[heap] Remove black pages and use black areas instead.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index eca2880acd174b0bc7e6e620899ad17f6cd3d794..5d3f13bd91400a8b8f802ab57b7092bec0738f95 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -104,8 +104,7 @@ static void VerifyMarking(Heap* heap, Address bottom, Address top) {
   VerifyMarkingVisitor visitor(heap);
   HeapObject* object;
   Address next_object_must_be_here_or_later = bottom;
-
-  for (Address current = bottom; current < top; current += kPointerSize) {
+  for (Address current = bottom; current < top;) {
     object = HeapObject::FromAddress(current);
     if (MarkCompactCollector::IsMarked(object)) {
       CHECK(Marking::IsBlack(ObjectMarking::MarkBitFrom(object)));
@@ -113,21 +112,13 @@ static void VerifyMarking(Heap* heap, Address bottom, Address top) {
       object->Iterate(&visitor);
       next_object_must_be_here_or_later = current + object->Size();
       // The next word for sure belongs to the current object, jump over it.
+      current = next_object_must_be_here_or_later;

[ulan, 2016/07/19 13:23:32]

This is making verification less strict.

How about additionally checking that either 
1) all bits are set in [object ... current) or
2) only the header bits are set?

[Hannes Payer (out of office), 2016/07/19 14:42:53]

Good idea! Done.

+    } else {
       current += kPointerSize;
     }
   }
 }
 
-static void VerifyMarkingBlackPage(Heap* heap, Page* page) {
-  CHECK(page->IsFlagSet(Page::BLACK_PAGE));
-  VerifyMarkingVisitor visitor(heap);
-  HeapObjectIterator it(page);
-  for (HeapObject* object = it.Next(); object != NULL; object = it.Next()) {
-    CHECK(Marking::IsBlack(ObjectMarking::MarkBitFrom(object)));
-    object->Iterate(&visitor);
-  }
-}
-
 static void VerifyMarking(NewSpace* space) {
   Address end = space->top();
   // The bottom position is at the start of its page. Allows us to use
@@ -146,11 +137,7 @@ static void VerifyMarking(NewSpace* space) {
 
 static void VerifyMarking(PagedSpace* space) {
   for (Page* p : *space) {
-    if (p->IsFlagSet(Page::BLACK_PAGE)) {
-      VerifyMarkingBlackPage(space->heap(), p);
-    } else {
-      VerifyMarking(space->heap(), p->area_start(), p->area_end());
-    }
+    VerifyMarking(space->heap(), p->area_start(), p->area_end());
   }
 }
 
@@ -409,9 +396,6 @@ void MarkCompactCollector::VerifyOmittedMapChecks() {
 static void ClearMarkbitsInPagedSpace(PagedSpace* space) {
   for (Page* p : *space) {
     p->ClearLiveness();
-    if (p->IsFlagSet(Page::BLACK_PAGE)) {
-      p->ClearFlag(Page::BLACK_PAGE);
-    }
   }
 }
 
@@ -435,9 +419,6 @@ void MarkCompactCollector::ClearMarkbits() {
     MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
     chunk->ResetProgressBar();
     chunk->ResetLiveBytes();
-    if (chunk->IsFlagSet(Page::BLACK_PAGE)) {
-      chunk->ClearFlag(Page::BLACK_PAGE);
-    }
   }
 }
 
@@ -659,7 +640,6 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
 
   for (Page* p : *space) {
     if (p->NeverEvacuate()) continue;
-    if (p->IsFlagSet(Page::BLACK_PAGE)) continue;
     // Invariant: Evacuation candidates are just created when marking is
     // started. This means that sweeping has finished. Furthermore, at the end
     // of a GC all evacuation candidates are cleared and their slot buffers are
@@ -1913,9 +1893,7 @@ class MarkCompactCollector::EvacuateRecordOnlyVisitor final
 
 void MarkCompactCollector::DiscoverGreyObjectsInSpace(PagedSpace* space) {
   for (Page* p : *space) {
-    if (!p->IsFlagSet(Page::BLACK_PAGE)) {
-      DiscoverGreyObjectsOnPage(p);
-    }
+    DiscoverGreyObjectsOnPage(p);
     if (marking_deque()->IsFull()) return;
   }
 }
@@ -2929,9 +2907,8 @@ bool MarkCompactCollector::IsSlotInBlackObject(MemoryChunk* p, Address slot) {
   DCHECK(owner != heap_->lo_space() && owner != nullptr);
   USE(owner);
 
-  // If we are on a black page, we cannot find the actual object start
-  // easiliy. We just return true but do not set the out_object.
-  if (p->IsFlagSet(Page::BLACK_PAGE)) {
+  // We may be part of a black area.
+  if (Marking::IsBlackOrGrey(ObjectMarking::MarkBitFrom(slot))) {
     return true;
   }
 
@@ -3028,27 +3005,16 @@ HeapObject* MarkCompactCollector::FindBlackObjectBySlotSlow(Address slot) {
     return nullptr;
   }
 
-  if (p->IsFlagSet(Page::BLACK_PAGE)) {
-    HeapObjectIterator it(p);
-    HeapObject* object = nullptr;
-    while ((object = it.Next()) != nullptr) {
-      int size = object->Size();
-      if (object->address() > slot) return nullptr;
-      if (object->address() <= slot && slot < (object->address() + size)) {
-        return object;
-      }
-    }
-  } else {
-    LiveObjectIterator<kBlackObjects> it(p);
-    HeapObject* object = nullptr;
-    while ((object = it.Next()) != nullptr) {
-      int size = object->Size();
-      if (object->address() > slot) return nullptr;
-      if (object->address() <= slot && slot < (object->address() + size)) {
-        return object;
-      }
+  LiveObjectIterator<kBlackObjects> it(p);
+  HeapObject* object = nullptr;
+  while ((object = it.Next()) != nullptr) {
+    int size = object->Size();
+    if (object->address() > slot) return nullptr;
+    if (object->address() <= slot && slot < (object->address() + size)) {
+      return object;
     }
   }
+
   return nullptr;
 }
 
@@ -3385,7 +3351,6 @@ int MarkCompactCollector::Sweeper::RawSweep(
   DCHECK(free_list_mode == IGNORE_FREE_LIST || space->identity() == OLD_SPACE ||
          space->identity() == CODE_SPACE || space->identity() == MAP_SPACE);
   DCHECK(!p->IsEvacuationCandidate() && !p->SweepingDone());
-  DCHECK(!p->IsFlagSet(Page::BLACK_PAGE));
 
   // Before we sweep objects on the page, we free dead array buffers which
   // requires valid mark bits.
@@ -3938,7 +3903,6 @@ void MarkCompactCollector::Sweeper::AddSweepingPageSafe(AllocationSpace space,
 }
 
 void MarkCompactCollector::StartSweepSpace(PagedSpace* space) {
-  Address space_top = space->top();
   space->ClearStats();
 
   int will_be_swept = 0;
@@ -3955,24 +3919,6 @@ void MarkCompactCollector::StartSweepSpace(PagedSpace* space) {
       continue;
     }
 
-    // We can not sweep black pages, since all mark bits are set for these
-    // pages.
-    if (p->IsFlagSet(Page::BLACK_PAGE)) {
-      p->ClearLiveness();
-      p->concurrent_sweeping_state().SetValue(Page::kSweepingDone);
-      p->ClearFlag(Page::BLACK_PAGE);
-      // Area above the high watermark is free.
-      Address free_start = p->HighWaterMark();
-      // Check if the space top was in this page, which means that the
-      // high watermark is not up-to-date.
-      if (free_start < space_top && space_top <= p->area_end()) {
-        free_start = space_top;
-      }
-      int size = static_cast<int>(p->area_end() - free_start);
-      space->Free(free_start, size);
-      continue;
-    }
-
     if (p->IsFlagSet(Page::NEVER_ALLOCATE_ON_PAGE)) {
       // We need to sweep the page to get it into an iterable state again. Note
       // that this adds unusable memory into the free list that is later on