Start using store buffers. Handle store buffer overflow situation....

src/spaces.h

 // Copyright 2006-2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 28 matching lines @@
 //
 // A JS heap consists of a young generation, an old generation, and a large
 // object space. The young generation is divided into two semispaces. A
 // scavenger implements Cheney's copying algorithm. The old generation is
 // separated into a map space and an old object space. The map space contains
 // all (and only) map objects, the rest of old objects go into the old space.
 // The old generation is collected by a mark-sweep-compact collector.
 //
 // The semispaces of the young generation are contiguous.  The old and map
 // spaces consists of a list of pages. A page has a page header and an object
-// area. A page size is deliberately chosen as 8K bytes.
-// The first word of a page is an opaque page header that has the
-// address of the next page and its ownership information. The second word may
-// have the allocation top address of this page. Heap objects are aligned to the
-// pointer size.
+// area.
 //
 // There is a separate large object space for objects larger than
 // Page::kMaxHeapObjectSize, so that they do not have to move during
 // collection. The large object space is paged. Pages in large object space
-// may be larger than 8K.
+// may be larger than the page size.
 //
-// A card marking write barrier is used to keep track of intergenerational
-// references. Old space pages are divided into regions of Page::kRegionSize
-// size. Each region has a corresponding dirty bit in the page header which is
-// set if the region might contain pointers to new space. For details about
-// dirty bits encoding see comments in the Page::GetRegionNumberForAddress()
-// method body.
+// A store-buffer based write barrier is used to keep track of intergenerational
+// references.  See store-buffer.h.
 //
-// During scavenges and mark-sweep collections we iterate intergenerational
-// pointers without decoding heap object maps so if the page belongs to old
-// pointer space or large object space it is essential to guarantee that
-// the page does not contain any garbage pointers to new space: every pointer
-// aligned word which satisfies the Heap::InNewSpace() predicate must be a
-// pointer to a live heap object in new space. Thus objects in old pointer
-// and large object spaces should have a special layout (e.g. no bare integer
-// fields). This requirement does not apply to map space which is iterated in
-// a special fashion. However we still require pointer fields of dead maps to
-// be cleaned.
+// During scavenges and mark-sweep collections we sometimes (after a store
+// buffer overflow) iterate intergenerational pointers without decoding heap
+// object maps so if the page belongs to old pointer space or large object
+// space it is essential to guarantee that the page does not contain any
+// garbage pointers to new space: every pointer aligned word which satisfies
+// the Heap::InNewSpace() predicate must be a pointer to a live heap object in
+// new space. Thus objects in old pointer and large object spaces should have a
+// special layout (e.g. no bare integer fields). This requirement does not
+// apply to map space which is iterated in a special fashion. However we still
+// require pointer fields of dead maps to be cleaned.
 //
 // To enable lazy cleaning of old space pages we use a notion of allocation
 // watermark. Every pointer under watermark is considered to be well formed.
 // Page allocation watermark is not necessarily equal to page allocation top but
 // all alive objects on page should reside under allocation watermark.
 // During scavenge allocation watermark might be bumped and invalid pointers
 // might appear below it. To avoid following them we store a valid watermark
 // into special field in the page header and set a page WATERMARK_INVALIDATED
 // flag. For details see comments in the Page::SetAllocationWatermark() method
 // body.
@@ skipping 404 matching lines @@
     return offset;
   }
 
   // Returns the address for a given offset to the this page.
   Address OffsetToAddress(int offset) {
     ASSERT_PAGE_OFFSET(offset);
     return address() + offset;
   }
 
   // ---------------------------------------------------------------------
-  // Card marking support
-
-  static const uint32_t kAllRegionsCleanMarks = 0x0;
-  static const uint32_t kAllRegionsDirtyMarks = 0xFFFFFFFF;
-
-  inline uint32_t GetRegionMarks();
-  inline void SetRegionMarks(uint32_t dirty);
-
-  inline uint32_t GetRegionMaskForAddress(Address addr);
-  inline uint32_t GetRegionMaskForSpan(Address start, int length_in_bytes);
-  inline int GetRegionNumberForAddress(Address addr);
-
-  inline void MarkRegionDirty(Address addr);
-  inline bool IsRegionDirty(Address addr);
-
-  inline void ClearRegionMarks(Address start,
-                               Address end,
-                               bool reaches_limit);
 
   // Page size in bytes.  This must be a multiple of the OS page size.
   static const int kPageSize = 1 << kPageSizeBits;
 
   // Page size mask.
   static const intptr_t kPageAlignmentMask = (1 << kPageSizeBits) - 1;
 
   // The start offset of the object area in a page. Aligned to both maps and
   // code alignment to be suitable for both.
   static const int kObjectStartOffset = kBodyOffset;
 
   // Object area size in bytes.
   static const int kObjectAreaSize = kPageSize - kObjectStartOffset;
 
   // Maximum object size that fits in a page.
   static const int kMaxHeapObjectSize = kObjectAreaSize;
 
   static const int kFirstUsedCell =
     (kBodyOffset/kPointerSize) >> MarkbitsBitmap::kBitsPerCellLog2;
 
   static const int kLastUsedCell =
     ((kPageSize - kPointerSize)/kPointerSize) >>
       MarkbitsBitmap::kBitsPerCellLog2;
 
 
-#ifdef ENABLE_CARDMARKING_WRITE_BARRIER
-  static const int kDirtyFlagOffset = 2 * kPointerSize;
-  static const int kRegionSizeLog2 = 8;
-  static const int kRegionSize = 1 << kRegionSizeLog2;
-  static const intptr_t kRegionAlignmentMask = (kRegionSize - 1);
-
-  STATIC_CHECK(kRegionSize == kPageSize / kBitsPerInt);
-#endif
-
   enum PageFlag {
     // Page allocation watermark was bumped by preallocation during scavenge.
     // Correct watermark can be retrieved by CachedAllocationWatermark() method
     WATERMARK_INVALIDATED = NUM_MEMORY_CHUNK_FLAGS,
 
     // We say that memory region [start_addr, end_addr[ is continuous if
     // and only if:
     //   a) start_addr coincides with the start of a valid heap object
     //   b) for any valid heap object o in this region address
     //      o->address() + o->Size() is either equal to end_addr or coincides
@@ skipping 1590 matching lines @@
   static const int kMaxMapPageIndex = 1 << 16;
 
   // Are map pointers encodable into map word?
   bool MapPointersEncodable() {
     return false;
   }
 
   // Should be called after forced sweep to find out if map space needs
   // compaction.
   bool NeedsCompaction(int live_maps) {
-    return !MapPointersEncodable() && live_maps <= CompactionThreshold();
-  }
-
-  Address TopAfterCompaction(int live_maps) {
-    ASSERT(NeedsCompaction(live_maps));
-
-    int pages_left = live_maps / kMapsPerPage;
-    PageIterator it(this, PageIterator::ALL_PAGES);
-    while (pages_left-- > 0) {
-      ASSERT(it.has_next());
-      it.next()->SetRegionMarks(Page::kAllRegionsCleanMarks);
-    }
-    ASSERT(it.has_next());
-    Page* top_page = it.next();
-    top_page->SetRegionMarks(Page::kAllRegionsCleanMarks);
-    ASSERT(top_page->is_valid());
-
-    int offset = live_maps % kMapsPerPage * Map::kSize;
-    Address top = top_page->ObjectAreaStart() + offset;
-    ASSERT(top < top_page->ObjectAreaEnd());
-    ASSERT(Contains(top));
-
-    return top;
-  }
-
-  void FinishCompaction(Address new_top, int live_maps) {
-    Page* top_page = Page::FromAddress(new_top);
-    ASSERT(top_page->is_valid());
-
-    SetAllocationInfo(&allocation_info_, top_page);
-    allocation_info_.top = new_top;
-
-    int new_size = live_maps * Map::kSize;
-    accounting_stats_.DeallocateBytes(accounting_stats_.Size());
-    accounting_stats_.AllocateBytes(new_size);
-
-#ifdef DEBUG
-    if (FLAG_enable_slow_asserts) {
-      intptr_t actual_size = 0;
-      for (Page* p = first_page_; p != top_page; p = p->next_page())
-        actual_size += kMapsPerPage * Map::kSize;
-      actual_size += (new_top - top_page->ObjectAreaStart());
-      ASSERT(accounting_stats_.Size() == actual_size);
-    }
-#endif
-
-    Shrink();
-    ResetFreeList();
+    return false;  // TODO(gc): Bring back map compaction.
   }
 
  protected:
 #ifdef DEBUG
   virtual void VerifyObject(HeapObject* obj);
 #endif
 
  private:
   static const int kMapsPerPage = Page::kObjectAreaSize / Map::kSize;
 
@@ skipping 77 matching lines @@
 
   // Finds an object for a given address, returns Failure::Exception()
   // if it is not found. The function iterates through all objects in this
   // space, may be slow.
   MaybeObject* FindObject(Address a);
 
   // Finds a large object page containing the given pc, returns NULL
   // if such a page doesn't exist.
   LargePage* FindPageContainingPc(Address pc);
 
-  // Iterates objects covered by dirty regions.
-  void IterateDirtyRegions(ObjectSlotCallback func);
+  // Iterates over pointers to new space.
+  void IteratePointersToNewSpace(ObjectSlotCallback func);
 
   // Frees unmarked objects.
   void FreeUnmarkedObjects();
 
   // Checks whether a heap object is in this space; O(1).
   bool Contains(HeapObject* obj);
 
   // Checks whether the space is empty.
   bool IsEmpty() { return first_page_ == NULL; }
 
@@ skipping 49 matching lines @@
 
  private:
   LargePage* current_;
   HeapObjectCallback size_func_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_