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

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 86 matching lines @@
 
  private:
   Heap* heap_;
 };
 
 
 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)));
       CHECK(current >= next_object_must_be_here_or_later);
       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
   // page->area_start() as start of range on all pages.
   CHECK_EQ(space->bottom(), Page::FromAddress(space->bottom())->area_start());
 
   NewSpacePageRange range(space->bottom(), end);
   for (auto it = range.begin(); it != range.end();) {
     Page* page = *(it++);
     Address limit = it != range.end() ? page->area_end() : end;
     CHECK(limit == end || !page->Contains(end));
     VerifyMarking(space->heap(), page->area_start(), limit);
   }
 }
 
 
 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());
   }
 }
 
 
 static void VerifyMarking(Heap* heap) {
   VerifyMarking(heap->old_space());
   VerifyMarking(heap->code_space());
   VerifyMarking(heap->map_space());
   VerifyMarking(heap->new_space());
 
@@ skipping 238 matching lines @@
     Map* map = Map::cast(obj);
     map->VerifyOmittedMapChecks();
   }
 }
 #endif  // VERIFY_HEAP
 
 
 static void ClearMarkbitsInPagedSpace(PagedSpace* space) {
   for (Page* p : *space) {
     p->ClearLiveness();
-    if (p->IsFlagSet(Page::BLACK_PAGE)) {
-      p->ClearFlag(Page::BLACK_PAGE);
-    }
   }
 }
 
 
 static void ClearMarkbitsInNewSpace(NewSpace* space) {
   for (Page* page : *space) {
     page->ClearLiveness();
   }
 }
 
 
 void MarkCompactCollector::ClearMarkbits() {
   ClearMarkbitsInPagedSpace(heap_->code_space());
   ClearMarkbitsInPagedSpace(heap_->map_space());
   ClearMarkbitsInPagedSpace(heap_->old_space());
   ClearMarkbitsInNewSpace(heap_->new_space());
 
   LargeObjectIterator it(heap_->lo_space());
   for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
     Marking::MarkWhite(ObjectMarking::MarkBitFrom(obj));
     MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
     chunk->ResetProgressBar();
     chunk->ResetLiveBytes();
-    if (chunk->IsFlagSet(Page::BLACK_PAGE)) {
-      chunk->ClearFlag(Page::BLACK_PAGE);
-    }
   }
 }
 
 class MarkCompactCollector::Sweeper::SweeperTask : public v8::Task {
  public:
   SweeperTask(Sweeper* sweeper, base::Semaphore* pending_sweeper_tasks,
               AllocationSpace space_to_start)
       : sweeper_(sweeper),
         pending_sweeper_tasks_(pending_sweeper_tasks),
         space_to_start_(space_to_start) {}
@@ skipping 201 matching lines @@
   int number_of_pages = space->CountTotalPages();
   int area_size = space->AreaSize();
 
   // Pairs of (live_bytes_in_page, page).
   typedef std::pair<int, Page*> LiveBytesPagePair;
   std::vector<LiveBytesPagePair> pages;
   pages.reserve(number_of_pages);
 
   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
     // released.
     CHECK(!p->IsEvacuationCandidate());
     CHECK_NULL(p->old_to_old_slots());
     CHECK_NULL(p->typed_old_to_old_slots());
     CHECK(p->SweepingDone());
     DCHECK(p->area_size() == area_size);
     pages.push_back(std::make_pair(p->LiveBytesFromFreeList(), p));
@@ skipping 1233 matching lines @@
     object->IterateBody(&visitor);
     return true;
   }
 
  private:
   Heap* heap_;
 };
 
 void MarkCompactCollector::DiscoverGreyObjectsInSpace(PagedSpace* space) {
   for (Page* p : *space) {
-    if (!p->IsFlagSet(Page::BLACK_PAGE)) {
-      DiscoverGreyObjectsOnPage(p);
-    }
+    DiscoverGreyObjectsOnPage(p);
     if (marking_deque()->IsFull()) return;
   }
 }
 
 
 void MarkCompactCollector::DiscoverGreyObjectsInNewSpace() {
   NewSpace* space = heap()->new_space();
   for (Page* page : NewSpacePageRange(space->bottom(), space->top())) {
     DiscoverGreyObjectsOnPage(page);
     if (marking_deque()->IsFull()) return;
@@ skipping 993 matching lines @@
   }
 
   return String::cast(*p);
 }
 
 bool MarkCompactCollector::IsSlotInBlackObject(MemoryChunk* p, Address slot) {
   Space* owner = p->owner();
   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;
   }
 
   uint32_t mark_bit_index = p->AddressToMarkbitIndex(slot);
   unsigned int cell_index = mark_bit_index >> Bitmap::kBitsPerCellLog2;
   MarkBit::CellType index_mask = 1u << Bitmap::IndexInCell(mark_bit_index);
   MarkBit::CellType* cells = p->markbits()->cells();
   Address base_address = p->area_start();
   unsigned int base_address_cell_index = Bitmap::IndexToCell(
       Bitmap::CellAlignIndex(p->AddressToMarkbitIndex(base_address)));
@@ skipping 76 matching lines @@
     // for it.
     CHECK(large_object->IsHeapObject());
     HeapObject* large_heap_object = HeapObject::cast(large_object);
 
     if (IsMarked(large_heap_object)) {
       return large_heap_object;
     }
     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;
 }
 
 
 void MarkCompactCollector::EvacuateNewSpacePrologue() {
   NewSpace* new_space = heap()->new_space();
   // Append the list of new space pages to be processed.
   for (Page* p : NewSpacePageRange(new_space->bottom(), new_space->top())) {
     newspace_evacuation_candidates_.Add(p);
   }
@@ skipping 316 matching lines @@
 };
 
 int MarkCompactCollector::Sweeper::RawSweep(
     Page* p, FreeListRebuildingMode free_list_mode,
     FreeSpaceTreatmentMode free_space_mode) {
   Space* space = p->owner();
   DCHECK_NOT_NULL(space);
   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.
   ArrayBufferTracker::FreeDead(p);
 
   Address free_start = p->area_start();
   DCHECK(reinterpret_cast<intptr_t>(free_start) % (32 * kPointerSize) == 0);
 
   // If we use the skip list for code space pages, we have to lock the skip
   // list because it could be accessed concurrently by the runtime or the
@@ skipping 532 matching lines @@
   return page;
 }
 
 void MarkCompactCollector::Sweeper::AddSweepingPageSafe(AllocationSpace space,
                                                         Page* page) {
   base::LockGuard<base::Mutex> guard(&mutex_);
   sweeping_list_[space].push_back(page);
 }
 
 void MarkCompactCollector::StartSweepSpace(PagedSpace* space) {
-  Address space_top = space->top();
   space->ClearStats();
 
   int will_be_swept = 0;
   bool unused_page_present = false;
 
   // Loop needs to support deletion if live bytes == 0 for a page.
   for (auto it = space->begin(); it != space->end();) {
     Page* p = *(it++);
     DCHECK(p->SweepingDone());
 
     if (p->IsEvacuationCandidate()) {
       // Will be processed in EvacuateNewSpaceAndCandidates.
       DCHECK(evacuation_candidates_.length() > 0);
       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
       // (in the free list) dropped again. Since we only use the flag for
       // testing this is fine.
       p->concurrent_sweeping_state().SetValue(Page::kSweepingInProgress);
       Sweeper::RawSweep(p, Sweeper::IGNORE_FREE_LIST,
                         Heap::ShouldZapGarbage() ? Sweeper::ZAP_FREE_SPACE
                                                  : Sweeper::IGNORE_FREE_SPACE);
       continue;
@@ skipping 97 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