Merge experimental/gc branch to the bleeding_edge.

src/spaces.h

Index: src/spaces.h
===================================================================
--- src/spaces.h	(revision 9327)
+++ src/spaces.h	(working copy)
@@ -49,45 +49,47 @@
 //
 // 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.
+// To enable lazy cleaning of old space pages we can mark chunks of the page
+// as being garbage.  Garbage sections are marked with a special map.  These
+// sections are skipped when scanning the page, even if we are otherwise
+// scanning without regard for object boundaries.  Garbage sections are chained
+// together to form a free list after a GC.  Garbage sections created outside
+// of GCs by object trunctation etc. may not be in the free list chain.  Very
+// small free spaces are ignored, they need only be cleaned of bogus pointers
+// into new space.
 //
+// Each page may have up to one special garbage section.  The start of this
+// section is denoted by the top field in the space.  The end of the section
+// is denoted by the limit field in the space.  This special garbage section
+// is not marked with a free space map in the data.  The point of this section
+// is to enable linear allocation without having to constantly update the byte
+// array every time the top field is updated and a new object is created.  The
+// special garbage section is not in the chain of garbage sections.
+//
+// Since the top and limit fields are in the space, not the page, only one page
+// has a special garbage section, and if the top and limit are equal then there
+// is no special garbage section.
 
 // Some assertion macros used in the debugging mode.
 
@@ -114,30 +116,505 @@
 class PagedSpace;
 class MemoryAllocator;
 class AllocationInfo;
+class Space;
+class FreeList;
+class MemoryChunk;
 
+class MarkBit {
+ public:
+  typedef uint32_t CellType;
+
+  inline MarkBit(CellType* cell, CellType mask, bool data_only)
+      : cell_(cell), mask_(mask), data_only_(data_only) { }
+
+  inline CellType* cell() { return cell_; }
+  inline CellType mask() { return mask_; }
+
+#ifdef DEBUG
+  bool operator==(const MarkBit& other) {
+    return cell_ == other.cell_ && mask_ == other.mask_;
+  }
+#endif
+
+  inline void Set() { *cell_ |= mask_; }
+  inline bool Get() { return (*cell_ & mask_) != 0; }
+  inline void Clear() { *cell_ &= ~mask_; }
+
+  inline bool data_only() { return data_only_; }
+
+  inline MarkBit Next() {
+    CellType new_mask = mask_ << 1;
+    if (new_mask == 0) {
+      return MarkBit(cell_ + 1, 1, data_only_);
+    } else {
+      return MarkBit(cell_, new_mask, data_only_);
+    }
+  }
+
+ private:
+  CellType* cell_;
+  CellType mask_;
+  // This boolean indicates that the object is in a data-only space with no
+  // pointers.  This enables some optimizations when marking.
+  // It is expected that this field is inlined and turned into control flow
+  // at the place where the MarkBit object is created.
+  bool data_only_;
+};
+
+
+// Bitmap is a sequence of cells each containing fixed number of bits.
+class Bitmap {
+ public:
+  static const uint32_t kBitsPerCell = 32;
+  static const uint32_t kBitsPerCellLog2 = 5;
+  static const uint32_t kBitIndexMask = kBitsPerCell - 1;
+  static const uint32_t kBytesPerCell = kBitsPerCell / kBitsPerByte;
+  static const uint32_t kBytesPerCellLog2 = kBitsPerCellLog2 - kBitsPerByteLog2;
+
+  static const size_t kLength =
+    (1 << kPageSizeBits) >> (kPointerSizeLog2);
+
+  static const size_t kSize =
+    (1 << kPageSizeBits) >> (kPointerSizeLog2 + kBitsPerByteLog2);
+
+
+  static int CellsForLength(int length) {
+    return (length + kBitsPerCell - 1) >> kBitsPerCellLog2;
+  }
+
+  int CellsCount() {
+    return CellsForLength(kLength);
+  }
+
+  static int SizeFor(int cells_count) {
+    return sizeof(MarkBit::CellType)*cells_count;
+  }
+
+  INLINE(static uint32_t IndexToCell(uint32_t index)) {
+    return index >> kBitsPerCellLog2;
+  }
+
+  INLINE(static uint32_t CellToIndex(uint32_t index)) {
+    return index << kBitsPerCellLog2;
+  }
+
+  INLINE(static uint32_t CellAlignIndex(uint32_t index)) {
+    return (index + kBitIndexMask) & ~kBitIndexMask;
+  }
+
+  INLINE(MarkBit::CellType* cells()) {
+    return reinterpret_cast<MarkBit::CellType*>(this);
+  }
+
+  INLINE(Address address()) {
+    return reinterpret_cast<Address>(this);
+  }
+
+  INLINE(static Bitmap* FromAddress(Address addr)) {
+    return reinterpret_cast<Bitmap*>(addr);
+  }
+
+  inline MarkBit MarkBitFromIndex(uint32_t index, bool data_only = false) {
+    MarkBit::CellType mask = 1 << (index & kBitIndexMask);
+    MarkBit::CellType* cell = this->cells() + (index >> kBitsPerCellLog2);
+    return MarkBit(cell, mask, data_only);
+  }
+
+  static inline void Clear(MemoryChunk* chunk);
+
+  static void PrintWord(uint32_t word, uint32_t himask = 0) {
+    for (uint32_t mask = 1; mask != 0; mask <<= 1) {
+      if ((mask & himask) != 0) PrintF("[");
+      PrintF((mask & word) ? "1" : "0");
+      if ((mask & himask) != 0) PrintF("]");
+    }
+  }
+
+  class CellPrinter {
+   public:
+    CellPrinter() : seq_start(0), seq_type(0), seq_length(0) { }
+
+    void Print(uint32_t pos, uint32_t cell) {
+      if (cell == seq_type) {
+        seq_length++;
+        return;
+      }
+
+      Flush();
+
+      if (IsSeq(cell)) {
+        seq_start = pos;
+        seq_length = 0;
+        seq_type = cell;
+        return;
+      }
+
+      PrintF("%d: ", pos);
+      PrintWord(cell);
+      PrintF("\n");
+    }
+
+    void Flush() {
+      if (seq_length > 0) {
+        PrintF("%d: %dx%d\n",
+               seq_start,
+               seq_type == 0 ? 0 : 1,
+               seq_length * kBitsPerCell);
+        seq_length = 0;
+      }
+    }
+
+    static bool IsSeq(uint32_t cell) { return cell == 0 || cell == 0xFFFFFFFF; }
+   private:
+    uint32_t seq_start;
+    uint32_t seq_type;
+    uint32_t seq_length;
+  };
+
+  void Print() {
+    CellPrinter printer;
+    for (int i = 0; i < CellsCount(); i++) {
+      printer.Print(i, cells()[i]);
+    }
+    printer.Flush();
+    PrintF("\n");
+  }
+
+  bool IsClean() {
+    for (int i = 0; i < CellsCount(); i++) {
+      if (cells()[i] != 0) return false;
+    }
+    return true;
+  }
+};
+
+
+class SkipList;
+class SlotsBuffer;
+
+// MemoryChunk represents a memory region owned by a specific space.
+// It is divided into the header and the body. Chunk start is always
+// 1MB aligned. Start of the body is aligned so it can accomodate
+// any heap object.
+class MemoryChunk {
+ public:
+  // Only works if the pointer is in the first kPageSize of the MemoryChunk.
+  static MemoryChunk* FromAddress(Address a) {
+    return reinterpret_cast<MemoryChunk*>(OffsetFrom(a) & ~kAlignmentMask);
+  }
+
+  // Only works for addresses in pointer spaces, not data or code spaces.
+  static inline MemoryChunk* FromAnyPointerAddress(Address addr);
+
+  Address address() { return reinterpret_cast<Address>(this); }
+
+  bool is_valid() { return address() != NULL; }
+
+  MemoryChunk* next_chunk() const { return next_chunk_; }
+  MemoryChunk* prev_chunk() const { return prev_chunk_; }
+
+  void set_next_chunk(MemoryChunk* next) { next_chunk_ = next; }
+  void set_prev_chunk(MemoryChunk* prev) { prev_chunk_ = prev; }
+
+  Space* owner() const {
+    if ((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
+        kFailureTag) {
+      return reinterpret_cast<Space*>(owner_ - kFailureTag);
+    } else {
+      return NULL;
+    }
+  }
+
+  void set_owner(Space* space) {
+    ASSERT((reinterpret_cast<intptr_t>(space) & kFailureTagMask) == 0);
+    owner_ = reinterpret_cast<Address>(space) + kFailureTag;
+    ASSERT((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
+           kFailureTag);
+  }
+
+  VirtualMemory* reserved_memory() {
+    return &reservation_;
+  }
+
+  void InitializeReservedMemory() {
+    reservation_.Reset();
+  }
+
+  void set_reserved_memory(VirtualMemory* reservation) {
+    ASSERT_NOT_NULL(reservation);
+    reservation_.TakeControl(reservation);
+  }
+
+  bool scan_on_scavenge() { return IsFlagSet(SCAN_ON_SCAVENGE); }
+  void initialize_scan_on_scavenge(bool scan) {
+    if (scan) {
+      SetFlag(SCAN_ON_SCAVENGE);
+    } else {
+      ClearFlag(SCAN_ON_SCAVENGE);
+    }
+  }
+  inline void set_scan_on_scavenge(bool scan);
+
+  int store_buffer_counter() { return store_buffer_counter_; }
+  void set_store_buffer_counter(int counter) {
+    store_buffer_counter_ = counter;
+  }
+
+  Address body() { return address() + kObjectStartOffset; }
+
+  Address body_limit() { return address() + size(); }
+
+  int body_size() { return static_cast<int>(size() - kObjectStartOffset); }
+
+  bool Contains(Address addr) {
+    return addr >= body() && addr < address() + size();
+  }
+
+  // Checks whether addr can be a limit of addresses in this page.
+  // It's a limit if it's in the page, or if it's just after the
+  // last byte of the page.
+  bool ContainsLimit(Address addr) {
+    return addr >= body() && addr <= address() + size();
+  }
+
+  enum MemoryChunkFlags {
+    IS_EXECUTABLE,
+    ABOUT_TO_BE_FREED,
+    POINTERS_TO_HERE_ARE_INTERESTING,
+    POINTERS_FROM_HERE_ARE_INTERESTING,
+    SCAN_ON_SCAVENGE,
+    IN_FROM_SPACE,  // Mutually exclusive with IN_TO_SPACE.
+    IN_TO_SPACE,    // All pages in new space has one of these two set.
+    NEW_SPACE_BELOW_AGE_MARK,
+    CONTAINS_ONLY_DATA,
+    EVACUATION_CANDIDATE,
+    RESCAN_ON_EVACUATION,
+
+    // Pages swept precisely can be iterated, hitting only the live objects.
+    // Whereas those swept conservatively cannot be iterated over. Both flags
+    // indicate that marking bits have been cleared by the sweeper, otherwise
+    // marking bits are still intact.
+    WAS_SWEPT_PRECISELY,
+    WAS_SWEPT_CONSERVATIVELY,
+
+    // Last flag, keep at bottom.
+    NUM_MEMORY_CHUNK_FLAGS
+  };
+
+
+  static const int kPointersToHereAreInterestingMask =
+      1 << POINTERS_TO_HERE_ARE_INTERESTING;
+
+  static const int kPointersFromHereAreInterestingMask =
+      1 << POINTERS_FROM_HERE_ARE_INTERESTING;
+
+  static const int kEvacuationCandidateMask =
+      1 << EVACUATION_CANDIDATE;
+
+  static const int kSkipEvacuationSlotsRecordingMask =
+      (1 << EVACUATION_CANDIDATE) |
+      (1 << RESCAN_ON_EVACUATION) |
+      (1 << IN_FROM_SPACE) |
+      (1 << IN_TO_SPACE);
+
+
+  void SetFlag(int flag) {
+    flags_ |= static_cast<uintptr_t>(1) << flag;
+  }
+
+  void ClearFlag(int flag) {
+    flags_ &= ~(static_cast<uintptr_t>(1) << flag);
+  }
+
+  void SetFlagTo(int flag, bool value) {
+    if (value) {
+      SetFlag(flag);
+    } else {
+      ClearFlag(flag);
+    }
+  }
+
+  bool IsFlagSet(int flag) {
+    return (flags_ & (static_cast<uintptr_t>(1) << flag)) != 0;
+  }
+
+  // Set or clear multiple flags at a time. The flags in the mask
+  // are set to the value in "flags", the rest retain the current value
+  // in flags_.
+  void SetFlags(intptr_t flags, intptr_t mask) {
+    flags_ = (flags_ & ~mask) | (flags & mask);
+  }
+
+  // Return all current flags.
+  intptr_t GetFlags() { return flags_; }
+
+  // Manage live byte count (count of bytes known to be live,
+  // because they are marked black).
+  void ResetLiveBytes() {
+    live_byte_count_ = 0;
+  }
+  void IncrementLiveBytes(int by) {
+    live_byte_count_ += by;
+  }
+  int LiveBytes() { return live_byte_count_; }
+  static void IncrementLiveBytes(Address address, int by) {
+    MemoryChunk::FromAddress(address)->IncrementLiveBytes(by);
+  }
+
+  static const intptr_t kAlignment =
+      (static_cast<uintptr_t>(1) << kPageSizeBits);
+
+  static const intptr_t kAlignmentMask = kAlignment - 1;
+
+  static const intptr_t kLiveBytesOffset =
+      kPointerSize + kPointerSize + kPointerSize + kPointerSize +
+      kPointerSize + kPointerSize + kPointerSize + kPointerSize +
+      kIntSize;
+
+  static const size_t kSlotsBufferOffset = kLiveBytesOffset + kIntSize;
+
+  static const size_t kHeaderSize =
+      kSlotsBufferOffset + kPointerSize + kPointerSize;
+
+  static const int kBodyOffset =
+    CODE_POINTER_ALIGN(MAP_POINTER_ALIGN(kHeaderSize + Bitmap::kSize));
+
+  // The start offset of the object area in a page. Aligned to both maps and
+  // code alignment to be suitable for both.  Also aligned to 32 words because
+  // the marking bitmap is arranged in 32 bit chunks.
+  static const int kObjectStartAlignment = 32 * kPointerSize;
+  static const int kObjectStartOffset = kBodyOffset - 1 +
+      (kObjectStartAlignment - (kBodyOffset - 1) % kObjectStartAlignment);
+
+  size_t size() const { return size_; }
+
+  Executability executable() {
+    return IsFlagSet(IS_EXECUTABLE) ? EXECUTABLE : NOT_EXECUTABLE;
+  }
+
+  bool ContainsOnlyData() {
+    return IsFlagSet(CONTAINS_ONLY_DATA);
+  }
+
+  bool InNewSpace() {
+    return (flags_ & ((1 << IN_FROM_SPACE) | (1 << IN_TO_SPACE))) != 0;
+  }
+
+  bool InToSpace() {
+    return IsFlagSet(IN_TO_SPACE);
+  }
+
+  bool InFromSpace() {
+    return IsFlagSet(IN_FROM_SPACE);
+  }
+
+  // ---------------------------------------------------------------------
+  // Markbits support
+
+  inline Bitmap* markbits() {
+    return Bitmap::FromAddress(address() + kHeaderSize);
+  }
+
+  void PrintMarkbits() { markbits()->Print(); }
+
+  inline uint32_t AddressToMarkbitIndex(Address addr) {
+    return static_cast<uint32_t>(addr - this->address()) >> kPointerSizeLog2;
+  }
+
+  inline static uint32_t FastAddressToMarkbitIndex(Address addr) {
+    const intptr_t offset =
+        reinterpret_cast<intptr_t>(addr) & kAlignmentMask;
+
+    return static_cast<uint32_t>(offset) >> kPointerSizeLog2;
+  }
+
+  inline Address MarkbitIndexToAddress(uint32_t index) {
+    return this->address() + (index << kPointerSizeLog2);
+  }
+
+  void InsertAfter(MemoryChunk* other);
+  void Unlink();
+
+  inline Heap* heap() { return heap_; }
+
+  static const int kFlagsOffset = kPointerSize * 3;
+
+  bool IsEvacuationCandidate() { return IsFlagSet(EVACUATION_CANDIDATE); }
+
+  bool ShouldSkipEvacuationSlotRecording() {
+    return (flags_ & kSkipEvacuationSlotsRecordingMask) != 0;
+  }
+
+  inline SkipList* skip_list() {
+    return skip_list_;
+  }
+
+  inline void set_skip_list(SkipList* skip_list) {
+    skip_list_ = skip_list;
+  }
+
+  inline SlotsBuffer* slots_buffer() {
+    return slots_buffer_;
+  }
+
+  inline SlotsBuffer** slots_buffer_address() {
+    return &slots_buffer_;
+  }
+
+  void MarkEvacuationCandidate() {
+    ASSERT(slots_buffer_ == NULL);
+    SetFlag(EVACUATION_CANDIDATE);
+  }
+
+  void ClearEvacuationCandidate() {
+    ASSERT(slots_buffer_ == NULL);
+    ClearFlag(EVACUATION_CANDIDATE);
+  }
+
+
+ protected:
+  MemoryChunk* next_chunk_;
+  MemoryChunk* prev_chunk_;
+  size_t size_;
+  intptr_t flags_;
+  // If the chunk needs to remember its memory reservation, it is stored here.
+  VirtualMemory reservation_;
+  // The identity of the owning space.  This is tagged as a failure pointer, but
+  // no failure can be in an object, so this can be distinguished from any entry
+  // in a fixed array.
+  Address owner_;
+  Heap* heap_;
+  // Used by the store buffer to keep track of which pages to mark scan-on-
+  // scavenge.
+  int store_buffer_counter_;
+  // Count of bytes marked black on page.
+  int live_byte_count_;
+  SlotsBuffer* slots_buffer_;
+  SkipList* skip_list_;
+
+  static MemoryChunk* Initialize(Heap* heap,
+                                 Address base,
+                                 size_t size,
+                                 Executability executable,
+                                 Space* owner);
+
+  friend class MemoryAllocator;
+};
+
+STATIC_CHECK(sizeof(MemoryChunk) <= MemoryChunk::kHeaderSize);
+
 // -----------------------------------------------------------------------------
-// A page normally has 8K bytes. Large object pages may be larger.  A page
-// address is always aligned to the 8K page size.
+// A page is a memory chunk of a size 1MB. Large object pages may be larger.
 //
-// Each page starts with a header of Page::kPageHeaderSize size which contains
-// bookkeeping data.
-//
-// The mark-compact collector transforms a map pointer into a page index and a
-// page offset. The exact encoding is described in the comments for
-// class MapWord in objects.h.
-//
 // The only way to get a page pointer is by calling factory methods:
 //   Page* p = Page::FromAddress(addr); or
 //   Page* p = Page::FromAllocationTop(top);
-class Page {
+class Page : public MemoryChunk {
  public:
   // Returns the page containing a given address. The address ranges
   // from [page_addr .. page_addr + kPageSize[
-  //
-  // Note that this function only works for addresses in normal paged
-  // spaces and addresses in the first 8K of large object pages (i.e.,
-  // the start of large objects but not necessarily derived pointers
-  // within them).
+  // This only works if the object is in fact in a page.  See also MemoryChunk::
+  // FromAddress() and FromAnyAddress().
   INLINE(static Page* FromAddress(Address a)) {
     return reinterpret_cast<Page*>(OffsetFrom(a) & ~kPageAlignmentMask);
   }
@@ -152,31 +629,12 @@
     return p;
   }
 
-  // Returns the start address of this page.
-  Address address() { return reinterpret_cast<Address>(this); }
-
-  // Checks whether this is a valid page address.
-  bool is_valid() { return address() != NULL; }
-
-  // Returns the next page of this page.
+  // Returns the next page in the chain of pages owned by a space.
   inline Page* next_page();
+  inline Page* prev_page();
+  inline void set_next_page(Page* page);
+  inline void set_prev_page(Page* page);
 
-  // Return the end of allocation in this page. Undefined for unused pages.
-  inline Address AllocationTop();
-
-  // Return the allocation watermark for the page.
-  // For old space pages it is guaranteed that the area under the watermark
-  // does not contain any garbage pointers to new space.
-  inline Address AllocationWatermark();
-
-  // Return the allocation watermark offset from the beginning of the page.
-  inline uint32_t AllocationWatermarkOffset();
-
-  inline void SetAllocationWatermark(Address allocation_watermark);
-
-  inline void SetCachedAllocationWatermark(Address allocation_watermark);
-  inline Address CachedAllocationWatermark();
-
   // Returns the start address of the object area in this page.
   Address ObjectAreaStart() { return address() + kObjectStartOffset; }
 
@@ -188,22 +646,6 @@
     return 0 == (OffsetFrom(a) & kPageAlignmentMask);
   }
 
-  // True if this page was in use before current compaction started.
-  // Result is valid only for pages owned by paged spaces and
-  // only after PagedSpace::PrepareForMarkCompact was called.
-  inline bool WasInUseBeforeMC();
-
-  inline void SetWasInUseBeforeMC(bool was_in_use);
-
-  // True if this page is a large object page.
-  inline bool IsLargeObjectPage();
-
-  inline void SetIsLargeObjectPage(bool is_large_object_page);
-
-  inline Executability PageExecutability();
-
-  inline void SetPageExecutability(Executability executable);
-
   // Returns the offset of a given address to this page.
   INLINE(int Offset(Address a)) {
     int offset = static_cast<int>(a - address());
@@ -218,143 +660,72 @@
   }
 
   // ---------------------------------------------------------------------
-  // 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;
 
-  static const int kPageHeaderSize = kPointerSize + kPointerSize + kIntSize +
-    kIntSize + kPointerSize + kPointerSize;
-
-  // 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 =
-      CODE_POINTER_ALIGN(MAP_POINTER_ALIGN(kPageHeaderSize));
-
   // 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 kDirtyFlagOffset = 2 * kPointerSize;
-  static const int kRegionSizeLog2 = 8;
-  static const int kRegionSize = 1 << kRegionSizeLog2;
-  static const intptr_t kRegionAlignmentMask = (kRegionSize - 1);
+  static const int kFirstUsedCell =
+    (kObjectStartOffset/kPointerSize) >> Bitmap::kBitsPerCellLog2;
 
-  STATIC_CHECK(kRegionSize == kPageSize / kBitsPerInt);
+  static const int kLastUsedCell =
+    ((kPageSize - kPointerSize)/kPointerSize) >>
+      Bitmap::kBitsPerCellLog2;
 
-  enum PageFlag {
-    IS_NORMAL_PAGE = 0,
-    WAS_IN_USE_BEFORE_MC,
+  inline void ClearGCFields();
 
-    // Page allocation watermark was bumped by preallocation during scavenge.
-    // Correct watermark can be retrieved by CachedAllocationWatermark() method
-    WATERMARK_INVALIDATED,
-    IS_EXECUTABLE,
-    NUM_PAGE_FLAGS  // Must be last
-  };
-  static const int kPageFlagMask = (1 << NUM_PAGE_FLAGS) - 1;
+  static inline Page* Initialize(Heap* heap,
+                                 MemoryChunk* chunk,
+                                 Executability executable,
+                                 PagedSpace* owner);
 
-  // To avoid an additional WATERMARK_INVALIDATED flag clearing pass during
-  // scavenge we just invalidate the watermark on each old space page after
-  // processing it. And then we flip the meaning of the WATERMARK_INVALIDATED
-  // flag at the beginning of the next scavenge and each page becomes marked as
-  // having a valid watermark.
-  //
-  // The following invariant must hold for pages in old pointer and map spaces:
-  //     If page is in use then page is marked as having invalid watermark at
-  //     the beginning and at the end of any GC.
-  //
-  // This invariant guarantees that after flipping flag meaning at the
-  // beginning of scavenge all pages in use will be marked as having valid
-  // watermark.
-  static inline void FlipMeaningOfInvalidatedWatermarkFlag(Heap* heap);
+  void InitializeAsAnchor(PagedSpace* owner);
 
-  // Returns true if the page allocation watermark was not altered during
-  // scavenge.
-  inline bool IsWatermarkValid();
+  bool WasSweptPrecisely() { return IsFlagSet(WAS_SWEPT_PRECISELY); }
+  bool WasSweptConservatively() { return IsFlagSet(WAS_SWEPT_CONSERVATIVELY); }
+  bool WasSwept() { return WasSweptPrecisely() || WasSweptConservatively(); }
 
-  inline void InvalidateWatermark(bool value);
+  void MarkSweptPrecisely() { SetFlag(WAS_SWEPT_PRECISELY); }
+  void MarkSweptConservatively() { SetFlag(WAS_SWEPT_CONSERVATIVELY); }
 
-  inline bool GetPageFlag(PageFlag flag);
-  inline void SetPageFlag(PageFlag flag, bool value);
-  inline void ClearPageFlags();
+  void ClearSweptPrecisely() { ClearFlag(WAS_SWEPT_PRECISELY); }
+  void ClearSweptConservatively() { ClearFlag(WAS_SWEPT_CONSERVATIVELY); }
 
-  inline void ClearGCFields();
+  friend class MemoryAllocator;
+};
 
-  static const int kAllocationWatermarkOffsetShift = WATERMARK_INVALIDATED + 1;
-  static const int kAllocationWatermarkOffsetBits  = kPageSizeBits + 1;
-  static const uint32_t kAllocationWatermarkOffsetMask =
-      ((1 << kAllocationWatermarkOffsetBits) - 1) <<
-      kAllocationWatermarkOffsetShift;
 
-  static const uint32_t kFlagsMask =
-    ((1 << kAllocationWatermarkOffsetShift) - 1);
+STATIC_CHECK(sizeof(Page) <= MemoryChunk::kHeaderSize);
 
-  STATIC_CHECK(kBitsPerInt - kAllocationWatermarkOffsetShift >=
-               kAllocationWatermarkOffsetBits);
 
-  //---------------------------------------------------------------------------
-  // Page header description.
-  //
-  // If a page is not in the large object space, the first word,
-  // opaque_header, encodes the next page address (aligned to kPageSize 8K)
-  // and the chunk number (0 ~ 8K-1).  Only MemoryAllocator should use
-  // opaque_header. The value range of the opaque_header is [0..kPageSize[,
-  // or [next_page_start, next_page_end[. It cannot point to a valid address
-  // in the current page.  If a page is in the large object space, the first
-  // word *may* (if the page start and large object chunk start are the
-  // same) contain the address of the next large object chunk.
-  intptr_t opaque_header;
+class LargePage : public MemoryChunk {
+ public:
+  HeapObject* GetObject() {
+    return HeapObject::FromAddress(body());
+  }
 
-  // If the page is not in the large object space, the low-order bit of the
-  // second word is set. If the page is in the large object space, the
-  // second word *may* (if the page start and large object chunk start are
-  // the same) contain the large object chunk size.  In either case, the
-  // low-order bit for large object pages will be cleared.
-  // For normal pages this word is used to store page flags and
-  // offset of allocation top.
-  intptr_t flags_;
+  inline LargePage* next_page() const {
+    return static_cast<LargePage*>(next_chunk());
+  }
 
-  // This field contains dirty marks for regions covering the page. Only dirty
-  // regions might contain intergenerational references.
-  // Only 32 dirty marks are supported so for large object pages several regions
-  // might be mapped to a single dirty mark.
-  uint32_t dirty_regions_;
+  inline void set_next_page(LargePage* page) {
+    set_next_chunk(page);
+  }
+ private:
+  static inline LargePage* Initialize(Heap* heap, MemoryChunk* chunk);
 
-  // The index of the page in its owner space.
-  int mc_page_index;
-
-  // During mark-compact collections this field contains the forwarding address
-  // of the first live object in this page.
-  // During scavenge collection this field is used to store allocation watermark
-  // if it is altered during scavenge.
-  Address mc_first_forwarded;
-
-  Heap* heap_;
+  friend class MemoryAllocator;
 };
 
+STATIC_CHECK(sizeof(LargePage) <= MemoryChunk::kHeaderSize);
 
 // ----------------------------------------------------------------------------
 // Space is the abstract superclass for all allocation spaces.
@@ -380,6 +751,14 @@
   // (e.g. see LargeObjectSpace).
   virtual intptr_t SizeOfObjects() { return Size(); }
 
+  virtual int RoundSizeDownToObjectAlignment(int size) {
+    if (id_ == CODE_SPACE) {
+      return RoundDown(size, kCodeAlignment);
+    } else {
+      return RoundDown(size, kPointerSize);
+    }
+  }
+
 #ifdef DEBUG
   virtual void Print() = 0;
 #endif
@@ -430,9 +809,9 @@
   // Allocates a chunk of memory from the large-object portion of
   // the code range.  On platforms with no separate code range, should
   // not be called.
-  MUST_USE_RESULT void* AllocateRawMemory(const size_t requested,
-                                          size_t* allocated);
-  void FreeRawMemory(void* buf, size_t length);
+  MUST_USE_RESULT Address AllocateRawMemory(const size_t requested,
+                                            size_t* allocated);
+  void FreeRawMemory(Address buf, size_t length);
 
  private:
   Isolate* isolate_;
@@ -443,9 +822,15 @@
   class FreeBlock {
    public:
     FreeBlock(Address start_arg, size_t size_arg)
-        : start(start_arg), size(size_arg) {}
+        : start(start_arg), size(size_arg) {
+      ASSERT(IsAddressAligned(start, MemoryChunk::kAlignment));
+      ASSERT(size >= static_cast<size_t>(Page::kPageSize));
+    }
     FreeBlock(void* start_arg, size_t size_arg)
-        : start(static_cast<Address>(start_arg)), size(size_arg) {}
+        : start(static_cast<Address>(start_arg)), size(size_arg) {
+      ASSERT(IsAddressAligned(start, MemoryChunk::kAlignment));
+      ASSERT(size >= static_cast<size_t>(Page::kPageSize));
+    }
 
     Address start;
     size_t size;
@@ -473,30 +858,63 @@
 };
 
 
+class SkipList {
+ public:
+  SkipList() {
+    Clear();
+  }
+
+  void Clear() {
+    for (int idx = 0; idx < kSize; idx++) {
+      starts_[idx] = reinterpret_cast<Address>(-1);
+    }
+  }
+
+  Address StartFor(Address addr) {
+    return starts_[RegionNumber(addr)];
+  }
+
+  void AddObject(Address addr, int size) {
+    int start_region = RegionNumber(addr);
+    int end_region = RegionNumber(addr + size - kPointerSize);
+    for (int idx = start_region; idx <= end_region; idx++) {
+      if (starts_[idx] > addr) starts_[idx] = addr;
+    }
+  }
+
+  static inline int RegionNumber(Address addr) {
+    return (OffsetFrom(addr) & Page::kPageAlignmentMask) >> kRegionSizeLog2;
+  }
+
+  static void Update(Address addr, int size) {
+    Page* page = Page::FromAddress(addr);
+    SkipList* list = page->skip_list();
+    if (list == NULL) {
+      list = new SkipList();
+      page->set_skip_list(list);
+    }
+
+    list->AddObject(addr, size);
+  }
+
+ private:
+  static const int kRegionSizeLog2 = 13;
+  static const int kRegionSize = 1 << kRegionSizeLog2;
+  static const int kSize = Page::kPageSize / kRegionSize;
+
+  STATIC_ASSERT(Page::kPageSize % kRegionSize == 0);
+
+  Address starts_[kSize];
+};
+
+
 // ----------------------------------------------------------------------------
 // A space acquires chunks of memory from the operating system. The memory
-// allocator manages chunks for the paged heap spaces (old space and map
-// space).  A paged chunk consists of pages. Pages in a chunk have contiguous
-// addresses and are linked as a list.
+// allocator allocated and deallocates pages for the paged heap spaces and large
+// pages for large object space.
 //
-// The allocator keeps an initial chunk which is used for the new space.  The
-// leftover regions of the initial chunk are used for the initial chunks of
-// old space and map space if they are big enough to hold at least one page.
-// The allocator assumes that there is one old space and one map space, each
-// expands the space by allocating kPagesPerChunk pages except the last
-// expansion (before running out of space).  The first chunk may contain fewer
-// than kPagesPerChunk pages as well.
+// Each space has to manage it's own pages.
 //
-// The memory allocator also allocates chunks for the large object space, but
-// they are managed by the space itself.  The new space does not expand.
-//
-// The fact that pages for paged spaces are allocated and deallocated in chunks
-// induces a constraint on the order of pages in a linked lists. We say that
-// pages are linked in the chunk-order if and only if every two consecutive
-// pages from the same chunk are consecutive in the linked list.
-//
-
-
 class MemoryAllocator {
  public:
   explicit MemoryAllocator(Isolate* isolate);
@@ -505,92 +923,16 @@
   // Max capacity of the total space and executable memory limit.
   bool Setup(intptr_t max_capacity, intptr_t capacity_executable);
 
-  // Deletes valid chunks.
   void TearDown();
 
-  // Reserves an initial address range of virtual memory to be split between
-  // the two new space semispaces, the old space, and the map space.  The
-  // memory is not yet committed or assigned to spaces and split into pages.
-  // The initial chunk is unmapped when the memory allocator is torn down.
-  // This function should only be called when there is not already a reserved
-  // initial chunk (initial_chunk_ should be NULL).  It returns the start
-  // address of the initial chunk if successful, with the side effect of
-  // setting the initial chunk, or else NULL if unsuccessful and leaves the
-  // initial chunk NULL.
-  void* ReserveInitialChunk(const size_t requested);
+  Page* AllocatePage(PagedSpace* owner, Executability executable);
 
-  // Commits pages from an as-yet-unmanaged block of virtual memory into a
-  // paged space.  The block should be part of the initial chunk reserved via
-  // a call to ReserveInitialChunk.  The number of pages is always returned in
-  // the output parameter num_pages.  This function assumes that the start
-  // address is non-null and that it is big enough to hold at least one
-  // page-aligned page.  The call always succeeds, and num_pages is always
-  // greater than zero.
-  Page* CommitPages(Address start, size_t size, PagedSpace* owner,
-                    int* num_pages);
+  LargePage* AllocateLargePage(intptr_t object_size,
+                                      Executability executable,
+                                      Space* owner);
 
-  // Commit a contiguous block of memory from the initial chunk.  Assumes that
-  // the address is not NULL, the size is greater than zero, and that the
-  // block is contained in the initial chunk.  Returns true if it succeeded
-  // and false otherwise.
-  bool CommitBlock(Address start, size_t size, Executability executable);
+  void Free(MemoryChunk* chunk);
 
-  // Uncommit a contiguous block of memory [start..(start+size)[.
-  // start is not NULL, the size is greater than zero, and the
-  // block is contained in the initial chunk.  Returns true if it succeeded
-  // and false otherwise.
-  bool UncommitBlock(Address start, size_t size);
-
-  // Zaps a contiguous block of memory [start..(start+size)[ thus
-  // filling it up with a recognizable non-NULL bit pattern.
-  void ZapBlock(Address start, size_t size);
-
-  // Attempts to allocate the requested (non-zero) number of pages from the
-  // OS.  Fewer pages might be allocated than requested. If it fails to
-  // allocate memory for the OS or cannot allocate a single page, this
-  // function returns an invalid page pointer (NULL). The caller must check
-  // whether the returned page is valid (by calling Page::is_valid()).  It is
-  // guaranteed that allocated pages have contiguous addresses.  The actual
-  // number of allocated pages is returned in the output parameter
-  // allocated_pages.  If the PagedSpace owner is executable and there is
-  // a code range, the pages are allocated from the code range.
-  Page* AllocatePages(int requested_pages, int* allocated_pages,
-                      PagedSpace* owner);
-
-  // Frees pages from a given page and after. Requires pages to be
-  // linked in chunk-order (see comment for class).
-  // If 'p' is the first page of a chunk, pages from 'p' are freed
-  // and this function returns an invalid page pointer.
-  // Otherwise, the function searches a page after 'p' that is
-  // the first page of a chunk. Pages after the found page
-  // are freed and the function returns 'p'.
-  Page* FreePages(Page* p);
-
-  // Frees all pages owned by given space.
-  void FreeAllPages(PagedSpace* space);
-
-  // Allocates and frees raw memory of certain size.
-  // These are just thin wrappers around OS::Allocate and OS::Free,
-  // but keep track of allocated bytes as part of heap.
-  // If the flag is EXECUTABLE and a code range exists, the requested
-  // memory is allocated from the code range.  If a code range exists
-  // and the freed memory is in it, the code range manages the freed memory.
-  MUST_USE_RESULT void* AllocateRawMemory(const size_t requested,
-                                          size_t* allocated,
-                                          Executability executable);
-  void FreeRawMemory(void* buf,
-                     size_t length,
-                     Executability executable);
-  void PerformAllocationCallback(ObjectSpace space,
-                                 AllocationAction action,
-                                 size_t size);
-
-  void AddMemoryAllocationCallback(MemoryAllocationCallback callback,
-                                   ObjectSpace space,
-                                   AllocationAction action);
-  void RemoveMemoryAllocationCallback(MemoryAllocationCallback callback);
-  bool MemoryAllocationCallbackRegistered(MemoryAllocationCallback callback);
-
   // Returns the maximum available bytes of heaps.
   intptr_t Available() { return capacity_ < size_ ? 0 : capacity_ - size_; }
 
@@ -611,67 +953,68 @@
     return (Available() / Page::kPageSize) * Page::kObjectAreaSize;
   }
 
-  // Links two pages.
-  inline void SetNextPage(Page* prev, Page* next);
+#ifdef DEBUG
+  // Reports statistic info of the space.
+  void ReportStatistics();
+#endif
 
-  // Returns the next page of a given page.
-  inline Page* GetNextPage(Page* p);
+  MemoryChunk* AllocateChunk(intptr_t body_size,
+                             Executability executable,
+                             Space* space);
 
-  // Checks whether a page belongs to a space.
-  inline bool IsPageInSpace(Page* p, PagedSpace* space);
+  Address ReserveAlignedMemory(size_t requested,
+                               size_t alignment,
+                               VirtualMemory* controller);
+  Address AllocateAlignedMemory(size_t requested,
+                                size_t alignment,
+                                Executability executable,
+                                VirtualMemory* controller);
 
-  // Returns the space that owns the given page.
-  inline PagedSpace* PageOwner(Page* page);
+  void FreeMemory(VirtualMemory* reservation, Executability executable);
+  void FreeMemory(Address addr, size_t size, Executability executable);
 
-  // Finds the first/last page in the same chunk as a given page.
-  Page* FindFirstPageInSameChunk(Page* p);
-  Page* FindLastPageInSameChunk(Page* p);
+  // Commit a contiguous block of memory from the initial chunk.  Assumes that
+  // the address is not NULL, the size is greater than zero, and that the
+  // block is contained in the initial chunk.  Returns true if it succeeded
+  // and false otherwise.
+  bool CommitBlock(Address start, size_t size, Executability executable);
 
-  // Relinks list of pages owned by space to make it chunk-ordered.
-  // Returns new first and last pages of space.
-  // Also returns last page in relinked list which has WasInUsedBeforeMC
-  // flag set.
-  void RelinkPageListInChunkOrder(PagedSpace* space,
-                                  Page** first_page,
-                                  Page** last_page,
-                                  Page** last_page_in_use);
+  // Uncommit a contiguous block of memory [start..(start+size)[.
+  // start is not NULL, the size is greater than zero, and the
+  // block is contained in the initial chunk.  Returns true if it succeeded
+  // and false otherwise.
+  bool UncommitBlock(Address start, size_t size);
 
-#ifdef DEBUG
-  // Reports statistic info of the space.
-  void ReportStatistics();
-#endif
+  // Zaps a contiguous block of memory [start..(start+size)[ thus
+  // filling it up with a recognizable non-NULL bit pattern.
+  void ZapBlock(Address start, size_t size);
 
-  // Due to encoding limitation, we can only have 8K chunks.
-  static const int kMaxNofChunks = 1 << kPageSizeBits;
-  // If a chunk has at least 16 pages, the maximum heap size is about
-  // 8K * 8K * 16 = 1G bytes.
-#ifdef V8_TARGET_ARCH_X64
-  static const int kPagesPerChunk = 32;
-  // On 64 bit the chunk table consists of 4 levels of 4096-entry tables.
-  static const int kChunkTableLevels = 4;
-  static const int kChunkTableBitsPerLevel = 12;
-#else
-  static const int kPagesPerChunk = 16;
-  // On 32 bit the chunk table consists of 2 levels of 256-entry tables.
-  static const int kChunkTableLevels = 2;
-  static const int kChunkTableBitsPerLevel = 8;
-#endif
+  void PerformAllocationCallback(ObjectSpace space,
+                                 AllocationAction action,
+                                 size_t size);
 
+  void AddMemoryAllocationCallback(MemoryAllocationCallback callback,
+                                          ObjectSpace space,
+                                          AllocationAction action);
+
+  void RemoveMemoryAllocationCallback(
+      MemoryAllocationCallback callback);
+
+  bool MemoryAllocationCallbackRegistered(
+      MemoryAllocationCallback callback);
+
  private:
-  static const int kChunkSize = kPagesPerChunk * Page::kPageSize;
-
   Isolate* isolate_;
 
   // Maximum space size in bytes.
-  intptr_t capacity_;
+  size_t capacity_;
   // Maximum subset of capacity_ that can be executable
-  intptr_t capacity_executable_;
+  size_t capacity_executable_;
 
   // Allocated space size in bytes.
-  intptr_t size_;
-
+  size_t size_;
   // Allocated executable space size in bytes.
-  intptr_t size_executable_;
+  size_t size_executable_;
 
   struct MemoryAllocationCallbackRegistration {
     MemoryAllocationCallbackRegistration(MemoryAllocationCallback callback,
@@ -683,64 +1026,11 @@
     ObjectSpace space;
     AllocationAction action;
   };
+
   // A List of callback that are triggered when memory is allocated or free'd
   List<MemoryAllocationCallbackRegistration>
       memory_allocation_callbacks_;
 
-  // The initial chunk of virtual memory.
-  VirtualMemory* initial_chunk_;
-
-  // Allocated chunk info: chunk start address, chunk size, and owning space.
-  class ChunkInfo BASE_EMBEDDED {
-   public:
-    ChunkInfo() : address_(NULL),
-                  size_(0),
-                  owner_(NULL),
-                  executable_(NOT_EXECUTABLE),
-                  owner_identity_(FIRST_SPACE) {}
-    inline void init(Address a, size_t s, PagedSpace* o);
-    Address address() { return address_; }
-    size_t size() { return size_; }
-    PagedSpace* owner() { return owner_; }
-    // We save executability of the owner to allow using it
-    // when collecting stats after the owner has been destroyed.
-    Executability executable() const { return executable_; }
-    AllocationSpace owner_identity() const { return owner_identity_; }
-
-   private:
-    Address address_;
-    size_t size_;
-    PagedSpace* owner_;
-    Executability executable_;
-    AllocationSpace owner_identity_;
-  };
-
-  // Chunks_, free_chunk_ids_ and top_ act as a stack of free chunk ids.
-  List<ChunkInfo> chunks_;
-  List<int> free_chunk_ids_;
-  int max_nof_chunks_;
-  int top_;
-
-  // Push/pop a free chunk id onto/from the stack.
-  void Push(int free_chunk_id);
-  int Pop();
-  bool OutOfChunkIds() { return top_ == 0; }
-
-  // Frees a chunk.
-  void DeleteChunk(int chunk_id);
-
-  // Basic check whether a chunk id is in the valid range.
-  inline bool IsValidChunkId(int chunk_id);
-
-  // Checks whether a chunk id identifies an allocated chunk.
-  inline bool IsValidChunk(int chunk_id);
-
-  // Returns the chunk id that a page belongs to.
-  inline int GetChunkId(Page* p);
-
-  // True if the address lies in the initial chunk.
-  inline bool InInitialChunk(Address address);
-
   // Initializes pages in a chunk. Returns the first page address.
   // This function and GetChunkId() are provided for the mark-compact
   // collector to rebuild page headers in the from space, which is
@@ -748,13 +1038,7 @@
   Page* InitializePagesInChunk(int chunk_id, int pages_in_chunk,
                                PagedSpace* owner);
 
-  Page* RelinkPagesInChunk(int chunk_id,
-                           Address chunk_start,
-                           size_t chunk_size,
-                           Page* prev,
-                           Page** last_page_in_use);
-
-  DISALLOW_COPY_AND_ASSIGN(MemoryAllocator);
+  DISALLOW_IMPLICIT_CONSTRUCTORS(MemoryAllocator);
 };
 
 
@@ -777,71 +1061,58 @@
 // -----------------------------------------------------------------------------
 // Heap object iterator in new/old/map spaces.
 //
-// A HeapObjectIterator iterates objects from a given address to the
-// top of a space. The given address must be below the current
-// allocation pointer (space top). There are some caveats.
+// A HeapObjectIterator iterates objects from the bottom of the given space
+// to its top or from the bottom of the given page to its top.
 //
-// (1) If the space top changes upward during iteration (because of
-//     allocating new objects), the iterator does not iterate objects
-//     above the original space top. The caller must create a new
-//     iterator starting from the old top in order to visit these new
-//     objects.
-//
-// (2) If new objects are allocated below the original allocation top
-//     (e.g., free-list allocation in paged spaces), the new objects
-//     may or may not be iterated depending on their position with
-//     respect to the current point of iteration.
-//
-// (3) The space top should not change downward during iteration,
-//     otherwise the iterator will return not-necessarily-valid
-//     objects.
-
+// If objects are allocated in the page during iteration the iterator may
+// or may not iterate over those objects.  The caller must create a new
+// iterator in order to be sure to visit these new objects.
 class HeapObjectIterator: public ObjectIterator {
  public:
-  // Creates a new object iterator in a given space. If a start
-  // address is not given, the iterator starts from the space bottom.
+  // Creates a new object iterator in a given space.
   // If the size function is not given, the iterator calls the default
   // Object::Size().
   explicit HeapObjectIterator(PagedSpace* space);
   HeapObjectIterator(PagedSpace* space, HeapObjectCallback size_func);
-  HeapObjectIterator(PagedSpace* space, Address start);
-  HeapObjectIterator(PagedSpace* space,
-                     Address start,
-                     HeapObjectCallback size_func);
   HeapObjectIterator(Page* page, HeapObjectCallback size_func);
 
-  inline HeapObject* next() {
-    return (cur_addr_ < cur_limit_) ? FromCurrentPage() : FromNextPage();
+  // Advance to the next object, skipping free spaces and other fillers and
+  // skipping the special garbage section of which there is one per space.
+  // Returns NULL when the iteration has ended.
+  inline HeapObject* Next() {
+    do {
+      HeapObject* next_obj = FromCurrentPage();
+      if (next_obj != NULL) return next_obj;
+    } while (AdvanceToNextPage());
+    return NULL;
   }
 
-  // implementation of ObjectIterator.
-  virtual HeapObject* next_object() { return next(); }
+  virtual HeapObject* next_object() {
+    return Next();
+  }
 
  private:
-  Address cur_addr_;  // current iteration point
-  Address end_addr_;  // end iteration point
-  Address cur_limit_;  // current page limit
-  HeapObjectCallback size_func_;  // size function
-  Page* end_page_;  // caches the page of the end address
+  enum PageMode { kOnePageOnly, kAllPagesInSpace };
 
-  HeapObject* FromCurrentPage() {
-    ASSERT(cur_addr_ < cur_limit_);
+  Address cur_addr_;  // Current iteration point.
+  Address cur_end_;   // End iteration point.
+  HeapObjectCallback size_func_;  // Size function or NULL.
+  PagedSpace* space_;
+  PageMode page_mode_;
 
-    HeapObject* obj = HeapObject::FromAddress(cur_addr_);
-    int obj_size = (size_func_ == NULL) ? obj->Size() : size_func_(obj);
-    ASSERT_OBJECT_SIZE(obj_size);
+  // Fast (inlined) path of next().
+  inline HeapObject* FromCurrentPage();
 
-    cur_addr_ += obj_size;
-    ASSERT(cur_addr_ <= cur_limit_);
+  // Slow path of next(), goes into the next page.  Returns false if the
+  // iteration has ended.
+  bool AdvanceToNextPage();
 
-    return obj;
-  }
-
-  // Slow path of next, goes into the next page.
-  HeapObject* FromNextPage();
-
   // Initializes fields.
-  void Initialize(Address start, Address end, HeapObjectCallback size_func);
+  inline void Initialize(PagedSpace* owner,
+                         Address start,
+                         Address end,
+                         PageMode mode,
+                         HeapObjectCallback size_func);
 
 #ifdef DEBUG
   // Verifies whether fields have valid values.
@@ -852,59 +1123,37 @@
 
 // -----------------------------------------------------------------------------
 // A PageIterator iterates the pages in a paged space.
-//
-// The PageIterator class provides three modes for iterating pages in a space:
-//   PAGES_IN_USE iterates pages containing allocated objects.
-//   PAGES_USED_BY_MC iterates pages that hold relocated objects during a
-//                    mark-compact collection.
-//   ALL_PAGES iterates all pages in the space.
-//
-// There are some caveats.
-//
-// (1) If the space expands during iteration, new pages will not be
-//     returned by the iterator in any mode.
-//
-// (2) If new objects are allocated during iteration, they will appear
-//     in pages returned by the iterator.  Allocation may cause the
-//     allocation pointer or MC allocation pointer in the last page to
-//     change between constructing the iterator and iterating the last
-//     page.
-//
-// (3) The space should not shrink during iteration, otherwise the
-//     iterator will return deallocated pages.
 
 class PageIterator BASE_EMBEDDED {
  public:
-  enum Mode {
-    PAGES_IN_USE,
-    PAGES_USED_BY_MC,
-    ALL_PAGES
-  };
+  explicit inline PageIterator(PagedSpace* space);
 
-  PageIterator(PagedSpace* space, Mode mode);
-
   inline bool has_next();
   inline Page* next();
 
  private:
   PagedSpace* space_;
   Page* prev_page_;  // Previous page returned.
-  Page* stop_page_;  // Page to stop at (last page returned by the iterator).
+  // Next page that will be returned.  Cached here so that we can use this
+  // iterator for operations that deallocate pages.
+  Page* next_page_;
 };
 
 
 // -----------------------------------------------------------------------------
-// A space has a list of pages. The next page can be accessed via
-// Page::next_page() call. The next page of the last page is an
-// invalid page pointer. A space can expand and shrink dynamically.
+// A space has a circular list of pages. The next page can be accessed via
+// Page::next_page() call.
 
 // An abstraction of allocation and relocation pointers in a page-structured
 // space.
 class AllocationInfo {
  public:
-  Address top;  // current allocation top
-  Address limit;  // current allocation limit
+  AllocationInfo() : top(NULL), limit(NULL) {
+  }
 
+  Address top;  // Current allocation top.
+  Address limit;  // Current allocation limit.
+
 #ifdef DEBUG
   bool VerifyPagedAllocation() {
     return (Page::FromAllocationTop(top) == Page::FromAllocationTop(limit))
@@ -935,70 +1184,190 @@
   // Zero out all the allocation statistics (ie, no capacity).
   void Clear() {
     capacity_ = 0;
-    available_ = 0;
     size_ = 0;
     waste_ = 0;
   }
 
+  void ClearSizeWaste() {
+    size_ = capacity_;
+    waste_ = 0;
+  }
+
   // Reset the allocation statistics (ie, available = capacity with no
   // wasted or allocated bytes).
   void Reset() {
-    available_ = capacity_;
     size_ = 0;
     waste_ = 0;
   }
 
   // Accessors for the allocation statistics.
   intptr_t Capacity() { return capacity_; }
-  intptr_t Available() { return available_; }
   intptr_t Size() { return size_; }
   intptr_t Waste() { return waste_; }
 
-  // Grow the space by adding available bytes.
+  // Grow the space by adding available bytes.  They are initially marked as
+  // being in use (part of the size), but will normally be immediately freed,
+  // putting them on the free list and removing them from size_.
   void ExpandSpace(int size_in_bytes) {
     capacity_ += size_in_bytes;
-    available_ += size_in_bytes;
+    size_ += size_in_bytes;
+    ASSERT(size_ >= 0);
   }
 
-  // Shrink the space by removing available bytes.
-  void ShrinkSpace(int size_in_bytes) {
-    capacity_ -= size_in_bytes;
-    available_ -= size_in_bytes;
-  }
-
   // Allocate from available bytes (available -> size).
   void AllocateBytes(intptr_t size_in_bytes) {
-    available_ -= size_in_bytes;
     size_ += size_in_bytes;
+    ASSERT(size_ >= 0);
   }
 
   // Free allocated bytes, making them available (size -> available).
   void DeallocateBytes(intptr_t size_in_bytes) {
     size_ -= size_in_bytes;
-    available_ += size_in_bytes;
+    ASSERT(size_ >= 0);
   }
 
   // Waste free bytes (available -> waste).
   void WasteBytes(int size_in_bytes) {
-    available_ -= size_in_bytes;
+    size_ -= size_in_bytes;
     waste_ += size_in_bytes;
+    ASSERT(size_ >= 0);
   }
 
-  // Consider the wasted bytes to be allocated, as they contain filler
-  // objects (waste -> size).
-  void FillWastedBytes(intptr_t size_in_bytes) {
-    waste_ -= size_in_bytes;
-    size_ += size_in_bytes;
-  }
-
  private:
   intptr_t capacity_;
-  intptr_t available_;
   intptr_t size_;
   intptr_t waste_;
 };
 
 
+// -----------------------------------------------------------------------------
+// Free lists for old object spaces
+//
+// Free-list nodes are free blocks in the heap.  They look like heap objects
+// (free-list node pointers have the heap object tag, and they have a map like
+// a heap object).  They have a size and a next pointer.  The next pointer is
+// the raw address of the next free list node (or NULL).
+class FreeListNode: public HeapObject {
+ public:
+  // Obtain a free-list node from a raw address.  This is not a cast because
+  // it does not check nor require that the first word at the address is a map
+  // pointer.
+  static FreeListNode* FromAddress(Address address) {
+    return reinterpret_cast<FreeListNode*>(HeapObject::FromAddress(address));
+  }
+
+  static inline bool IsFreeListNode(HeapObject* object);
+
+  // Set the size in bytes, which can be read with HeapObject::Size().  This
+  // function also writes a map to the first word of the block so that it
+  // looks like a heap object to the garbage collector and heap iteration
+  // functions.
+  void set_size(Heap* heap, int size_in_bytes);
+
+  // Accessors for the next field.
+  inline FreeListNode* next();
+  inline FreeListNode** next_address();
+  inline void set_next(FreeListNode* next);
+
+  inline void Zap();
+
+ private:
+  static const int kNextOffset = POINTER_SIZE_ALIGN(FreeSpace::kHeaderSize);
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(FreeListNode);
+};
+
+
+// The free list for the old space.  The free list is organized in such a way
+// as to encourage objects allocated around the same time to be near each
+// other.  The normal way to allocate is intended to be by bumping a 'top'
+// pointer until it hits a 'limit' pointer.  When the limit is hit we need to
+// find a new space to allocate from.  This is done with the free list, which
+// is divided up into rough categories to cut down on waste.  Having finer
+// categories would scatter allocation more.
+
+// The old space free list is organized in categories.
+// 1-31 words:  Such small free areas are discarded for efficiency reasons.
+//     They can be reclaimed by the compactor.  However the distance between top
+//     and limit may be this small.
+// 32-255 words: There is a list of spaces this large.  It is used for top and
+//     limit when the object we need to allocate is 1-31 words in size.  These
+//     spaces are called small.
+// 256-2047 words: There is a list of spaces this large.  It is used for top and
+//     limit when the object we need to allocate is 32-255 words in size.  These
+//     spaces are called medium.
+// 1048-16383 words: There is a list of spaces this large.  It is used for top
+//     and limit when the object we need to allocate is 256-2047 words in size.
+//     These spaces are call large.
+// At least 16384 words.  This list is for objects of 2048 words or larger.
+//     Empty pages are added to this list.  These spaces are called huge.
+class FreeList BASE_EMBEDDED {
+ public:
+  explicit FreeList(PagedSpace* owner);
+
+  // Clear the free list.
+  void Reset();
+
+  // Return the number of bytes available on the free list.
+  intptr_t available() { return available_; }
+
+  // Place a node on the free list.  The block of size 'size_in_bytes'
+  // starting at 'start' is placed on the free list.  The return value is the
+  // number of bytes that have been lost due to internal fragmentation by
+  // freeing the block.  Bookkeeping information will be written to the block,
+  // ie, its contents will be destroyed.  The start address should be word
+  // aligned, and the size should be a non-zero multiple of the word size.
+  int Free(Address start, int size_in_bytes);
+
+  // Allocate a block of size 'size_in_bytes' from the free list.  The block
+  // is unitialized.  A failure is returned if no block is available.  The
+  // number of bytes lost to fragmentation is returned in the output parameter
+  // 'wasted_bytes'.  The size should be a non-zero multiple of the word size.
+  MUST_USE_RESULT HeapObject* Allocate(int size_in_bytes);
+
+  void MarkNodes();
+
+#ifdef DEBUG
+  void Zap();
+  static intptr_t SumFreeList(FreeListNode* node);
+  static int FreeListLength(FreeListNode* cur);
+  intptr_t SumFreeLists();
+  bool IsVeryLong();
+#endif
+
+  void CountFreeListItems(Page* p, intptr_t* sizes);
+
+ private:
+  // The size range of blocks, in bytes.
+  static const int kMinBlockSize = 3 * kPointerSize;
+  static const int kMaxBlockSize = Page::kMaxHeapObjectSize;
+
+  FreeListNode* PickNodeFromList(FreeListNode** list, int* node_size);
+
+  FreeListNode* FindNodeFor(int size_in_bytes, int* node_size);
+
+  PagedSpace* owner_;
+  Heap* heap_;
+
+  // Total available bytes in all blocks on this free list.
+  int available_;
+
+  static const int kSmallListMin = 0x20 * kPointerSize;
+  static const int kSmallListMax = 0xff * kPointerSize;
+  static const int kMediumListMax = 0x7ff * kPointerSize;
+  static const int kLargeListMax = 0x3fff * kPointerSize;
+  static const int kSmallAllocationMax = kSmallListMin - kPointerSize;
+  static const int kMediumAllocationMax = kSmallListMax;
+  static const int kLargeAllocationMax = kMediumListMax;
+  FreeListNode* small_list_;
+  FreeListNode* medium_list_;
+  FreeListNode* large_list_;
+  FreeListNode* huge_list_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(FreeList);
+};
+
+
 class PagedSpace : public Space {
  public:
   // Creates a space with a maximum capacity, and an id.
@@ -1013,7 +1382,7 @@
   // the memory allocator's initial chunk) if possible.  If the block of
   // addresses is not big enough to contain a single page-aligned page, a
   // fresh chunk will be allocated.
-  bool Setup(Address start, size_t size);
+  bool Setup();
 
   // Returns true if the space has been successfully set up and not
   // subsequently torn down.
@@ -1026,8 +1395,6 @@
   // Checks whether an object/address is in this space.
   inline bool Contains(Address a);
   bool Contains(HeapObject* o) { return Contains(o->address()); }
-  // Never crashes even if a is not a valid pointer.
-  inline bool SafeContains(Address a);
 
   // Given an address occupied by a live object, return that object if it is
   // in this space, or Failure::Exception() if it is not. The implementation
@@ -1035,105 +1402,94 @@
   // linear in the number of objects in the page. It may be slow.
   MUST_USE_RESULT MaybeObject* FindObject(Address addr);
 
-  // Checks whether page is currently in use by this space.
-  bool IsUsed(Page* page);
-
-  void MarkAllPagesClean();
-
   // Prepares for a mark-compact GC.
-  virtual void PrepareForMarkCompact(bool will_compact);
+  virtual void PrepareForMarkCompact();
 
-  // The top of allocation in a page in this space. Undefined if page is unused.
-  Address PageAllocationTop(Page* page) {
-    return page == TopPageOf(allocation_info_) ? top()
-        : PageAllocationLimit(page);
-  }
-
-  // The limit of allocation for a page in this space.
-  virtual Address PageAllocationLimit(Page* page) = 0;
-
-  void FlushTopPageWatermark() {
-    AllocationTopPage()->SetCachedAllocationWatermark(top());
-    AllocationTopPage()->InvalidateWatermark(true);
-  }
-
-  // Current capacity without growing (Size() + Available() + Waste()).
+  // Current capacity without growing (Size() + Available()).
   intptr_t Capacity() { return accounting_stats_.Capacity(); }
 
   // Total amount of memory committed for this space.  For paged
   // spaces this equals the capacity.
   intptr_t CommittedMemory() { return Capacity(); }
 
-  // Available bytes without growing.
-  intptr_t Available() { return accounting_stats_.Available(); }
+  // Sets the capacity, the available space and the wasted space to zero.
+  // The stats are rebuilt during sweeping by adding each page to the
+  // capacity and the size when it is encountered.  As free spaces are
+  // discovered during the sweeping they are subtracted from the size and added
+  // to the available and wasted totals.
+  void ClearStats() {
+    accounting_stats_.ClearSizeWaste();
+  }
 
-  // Allocated bytes in this space.
+  // Available bytes without growing.  These are the bytes on the free list.
+  // The bytes in the linear allocation area are not included in this total
+  // because updating the stats would slow down allocation.  New pages are
+  // immediately added to the free list so they show up here.
+  intptr_t Available() { return free_list_.available(); }
+
+  // Allocated bytes in this space.  Garbage bytes that were not found due to
+  // lazy sweeping are counted as being allocated!  The bytes in the current
+  // linear allocation area (between top and limit) are also counted here.
   virtual intptr_t Size() { return accounting_stats_.Size(); }
 
-  // Wasted bytes due to fragmentation and not recoverable until the
-  // next GC of this space.
-  intptr_t Waste() { return accounting_stats_.Waste(); }
+  // As size, but the bytes in the current linear allocation area are not
+  // included.
+  virtual intptr_t SizeOfObjects() { return Size() - (limit() - top()); }
 
-  // Returns the address of the first object in this space.
-  Address bottom() { return first_page_->ObjectAreaStart(); }
+  // Wasted bytes in this space.  These are just the bytes that were thrown away
+  // due to being too small to use for allocation.  They do not include the
+  // free bytes that were not found at all due to lazy sweeping.
+  virtual intptr_t Waste() { return accounting_stats_.Waste(); }
 
   // Returns the allocation pointer in this space.
-  Address top() { return allocation_info_.top; }
+  Address top() {
+    return allocation_info_.top;
+  }
+  Address limit() { return allocation_info_.limit; }
 
   // Allocate the requested number of bytes in the space if possible, return a
   // failure object if not.
   MUST_USE_RESULT inline MaybeObject* AllocateRaw(int size_in_bytes);
 
-  // Allocate the requested number of bytes for relocation during mark-compact
-  // collection.
-  MUST_USE_RESULT inline MaybeObject* MCAllocateRaw(int size_in_bytes);
-
   virtual bool ReserveSpace(int bytes);
 
-  // Used by ReserveSpace.
-  virtual void PutRestOfCurrentPageOnFreeList(Page* current_page) = 0;
+  // Give a block of memory to the space's free list.  It might be added to
+  // the free list or accounted as waste.
+  // If add_to_freelist is false then just accounting stats are updated and
+  // no attempt to add area to free list is made.
+  int Free(Address start, int size_in_bytes) {
+    int wasted = free_list_.Free(start, size_in_bytes);
+    accounting_stats_.DeallocateBytes(size_in_bytes - wasted);
+    return size_in_bytes - wasted;
+  }
 
-  // Free all pages in range from prev (exclusive) to last (inclusive).
-  // Freed pages are moved to the end of page list.
-  void FreePages(Page* prev, Page* last);
+  int FreeOrUnmapPage(Page* page, Address start, int size_in_bytes);
 
-  // Deallocates a block.
-  virtual void DeallocateBlock(Address start,
-                               int size_in_bytes,
-                               bool add_to_freelist) = 0;
-
   // Set space allocation info.
-  void SetTop(Address top) {
+  void SetTop(Address top, Address limit) {
+    ASSERT(top == limit ||
+           Page::FromAddress(top) == Page::FromAddress(limit - 1));
     allocation_info_.top = top;
-    allocation_info_.limit = PageAllocationLimit(Page::FromAllocationTop(top));
+    allocation_info_.limit = limit;
   }
 
-  // ---------------------------------------------------------------------------
-  // Mark-compact collection support functions
+  void Allocate(int bytes) {
+    accounting_stats_.AllocateBytes(bytes);
+  }
 
-  // Set the relocation point to the beginning of the space.
-  void MCResetRelocationInfo();
-
-  // Writes relocation info to the top page.
-  void MCWriteRelocationInfoToPage() {
-    TopPageOf(mc_forwarding_info_)->
-        SetAllocationWatermark(mc_forwarding_info_.top);
+  void IncreaseCapacity(int size) {
+    accounting_stats_.ExpandSpace(size);
   }
 
-  // Computes the offset of a given address in this space to the beginning
-  // of the space.
-  int MCSpaceOffsetForAddress(Address addr);
-
-  // Updates the allocation pointer to the relocation top after a mark-compact
-  // collection.
-  virtual void MCCommitRelocationInfo() = 0;
-
   // Releases half of unused pages.
   void Shrink();
 
   // Ensures that the capacity is at least 'capacity'. Returns false on failure.
   bool EnsureCapacity(int capacity);
 
+  // The dummy page that anchors the linked list of pages.
+  Page* anchor() { return &anchor_; }
+
 #ifdef DEBUG
   // Print meta info and objects in this space.
   virtual void Print();
@@ -1141,6 +1497,9 @@
   // Verify integrity of this space.
   virtual void Verify(ObjectVisitor* visitor);
 
+  // Reports statistics for the space
+  void ReportStatistics();
+
   // Overridden by subclasses to verify space-specific object
   // properties (e.g., only maps or free-list nodes are in map space).
   virtual void VerifyObject(HeapObject* obj) {}
@@ -1151,11 +1510,67 @@
   static void ResetCodeStatistics();
 #endif
 
-  // Returns the page of the allocation pointer.
-  Page* AllocationTopPage() { return TopPageOf(allocation_info_); }
+  bool was_swept_conservatively() { return was_swept_conservatively_; }
+  void set_was_swept_conservatively(bool b) { was_swept_conservatively_ = b; }
 
-  void RelinkPageListInChunkOrder(bool deallocate_blocks);
+  // Evacuation candidates are swept by evacuator.  Needs to return a valid
+  // result before _and_ after evacuation has finished.
+  static bool ShouldBeSweptLazily(Page* p) {
+    return !p->IsEvacuationCandidate() &&
+           !p->IsFlagSet(Page::RESCAN_ON_EVACUATION) &&
+           !p->WasSweptPrecisely();
+  }
 
+  void SetPagesToSweep(Page* first, Page* last) {
+    first_unswept_page_ = first;
+    last_unswept_page_ = last;
+  }
+
+  bool AdvanceSweeper(intptr_t bytes_to_sweep);
+
+  bool IsSweepingComplete() {
+    return !first_unswept_page_->is_valid();
+  }
+
+  Page* FirstPage() { return anchor_.next_page(); }
+  Page* LastPage() { return anchor_.prev_page(); }
+
+  bool IsFragmented(Page* p) {
+    intptr_t sizes[4];
+    free_list_.CountFreeListItems(p, sizes);
+
+    intptr_t ratio;
+    intptr_t ratio_threshold;
+    if (identity() == CODE_SPACE) {
+      ratio = (sizes[1] * 10 + sizes[2] * 2) * 100 / Page::kObjectAreaSize;
+      ratio_threshold = 10;
+    } else {
+      ratio = (sizes[0] * 5 + sizes[1]) * 100 / Page::kObjectAreaSize;
+      ratio_threshold = 15;
+    }
+
+    if (FLAG_trace_fragmentation) {
+      PrintF("%p [%d]: %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %s\n",
+             reinterpret_cast<void*>(p),
+             identity(),
+             static_cast<int>(sizes[0]),
+             static_cast<double>(sizes[0] * 100) / Page::kObjectAreaSize,
+             static_cast<int>(sizes[1]),
+             static_cast<double>(sizes[1] * 100) / Page::kObjectAreaSize,
+             static_cast<int>(sizes[2]),
+             static_cast<double>(sizes[2] * 100) / Page::kObjectAreaSize,
+             static_cast<int>(sizes[3]),
+             static_cast<double>(sizes[3] * 100) / Page::kObjectAreaSize,
+             (ratio > ratio_threshold) ? "[fragmented]" : "");
+    }
+
+    return (ratio > ratio_threshold) || FLAG_always_compact;
+  }
+
+  void EvictEvacuationCandidatesFromFreeLists();
+
+  bool CanExpand();
+
  protected:
   // Maximum capacity of this space.
   intptr_t max_capacity_;
@@ -1163,80 +1578,43 @@
   // Accounting information for this space.
   AllocationStats accounting_stats_;
 
-  // The first page in this space.
-  Page* first_page_;
+  // The dummy page that anchors the double linked list of pages.
+  Page anchor_;
 
-  // The last page in this space.  Initially set in Setup, updated in
-  // Expand and Shrink.
-  Page* last_page_;
+  // The space's free list.
+  FreeList free_list_;
 
-  // True if pages owned by this space are linked in chunk-order.
-  // See comment for class MemoryAllocator for definition of chunk-order.
-  bool page_list_is_chunk_ordered_;
-
   // Normal allocation information.
   AllocationInfo allocation_info_;
 
-  // Relocation information during mark-compact collections.
-  AllocationInfo mc_forwarding_info_;
-
   // Bytes of each page that cannot be allocated.  Possibly non-zero
   // for pages in spaces with only fixed-size objects.  Always zero
   // for pages in spaces with variable sized objects (those pages are
   // padded with free-list nodes).
   int page_extra_;
 
-  // Sets allocation pointer to a page bottom.
-  static void SetAllocationInfo(AllocationInfo* alloc_info, Page* p);
+  bool was_swept_conservatively_;
 
-  // Returns the top page specified by an allocation info structure.
-  static Page* TopPageOf(AllocationInfo alloc_info) {
-    return Page::FromAllocationTop(alloc_info.limit);
-  }
+  Page* first_unswept_page_;
+  Page* last_unswept_page_;
 
-  int CountPagesToTop() {
-    Page* p = Page::FromAllocationTop(allocation_info_.top);
-    PageIterator it(this, PageIterator::ALL_PAGES);
-    int counter = 1;
-    while (it.has_next()) {
-      if (it.next() == p) return counter;
-      counter++;
-    }
-    UNREACHABLE();
-    return -1;
-  }
-
   // Expands the space by allocating a fixed number of pages. Returns false if
-  // it cannot allocate requested number of pages from OS. Newly allocated
-  // pages are append to the last_page;
-  bool Expand(Page* last_page);
+  // it cannot allocate requested number of pages from OS.
+  bool Expand();
 
-  // Generic fast case allocation function that tries linear allocation in
-  // the top page of 'alloc_info'.  Returns NULL on failure.
+  // Generic fast case allocation function that tries linear allocation at the
+  // address denoted by top in allocation_info_.
   inline HeapObject* AllocateLinearly(AllocationInfo* alloc_info,
                                       int size_in_bytes);
 
-  // During normal allocation or deserialization, roll to the next page in
-  // the space (there is assumed to be one) and allocate there.  This
-  // function is space-dependent.
-  virtual HeapObject* AllocateInNextPage(Page* current_page,
-                                         int size_in_bytes) = 0;
-
   // Slow path of AllocateRaw.  This function is space-dependent.
-  MUST_USE_RESULT virtual HeapObject* SlowAllocateRaw(int size_in_bytes) = 0;
+  MUST_USE_RESULT virtual HeapObject* SlowAllocateRaw(int size_in_bytes);
 
-  // Slow path of MCAllocateRaw.
-  MUST_USE_RESULT HeapObject* SlowMCAllocateRaw(int size_in_bytes);
-
 #ifdef DEBUG
   // Returns the number of total pages in this space.
   int CountTotalPages();
 #endif
 
- private:
-  // Returns a pointer to the page of the relocation pointer.
-  Page* MCRelocationTopPage() { return TopPageOf(mc_forwarding_info_); }
-
   friend class PageIterator;
 };
 
@@ -1276,20 +1654,113 @@
 };
 
 
+enum SemiSpaceId {
+  kFromSpace = 0,
+  kToSpace = 1
+};
+
+
+class SemiSpace;
+
+
+class NewSpacePage : public MemoryChunk {
+ public:
+  // GC related flags copied from from-space to to-space when
+  // flipping semispaces.
+  static const intptr_t kCopyOnFlipFlagsMask =
+    (1 << MemoryChunk::POINTERS_TO_HERE_ARE_INTERESTING) |
+    (1 << MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING) |
+    (1 << MemoryChunk::SCAN_ON_SCAVENGE);
+
+  inline NewSpacePage* next_page() const {
+    return static_cast<NewSpacePage*>(next_chunk());
+  }
+
+  inline void set_next_page(NewSpacePage* page) {
+    set_next_chunk(page);
+  }
+
+  inline NewSpacePage* prev_page() const {
+    return static_cast<NewSpacePage*>(prev_chunk());
+  }
+
+  inline void set_prev_page(NewSpacePage* page) {
+    set_prev_chunk(page);
+  }
+
+  SemiSpace* semi_space() {
+    return reinterpret_cast<SemiSpace*>(owner());
+  }
+
+  bool is_anchor() { return !this->InNewSpace(); }
+
+  static bool IsAtStart(Address addr) {
+    return (reinterpret_cast<intptr_t>(addr) & Page::kPageAlignmentMask)
+        == kObjectStartOffset;
+  }
+
+  static bool IsAtEnd(Address addr) {
+    return (reinterpret_cast<intptr_t>(addr) & Page::kPageAlignmentMask) == 0;
+  }
+
+  Address address() {
+    return reinterpret_cast<Address>(this);
+  }
+
+  // Finds the NewSpacePage containg the given address.
+  static inline NewSpacePage* FromAddress(Address address_in_page) {
+    Address page_start =
+        reinterpret_cast<Address>(reinterpret_cast<uintptr_t>(address_in_page) &
+                                  ~Page::kPageAlignmentMask);
+    NewSpacePage* page = reinterpret_cast<NewSpacePage*>(page_start);
+    ASSERT(page->InNewSpace());
+    return page;
+  }
+
+  // Find the page for a limit address. A limit address is either an address
+  // inside a page, or the address right after the last byte of a page.
+  static inline NewSpacePage* FromLimit(Address address_limit) {
+    return NewSpacePage::FromAddress(address_limit - 1);
+  }
+
+ private:
+  // Create a NewSpacePage object that is only used as anchor
+  // for the doubly-linked list of real pages.
+  explicit NewSpacePage(SemiSpace* owner) {
+    InitializeAsAnchor(owner);
+  }
+
+  static NewSpacePage* Initialize(Heap* heap,
+                                  Address start,
+                                  SemiSpace* semi_space);
+
+  // Intialize a fake NewSpacePage used as sentinel at the ends
+  // of a doubly-linked list of real NewSpacePages.
+  // Only uses the prev/next links, and sets flags to not be in new-space.
+  void InitializeAsAnchor(SemiSpace* owner);
+
+  friend class SemiSpace;
+  friend class SemiSpaceIterator;
+};
+
+
 // -----------------------------------------------------------------------------
 // SemiSpace in young generation
 //
-// A semispace is a contiguous chunk of memory. The mark-compact collector
-// uses the memory in the from space as a marking stack when tracing live
-// objects.
+// A semispace is a contiguous chunk of memory holding page-like memory
+// chunks. The mark-compact collector  uses the memory of the first page in
+// the from space as a marking stack when tracing live objects.
 
 class SemiSpace : public Space {
  public:
   // Constructor.
-  explicit SemiSpace(Heap* heap) : Space(heap, NEW_SPACE, NOT_EXECUTABLE) {
-    start_ = NULL;
-    age_mark_ = NULL;
-  }
+  SemiSpace(Heap* heap, SemiSpaceId semispace)
+    : Space(heap, NEW_SPACE, NOT_EXECUTABLE),
+      start_(NULL),
+      age_mark_(NULL),
+      id_(semispace),
+      anchor_(this),
+      current_page_(NULL) { }
 
   // Sets up the semispace using the given chunk.
   bool Setup(Address start, int initial_capacity, int maximum_capacity);
@@ -1316,14 +1787,41 @@
   // semispace and less than the current capacity.
   bool ShrinkTo(int new_capacity);
 
-  // Returns the start address of the space.
-  Address low() { return start_; }
+  // Returns the start address of the first page of the space.
+  Address space_start() {
+    ASSERT(anchor_.next_page() != &anchor_);
+    return anchor_.next_page()->body();
+  }
+
+  // Returns the start address of the current page of the space.
+  Address page_low() {
+    ASSERT(anchor_.next_page() != &anchor_);
+    return current_page_->body();
+  }
+
   // Returns one past the end address of the space.
-  Address high() { return low() + capacity_; }
+  Address space_end() {
+    return anchor_.prev_page()->body_limit();
+  }
 
+  // Returns one past the end address of the current page of the space.
+  Address page_high() {
+    return current_page_->body_limit();
+  }
+
+  bool AdvancePage() {
+    NewSpacePage* next_page = current_page_->next_page();
+    if (next_page == anchor()) return false;
+    current_page_ = next_page;
+    return true;
+  }
+
+  // Resets the space to using the first page.
+  void Reset();
+
   // Age mark accessors.
   Address age_mark() { return age_mark_; }
-  void set_age_mark(Address mark) { age_mark_ = mark; }
+  void set_age_mark(Address mark);
 
   // True if the address is in the address range of this semispace (not
   // necessarily below the allocation pointer).
@@ -1338,11 +1836,6 @@
     return (reinterpret_cast<uintptr_t>(o) & object_mask_) == object_expected_;
   }
 
-  // The offset of an address from the beginning of the space.
-  int SpaceOffsetForAddress(Address addr) {
-    return static_cast<int>(addr - low());
-  }
-
   // If we don't have these here then SemiSpace will be abstract.  However
   // they should never be called.
   virtual intptr_t Size() {
@@ -1359,9 +1852,19 @@
   bool Commit();
   bool Uncommit();
 
+  NewSpacePage* first_page() { return anchor_.next_page(); }
+  NewSpacePage* current_page() { return current_page_; }
+
 #ifdef DEBUG
   virtual void Print();
   virtual void Verify();
+  // Validate a range of of addresses in a SemiSpace.
+  // The "from" address must be on a page prior to the "to" address,
+  // in the linked page order, or it must be earlier on the same page.
+  static void AssertValidRange(Address from, Address to);
+#else
+  // Do nothing.
+  inline static void AssertValidRange(Address from, Address to) {}
 #endif
 
   // Returns the current capacity of the semi space.
@@ -1373,7 +1876,17 @@
   // Returns the initial capacity of the semi space.
   int InitialCapacity() { return initial_capacity_; }
 
+  SemiSpaceId id() { return id_; }
+
+  static void Swap(SemiSpace* from, SemiSpace* to);
+
  private:
+  // Flips the semispace between being from-space and to-space.
+  // Copies the flags into the masked positions on all pages in the space.
+  void FlipPages(intptr_t flags, intptr_t flag_mask);
+
+  NewSpacePage* anchor() { return &anchor_; }
+
   // The current and maximum capacity of the space.
   int capacity_;
   int maximum_capacity_;
@@ -1390,7 +1903,13 @@
   uintptr_t object_expected_;
 
   bool committed_;
+  SemiSpaceId id_;
 
+  NewSpacePage anchor_;
+  NewSpacePage* current_page_;
+
+  friend class SemiSpaceIterator;
+  friend class NewSpacePageIterator;
  public:
   TRACK_MEMORY("SemiSpace")
 };
@@ -1406,12 +1925,26 @@
   // Create an iterator over the objects in the given space.  If no start
   // address is given, the iterator starts from the bottom of the space.  If
   // no size function is given, the iterator calls Object::Size().
+
+  // Iterate over all of allocated to-space.
   explicit SemiSpaceIterator(NewSpace* space);
+  // Iterate over all of allocated to-space, with a custome size function.
   SemiSpaceIterator(NewSpace* space, HeapObjectCallback size_func);
+  // Iterate over part of allocated to-space, from start to the end
+  // of allocation.
   SemiSpaceIterator(NewSpace* space, Address start);
+  // Iterate from one address to another in the same semi-space.
+  SemiSpaceIterator(Address from, Address to);
 
-  HeapObject* next() {
+  HeapObject* Next() {
     if (current_ == limit_) return NULL;
+    if (NewSpacePage::IsAtEnd(current_)) {
+      NewSpacePage* page = NewSpacePage::FromLimit(current_);
+      page = page->next_page();
+      ASSERT(!page->is_anchor());
+      current_ = page->body();
+      if (current_ == limit_) return NULL;
+    }
 
     HeapObject* object = HeapObject::FromAddress(current_);
     int size = (size_func_ == NULL) ? object->Size() : size_func_(object);
@@ -1421,14 +1954,13 @@
   }
 
   // Implementation of the ObjectIterator functions.
-  virtual HeapObject* next_object() { return next(); }
+  virtual HeapObject* next_object() { return Next(); }
 
  private:
-  void Initialize(NewSpace* space, Address start, Address end,
+  void Initialize(Address start,
+                  Address end,
                   HeapObjectCallback size_func);
 
-  // The semispace.
-  SemiSpace* space_;
   // The current iteration point.
   Address current_;
   // The end of iteration.
@@ -1439,6 +1971,34 @@
 
 
 // -----------------------------------------------------------------------------
+// A PageIterator iterates the pages in a semi-space.
+class NewSpacePageIterator BASE_EMBEDDED {
+ public:
+  // Make an iterator that runs over all pages in to-space.
+  explicit inline NewSpacePageIterator(NewSpace* space);
+
+  // Make an iterator that runs over all pages in the given semispace,
+  // even those not used in allocation.
+  explicit inline NewSpacePageIterator(SemiSpace* space);
+
+  // Make iterator that iterates from the page containing start
+  // to the page that contains limit in the same semispace.
+  inline NewSpacePageIterator(Address start, Address limit);
+
+  inline bool has_next();
+  inline NewSpacePage* next();
+
+ private:
+  NewSpacePage* prev_page_;  // Previous page returned.
+  // Next page that will be returned.  Cached here so that we can use this
+  // iterator for operations that deallocate pages.
+  NewSpacePage* next_page_;
+  // Last page returned.
+  NewSpacePage* last_page_;
+};
+
+
+// -----------------------------------------------------------------------------
 // The young generation space.
 //
 // The new space consists of a contiguous pair of semispaces.  It simply
@@ -1449,11 +2009,13 @@
   // Constructor.
   explicit NewSpace(Heap* heap)
     : Space(heap, NEW_SPACE, NOT_EXECUTABLE),
-      to_space_(heap),
-      from_space_(heap) {}
+      to_space_(heap, kToSpace),
+      from_space_(heap, kFromSpace),
+      reservation_(),
+      inline_allocation_limit_step_(0) {}
 
   // Sets up the new space using the given chunk.
-  bool Setup(Address start, int size);
+  bool Setup(int reserved_semispace_size_, int max_semispace_size);
 
   // Tears down the space.  Heap memory was not allocated by the space, so it
   // is not deallocated here.
@@ -1480,18 +2042,30 @@
     return (reinterpret_cast<uintptr_t>(a) & address_mask_)
         == reinterpret_cast<uintptr_t>(start_);
   }
+
   bool Contains(Object* o) {
-    return (reinterpret_cast<uintptr_t>(o) & object_mask_) == object_expected_;
+    Address a = reinterpret_cast<Address>(o);
+    return (reinterpret_cast<uintptr_t>(a) & object_mask_) == object_expected_;
   }
 
   // Return the allocated bytes in the active semispace.
-  virtual intptr_t Size() { return static_cast<int>(top() - bottom()); }
+  virtual intptr_t Size() {
+    return pages_used_ * Page::kObjectAreaSize +
+        static_cast<int>(top() - to_space_.page_low());
+  }
+
   // The same, but returning an int.  We have to have the one that returns
   // intptr_t because it is inherited, but if we know we are dealing with the
   // new space, which can't get as big as the other spaces then this is useful:
   int SizeAsInt() { return static_cast<int>(Size()); }
 
   // Return the current capacity of a semispace.
+  intptr_t EffectiveCapacity() {
+    ASSERT(to_space_.Capacity() == from_space_.Capacity());
+    return (to_space_.Capacity() / Page::kPageSize) * Page::kObjectAreaSize;
+  }
+
+  // Return the current capacity of a semispace.
   intptr_t Capacity() {
     ASSERT(to_space_.Capacity() == from_space_.Capacity());
     return to_space_.Capacity();
@@ -1503,8 +2077,11 @@
     return Capacity();
   }
 
-  // Return the available bytes without growing in the active semispace.
-  intptr_t Available() { return Capacity() - Size(); }
+  // Return the available bytes without growing or switching page in the
+  // active semispace.
+  intptr_t Available() {
+    return allocation_info_.limit - allocation_info_.top;
+  }
 
   // Return the maximum capacity of a semispace.
   int MaximumCapacity() {
@@ -1519,9 +2096,12 @@
   }
 
   // Return the address of the allocation pointer in the active semispace.
-  Address top() { return allocation_info_.top; }
+  Address top() {
+    ASSERT(to_space_.current_page()->ContainsLimit(allocation_info_.top));
+    return allocation_info_.top;
+  }
   // Return the address of the first object in the active semispace.
-  Address bottom() { return to_space_.low(); }
+  Address bottom() { return to_space_.space_start(); }
 
   // Get the age mark of the inactive semispace.
   Address age_mark() { return from_space_.age_mark(); }
@@ -1533,54 +2113,70 @@
   Address start() { return start_; }
   uintptr_t mask() { return address_mask_; }
 
+  INLINE(uint32_t AddressToMarkbitIndex(Address addr)) {
+    ASSERT(Contains(addr));
+    ASSERT(IsAligned(OffsetFrom(addr), kPointerSize) ||
+           IsAligned(OffsetFrom(addr) - 1, kPointerSize));
+    return static_cast<uint32_t>(addr - start_) >> kPointerSizeLog2;
+  }
+
+  INLINE(Address MarkbitIndexToAddress(uint32_t index)) {
+    return reinterpret_cast<Address>(index << kPointerSizeLog2);
+  }
+
   // The allocation top and limit addresses.
   Address* allocation_top_address() { return &allocation_info_.top; }
   Address* allocation_limit_address() { return &allocation_info_.limit; }
 
   MUST_USE_RESULT MaybeObject* AllocateRaw(int size_in_bytes) {
-    return AllocateRawInternal(size_in_bytes, &allocation_info_);
+    return AllocateRawInternal(size_in_bytes);
   }
 
-  // Allocate the requested number of bytes for relocation during mark-compact
-  // collection.
-  MUST_USE_RESULT MaybeObject* MCAllocateRaw(int size_in_bytes) {
-    return AllocateRawInternal(size_in_bytes, &mc_forwarding_info_);
-  }
-
   // Reset the allocation pointer to the beginning of the active semispace.
   void ResetAllocationInfo();
-  // Reset the reloction pointer to the bottom of the inactive semispace in
-  // preparation for mark-compact collection.
-  void MCResetRelocationInfo();
-  // Update the allocation pointer in the active semispace after a
-  // mark-compact collection.
-  void MCCommitRelocationInfo();
 
-  // Get the extent of the inactive semispace (for use as a marking stack).
-  Address FromSpaceLow() { return from_space_.low(); }
-  Address FromSpaceHigh() { return from_space_.high(); }
+  void LowerInlineAllocationLimit(intptr_t step) {
+    inline_allocation_limit_step_ = step;
+    if (step == 0) {
+      allocation_info_.limit = to_space_.page_high();
+    } else {
+      allocation_info_.limit = Min(
+          allocation_info_.top + inline_allocation_limit_step_,
+          allocation_info_.limit);
+    }
+    top_on_previous_step_ = allocation_info_.top;
+  }
 
-  // Get the extent of the active semispace (to sweep newly copied objects
-  // during a scavenge collection).
-  Address ToSpaceLow() { return to_space_.low(); }
-  Address ToSpaceHigh() { return to_space_.high(); }
+  // Get the extent of the inactive semispace (for use as a marking stack,
+  // or to zap it). Notice: space-addresses are not necessarily on the
+  // same page, so FromSpaceStart() might be above FromSpaceEnd().
+  Address FromSpacePageLow() { return from_space_.page_low(); }
+  Address FromSpacePageHigh() { return from_space_.page_high(); }
+  Address FromSpaceStart() { return from_space_.space_start(); }
+  Address FromSpaceEnd() { return from_space_.space_end(); }
 
-  // Offsets from the beginning of the semispaces.
-  int ToSpaceOffsetForAddress(Address a) {
-    return to_space_.SpaceOffsetForAddress(a);
+  // Get the extent of the active semispace's pages' memory.
+  Address ToSpaceStart() { return to_space_.space_start(); }
+  Address ToSpaceEnd() { return to_space_.space_end(); }
+
+  inline bool ToSpaceContains(Address address) {
+    return to_space_.Contains(address);
   }
-  int FromSpaceOffsetForAddress(Address a) {
-    return from_space_.SpaceOffsetForAddress(a);
+  inline bool FromSpaceContains(Address address) {
+    return from_space_.Contains(address);
   }
 
   // True if the object is a heap object in the address range of the
   // respective semispace (not necessarily below the allocation pointer of the
   // semispace).
-  bool ToSpaceContains(Object* o) { return to_space_.Contains(o); }
-  bool FromSpaceContains(Object* o) { return from_space_.Contains(o); }
+  inline bool ToSpaceContains(Object* o) { return to_space_.Contains(o); }
+  inline bool FromSpaceContains(Object* o) { return from_space_.Contains(o); }
 
-  bool ToSpaceContains(Address a) { return to_space_.Contains(a); }
-  bool FromSpaceContains(Address a) { return from_space_.Contains(a); }
+  // Try to switch the active semispace to a new, empty, page.
+  // Returns false if this isn't possible or reasonable (i.e., there
+  // are no pages, or the current page is already empty), or true
+  // if successful.
+  bool AddFreshPage();
 
   virtual bool ReserveSpace(int bytes);
 
@@ -1620,10 +2216,24 @@
     return from_space_.Uncommit();
   }
 
+  inline intptr_t inline_allocation_limit_step() {
+    return inline_allocation_limit_step_;
+  }
+
+  SemiSpace* active_space() { return &to_space_; }
+
  private:
+  // Update allocation info to match the current to-space page.
+  void UpdateAllocationInfo();
+
+  Address chunk_base_;
+  uintptr_t chunk_size_;
+
   // The semispaces.
   SemiSpace to_space_;
   SemiSpace from_space_;
+  VirtualMemory reservation_;
+  int pages_used_;
 
   // Start address and bit mask for containment testing.
   Address start_;
@@ -1634,15 +2244,20 @@
   // Allocation pointer and limit for normal allocation and allocation during
   // mark-compact collection.
   AllocationInfo allocation_info_;
-  AllocationInfo mc_forwarding_info_;
 
+  // When incremental marking is active we will set allocation_info_.limit
+  // to be lower than actual limit and then will gradually increase it
+  // in steps to guarantee that we do incremental marking steps even
+  // when all allocation is performed from inlined generated code.
+  intptr_t inline_allocation_limit_step_;
+
+  Address top_on_previous_step_;
+
   HistogramInfo* allocated_histogram_;
   HistogramInfo* promoted_histogram_;
 
-  // Implementation of AllocateRaw and MCAllocateRaw.
-  MUST_USE_RESULT inline MaybeObject* AllocateRawInternal(
-      int size_in_bytes,
-      AllocationInfo* alloc_info);
+  // Implementation of AllocateRaw.
+  MUST_USE_RESULT inline MaybeObject* AllocateRawInternal(int size_in_bytes);
 
   friend class SemiSpaceIterator;
 
@@ -1652,193 +2267,6 @@
 
 
 // -----------------------------------------------------------------------------
-// Free lists for old object spaces
-//
-// Free-list nodes are free blocks in the heap.  They look like heap objects
-// (free-list node pointers have the heap object tag, and they have a map like
-// a heap object).  They have a size and a next pointer.  The next pointer is
-// the raw address of the next free list node (or NULL).
-class FreeListNode: public HeapObject {
- public:
-  // Obtain a free-list node from a raw address.  This is not a cast because
-  // it does not check nor require that the first word at the address is a map
-  // pointer.
-  static FreeListNode* FromAddress(Address address) {
-    return reinterpret_cast<FreeListNode*>(HeapObject::FromAddress(address));
-  }
-
-  static inline bool IsFreeListNode(HeapObject* object);
-
-  // Set the size in bytes, which can be read with HeapObject::Size().  This
-  // function also writes a map to the first word of the block so that it
-  // looks like a heap object to the garbage collector and heap iteration
-  // functions.
-  void set_size(Heap* heap, int size_in_bytes);
-
-  // Accessors for the next field.
-  inline Address next(Heap* heap);
-  inline void set_next(Heap* heap, Address next);
-
- private:
-  static const int kNextOffset = POINTER_SIZE_ALIGN(ByteArray::kHeaderSize);
-
-  DISALLOW_IMPLICIT_CONSTRUCTORS(FreeListNode);
-};
-
-
-// The free list for the old space.
-class OldSpaceFreeList BASE_EMBEDDED {
- public:
-  OldSpaceFreeList(Heap* heap, AllocationSpace owner);
-
-  // Clear the free list.
-  void Reset();
-
-  // Return the number of bytes available on the free list.
-  intptr_t available() { return available_; }
-
-  // Place a node on the free list.  The block of size 'size_in_bytes'
-  // starting at 'start' is placed on the free list.  The return value is the
-  // number of bytes that have been lost due to internal fragmentation by
-  // freeing the block.  Bookkeeping information will be written to the block,
-  // ie, its contents will be destroyed.  The start address should be word
-  // aligned, and the size should be a non-zero multiple of the word size.
-  int Free(Address start, int size_in_bytes);
-
-  // Allocate a block of size 'size_in_bytes' from the free list.  The block
-  // is unitialized.  A failure is returned if no block is available.  The
-  // number of bytes lost to fragmentation is returned in the output parameter
-  // 'wasted_bytes'.  The size should be a non-zero multiple of the word size.
-  MUST_USE_RESULT MaybeObject* Allocate(int size_in_bytes, int* wasted_bytes);
-
-  void MarkNodes();
-
- private:
-  // The size range of blocks, in bytes. (Smaller allocations are allowed, but
-  // will always result in waste.)
-  static const int kMinBlockSize = 2 * kPointerSize;
-  static const int kMaxBlockSize = Page::kMaxHeapObjectSize;
-
-  Heap* heap_;
-
-  // The identity of the owning space, for building allocation Failure
-  // objects.
-  AllocationSpace owner_;
-
-  // Total available bytes in all blocks on this free list.
-  int available_;
-
-  // Blocks are put on exact free lists in an array, indexed by size in words.
-  // The available sizes are kept in an increasingly ordered list. Entries
-  // corresponding to sizes < kMinBlockSize always have an empty free list
-  // (but index kHead is used for the head of the size list).
-  struct SizeNode {
-    // Address of the head FreeListNode of the implied block size or NULL.
-    Address head_node_;
-    // Size (words) of the next larger available size if head_node_ != NULL.
-    int next_size_;
-  };
-  static const int kFreeListsLength = kMaxBlockSize / kPointerSize + 1;
-  SizeNode free_[kFreeListsLength];
-
-  // Sentinel elements for the size list. Real elements are in ]kHead..kEnd[.
-  static const int kHead = kMinBlockSize / kPointerSize - 1;
-  static const int kEnd = kMaxInt;
-
-  // We keep a "finger" in the size list to speed up a common pattern:
-  // repeated requests for the same or increasing sizes.
-  int finger_;
-
-  // Starting from *prev, find and return the smallest size >= index (words),
-  // or kEnd. Update *prev to be the largest size < index, or kHead.
-  int FindSize(int index, int* prev) {
-    int cur = free_[*prev].next_size_;
-    while (cur < index) {
-      *prev = cur;
-      cur = free_[cur].next_size_;
-    }
-    return cur;
-  }
-
-  // Remove an existing element from the size list.
-  void RemoveSize(int index) {
-    int prev = kHead;
-    int cur = FindSize(index, &prev);
-    ASSERT(cur == index);
-    free_[prev].next_size_ = free_[cur].next_size_;
-    finger_ = prev;
-  }
-
-  // Insert a new element into the size list.
-  void InsertSize(int index) {
-    int prev = kHead;
-    int cur = FindSize(index, &prev);
-    ASSERT(cur != index);
-    free_[prev].next_size_ = index;
-    free_[index].next_size_ = cur;
-  }
-
-  // The size list is not updated during a sequence of calls to Free, but is
-  // rebuilt before the next allocation.
-  void RebuildSizeList();
-  bool needs_rebuild_;
-
-#ifdef DEBUG
-  // Does this free list contain a free block located at the address of 'node'?
-  bool Contains(FreeListNode* node);
-#endif
-
-  DISALLOW_COPY_AND_ASSIGN(OldSpaceFreeList);
-};
-
-
-// The free list for the map space.
-class FixedSizeFreeList BASE_EMBEDDED {
- public:
-  FixedSizeFreeList(Heap* heap, AllocationSpace owner, int object_size);
-
-  // Clear the free list.
-  void Reset();
-
-  // Return the number of bytes available on the free list.
-  intptr_t available() { return available_; }
-
-  // Place a node on the free list.  The block starting at 'start' (assumed to
-  // have size object_size_) is placed on the free list.  Bookkeeping
-  // information will be written to the block, ie, its contents will be
-  // destroyed.  The start address should be word aligned.
-  void Free(Address start);
-
-  // Allocate a fixed sized block from the free list.  The block is unitialized.
-  // A failure is returned if no block is available.
-  MUST_USE_RESULT MaybeObject* Allocate();
-
-  void MarkNodes();
-
- private:
-  Heap* heap_;
-
-  // Available bytes on the free list.
-  intptr_t available_;
-
-  // The head of the free list.
-  Address head_;
-
-  // The tail of the free list.
-  Address tail_;
-
-  // The identity of the owning space, for building allocation Failure
-  // objects.
-  AllocationSpace owner_;
-
-  // The size of the objects in this space.
-  int object_size_;
-
-  DISALLOW_COPY_AND_ASSIGN(FixedSizeFreeList);
-};
-
-
-// -----------------------------------------------------------------------------
 // Old object space (excluding map objects)
 
 class OldSpace : public PagedSpace {
@@ -1849,71 +2277,28 @@
            intptr_t max_capacity,
            AllocationSpace id,
            Executability executable)
-      : PagedSpace(heap, max_capacity, id, executable),
-        free_list_(heap, id) {
+      : PagedSpace(heap, max_capacity, id, executable) {
     page_extra_ = 0;
   }
 
-  // The bytes available on the free list (ie, not above the linear allocation
-  // pointer).
-  intptr_t AvailableFree() { return free_list_.available(); }
-
   // The limit of allocation for a page in this space.
   virtual Address PageAllocationLimit(Page* page) {
     return page->ObjectAreaEnd();
   }
 
-  // Give a block of memory to the space's free list.  It might be added to
-  // the free list or accounted as waste.
-  // If add_to_freelist is false then just accounting stats are updated and
-  // no attempt to add area to free list is made.
-  void Free(Address start, int size_in_bytes, bool add_to_freelist) {
-    accounting_stats_.DeallocateBytes(size_in_bytes);
-
-    if (add_to_freelist) {
-      int wasted_bytes = free_list_.Free(start, size_in_bytes);
-      accounting_stats_.WasteBytes(wasted_bytes);
-    }
-  }
-
-  virtual void DeallocateBlock(Address start,
-                               int size_in_bytes,
-                               bool add_to_freelist);
-
-  // Prepare for full garbage collection.  Resets the relocation pointer and
-  // clears the free list.
-  virtual void PrepareForMarkCompact(bool will_compact);
-
-  // Updates the allocation pointer to the relocation top after a mark-compact
-  // collection.
-  virtual void MCCommitRelocationInfo();
-
-  virtual void PutRestOfCurrentPageOnFreeList(Page* current_page);
-
-  void MarkFreeListNodes() { free_list_.MarkNodes(); }
-
-#ifdef DEBUG
-  // Reports statistics for the space
-  void ReportStatistics();
-#endif
-
- protected:
-  // Virtual function in the superclass.  Slow path of AllocateRaw.
-  MUST_USE_RESULT HeapObject* SlowAllocateRaw(int size_in_bytes);
-
-  // Virtual function in the superclass.  Allocate linearly at the start of
-  // the page after current_page (there is assumed to be one).
-  HeapObject* AllocateInNextPage(Page* current_page, int size_in_bytes);
-
- private:
-  // The space's free list.
-  OldSpaceFreeList free_list_;
-
  public:
   TRACK_MEMORY("OldSpace")
 };
 
 
+// For contiguous spaces, top should be in the space (or at the end) and limit
+// should be the end of the space.
+#define ASSERT_SEMISPACE_ALLOCATION_INFO(info, space) \
+  ASSERT((space).page_low() <= (info).top             \
+         && (info).top <= (space).page_high()         \
+         && (info).limit <= (space).page_high())
+
+
 // -----------------------------------------------------------------------------
 // Old space for objects of a fixed size
 
@@ -1926,8 +2311,7 @@
              const char* name)
       : PagedSpace(heap, max_capacity, id, NOT_EXECUTABLE),
         object_size_in_bytes_(object_size_in_bytes),
-        name_(name),
-        free_list_(heap, id, object_size_in_bytes) {
+        name_(name) {
     page_extra_ = Page::kObjectAreaSize % object_size_in_bytes;
   }
 
@@ -1938,44 +2322,12 @@
 
   int object_size_in_bytes() { return object_size_in_bytes_; }
 
-  // Give a fixed sized block of memory to the space's free list.
-  // If add_to_freelist is false then just accounting stats are updated and
-  // no attempt to add area to free list is made.
-  void Free(Address start, bool add_to_freelist) {
-    if (add_to_freelist) {
-      free_list_.Free(start);
-    }
-    accounting_stats_.DeallocateBytes(object_size_in_bytes_);
-  }
-
   // Prepares for a mark-compact GC.
-  virtual void PrepareForMarkCompact(bool will_compact);
+  virtual void PrepareForMarkCompact();
 
-  // Updates the allocation pointer to the relocation top after a mark-compact
-  // collection.
-  virtual void MCCommitRelocationInfo();
-
-  virtual void PutRestOfCurrentPageOnFreeList(Page* current_page);
-
-  virtual void DeallocateBlock(Address start,
-                               int size_in_bytes,
-                               bool add_to_freelist);
-
   void MarkFreeListNodes() { free_list_.MarkNodes(); }
 
-#ifdef DEBUG
-  // Reports statistic info of the space
-  void ReportStatistics();
-#endif
-
  protected:
-  // Virtual function in the superclass.  Slow path of AllocateRaw.
-  MUST_USE_RESULT HeapObject* SlowAllocateRaw(int size_in_bytes);
-
-  // Virtual function in the superclass.  Allocate linearly at the start of
-  // the page after current_page (there is assumed to be one).
-  HeapObject* AllocateInNextPage(Page* current_page, int size_in_bytes);
-
   void ResetFreeList() {
     free_list_.Reset();
   }
@@ -1986,9 +2338,6 @@
 
   // The name of this space.
   const char* name_;
-
-  // The space's free list.
-  FixedSizeFreeList free_list_;
 };
 
 
@@ -2004,85 +2353,20 @@
            AllocationSpace id)
       : FixedSpace(heap, max_capacity, id, Map::kSize, "map"),
         max_map_space_pages_(max_map_space_pages) {
-    ASSERT(max_map_space_pages < kMaxMapPageIndex);
   }
 
-  // Prepares for a mark-compact GC.
-  virtual void PrepareForMarkCompact(bool will_compact);
-
   // Given an index, returns the page address.
-  Address PageAddress(int page_index) { return page_addresses_[page_index]; }
+  // TODO(1600): this limit is artifical just to keep code compilable
+  static const int kMaxMapPageIndex = 1 << 16;
 
-  static const int kMaxMapPageIndex = 1 << MapWord::kMapPageIndexBits;
-
-  // Are map pointers encodable into map word?
-  bool MapPointersEncodable() {
-    if (!FLAG_use_big_map_space) {
-      ASSERT(CountPagesToTop() <= kMaxMapPageIndex);
-      return true;
+  virtual int RoundSizeDownToObjectAlignment(int size) {
+    if (IsPowerOf2(Map::kSize)) {
+      return RoundDown(size, Map::kSize);
+    } else {
+      return (size / Map::kSize) * Map::kSize;
     }
-    return CountPagesToTop() <= max_map_space_pages_;
   }
 
-  // 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);
-
-    // Flush allocation watermarks.
-    for (Page* p = first_page_; p != top_page; p = p->next_page()) {
-      p->SetAllocationWatermark(p->AllocationTop());
-    }
-    top_page->SetAllocationWatermark(new_top);
-
-#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();
-  }
-
  protected:
 #ifdef DEBUG
   virtual void VerifyObject(HeapObject* obj);
@@ -2098,9 +2382,6 @@
 
   const int max_map_space_pages_;
 
-  // An array of page start address in a map space.
-  Address page_addresses_[kMaxMapPageIndex];
-
  public:
   TRACK_MEMORY("MapSpace")
 };
@@ -2116,6 +2397,14 @@
       : FixedSpace(heap, max_capacity, id, JSGlobalPropertyCell::kSize, "cell")
   {}
 
+  virtual int RoundSizeDownToObjectAlignment(int size) {
+    if (IsPowerOf2(JSGlobalPropertyCell::kSize)) {
+      return RoundDown(size, JSGlobalPropertyCell::kSize);
+    } else {
+      return (size / JSGlobalPropertyCell::kSize) * JSGlobalPropertyCell::kSize;
+    }
+  }
+
  protected:
 #ifdef DEBUG
   virtual void VerifyObject(HeapObject* obj);
@@ -2133,64 +2422,6 @@
 // A large object always starts at Page::kObjectStartOffset to a page.
 // Large objects do not move during garbage collections.
 
-// A LargeObjectChunk holds exactly one large object page with exactly one
-// large object.
-class LargeObjectChunk {
- public:
-  // Allocates a new LargeObjectChunk that contains a large object page
-  // (Page::kPageSize aligned) that has at least size_in_bytes (for a large
-  // object) bytes after the object area start of that page.
-  static LargeObjectChunk* New(int size_in_bytes, Executability executable);
-
-  // Free the memory associated with the chunk.
-  void Free(Executability executable);
-
-  // Interpret a raw address as a large object chunk.
-  static LargeObjectChunk* FromAddress(Address address) {
-    return reinterpret_cast<LargeObjectChunk*>(address);
-  }
-
-  // Returns the address of this chunk.
-  Address address() { return reinterpret_cast<Address>(this); }
-
-  Page* GetPage() {
-    return Page::FromAddress(RoundUp(address(), Page::kPageSize));
-  }
-
-  // Accessors for the fields of the chunk.
-  LargeObjectChunk* next() { return next_; }
-  void set_next(LargeObjectChunk* chunk) { next_ = chunk; }
-  size_t size() { return size_ & ~Page::kPageFlagMask; }
-
-  // Compute the start address in the chunk.
-  Address GetStartAddress() { return GetPage()->ObjectAreaStart(); }
-
-  // Returns the object in this chunk.
-  HeapObject* GetObject() { return HeapObject::FromAddress(GetStartAddress()); }
-
-  // Given a requested size returns the physical size of a chunk to be
-  // allocated.
-  static int ChunkSizeFor(int size_in_bytes);
-
-  // Given a chunk size, returns the object size it can accommodate.  Used by
-  // LargeObjectSpace::Available.
-  static intptr_t ObjectSizeFor(intptr_t chunk_size) {
-    if (chunk_size <= (Page::kPageSize + Page::kObjectStartOffset)) return 0;
-    return chunk_size - Page::kPageSize - Page::kObjectStartOffset;
-  }
-
- private:
-  // A pointer to the next large object chunk in the space or NULL.
-  LargeObjectChunk* next_;
-
-  // The total size of this chunk.
-  size_t size_;
-
- public:
-  TRACK_MEMORY("LargeObjectChunk")
-};
-
-
 class LargeObjectSpace : public Space {
  public:
   LargeObjectSpace(Heap* heap, AllocationSpace id);
@@ -2202,13 +2433,16 @@
   // Releases internal resources, frees objects in this space.
   void TearDown();
 
-  // Allocates a (non-FixedArray, non-Code) large object.
-  MUST_USE_RESULT MaybeObject* AllocateRaw(int size_in_bytes);
-  // Allocates a large Code object.
-  MUST_USE_RESULT MaybeObject* AllocateRawCode(int size_in_bytes);
-  // Allocates a large FixedArray.
-  MUST_USE_RESULT MaybeObject* AllocateRawFixedArray(int size_in_bytes);
+  static intptr_t ObjectSizeFor(intptr_t chunk_size) {
+    if (chunk_size <= (Page::kPageSize + Page::kObjectStartOffset)) return 0;
+    return chunk_size - Page::kPageSize - Page::kObjectStartOffset;
+  }
 
+  // Shared implementation of AllocateRaw, AllocateRawCode and
+  // AllocateRawFixedArray.
+  MUST_USE_RESULT MaybeObject* AllocateRaw(int object_size,
+                                           Executability executable);
+
   // Available bytes for objects in this space.
   inline intptr_t Available();
 
@@ -2231,11 +2465,8 @@
 
   // Finds a large object page containing the given pc, returns NULL
   // if such a page doesn't exist.
-  LargeObjectChunk* FindChunkContainingPc(Address pc);
+  LargePage* FindPageContainingPc(Address pc);
 
-  // Iterates objects covered by dirty regions.
-  void IterateDirtyRegions(ObjectSlotCallback func);
-
   // Frees unmarked objects.
   void FreeUnmarkedObjects();
 
@@ -2243,13 +2474,15 @@
   bool Contains(HeapObject* obj);
 
   // Checks whether the space is empty.
-  bool IsEmpty() { return first_chunk_ == NULL; }
+  bool IsEmpty() { return first_page_ == NULL; }
 
   // See the comments for ReserveSpace in the Space class.  This has to be
   // called after ReserveSpace has been called on the paged spaces, since they
   // may use some memory, leaving less for large objects.
   virtual bool ReserveSpace(int bytes);
 
+  LargePage* first_page() { return first_page_; }
+
 #ifdef DEBUG
   virtual void Verify();
   virtual void Print();
@@ -2262,17 +2495,11 @@
 
  private:
   // The head of the linked list of large object chunks.
-  LargeObjectChunk* first_chunk_;
+  LargePage* first_page_;
   intptr_t size_;  // allocated bytes
   int page_count_;  // number of chunks
   intptr_t objects_size_;  // size of objects
 
-  // Shared implementation of AllocateRaw, AllocateRawCode and
-  // AllocateRawFixedArray.
-  MUST_USE_RESULT MaybeObject* AllocateRawInternal(int requested_size,
-                                                   int object_size,
-                                                   Executability executable);
-
   friend class LargeObjectIterator;
 
  public:
@@ -2285,17 +2512,78 @@
   explicit LargeObjectIterator(LargeObjectSpace* space);
   LargeObjectIterator(LargeObjectSpace* space, HeapObjectCallback size_func);
 
-  HeapObject* next();
+  HeapObject* Next();
 
   // implementation of ObjectIterator.
-  virtual HeapObject* next_object() { return next(); }
+  virtual HeapObject* next_object() { return Next(); }
 
  private:
-  LargeObjectChunk* current_;
+  LargePage* current_;
   HeapObjectCallback size_func_;
 };
 
 
+// Iterates over the chunks (pages and large object pages) that can contain
+// pointers to new space.
+class PointerChunkIterator BASE_EMBEDDED {
+ public:
+  inline explicit PointerChunkIterator(Heap* heap);
+
+  // Return NULL when the iterator is done.
+  MemoryChunk* next() {
+    switch (state_) {
+      case kOldPointerState: {
+        if (old_pointer_iterator_.has_next()) {
+          return old_pointer_iterator_.next();
+        }
+        state_ = kMapState;
+        // Fall through.
+      }
+      case kMapState: {
+        if (map_iterator_.has_next()) {
+          return map_iterator_.next();
+        }
+        state_ = kLargeObjectState;
+        // Fall through.
+      }
+      case kLargeObjectState: {
+        HeapObject* heap_object;
+        do {
+          heap_object = lo_iterator_.Next();
+          if (heap_object == NULL) {
+            state_ = kFinishedState;
+            return NULL;
+          }
+          // Fixed arrays are the only pointer-containing objects in large
+          // object space.
+        } while (!heap_object->IsFixedArray());
+        MemoryChunk* answer = MemoryChunk::FromAddress(heap_object->address());
+        return answer;
+      }
+      case kFinishedState:
+        return NULL;
+      default:
+        break;
+    }
+    UNREACHABLE();
+    return NULL;
+  }
+
+
+ private:
+  enum State {
+    kOldPointerState,
+    kMapState,
+    kLargeObjectState,
+    kFinishedState
+  };
+  State state_;
+  PageIterator old_pointer_iterator_;
+  PageIterator map_iterator_;
+  LargeObjectIterator lo_iterator_;
+};
+
+
 #ifdef DEBUG
 struct CommentStatistic {
   const char* comment;