[heap] Black allocation.

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 126 matching lines @@
     VerifyMarking(space->heap(), page->area_start(), limit);
   }
 }
 
 
 static void VerifyMarking(PagedSpace* space) {
   PageIterator it(space);
 
   while (it.has_next()) {
     Page* p = it.next();
-    VerifyMarking(space->heap(), p->area_start(), p->area_end());
+    if (!p->IsFlagSet(Page::BLACK_PAGE)) {
+      VerifyMarking(space->heap(), p->area_start(), p->area_end());
+    }

[ulan, 2016/02/10 10:27:39]

It would be great to verify coloring invariant for black pages too.

How about adding black page handling to VerifyMarking? 
On a black page it wouldn't use marking bits but instead advance the current
pointer by current + object->Size() and stops before the linear allocation area.

[Hannes Payer (out of office), 2016/02/11 18:18:07]

Done.

   }
 }
 
 
 static void VerifyMarking(Heap* heap) {
   VerifyMarking(heap->old_space());
   VerifyMarking(heap->code_space());
   VerifyMarking(heap->map_space());
   VerifyMarking(heap->new_space());
 
@@ skipping 283 matching lines @@
     map->VerifyOmittedMapChecks();
   }
 }
 #endif  // VERIFY_HEAP
 
 
 static void ClearMarkbitsInPagedSpace(PagedSpace* space) {
   PageIterator it(space);
 
   while (it.has_next()) {
-    Bitmap::Clear(it.next());
+    Page* p = it.next();
+    Bitmap::Clear(p);
+    if (p->IsFlagSet(Page::BLACK_PAGE)) {
+      p->ClearFlag(Page::BLACK_PAGE);
+    }
   }
 }
 
 
 static void ClearMarkbitsInNewSpace(NewSpace* space) {
   NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
 
   while (it.has_next()) {
     Bitmap::Clear(it.next());
   }
 }
 
 
 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(Marking::MarkBitFrom(obj));
-    Page::FromAddress(obj->address())->ResetProgressBar();
-    Page::FromAddress(obj->address())->ResetLiveBytes();
+    MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
+    chunk->ResetProgressBar();
+    chunk->ResetLiveBytes();
+    if (chunk->IsFlagSet(Page::BLACK_PAGE)) {
+      chunk->ClearFlag(Page::BLACK_PAGE);
+    }
   }
 }
 
 
 class MarkCompactCollector::SweeperTask : public v8::Task {
  public:
   SweeperTask(Heap* heap, PagedSpace* space) : heap_(heap), space_(space) {}
 
   virtual ~SweeperTask() {}
 
@@ skipping 88 matching lines @@
   pending_sweeper_tasks_semaphore_.Signal();
   return true;
 }
 
 
 void Marking::TransferMark(Heap* heap, Address old_start, Address new_start) {
   // This is only used when resizing an object.
   DCHECK(MemoryChunk::FromAddress(old_start) ==
          MemoryChunk::FromAddress(new_start));
 
-  if (!heap->incremental_marking()->IsMarking()) return;
+  if (!heap->incremental_marking()->IsMarking() ||
+      Page::FromAddress(old_start)->IsFlagSet(Page::BLACK_PAGE))
+    return;
 
   // If the mark doesn't move, we don't check the color of the object.
   // It doesn't matter whether the object is black, since it hasn't changed
   // size, so the adjustment to the live data count will be zero anyway.
   if (old_start == new_start) return;
 
   MarkBit new_mark_bit = MarkBitFrom(new_start);
   MarkBit old_mark_bit = MarkBitFrom(old_start);
 
 #ifdef DEBUG
@@ skipping 88 matching lines @@
 
   // Pairs of (live_bytes_in_page, page).
   typedef std::pair<int, Page*> LiveBytesPagePair;
   std::vector<LiveBytesPagePair> pages;
   pages.reserve(number_of_pages);
 
   PageIterator it(space);
   while (it.has_next()) {
     Page* p = it.next();
     if (p->NeverEvacuate()) continue;
+    if (p->IsFlagSet(Page::BLACK_PAGE)) continue;
     if (p->IsFlagSet(Page::POPULAR_PAGE)) {
       // This page had slots buffer overflow on previous GC, skip it.
       p->ClearFlag(Page::POPULAR_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());
@@ skipping 1023 matching lines @@
     }
     return false;
   }
 };
 
 
 void MarkCompactCollector::DiscoverGreyObjectsInSpace(PagedSpace* space) {
   PageIterator it(space);
   while (it.has_next()) {
     Page* p = it.next();
-    DiscoverGreyObjectsOnPage(p);
-    if (marking_deque()->IsFull()) return;
+    if (!p->IsFlagSet(Page::BLACK_PAGE)) {
+      DiscoverGreyObjectsOnPage(p);
+      if (marking_deque()->IsFull()) return;
+    }
   }
 }
 
 
 void MarkCompactCollector::DiscoverGreyObjectsInNewSpace() {
   NewSpace* space = heap()->new_space();
   NewSpacePageIterator it(space->bottom(), space->top());
   while (it.has_next()) {
     NewSpacePage* page = it.next();
     DiscoverGreyObjectsOnPage(page);
@@ skipping 1158 matching lines @@
     // for it.
     CHECK(large_object->IsHeapObject());
     HeapObject* large_heap_object = HeapObject::cast(large_object);
     if (IsMarked(large_heap_object)) {
       *out_object = large_heap_object;
       return true;
     }
     return false;
   }
 
+  // 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)) {
+    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)));
 
   // Check if the slot points to the start of an object. This can happen e.g.
   // when we left trim a fixed array. Such slots are invalid and we can remove
@@ skipping 60 matching lines @@
     // Slots pointing to the first word of an object are invalid and removed.
     // This can happen when we move the object header while left trimming.
     *out_object = object;
     return true;
   }
   return false;
 }
 
 
 bool MarkCompactCollector::IsSlotInBlackObjectSlow(Page* p, Address slot) {
-  // This function does not support large objects right now.
   Space* owner = p->owner();
   if (owner == heap_->lo_space() || owner == NULL) {
     Object* large_object = heap_->lo_space()->FindObject(slot);
     // This object has to exist, otherwise we would not have recorded a slot
     // for it.
     CHECK(large_object->IsHeapObject());
     HeapObject* large_heap_object = HeapObject::cast(large_object);
     if (IsMarked(large_heap_object)) {
       return true;
     }
     return false;
   }
 
+  if (p->IsFlagSet(Page::BLACK_PAGE)) return true;
+
   LiveObjectIterator<kBlackObjects> it(p);
   HeapObject* object = NULL;
   while ((object = it.Next()) != NULL) {
     int size = object->Size();
 
     if (object->address() > slot) return false;
     if (object->address() <= slot && slot < (object->address() + size)) {
       return true;
     }
   }
   return false;
 }
 
 
 bool MarkCompactCollector::IsSlotInLiveObject(Address slot) {
-  HeapObject* object = NULL;
   // The target object is black but we don't know if the source slot is black.
   // The source object could have died and the slot could be part of a free
   // space. Find out based on mark bits if the slot is part of a live object.
-  if (!IsSlotInBlackObject(Page::FromAddress(slot), slot, &object)) {
+  Page* page = Page::FromAddress(slot);
+  HeapObject* object = NULL;
+  if (!IsSlotInBlackObject(page, slot, &object)) {
     return false;
   }
 
-  DCHECK(object != NULL);
+  // If the slot is on a black page, the object will be live.
+  DCHECK(object != NULL || page->IsFlagSet(Page::BLACK_PAGE));
+  if (page->IsFlagSet(Page::BLACK_PAGE)) {
+    return true;
+  }
+
   int offset = static_cast<int>(slot - object->address());
   return object->IsValidSlot(offset);
 }
 
 
 void MarkCompactCollector::VerifyIsSlotInLiveObject(Address slot,
                                                     HeapObject* object) {
   // The target object has to be black.
   CHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
 
@@ skipping 382 matching lines @@
 // Slots in live objects pointing into evacuation candidates are updated
 // if requested.
 // Returns the size of the biggest continuous freed memory chunk in bytes.
 template <SweepingMode sweeping_mode,
           MarkCompactCollector::SweepingParallelism parallelism,
           SkipListRebuildingMode skip_list_mode,
           FreeSpaceTreatmentMode free_space_mode>
 static int Sweep(PagedSpace* space, FreeList* free_list, Page* p,
                  ObjectVisitor* v) {
   DCHECK(!p->IsEvacuationCandidate() && !p->SweepingDone());
+  DCHECK(!p->IsFlagSet(Page::BLACK_PAGE));
   DCHECK_EQ(skip_list_mode == REBUILD_SKIP_LIST,
             space->identity() == CODE_SPACE);
   DCHECK((p->skip_list() == NULL) || (skip_list_mode == REBUILD_SKIP_LIST));
   DCHECK(parallelism == MarkCompactCollector::SWEEP_ON_MAIN_THREAD ||
          sweeping_mode == SWEEP_ONLY);
 
   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
@@ skipping 436 matching lines @@
 
   PageIterator it(space);
 
   int will_be_swept = 0;
   bool unused_page_present = false;
 
   while (it.has_next()) {
     Page* p = it.next();
     DCHECK(p->SweepingDone());
 
+    // We can not sweep black pages, since all mark bits are set for these
+    // pages.
+    if (p->IsFlagSet(Page::BLACK_PAGE)) {
+      Bitmap::Clear(p);
+      p->concurrent_sweeping_state().SetValue(Page::kSweepingDone);
+      p->ClearFlag(Page::BLACK_PAGE);
+      // TODO(hpayer): Free unused memory of last black page.
+      continue;
+    }
+
     if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION) ||
         p->IsEvacuationCandidate()) {
       // Will be processed in EvacuateNewSpaceAndCandidates.
       DCHECK(evacuation_candidates_.length() > 0);
       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
@@ skipping 154 matching lines @@
     MarkBit mark_bit = Marking::MarkBitFrom(host);
     if (Marking::IsBlack(mark_bit)) {
       RelocInfo rinfo(isolate(), pc, RelocInfo::CODE_TARGET, 0, host);
       RecordRelocSlot(&rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8