DCHECK_OBJECT_SIZE(size);
       DCHECK(dest == NEW_SPACE);
       heap_->CopyBlock(dst_addr, src_addr, size);
+      migration_observer_->Move(src, dst);
     }
     if (mode == kProfiled) {
       heap_->OnMoveEvent(dst, src, size);
     }
     base::NoBarrier_Store(reinterpret_cast<base::AtomicWord*>(src_addr),
                           reinterpret_cast<base::AtomicWord>(dst_addr));
   }
 
 #ifdef VERIFY_HEAP
   bool AbortCompactionForTesting(HeapObject* object) {
@@ skipping 11 matching lines @@
         }
       }
     }
     return false;
   }
 #endif  // VERIFY_HEAP
 
   Heap* heap_;
   CompactionSpaceCollection* compaction_spaces_;
   RecordMigratedSlotVisitor* record_visitor_;
+  MigrationObserver* migration_observer_;
   bool profiling_;
 };
 
 class EvacuateNewSpaceVisitor final : public EvacuateVisitorBase {
  public:
   static const intptr_t kLabSize = 4 * KB;
   static const intptr_t kMaxLabObjectSize = 256;
 
   explicit EvacuateNewSpaceVisitor(Heap* heap,
                                    CompactionSpaceCollection* compaction_spaces,
                                    RecordMigratedSlotVisitor* record_visitor,
+                                   MigrationObserver* migration_observer,
                                    base::HashMap* local_pretenuring_feedback)
-      : EvacuateVisitorBase(heap, compaction_spaces, record_visitor),
+      : EvacuateVisitorBase(heap, compaction_spaces, record_visitor,
+                            migration_observer),
         buffer_(LocalAllocationBuffer::InvalidBuffer()),
         space_to_allocate_(NEW_SPACE),
         promoted_size_(0),
         semispace_copied_size_(0),
         local_pretenuring_feedback_(local_pretenuring_feedback) {}
 
   inline bool Visit(HeapObject* object) override {
     heap_->UpdateAllocationSite<Heap::kCached>(object,
                                                local_pretenuring_feedback_);
     int size = object->Size();
@@ skipping 162 matching lines @@
   Heap* heap_;
   RecordMigratedSlotVisitor* record_visitor_;
   intptr_t moved_bytes_;
   base::HashMap* local_pretenuring_feedback_;
 };
 
 class EvacuateOldSpaceVisitor final : public EvacuateVisitorBase {
  public:
   EvacuateOldSpaceVisitor(Heap* heap,
                           CompactionSpaceCollection* compaction_spaces,
-                          RecordMigratedSlotVisitor* record_visitor)
-      : EvacuateVisitorBase(heap, compaction_spaces, record_visitor) {}
+                          RecordMigratedSlotVisitor* record_visitor,
+                          MigrationObserver* migration_observer)
+      : EvacuateVisitorBase(heap, compaction_spaces, record_visitor,
+                            migration_observer) {}
 
   inline bool Visit(HeapObject* object) override {
     CompactionSpace* target_space = compaction_spaces_->Get(
         Page::FromAddress(object->address())->owner()->identity());
     HeapObject* target_object = nullptr;
     if (TryEvacuateObject(target_space, object, &target_object)) {
       DCHECK(object->map_word().IsForwardingAddress());
       return true;
     }
     return false;
@@ skipping 339 matching lines @@
                                                      heap_object);
     return KEEP_SLOT;
   }
   return REMOVE_SLOT;
 }
 
 static bool IsUnmarkedObject(Heap* heap, Object** p) {
   DCHECK_IMPLIES(heap->InNewSpace(*p), heap->InToSpace(*p));
   return heap->InNewSpace(*p) &&
          !ObjectMarking::IsBlack(HeapObject::cast(*p),
-                                 MarkingState::Internal(HeapObject::cast(*p)));
+                                 MarkingState::External(HeapObject::cast(*p)));
 }
 
 void MinorMarkCompactCollector::MarkLiveObjects() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_MARK);
 
   PostponeInterruptsScope postpone(isolate());
 
   StaticYoungGenerationMarkingVisitor::Initialize(heap());
   RootMarkingVisitor root_visitor(this);
 
@@ skipping 31 matching lines @@
     heap()->IterateEncounteredWeakCollections(&root_visitor);
     ProcessMarkingDeque();
   }
 
   {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_MARK_GLOBAL_HANDLES);
     isolate()->global_handles()->MarkNewSpaceWeakUnmodifiedObjectsPending(
         &IsUnmarkedObject);
     isolate()
         ->global_handles()
-        ->IterateNewSpaceWeakUnmodifiedRoots<GlobalHandles::VISIT_OTHERS>(
-            &root_visitor);
+        ->IterateNewSpaceWeakUnmodifiedRoots<
+            GlobalHandles::HANDLE_PHANTOM_NODES_VISIT_OTHERS>(&root_visitor);
     ProcessMarkingDeque();
   }
 
   marking_deque()->StopUsing();
 }
 
 void MinorMarkCompactCollector::ProcessMarkingDeque() {
   EmptyMarkingDeque();
   DCHECK(!marking_deque()->overflowed());
   DCHECK(marking_deque()->IsEmpty());
@@ skipping 11 matching lines @@
         object, MarkingState::External(object))));
 
     Map* map = object->map();
     DCHECK((ObjectMarking::IsBlack<MarkBit::NON_ATOMIC>(
         object, MarkingState::External(object))));
     StaticYoungGenerationMarkingVisitor::IterateBody(map, object);
   }
 }
 
 void MinorMarkCompactCollector::CollectGarbage() {
+  heap()->mark_compact_collector()->sweeper().EnsureNewSpaceCompleted();
+
   MarkLiveObjects();
-
+  ClearNonLiveReferences();
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     YoungGenerationMarkingVerifier verifier(heap());
     verifier.Run();
   }
 #endif  // VERIFY_HEAP
+
+  std::vector<HeapObject*> black_allocation_objects;
+  EvacuateNewSpace(&black_allocation_objects);
+#ifdef VERIFY_HEAP
+  if (FLAG_verify_heap) {
+    YoungGenerationEvacuationVerifier verifier(heap());
+    verifier.Run();
+  }
+#endif  // VERIFY_HEAP
+
+  heap()->incremental_marking()->UpdateMarkingDequeAfterScavenge();
+
+  // Process black allocation objects after updating pointers as we otherwise
+  // would end up with objects on the marking deque that potentially forward
+  // to white objects.
+  // TODO(mlippautz): Instead of processing them explicitly, we should just add
+  // them to the marking deque for further processing.
+  {
+    TRACE_GC(heap()->tracer(),
+             GCTracer::Scope::MINOR_MC_EVACUATE_PROCESS_BLACK_ALLOCATION);
+    for (HeapObject* object : black_allocation_objects) {
+      CHECK(ObjectMarking::IsBlack(object, MarkingState::Internal(object)));
+      heap()->incremental_marking()->IterateBlackObject(object);
+    }
+    heap()->local_embedder_heap_tracer()->RegisterWrappersWithRemoteTracer();
+  }
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_CLEAR_LIVENESS);
+    for (Page* p : PageRange(heap()->new_space()->FromSpaceStart(),
+                             heap()->new_space()->FromSpaceEnd())) {
+      marking_state(p).ClearLiveness();
+    }
+  }
+}
+
+void MinorMarkCompactCollector::ClearNonLiveReferences() {
+  TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR);
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_STRING_TABLE);
+    // Internalized strings are always stored in old space, so there is no need
+    // to clean them here.
+    YoungGenerationExternalStringTableCleaner external_visitor(*this);
+    heap()->external_string_table_.IterateNewSpaceStrings(&external_visitor);
+    heap()->external_string_table_.CleanUpNewSpaceStrings();
+  }
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_WEAK_LISTS);
+    // Process the weak references.
+    MinorMarkCompactWeakObjectRetainer retainer(*this);
+    heap()->ProcessYoungWeakReferences(&retainer);
+  }
+}
+
+void MinorMarkCompactCollector::EvacuatePrologue() {
+  NewSpace* new_space = heap()->new_space();
+  // Append the list of new space pages to be processed.
+  for (Page* p : PageRange(new_space->bottom(), new_space->top())) {
+    new_space_evacuation_pages_.Add(p);
+  }
+  new_space->Flip();
+  new_space->ResetAllocationInfo();
+}
+
+void MinorMarkCompactCollector::EvacuateEpilogue() {
+  heap()->new_space()->set_age_mark(heap()->new_space()->top());
+}
+
+void MinorMarkCompactCollector::EvacuateNewSpace(
+    std::vector<HeapObject*>* black_allocation_objects) {
+  TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE);
+  Heap::RelocationLock relocation_lock(heap());
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_PROLOGUE);
+    EvacuatePrologue();
+  }
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_COPY);
+    EvacuatePagesInParallel(black_allocation_objects);
+  }
+
+  UpdatePointersAfterEvacuation();
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_REBALANCE);
+    if (!heap()->new_space()->Rebalance()) {
+      FatalProcessOutOfMemory("NewSpace::Rebalance");
+    }
+  }
+
+  // Give pages that are queued to be freed back to the OS.
+  heap()->memory_allocator()->unmapper()->FreeQueuedChunks();
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_CLEAN_UP);
+    // TODO(mlippautz): Implement page promotion.
+    new_space_evacuation_pages_.Rewind(0);
+  }
+
+  {
+    TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_EPILOGUE);
+    EvacuateEpilogue();
+  }
 }
 
 void MarkCompactCollector::MarkLiveObjects() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK);
   // The recursive GC marker detects when it is nearing stack overflow,
   // and switches to a different marking system.  JS interrupts interfere
   // with the C stack limit check.
   PostponeInterruptsScope postpone(isolate());
 
   {
@@ skipping 659 matching lines @@
   }
 
   // NewSpacePages with more live bytes than this threshold qualify for fast
   // evacuation.
   static int PageEvacuationThreshold() {
     if (FLAG_page_promotion)
       return FLAG_page_promotion_threshold * Page::kAllocatableMemory / 100;
     return Page::kAllocatableMemory + kPointerSize;
   }
 
-  Evacuator(Heap* heap, RecordMigratedSlotVisitor* record_visitor)
+  Evacuator(Heap* heap, RecordMigratedSlotVisitor* record_visitor,
+            MigrationObserver* migration_observer)
       : heap_(heap),
         compaction_spaces_(heap_),
         local_pretenuring_feedback_(kInitialLocalPretenuringFeedbackCapacity),
         new_space_visitor_(heap_, &compaction_spaces_, record_visitor,
-                           &local_pretenuring_feedback_),
+                           migration_observer, &local_pretenuring_feedback_),
         new_to_new_page_visitor_(heap_, record_visitor,
                                  &local_pretenuring_feedback_),
         new_to_old_page_visitor_(heap_, record_visitor,
                                  &local_pretenuring_feedback_),
 
-        old_space_visitor_(heap_, &compaction_spaces_, record_visitor),
+        old_space_visitor_(heap_, &compaction_spaces_, record_visitor,
+                           migration_observer),
         duration_(0.0),
         bytes_compacted_(0) {}
 
   virtual ~Evacuator() {}
 
   bool EvacuatePage(Page* page);
 
   // Merge back locally cached info sequentially. Note that this method needs
   // to be called from the main thread.
   inline void Finalize();
@@ skipping 75 matching lines @@
       new_space_visitor_.promoted_size() +
       new_space_visitor_.semispace_copied_size() +
       new_to_old_page_visitor_.moved_bytes() +
       new_to_new_page_visitor_.moved_bytes());
   heap()->MergeAllocationSitePretenuringFeedback(local_pretenuring_feedback_);
 }
 
 class FullEvacuator : public Evacuator {
  public:
   FullEvacuator(MarkCompactCollector* collector,
-                RecordMigratedSlotVisitor* record_visitor)
-      : Evacuator(collector->heap(), record_visitor), collector_(collector) {}
+                RecordMigratedSlotVisitor* record_visitor,
+                MigrationObserver* migration_observer)
+      : Evacuator(collector->heap(), record_visitor, migration_observer),
+        collector_(collector) {}
 
  protected:
   bool RawEvacuatePage(Page* page, intptr_t* live_bytes) override;
 
   MarkCompactCollector* collector_;
 };
 
 bool FullEvacuator::RawEvacuatePage(Page* page, intptr_t* live_bytes) {
   bool success = false;
   LiveObjectVisitor object_visitor;
@@ skipping 43 matching lines @@
         success = false;
       } else {
         ArrayBufferTracker::ProcessBuffers(
             page, ArrayBufferTracker::kUpdateForwardedRemoveOthers);
       }
       break;
   }
   return success;
 }
 
+class YoungGenerationEvacuator : public Evacuator {
+ public:
+  YoungGenerationEvacuator(MinorMarkCompactCollector* collector,
+                           RecordMigratedSlotVisitor* record_visitor,
+                           MigrationObserver* migration_observer)
+      : Evacuator(collector->heap(), record_visitor, migration_observer),
+        collector_(collector) {}
+
+ protected:
+  bool RawEvacuatePage(Page* page, intptr_t* live_bytes) override;
+
+  MinorMarkCompactCollector* collector_;
+};
+
+bool YoungGenerationEvacuator::RawEvacuatePage(Page* page,
+                                               intptr_t* live_bytes) {
+  bool success = false;
+  LiveObjectVisitor object_visitor;
+  const MarkingState state = collector_->marking_state(page);
+  *live_bytes = state.live_bytes();
+  switch (ComputeEvacuationMode(page)) {
+    case kObjectsNewToOld:
+      success = object_visitor.VisitBlackObjects(
+          page, state, &new_space_visitor_, LiveObjectVisitor::kClearMarkbits);
+      DCHECK(success);
+      ArrayBufferTracker::ProcessBuffers(
+          page, ArrayBufferTracker::kUpdateForwardedRemoveOthers);
+      break;
+    case kPageNewToOld:
+      // TODO(mlippautz): Implement page promotion.
+      UNREACHABLE();
+      break;
+    case kPageNewToNew:
+      // TODO(mlippautz): Implement page promotion.
+      UNREACHABLE();
+      break;
+    case kObjectsOldToOld:
+      UNREACHABLE();
+      break;
+  }
+  return success;
+}
+
 class EvacuationJobTraits {
  public:
-  typedef int* PerPageData;  // Pointer to number of aborted pages.
+  struct PageData {
+    int* abandoned_pages;  // Pointer to number of aborted pages.
+    MarkingState marking_state;
+  };
+
+  typedef PageData PerPageData;
   typedef Evacuator* PerTaskData;
 
   static const bool NeedSequentialFinalization = true;
 
   static bool ProcessPageInParallel(Heap* heap, PerTaskData evacuator,
                                     MemoryChunk* chunk, PerPageData) {
     return evacuator->EvacuatePage(reinterpret_cast<Page*>(chunk));
   }
 
   static void FinalizePageSequentially(Heap* heap, MemoryChunk* chunk,
@@ skipping 12 matching lines @@
         if (success) {
           DCHECK(p->IsEvacuationCandidate());
           DCHECK(p->SweepingDone());
           p->Unlink();
         } else {
           // We have partially compacted the page, i.e., some objects may have
           // moved, others are still in place.
           p->ClearEvacuationCandidate();
           // Slots have already been recorded so we just need to add it to the
           // sweeper, which will happen after updating pointers.
-          *data += 1;
+          *data.abandoned_pages += 1;
         }
         break;
       default:
         UNREACHABLE();
     }
   }
 };
 
+template <class Evacuator, class Collector>
+void MarkCompactCollectorBase::CreateAndExecuteEvacuationTasks(
+    Collector* collector, PageParallelJob<EvacuationJobTraits>* job,
+    RecordMigratedSlotVisitor* record_visitor, MigrationObserver* observer,
+    const intptr_t live_bytes, const int& abandoned_pages) {
+  // Used for trace summary.
+  double compaction_speed = 0;
+  if (FLAG_trace_evacuation) {
+    compaction_speed = heap()->tracer()->CompactionSpeedInBytesPerMillisecond();
+  }
+
+  const int wanted_num_tasks =
+      NumberOfParallelCompactionTasks(job->NumberOfPages(), live_bytes);
+  Evacuator** evacuators = new Evacuator*[wanted_num_tasks];
+  for (int i = 0; i < wanted_num_tasks; i++) {
+    evacuators[i] = new Evacuator(collector, record_visitor, observer);
+  }
+  job->Run(wanted_num_tasks, [evacuators](int i) { return evacuators[i]; });
+  const Address top = heap()->new_space()->top();
+  for (int i = 0; i < wanted_num_tasks; i++) {
+    evacuators[i]->Finalize();
+    // Try to find the last LAB that was used for new space allocation in
+    // evacuation tasks. If it was adjacent to the current top, move top back.
+    const AllocationInfo info = evacuators[i]->CloseNewSpaceLAB();
+    if (info.limit() != nullptr && info.limit() == top) {
+      DCHECK_NOT_NULL(info.top());
+      *heap()->new_space()->allocation_top_address() = info.top();
+    }
+    delete evacuators[i];
+  }
+  delete[] evacuators;
+
+  if (FLAG_trace_evacuation) {
+    PrintIsolate(isolate(),
+                 "%8.0f ms: evacuation-summary: parallel=%s pages=%d "
+                 "aborted=%d wanted_tasks=%d tasks=%d cores=%" PRIuS
+                 " live_bytes=%" V8PRIdPTR " compaction_speed=%.f\n",
+                 isolate()->time_millis_since_init(),
+                 FLAG_parallel_compaction ? "yes" : "no", job->NumberOfPages(),
+                 abandoned_pages, wanted_num_tasks, job->NumberOfTasks(),
+                 V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads(),
+                 live_bytes, compaction_speed);
+  }
+}
+
 void MarkCompactCollector::EvacuatePagesInParallel() {
   PageParallelJob<EvacuationJobTraits> job(
       heap_, heap_->isolate()->cancelable_task_manager(),
       &page_parallel_job_semaphore_);
 
   int abandoned_pages = 0;
   intptr_t live_bytes = 0;
   for (Page* page : old_space_evacuation_pages_) {
     live_bytes += MarkingState::Internal(page).live_bytes();
-    job.AddPage(page, &abandoned_pages);
+    job.AddPage(page, {&abandoned_pages, marking_state(page)});
   }
 
   const bool reduce_memory = heap()->ShouldReduceMemory();
   const Address age_mark = heap()->new_space()->age_mark();
   for (Page* page : new_space_evacuation_pages_) {
     intptr_t live_bytes_on_page = MarkingState::Internal(page).live_bytes();
     live_bytes += live_bytes_on_page;
     if (!reduce_memory && !page->NeverEvacuate() &&
         (live_bytes_on_page > Evacuator::PageEvacuationThreshold()) &&
         !page->Contains(age_mark) &&
         heap()->CanExpandOldGeneration(live_bytes_on_page)) {
       if (page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK)) {
         EvacuateNewSpacePageVisitor<NEW_TO_OLD>::Move(page);
       } else {
         EvacuateNewSpacePageVisitor<NEW_TO_NEW>::Move(page);
       }
     }
 
-    job.AddPage(page, &abandoned_pages);
+    job.AddPage(page, {&abandoned_pages, marking_state(page)});
   }
   DCHECK_GE(job.NumberOfPages(), 1);
 
-  // Used for trace summary.
-  double compaction_speed = 0;
-  if (FLAG_trace_evacuation) {
-    compaction_speed = heap()->tracer()->CompactionSpeedInBytesPerMillisecond();
+  MigrationObserver observer(heap());
+  RecordMigratedSlotVisitor record_visitor(this);
+  CreateAndExecuteEvacuationTasks<FullEvacuator>(
+      this, &job, &record_visitor, &observer, live_bytes, abandoned_pages);
+}
+
+void MinorMarkCompactCollector::EvacuatePagesInParallel(
+    std::vector<HeapObject*>* black_allocation_objects) {
+  PageParallelJob<EvacuationJobTraits> job(
+      heap_, heap_->isolate()->cancelable_task_manager(),
+      &page_parallel_job_semaphore_);
+  int abandoned_pages = 0;
+  intptr_t live_bytes = 0;
+
+  for (Page* page : new_space_evacuation_pages_) {
+    intptr_t live_bytes_on_page = marking_state(page).live_bytes();
+    live_bytes += live_bytes_on_page;
+    // TODO(mlippautz): Implement page promotion.
+    job.AddPage(page, {&abandoned_pages, marking_state(page)});
   }
+  DCHECK_GE(job.NumberOfPages(), 1);
 
-  const int wanted_num_tasks =
-      NumberOfParallelCompactionTasks(job.NumberOfPages(), live_bytes);
-  FullEvacuator** evacuators = new FullEvacuator*[wanted_num_tasks];
-  RecordMigratedSlotVisitor record_visitor(this);
-  for (int i = 0; i < wanted_num_tasks; i++) {
-    evacuators[i] = new FullEvacuator(this, &record_visitor);
-  }
-  job.Run(wanted_num_tasks, [evacuators](int i) { return evacuators[i]; });
-  const Address top = heap()->new_space()->top();
-  for (int i = 0; i < wanted_num_tasks; i++) {
-    evacuators[i]->Finalize();
-    // Try to find the last LAB that was used for new space allocation in
-    // evacuation tasks. If it was adjacent to the current top, move top back.
-    const AllocationInfo info = evacuators[i]->CloseNewSpaceLAB();
-    if (info.limit() != nullptr && info.limit() == top) {
-      DCHECK_NOT_NULL(info.top());
-      *heap()->new_space()->allocation_top_address() = info.top();
-    }
-    delete evacuators[i];
-  }
-  delete[] evacuators;
-
-  if (FLAG_trace_evacuation) {
-    PrintIsolate(isolate(),
-                 "%8.0f ms: evacuation-summary: parallel=%s pages=%d "
-                 "aborted=%d wanted_tasks=%d tasks=%d cores=%" PRIuS
-                 " live_bytes=%" V8PRIdPTR " compaction_speed=%.f\n",
-                 isolate()->time_millis_since_init(),
-                 FLAG_parallel_compaction ? "yes" : "no", job.NumberOfPages(),
-                 abandoned_pages, wanted_num_tasks, job.NumberOfTasks(),
-                 V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads(),
-                 live_bytes, compaction_speed);
-  }
+  YoungGenerationMigrationObserver observer(
+      heap(), heap()->mark_compact_collector(), black_allocation_objects);
+  YoungGenerationRecordMigratedSlotVisitor record_visitor(
+      heap()->mark_compact_collector());
+  CreateAndExecuteEvacuationTasks<YoungGenerationEvacuator>(
+      this, &job, &record_visitor, &observer, live_bytes, abandoned_pages);
 }
 
 class EvacuationWeakObjectRetainer : public WeakObjectRetainer {
  public:
   virtual Object* RetainAs(Object* object) {
     if (object->IsHeapObject()) {
       HeapObject* heap_object = HeapObject::cast(object);
       MapWord map_word = heap_object->map_word();
       if (map_word.IsForwardingAddress()) {
         return map_word.ToForwardingAddress();
@@ skipping 304 matching lines @@
     UpdateUntypedPointers(heap, chunk);
     UpdateTypedPointers(heap, chunk);
     return true;
   }
   static const bool NeedSequentialFinalization = false;
   static void FinalizePageSequentially(Heap*, MemoryChunk*, bool, PerPageData) {
   }
 
  private:
   static void UpdateUntypedPointers(Heap* heap, MemoryChunk* chunk) {
+    base::LockGuard<base::RecursiveMutex> guard(chunk->mutex());
     if (type == OLD_TO_NEW) {
       RememberedSet<OLD_TO_NEW>::Iterate(chunk, [heap](Address slot) {
         return CheckAndUpdateOldToNewSlot(heap, slot);
       });
     } else {
       RememberedSet<OLD_TO_OLD>::Iterate(chunk, [](Address slot) {
         return UpdateSlot(reinterpret_cast<Object**>(slot));
       });
     }
   }
@@ skipping 86 matching lines @@
       heap, heap->isolate()->cancelable_task_manager(), semaphore);
   RememberedSet<type>::IterateMemoryChunks(
       heap, [&job](MemoryChunk* chunk) { job.AddPage(chunk, 0); });
   int num_pages = job.NumberOfPages();
   int num_tasks = NumberOfPointerUpdateTasks(num_pages);
   job.Run(num_tasks, [](int i) { return 0; });
 }
 
 class ToSpacePointerUpdateJobTraits {
  public:
-  typedef std::pair<Address, Address> PerPageData;
+  struct PageData {
+    Address start;
+    Address end;
+    MarkingState marking_state;
+  };
+
+  typedef PageData PerPageData;
   typedef PointersUpdatingVisitor* PerTaskData;
 
   static bool ProcessPageInParallel(Heap* heap, PerTaskData visitor,
-                                    MemoryChunk* chunk, PerPageData limits) {
+                                    MemoryChunk* chunk, PerPageData page_data) {
     if (chunk->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION)) {
       // New->new promoted pages contain garbage so they require iteration
       // using markbits.
-      ProcessPageInParallelVisitLive(heap, visitor, chunk, limits);
+      ProcessPageInParallelVisitLive(heap, visitor, chunk, page_data);
     } else {
-      ProcessPageInParallelVisitAll(heap, visitor, chunk, limits);
+      ProcessPageInParallelVisitAll(heap, visitor, chunk, page_data);
     }
     return true;
   }
 
   static const bool NeedSequentialFinalization = false;
   static void FinalizePageSequentially(Heap*, MemoryChunk*, bool, PerPageData) {
   }
 
  private:
   static void ProcessPageInParallelVisitAll(Heap* heap, PerTaskData visitor,
                                             MemoryChunk* chunk,
-                                            PerPageData limits) {
-    for (Address cur = limits.first; cur < limits.second;) {
+                                            PerPageData page_data) {
+    for (Address cur = page_data.start; cur < page_data.end;) {
       HeapObject* object = HeapObject::FromAddress(cur);
       Map* map = object->map();
       int size = object->SizeFromMap(map);
       object->IterateBody(map->instance_type(), size, visitor);
       cur += size;
     }
   }
 
   static void ProcessPageInParallelVisitLive(Heap* heap, PerTaskData visitor,
                                              MemoryChunk* chunk,
-                                             PerPageData limits) {
-    LiveObjectIterator<kBlackObjects> it(chunk, MarkingState::Internal(chunk));
+                                             PerPageData page_data) {
+    LiveObjectIterator<kBlackObjects> it(chunk, page_data.marking_state);
     HeapObject* object = NULL;
     while ((object = it.Next()) != NULL) {
       Map* map = object->map();
       int size = object->SizeFromMap(map);
       object->IterateBody(map->instance_type(), size, visitor);
     }
   }
 };
 
-void UpdateToSpacePointersInParallel(Heap* heap, base::Semaphore* semaphore) {
+template <class MarkingStateProvider>
+void UpdateToSpacePointersInParallel(
+    Heap* heap, base::Semaphore* semaphore,
+    const MarkingStateProvider& marking_state_provider) {
   PageParallelJob<ToSpacePointerUpdateJobTraits> job(
       heap, heap->isolate()->cancelable_task_manager(), semaphore);
   Address space_start = heap->new_space()->bottom();
   Address space_end = heap->new_space()->top();
   for (Page* page : PageRange(space_start, space_end)) {
     Address start =
         page->Contains(space_start) ? space_start : page->area_start();
     Address end = page->Contains(space_end) ? space_end : page->area_end();
-    job.AddPage(page, std::make_pair(start, end));
+    job.AddPage(page, {start, end, marking_state_provider.marking_state(page)});
   }
   PointersUpdatingVisitor visitor;
   int num_tasks = FLAG_parallel_pointer_update ? job.NumberOfPages() : 1;
   job.Run(num_tasks, [&visitor](int i) { return &visitor; });
 }
 
 void MarkCompactCollector::UpdatePointersAfterEvacuation() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS);
 
 
   {
     TRACE_GC(heap()->tracer(),
              GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS_TO_NEW);
-    UpdateToSpacePointersInParallel(heap_, &page_parallel_job_semaphore_);
+    UpdateToSpacePointersInParallel(heap_, &page_parallel_job_semaphore_,
+                                    *this);
     // Update roots.
     PointersUpdatingVisitor updating_visitor;
     heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_SWEEP_NEWSPACE);
     UpdatePointersInParallel<OLD_TO_NEW>(heap_, &page_parallel_job_semaphore_);
   }
 
   {
     Heap* heap = this->heap();
     TRACE_GC(heap->tracer(),
              GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS_TO_EVACUATED);
     UpdatePointersInParallel<OLD_TO_OLD>(heap_, &page_parallel_job_semaphore_);
   }
 
   {
     TRACE_GC(heap()->tracer(),
              GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS_WEAK);
     // Update pointers from external string table.
     heap_->UpdateReferencesInExternalStringTable(
         &UpdateReferenceInExternalStringTableEntry);
 
     EvacuationWeakObjectRetainer evacuation_object_retainer;
     heap()->ProcessWeakListRoots(&evacuation_object_retainer);
   }
 }
 
+void MinorMarkCompactCollector::UpdatePointersAfterEvacuation() {
+  TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS);
+
+  PointersUpdatingVisitor updating_visitor;
+
+  {
+    TRACE_GC(heap()->tracer(),
+             GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS_TO_NEW);
+    UpdateToSpacePointersInParallel(heap_, &page_parallel_job_semaphore_,
+                                    *this);
+    // TODO(mlippautz): Iteration mode is not optimal as we process all
+    // global handles. Find a way to only process the ones related to new
+    // space.
+    heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_SWEEP_NEWSPACE);
+    UpdatePointersInParallel<OLD_TO_NEW>(heap_, &page_parallel_job_semaphore_);
+  }
+
+  {
+    TRACE_GC(heap()->tracer(),
+             GCTracer::Scope::MC_EVACUATE_UPDATE_POINTERS_WEAK);
+
+    EvacuationWeakObjectRetainer evacuation_object_retainer;
+    heap()->ProcessWeakListRoots(&evacuation_object_retainer);
+
+    // Update pointers from external string table.
+    heap()->UpdateNewSpaceReferencesInExternalStringTable(
+        &UpdateReferenceInExternalStringTableEntry);
+    heap()->IterateEncounteredWeakCollections(&updating_visitor);
+    heap()->set_encountered_weak_collections(Smi::kZero);
+  }
+}
 
 void MarkCompactCollector::ReleaseEvacuationCandidates() {
   for (Page* p : old_space_evacuation_pages_) {
     if (!p->IsEvacuationCandidate()) continue;
     PagedSpace* space = static_cast<PagedSpace*>(p->owner());
     MarkingState::Internal(p).SetLiveBytes(0);
     CHECK(p->SweepingDone());
     space->ReleasePage(p);
   }
   old_space_evacuation_pages_.Rewind(0);
@@ skipping 202 matching lines @@
       // The target is always in old space, we don't have to record the slot in
       // the old-to-new remembered set.
       DCHECK(!heap()->InNewSpace(target));
       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8