diff --git a/src/spaces.h b/src/spaces.h
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+// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_SPACES_H_
+#define V8_SPACES_H_
+
+#include "list-inl.h"
+#include "log.h"
+
+namespace v8 {
+namespace internal {
+
+// -----------------------------------------------------------------------------
+// Heap structures:
+//
+// A JS heap consists of a young generation, an old generation, and a large
+// object space. The young generation is divided into two semispaces. A
+// scavenger implements Cheney's copying algorithm. The old generation is
+// separated into a map space and an old object space. The map space contains
+// all (and only) map objects, the rest of old objects go into the old space.
+// The old generation is collected by a mark-sweep-compact collector.
+//
+// The semispaces of the young generation are contiguous.  The old and map
+// spaces consists of a list of pages. A page has a page header, a remembered
+// set area, 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. The next 248 bytes are
+// remembered sets. Heap objects are aligned to the pointer size (4 bytes). A
+// remembered set bit corresponds to a pointer in the object 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 and uses the same remembered
+// set implementation.  Pages in large object space may be larger than 8K.
+//
+// NOTE: The mark-compact collector rebuilds the remembered set after a
+// collection. It reuses first a few words of the remembered set for
+// bookkeeping relocation information.
+
+
+// Some assertion macros used in the debugging mode.
+
+#define ASSERT_PAGE_ALIGNED(address)                  \
+  ASSERT((OffsetFrom(address) & Page::kPageAlignmentMask) == 0)
+
+#define ASSERT_OBJECT_ALIGNED(address)                \
+  ASSERT((OffsetFrom(address) & kObjectAlignmentMask) == 0)
+
+#define ASSERT_OBJECT_SIZE(size)                      \
+  ASSERT((0 < size) && (size <= Page::kMaxHeapObjectSize))
+
+#define ASSERT_PAGE_OFFSET(offset)                    \
+  ASSERT((Page::kObjectStartOffset <= offset)         \
+      && (offset <= Page::kPageSize))
+
+#define ASSERT_MAP_PAGE_INDEX(index)                            \
+  ASSERT((0 <= index) && (index <= MapSpace::kMaxMapPageIndex))
+
+
+class PagedSpace;
+class MemoryAllocator;
+class AllocationInfo;
+
+// -----------------------------------------------------------------------------
+// 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 divided into
+// three areas: the first two words are used for bookkeeping, the next 248
+// bytes are used as remembered set, and the rest of the page is the object
+// area.
+//
+// Pointers are aligned to the pointer size (4), only 1 bit is needed
+// for a pointer in the remembered set. Given an address, its remembered set
+// bit position (offset from the start of the page) is calculated by dividing
+// its page offset by 32. Therefore, the object area in a page starts at the
+// 256th byte (8K/32). Bytes 0 to 255 do not need the remembered set, so that
+// the first two words (64 bits) in a page can be used for other purposes.
+//
+// On the 64-bit platform, we add an offset to the start of the remembered set,
+// and pointers are aligned to 8-byte pointer size. This means that we need
+// only 128 bytes for the RSet, and only get two bytes free in the RSet's RSet.
+// For this reason we add an offset to get room for the Page data at the start.
+//
+// The mark-compact collector transforms a map pointer into a page index and a
+// page offset. The map space can have up to 1024 pages, and 8M bytes (1024 *
+// 8K) in total.  Because a map pointer is aligned to the pointer size (4
+// bytes), 11 bits are enough to encode the page offset. 21 bits (10 for the
+// page index + 11 for the offset in the page) are required to encode a map
+// pointer.
+//
+// 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 {
+ 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).
+  INLINE(static Page* FromAddress(Address a)) {
+    return reinterpret_cast<Page*>(OffsetFrom(a) & ~kPageAlignmentMask);
+  }
+
+  // Returns the page containing an allocation top. Because an allocation
+  // top address can be the upper bound of the page, we need to subtract
+  // it with kPointerSize first. The address ranges from
+  // [page_addr + kObjectStartOffset .. page_addr + kPageSize].
+  INLINE(static Page* FromAllocationTop(Address top)) {
+    Page* p = FromAddress(top - kPointerSize);
+    ASSERT_PAGE_OFFSET(p->Offset(top));
+    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.
+  inline Page* next_page();
+
+  // Return the end of allocation in this page. Undefined for unused pages.
+  inline Address AllocationTop();
+
+  // Returns the start address of the object area in this page.
+  Address ObjectAreaStart() { return address() + kObjectStartOffset; }
+
+  // Returns the end address (exclusive) of the object area in this page.
+  Address ObjectAreaEnd() { return address() + Page::kPageSize; }
+
+  // Returns the start address of the remembered set area.
+  Address RSetStart() { return address() + kRSetStartOffset; }
+
+  // Returns the end address of the remembered set area (exclusive).
+  Address RSetEnd() { return address() + kRSetEndOffset; }
+
+  // Checks whether an address is page aligned.
+  static bool IsAlignedToPageSize(Address a) {
+    return 0 == (OffsetFrom(a) & kPageAlignmentMask);
+  }
+
+  // True if this page is a large object page.
+  bool IsLargeObjectPage() { return (is_normal_page & 0x1) == 0; }
+
+  // Returns the offset of a given address to this page.
+  INLINE(int Offset(Address a)) {
+    int offset = a - address();
+    ASSERT_PAGE_OFFSET(offset);
+    return offset;
+  }
+
+  // Returns the address for a given offset to the this page.
+  Address OffsetToAddress(int offset) {
+    ASSERT_PAGE_OFFSET(offset);
+    return address() + offset;
+  }
+
+  // ---------------------------------------------------------------------
+  // Remembered set support
+
+  // Clears remembered set in this page.
+  inline void ClearRSet();
+
+  // Return the address of the remembered set word corresponding to an
+  // object address/offset pair, and the bit encoded as a single-bit
+  // mask in the output parameter 'bitmask'.
+  INLINE(static Address ComputeRSetBitPosition(Address address, int offset,
+                                               uint32_t* bitmask));
+
+  // Sets the corresponding remembered set bit for a given address.
+  INLINE(static void SetRSet(Address address, int offset));
+
+  // Clears the corresponding remembered set bit for a given address.
+  static inline void UnsetRSet(Address address, int offset);
+
+  // Checks whether the remembered set bit for a given address is set.
+  static inline bool IsRSetSet(Address address, int offset);
+
+#ifdef DEBUG
+  // Use a state to mark whether remembered set space can be used for other
+  // purposes.
+  enum RSetState { IN_USE,  NOT_IN_USE };
+  static bool is_rset_in_use() { return rset_state_ == IN_USE; }
+  static void set_rset_state(RSetState state) { rset_state_ = state; }
+#endif
+
+  // 8K bytes per page.
+  static const int kPageSizeBits = 13;
+
+  // Page size in bytes.  This must be a multiple of the OS page size.
+  static const int kPageSize = 1 << kPageSizeBits;
+
+  // Page size mask.
+  static const intptr_t kPageAlignmentMask = (1 << kPageSizeBits) - 1;
+
+  // The offset of the remembered set in a page, in addition to the empty bytes
+  // formed as the remembered bits of the remembered set itself.
+#ifdef V8_TARGET_ARCH_X64
+  static const int kRSetOffset = 4 * kPointerSize;  // Room for four pointers.
+#else
+  static const int kRSetOffset = 0;
+#endif
+  // The end offset of the remembered set in a page
+  // (heaps are aligned to pointer size).
+  static const int kRSetEndOffset = kRSetOffset + kPageSize / kBitsPerPointer;
+
+  // The start offset of the object area in a page.
+  // This needs to be at least (bits per uint32_t) * kBitsPerPointer,
+  // to align start of rset to a uint32_t address.
+  static const int kObjectStartOffset = 256;
+
+  // The start offset of the used part of the remembered set in a page.
+  static const int kRSetStartOffset = kRSetOffset +
+      kObjectStartOffset / kBitsPerPointer;
+
+  // Object area size in bytes.
+  static const int kObjectAreaSize = kPageSize - kObjectStartOffset;
+
+  // Maximum object size that fits in a page.
+  static const int kMaxHeapObjectSize = kObjectAreaSize;
+
+  //---------------------------------------------------------------------------
+  // 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;
+
+  // 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.
+  int is_normal_page;
+
+  // The following fields may overlap with remembered set, they can only
+  // be used in the mark-compact collector when remembered set is not
+  // used.
+
+  // The index of the page in its owner space.
+  int mc_page_index;
+
+  // The allocation pointer after relocating objects to this page.
+  Address mc_relocation_top;
+
+  // The forwarding address of the first live object in this page.
+  Address mc_first_forwarded;
+
+#ifdef DEBUG
+ private:
+  static RSetState rset_state_;  // state of the remembered set
+#endif
+};
+
+
+// ----------------------------------------------------------------------------
+// Space is the abstract superclass for all allocation spaces.
+class Space : public Malloced {
+ public:
+  Space(AllocationSpace id, Executability executable)
+      : id_(id), executable_(executable) {}
+
+  virtual ~Space() {}
+
+  // Does the space need executable memory?
+  Executability executable() { return executable_; }
+
+  // Identity used in error reporting.
+  AllocationSpace identity() { return id_; }
+
+  virtual int Size() = 0;
+
+#ifdef DEBUG
+  virtual void Print() = 0;
+#endif
+
+ private:
+  AllocationSpace id_;
+  Executability executable_;
+};
+
+
+// ----------------------------------------------------------------------------
+// All heap objects containing executable code (code objects) must be allocated
+// from a 2 GB range of memory, so that they can call each other using 32-bit
+// displacements.  This happens automatically on 32-bit platforms, where 32-bit
+// displacements cover the entire 4GB virtual address space.  On 64-bit
+// platforms, we support this using the CodeRange object, which reserves and
+// manages a range of virtual memory.
+class CodeRange : public AllStatic {
+ public:
+  // Reserves a range of virtual memory, but does not commit any of it.
+  // Can only be called once, at heap initialization time.
+  // Returns false on failure.
+  static bool Setup(const size_t requested_size);
+
+  // Frees the range of virtual memory, and frees the data structures used to
+  // manage it.
+  static void TearDown();
+
+  static bool exists() { return code_range_ != NULL; }
+  static bool contains(Address address) {
+    if (code_range_ == NULL) return false;
+    Address start = static_cast<Address>(code_range_->address());
+    return start <= address && address < start + code_range_->size();
+  }
+
+  // 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.
+  static void* AllocateRawMemory(const size_t requested, size_t* allocated);
+  static void FreeRawMemory(void* buf, size_t length);
+
+ private:
+  // The reserved range of virtual memory that all code objects are put in.
+  static VirtualMemory* code_range_;
+  // Plain old data class, just a struct plus a constructor.
+  class FreeBlock {
+   public:
+    FreeBlock(Address start_arg, size_t size_arg)
+        : start(start_arg), size(size_arg) {}
+    FreeBlock(void* start_arg, size_t size_arg)
+        : start(static_cast<Address>(start_arg)), size(size_arg) {}
+
+    Address start;
+    size_t size;
+  };
+
+  // Freed blocks of memory are added to the free list.  When the allocation
+  // list is exhausted, the free list is sorted and merged to make the new
+  // allocation list.
+  static List<FreeBlock> free_list_;
+  // Memory is allocated from the free blocks on the allocation list.
+  // The block at current_allocation_block_index_ is the current block.
+  static List<FreeBlock> allocation_list_;
+  static int current_allocation_block_index_;
+
+  // Finds a block on the allocation list that contains at least the
+  // requested amount of memory.  If none is found, sorts and merges
+  // the existing free memory blocks, and searches again.
+  // If none can be found, terminates V8 with FatalProcessOutOfMemory.
+  static void GetNextAllocationBlock(size_t requested);
+  // Compares the start addresses of two free blocks.
+  static int CompareFreeBlockAddress(const FreeBlock* left,
+                                     const FreeBlock* right);
+};
+
+
+// ----------------------------------------------------------------------------
+// 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.
+//
+// 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.
+//
+// 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.
+
+class MemoryAllocator : public AllStatic {
+ public:
+  // Initializes its internal bookkeeping structures.
+  // Max capacity of the total space.
+  static bool Setup(int max_capacity);
+
+  // Deletes valid chunks.
+  static 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.
+  static void* ReserveInitialChunk(const size_t requested);
+
+  // 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.
+  static Page* CommitPages(Address start, size_t size, PagedSpace* owner,
+                           int* num_pages);
+
+  // 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.
+  static bool CommitBlock(Address start, size_t size, Executability executable);
+
+
+  // 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.
+  static bool UncommitBlock(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.
+  static Page* AllocatePages(int requested_pages, int* allocated_pages,
+                             PagedSpace* owner);
+
+  // Frees pages from a given page and after. 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'.
+  static Page* FreePages(Page* p);
+
+  // 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.
+  static void* AllocateRawMemory(const size_t requested,
+                                 size_t* allocated,
+                                 Executability executable);
+  static void FreeRawMemory(void* buf, size_t length);
+
+  // Returns the maximum available bytes of heaps.
+  static int Available() { return capacity_ < size_ ? 0 : capacity_ - size_; }
+
+  // Returns allocated spaces in bytes.
+  static int Size() { return size_; }
+
+  // Returns maximum available bytes that the old space can have.
+  static int MaxAvailable() {
+    return (Available() / Page::kPageSize) * Page::kObjectAreaSize;
+  }
+
+  // Links two pages.
+  static inline void SetNextPage(Page* prev, Page* next);
+
+  // Returns the next page of a given page.
+  static inline Page* GetNextPage(Page* p);
+
+  // Checks whether a page belongs to a space.
+  static inline bool IsPageInSpace(Page* p, PagedSpace* space);
+
+  // Returns the space that owns the given page.
+  static inline PagedSpace* PageOwner(Page* page);
+
+  // Finds the first/last page in the same chunk as a given page.
+  static Page* FindFirstPageInSameChunk(Page* p);
+  static Page* FindLastPageInSameChunk(Page* p);
+
+#ifdef ENABLE_HEAP_PROTECTION
+  // Protect/unprotect a block of memory by marking it read-only/writable.
+  static inline void Protect(Address start, size_t size);
+  static inline void Unprotect(Address start, size_t size,
+                               Executability executable);
+
+  // Protect/unprotect a chunk given a page in the chunk.
+  static inline void ProtectChunkFromPage(Page* page);
+  static inline void UnprotectChunkFromPage(Page* page);
+#endif
+
+#ifdef DEBUG
+  // Reports statistic info of the space.
+  static void ReportStatistics();
+#endif
+
+  // Due to encoding limitation, we can only have 8K chunks.
+  static const int kMaxNofChunks = 1 << Page::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;
+#else
+  static const int kPagesPerChunk = 16;
+#endif
+  static const int kChunkSize = kPagesPerChunk * Page::kPageSize;
+
+ private:
+  // Maximum space size in bytes.
+  static int capacity_;
+
+  // Allocated space size in bytes.
+  static int size_;
+
+  // The initial chunk of virtual memory.
+  static 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) {}
+    void init(Address a, size_t s, PagedSpace* o) {
+      address_ = a;
+      size_ = s;
+      owner_ = o;
+    }
+    Address address() { return address_; }
+    size_t size() { return size_; }
+    PagedSpace* owner() { return owner_; }
+
+   private:
+    Address address_;
+    size_t size_;
+    PagedSpace* owner_;
+  };
+
+  // Chunks_, free_chunk_ids_ and top_ act as a stack of free chunk ids.
+  static List<ChunkInfo> chunks_;
+  static List<int> free_chunk_ids_;
+  static int max_nof_chunks_;
+  static int top_;
+
+  // Push/pop a free chunk id onto/from the stack.
+  static void Push(int free_chunk_id);
+  static int Pop();
+  static bool OutOfChunkIds() { return top_ == 0; }
+
+  // Frees a chunk.
+  static void DeleteChunk(int chunk_id);
+
+  // Basic check whether a chunk id is in the valid range.
+  static inline bool IsValidChunkId(int chunk_id);
+
+  // Checks whether a chunk id identifies an allocated chunk.
+  static inline bool IsValidChunk(int chunk_id);
+
+  // Returns the chunk id that a page belongs to.
+  static inline int GetChunkId(Page* p);
+
+  // True if the address lies in the initial chunk.
+  static 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
+  // used as a marking stack and its page headers are destroyed.
+  static Page* InitializePagesInChunk(int chunk_id, int pages_in_chunk,
+                                      PagedSpace* owner);
+};
+
+
+// -----------------------------------------------------------------------------
+// Interface for heap object iterator to be implemented by all object space
+// object iterators.
+//
+// NOTE: The space specific object iterators also implements the own has_next()
+//       and next() methods which are used to avoid using virtual functions
+//       iterating a specific space.
+
+class ObjectIterator : public Malloced {
+ public:
+  virtual ~ObjectIterator() { }
+
+  virtual bool has_next_object() = 0;
+  virtual HeapObject* next_object() = 0;
+};
+
+
+// -----------------------------------------------------------------------------
+// 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.
+//
+// (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.
+
+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.
+  // 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);
+
+  inline bool has_next();
+  inline HeapObject* next();
+
+  // implementation of ObjectIterator.
+  virtual bool has_next_object() { return has_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
+
+  // Slow path of has_next, checks whether there are more objects in
+  // the next page.
+  bool HasNextInNextPage();
+
+  // Initializes fields.
+  void Initialize(Address start, Address end, HeapObjectCallback size_func);
+
+#ifdef DEBUG
+  // Verifies whether fields have valid values.
+  void Verify();
+#endif
+};
+
+
+// -----------------------------------------------------------------------------
+// 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
+  };
+
+  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).
+};
+
+
+// -----------------------------------------------------------------------------
+// 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.
+
+// 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
+
+#ifdef DEBUG
+  bool VerifyPagedAllocation() {
+    return (Page::FromAllocationTop(top) == Page::FromAllocationTop(limit))
+        && (top <= limit);
+  }
+#endif
+};
+
+
+// An abstraction of the accounting statistics of a page-structured space.
+// The 'capacity' of a space is the number of object-area bytes (ie, not
+// including page bookkeeping structures) currently in the space. The 'size'
+// of a space is the number of allocated bytes, the 'waste' in the space is
+// the number of bytes that are not allocated and not available to
+// allocation without reorganizing the space via a GC (eg, small blocks due
+// to internal fragmentation, top of page areas in map space), and the bytes
+// 'available' is the number of unallocated bytes that are not waste.  The
+// capacity is the sum of size, waste, and available.
+//
+// The stats are only set by functions that ensure they stay balanced. These
+// functions increase or decrease one of the non-capacity stats in
+// conjunction with capacity, or else they always balance increases and
+// decreases to the non-capacity stats.
+class AllocationStats BASE_EMBEDDED {
+ public:
+  AllocationStats() { Clear(); }
+
+  // Zero out all the allocation statistics (ie, no capacity).
+  void Clear() {
+    capacity_ = 0;
+    available_ = 0;
+    size_ = 0;
+    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.
+  int Capacity() { return capacity_; }
+  int Available() { return available_; }
+  int Size() { return size_; }
+  int Waste() { return waste_; }
+
+  // Grow the space by adding available bytes.
+  void ExpandSpace(int size_in_bytes) {
+    capacity_ += size_in_bytes;
+    available_ += size_in_bytes;
+  }
+
+  // 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(int size_in_bytes) {
+    available_ -= size_in_bytes;
+    size_ += size_in_bytes;
+  }
+
+  // Free allocated bytes, making them available (size -> available).
+  void DeallocateBytes(int size_in_bytes) {
+    size_ -= size_in_bytes;
+    available_ += size_in_bytes;
+  }
+
+  // Waste free bytes (available -> waste).
+  void WasteBytes(int size_in_bytes) {
+    available_ -= size_in_bytes;
+    waste_ += size_in_bytes;
+  }
+
+  // Consider the wasted bytes to be allocated, as they contain filler
+  // objects (waste -> size).
+  void FillWastedBytes(int size_in_bytes) {
+    waste_ -= size_in_bytes;
+    size_ += size_in_bytes;
+  }
+
+ private:
+  int capacity_;
+  int available_;
+  int size_;
+  int waste_;
+};
+
+
+class PagedSpace : public Space {
+ public:
+  // Creates a space with a maximum capacity, and an id.
+  PagedSpace(int max_capacity, AllocationSpace id, Executability executable);
+
+  virtual ~PagedSpace() {}
+
+  // Set up the space using the given address range of virtual memory (from
+  // 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);
+
+  // Returns true if the space has been successfully set up and not
+  // subsequently torn down.
+  bool HasBeenSetup();
+
+  // Cleans up the space, frees all pages in this space except those belonging
+  // to the initial chunk, uncommits addresses in the initial chunk.
+  void TearDown();
+
+  // Checks whether an object/address is in this space.
+  inline bool Contains(Address a);
+  bool Contains(HeapObject* o) { return Contains(o->address()); }
+
+  // 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
+  // iterates over objects in the page containing the address, the cost is
+  // linear in the number of objects in the page. It may be slow.
+  Object* FindObject(Address addr);
+
+  // Checks whether page is currently in use by this space.
+  bool IsUsed(Page* page);
+
+  // Clears remembered sets of pages in this space.
+  void ClearRSet();
+
+  // Prepares for a mark-compact GC.
+  virtual void PrepareForMarkCompact(bool will_compact) = 0;
+
+  virtual Address PageAllocationTop(Page* page) = 0;
+
+  // Current capacity without growing (Size() + Available() + Waste()).
+  int Capacity() { return accounting_stats_.Capacity(); }
+
+  // Available bytes without growing.
+  int Available() { return accounting_stats_.Available(); }
+
+  // Allocated bytes in this space.
+  virtual int Size() { return accounting_stats_.Size(); }
+
+  // Wasted bytes due to fragmentation and not recoverable until the
+  // next GC of this space.
+  int Waste() { return accounting_stats_.Waste(); }
+
+  // Returns the address of the first object in this space.
+  Address bottom() { return first_page_->ObjectAreaStart(); }
+
+  // Returns the allocation pointer in this space.
+  Address top() { return allocation_info_.top; }
+
+  // Allocate the requested number of bytes in the space if possible, return a
+  // failure object if not.
+  inline Object* AllocateRaw(int size_in_bytes);
+
+  // Allocate the requested number of bytes for relocation during mark-compact
+  // collection.
+  inline Object* MCAllocateRaw(int size_in_bytes);
+
+
+  // ---------------------------------------------------------------------------
+  // Mark-compact collection support functions
+
+  // 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_)->mc_relocation_top = mc_forwarding_info_.top;
+  }
+
+  // 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);
+
+#ifdef ENABLE_HEAP_PROTECTION
+  // Protect/unprotect the space by marking it read-only/writable.
+  void Protect();
+  void Unprotect();
+#endif
+
+#ifdef DEBUG
+  // Print meta info and objects in this space.
+  virtual void Print();
+
+  // Verify integrity of this space.
+  virtual void Verify(ObjectVisitor* visitor);
+
+  // 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) {}
+
+  // Report code object related statistics
+  void CollectCodeStatistics();
+  static void ReportCodeStatistics();
+  static void ResetCodeStatistics();
+#endif
+
+ protected:
+  // Maximum capacity of this space.
+  int max_capacity_;
+
+  // Accounting information for this space.
+  AllocationStats accounting_stats_;
+
+  // The first page in this space.
+  Page* first_page_;
+
+  // The last page in this space.  Initially set in Setup, updated in
+  // Expand and Shrink.
+  Page* last_page_;
+
+  // 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);
+
+  // Returns the top page specified by an allocation info structure.
+  static Page* TopPageOf(AllocationInfo alloc_info) {
+    return Page::FromAllocationTop(alloc_info.limit);
+  }
+
+  // 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);
+
+  // Generic fast case allocation function that tries linear allocation in
+  // the top page of 'alloc_info'.  Returns NULL on failure.
+  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.
+  virtual HeapObject* SlowAllocateRaw(int size_in_bytes) = 0;
+
+  // Slow path of MCAllocateRaw.
+  HeapObject* SlowMCAllocateRaw(int size_in_bytes);
+
+#ifdef DEBUG
+  void DoPrintRSet(const char* space_name);
+#endif
+ private:
+  // Returns the page of the allocation pointer.
+  Page* AllocationTopPage() { return TopPageOf(allocation_info_); }
+
+  // Returns a pointer to the page of the relocation pointer.
+  Page* MCRelocationTopPage() { return TopPageOf(mc_forwarding_info_); }
+
+#ifdef DEBUG
+  // Returns the number of total pages in this space.
+  int CountTotalPages();
+#endif
+
+  friend class PageIterator;
+};
+
+
+#if defined(DEBUG) || defined(ENABLE_LOGGING_AND_PROFILING)
+class NumberAndSizeInfo BASE_EMBEDDED {
+ public:
+  NumberAndSizeInfo() : number_(0), bytes_(0) {}
+
+  int number() const { return number_; }
+  void increment_number(int num) { number_ += num; }
+
+  int bytes() const { return bytes_; }
+  void increment_bytes(int size) { bytes_ += size; }
+
+  void clear() {
+    number_ = 0;
+    bytes_ = 0;
+  }
+
+ private:
+  int number_;
+  int bytes_;
+};
+
+
+// HistogramInfo class for recording a single "bar" of a histogram.  This
+// class is used for collecting statistics to print to stdout (when compiled
+// with DEBUG) or to the log file (when compiled with
+// ENABLE_LOGGING_AND_PROFILING).
+class HistogramInfo: public NumberAndSizeInfo {
+ public:
+  HistogramInfo() : NumberAndSizeInfo() {}
+
+  const char* name() { return name_; }
+  void set_name(const char* name) { name_ = name; }
+
+ private:
+  const char* name_;
+};
+#endif
+
+
+// -----------------------------------------------------------------------------
+// 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.
+
+class SemiSpace : public Space {
+ public:
+  // Constructor.
+  SemiSpace() :Space(NEW_SPACE, NOT_EXECUTABLE) {
+    start_ = NULL;
+    age_mark_ = NULL;
+  }
+
+  // Sets up the semispace using the given chunk.
+  bool Setup(Address start, int initial_capacity, int maximum_capacity);
+
+  // Tear down the space.  Heap memory was not allocated by the space, so it
+  // is not deallocated here.
+  void TearDown();
+
+  // True if the space has been set up but not torn down.
+  bool HasBeenSetup() { return start_ != NULL; }
+
+  // Grow the size of the semispace by committing extra virtual memory.
+  // Assumes that the caller has checked that the semispace has not reached
+  // its maximum capacity (and thus there is space available in the reserved
+  // address range to grow).
+  bool Grow();
+
+  // Grow the semispace to the new capacity.  The new capacity
+  // requested must be larger than the current capacity.
+  bool GrowTo(int new_capacity);
+
+  // Shrinks the semispace to the new capacity.  The new capacity
+  // requested must be more than the amount of used memory in the
+  // semispace and less than the current capacity.
+  bool ShrinkTo(int new_capacity);
+
+  // Returns the start address of the space.
+  Address low() { return start_; }
+  // Returns one past the end address of the space.
+  Address high() { return low() + capacity_; }
+
+  // Age mark accessors.
+  Address age_mark() { return age_mark_; }
+  void set_age_mark(Address mark) { age_mark_ = mark; }
+
+  // True if the address is in the address range of this semispace (not
+  // necessarily below the allocation pointer).
+  bool Contains(Address a) {
+    return (reinterpret_cast<uintptr_t>(a) & address_mask_)
+           == reinterpret_cast<uintptr_t>(start_);
+  }
+
+  // True if the object is a heap object in the address range of this
+  // semispace (not necessarily below the allocation pointer).
+  bool Contains(Object* o) {
+    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 addr - low(); }
+
+  // If we don't have this here then SemiSpace will be abstract.  However
+  // it should never be called.
+  virtual int Size() {
+    UNREACHABLE();
+    return 0;
+  }
+
+  bool is_committed() { return committed_; }
+  bool Commit();
+  bool Uncommit();
+
+#ifdef DEBUG
+  virtual void Print();
+  virtual void Verify();
+#endif
+
+  // Returns the current capacity of the semi space.
+  int Capacity() { return capacity_; }
+
+  // Returns the maximum capacity of the semi space.
+  int MaximumCapacity() { return maximum_capacity_; }
+
+  // Returns the initial capacity of the semi space.
+  int InitialCapacity() { return initial_capacity_; }
+
+ private:
+  // The current and maximum capacity of the space.
+  int capacity_;
+  int maximum_capacity_;
+  int initial_capacity_;
+
+  // The start address of the space.
+  Address start_;
+  // Used to govern object promotion during mark-compact collection.
+  Address age_mark_;
+
+  // Masks and comparison values to test for containment in this semispace.
+  uintptr_t address_mask_;
+  uintptr_t object_mask_;
+  uintptr_t object_expected_;
+
+  bool committed_;
+
+ public:
+  TRACK_MEMORY("SemiSpace")
+};
+
+
+// A SemiSpaceIterator is an ObjectIterator that iterates over the active
+// semispace of the heap's new space.  It iterates over the objects in the
+// semispace from a given start address (defaulting to the bottom of the
+// semispace) to the top of the semispace.  New objects allocated after the
+// iterator is created are not iterated.
+class SemiSpaceIterator : public ObjectIterator {
+ public:
+  // 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().
+  explicit SemiSpaceIterator(NewSpace* space);
+  SemiSpaceIterator(NewSpace* space, HeapObjectCallback size_func);
+  SemiSpaceIterator(NewSpace* space, Address start);
+
+  bool has_next() {return current_ < limit_; }
+
+  HeapObject* next() {
+    ASSERT(has_next());
+
+    HeapObject* object = HeapObject::FromAddress(current_);
+    int size = (size_func_ == NULL) ? object->Size() : size_func_(object);
+
+    current_ += size;
+    return object;
+  }
+
+  // Implementation of the ObjectIterator functions.
+  virtual bool has_next_object() { return has_next(); }
+  virtual HeapObject* next_object() { return next(); }
+
+ private:
+  void Initialize(NewSpace* space, Address start, Address end,
+                  HeapObjectCallback size_func);
+
+  // The semispace.
+  SemiSpace* space_;
+  // The current iteration point.
+  Address current_;
+  // The end of iteration.
+  Address limit_;
+  // The callback function.
+  HeapObjectCallback size_func_;
+};
+
+
+// -----------------------------------------------------------------------------
+// The young generation space.
+//
+// The new space consists of a contiguous pair of semispaces.  It simply
+// forwards most functions to the appropriate semispace.
+
+class NewSpace : public Space {
+ public:
+  // Constructor.
+  NewSpace() : Space(NEW_SPACE, NOT_EXECUTABLE) {}
+
+  // Sets up the new space using the given chunk.
+  bool Setup(Address start, int size);
+
+  // Tears down the space.  Heap memory was not allocated by the space, so it
+  // is not deallocated here.
+  void TearDown();
+
+  // True if the space has been set up but not torn down.
+  bool HasBeenSetup() {
+    return to_space_.HasBeenSetup() && from_space_.HasBeenSetup();
+  }
+
+  // Flip the pair of spaces.
+  void Flip();
+
+  // Grow the capacity of the semispaces.  Assumes that they are not at
+  // their maximum capacity.
+  void Grow();
+
+  // Shrink the capacity of the semispaces.
+  void Shrink();
+
+  // True if the address or object lies in the address range of either
+  // semispace (not necessarily below the allocation pointer).
+  bool Contains(Address a) {
+    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_;
+  }
+
+  // Return the allocated bytes in the active semispace.
+  virtual int Size() { return top() - bottom(); }
+  // Return the current capacity of a semispace.
+  int Capacity() {
+    ASSERT(to_space_.Capacity() == from_space_.Capacity());
+    return to_space_.Capacity();
+  }
+  // Return the available bytes without growing in the active semispace.
+  int Available() { return Capacity() - Size(); }
+
+  // Return the maximum capacity of a semispace.
+  int MaximumCapacity() {
+    ASSERT(to_space_.MaximumCapacity() == from_space_.MaximumCapacity());
+    return to_space_.MaximumCapacity();
+  }
+
+  // Returns the initial capacity of a semispace.
+  int InitialCapacity() {
+    ASSERT(to_space_.InitialCapacity() == from_space_.InitialCapacity());
+    return to_space_.InitialCapacity();
+  }
+
+  // Return the address of the allocation pointer in the active semispace.
+  Address top() { return allocation_info_.top; }
+  // Return the address of the first object in the active semispace.
+  Address bottom() { return to_space_.low(); }
+
+  // Get the age mark of the inactive semispace.
+  Address age_mark() { return from_space_.age_mark(); }
+  // Set the age mark in the active semispace.
+  void set_age_mark(Address mark) { to_space_.set_age_mark(mark); }
+
+  // The start address of the space and a bit mask. Anding an address in the
+  // new space with the mask will result in the start address.
+  Address start() { return start_; }
+  uintptr_t mask() { return address_mask_; }
+
+  // The allocation top and limit addresses.
+  Address* allocation_top_address() { return &allocation_info_.top; }
+  Address* allocation_limit_address() { return &allocation_info_.limit; }
+
+  Object* AllocateRaw(int size_in_bytes) {
+    return AllocateRawInternal(size_in_bytes, &allocation_info_);
+  }
+
+  // Allocate the requested number of bytes for relocation during mark-compact
+  // collection.
+  Object* 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(); }
+
+  // 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(); }
+
+  // Offsets from the beginning of the semispaces.
+  int ToSpaceOffsetForAddress(Address a) {
+    return to_space_.SpaceOffsetForAddress(a);
+  }
+  int FromSpaceOffsetForAddress(Address a) {
+    return from_space_.SpaceOffsetForAddress(a);
+  }
+
+  // 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); }
+
+  bool ToSpaceContains(Address a) { return to_space_.Contains(a); }
+  bool FromSpaceContains(Address a) { return from_space_.Contains(a); }
+
+#ifdef ENABLE_HEAP_PROTECTION
+  // Protect/unprotect the space by marking it read-only/writable.
+  virtual void Protect();
+  virtual void Unprotect();
+#endif
+
+#ifdef DEBUG
+  // Verify the active semispace.
+  virtual void Verify();
+  // Print the active semispace.
+  virtual void Print() { to_space_.Print(); }
+#endif
+
+#if defined(DEBUG) || defined(ENABLE_LOGGING_AND_PROFILING)
+  // Iterates the active semispace to collect statistics.
+  void CollectStatistics();
+  // Reports previously collected statistics of the active semispace.
+  void ReportStatistics();
+  // Clears previously collected statistics.
+  void ClearHistograms();
+
+  // Record the allocation or promotion of a heap object.  Note that we don't
+  // record every single allocation, but only those that happen in the
+  // to space during a scavenge GC.
+  void RecordAllocation(HeapObject* obj);
+  void RecordPromotion(HeapObject* obj);
+#endif
+
+  // Return whether the operation succeded.
+  bool CommitFromSpaceIfNeeded() {
+    if (from_space_.is_committed()) return true;
+    return from_space_.Commit();
+  }
+
+  bool UncommitFromSpace() {
+    if (!from_space_.is_committed()) return true;
+    return from_space_.Uncommit();
+  }
+
+ private:
+  // The semispaces.
+  SemiSpace to_space_;
+  SemiSpace from_space_;
+
+  // Start address and bit mask for containment testing.
+  Address start_;
+  uintptr_t address_mask_;
+  uintptr_t object_mask_;
+  uintptr_t object_expected_;
+
+  // Allocation pointer and limit for normal allocation and allocation during
+  // mark-compact collection.
+  AllocationInfo allocation_info_;
+  AllocationInfo mc_forwarding_info_;
+
+#if defined(DEBUG) || defined(ENABLE_LOGGING_AND_PROFILING)
+  HistogramInfo* allocated_histogram_;
+  HistogramInfo* promoted_histogram_;
+#endif
+
+  // Implementation of AllocateRaw and MCAllocateRaw.
+  inline Object* AllocateRawInternal(int size_in_bytes,
+                                     AllocationInfo* alloc_info);
+
+  friend class SemiSpaceIterator;
+
+ public:
+  TRACK_MEMORY("NewSpace")
+};
+
+
+// -----------------------------------------------------------------------------
+// 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));
+  }
+
+  // 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(int size_in_bytes);
+
+  // Accessors for the next field.
+  inline Address next();
+  inline void set_next(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:
+  explicit OldSpaceFreeList(AllocationSpace owner);
+
+  // Clear the free list.
+  void Reset();
+
+  // Return the number of bytes available on the free list.
+  int 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.
+  Object* Allocate(int size_in_bytes, int* wasted_bytes);
+
+ 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;
+
+  // 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(AllocationSpace owner, int object_size);
+
+  // Clear the free list.
+  void Reset();
+
+  // Return the number of bytes available on the free list.
+  int 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.
+  Object* Allocate();
+
+ private:
+  // Available bytes on the free list.
+  int available_;
+
+  // The head of the free list.
+  Address head_;
+
+  // 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 {
+ public:
+  // Creates an old space object with a given maximum capacity.
+  // The constructor does not allocate pages from OS.
+  explicit OldSpace(int max_capacity,
+                    AllocationSpace id,
+                    Executability executable)
+      : PagedSpace(max_capacity, id, executable), free_list_(id) {
+    page_extra_ = 0;
+  }
+
+  // The bytes available on the free list (ie, not above the linear allocation
+  // pointer).
+  int AvailableFree() { return free_list_.available(); }
+
+  // The top of allocation in a page in this space. Undefined if page is unused.
+  virtual Address PageAllocationTop(Page* page) {
+    return page == TopPageOf(allocation_info_) ? top() : 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.
+  void Free(Address start, int size_in_bytes) {
+    int wasted_bytes = free_list_.Free(start, size_in_bytes);
+    accounting_stats_.DeallocateBytes(size_in_bytes);
+    accounting_stats_.WasteBytes(wasted_bytes);
+  }
+
+  // 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();
+
+#ifdef DEBUG
+  // Reports statistics for the space
+  void ReportStatistics();
+  // Dump the remembered sets in the space to stdout.
+  void PrintRSet();
+#endif
+
+ protected:
+  // Virtual function in the superclass.  Slow path of AllocateRaw.
+  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")
+};
+
+
+// -----------------------------------------------------------------------------
+// Old space for objects of a fixed size
+
+class FixedSpace : public PagedSpace {
+ public:
+  FixedSpace(int max_capacity,
+             AllocationSpace id,
+             int object_size_in_bytes,
+             const char* name)
+      : PagedSpace(max_capacity, id, NOT_EXECUTABLE),
+        object_size_in_bytes_(object_size_in_bytes),
+        name_(name),
+        free_list_(id, object_size_in_bytes) {
+    page_extra_ = Page::kObjectAreaSize % object_size_in_bytes;
+  }
+
+  // The top of allocation in a page in this space. Undefined if page is unused.
+  virtual Address PageAllocationTop(Page* page) {
+    return page == TopPageOf(allocation_info_) ? top()
+        : page->ObjectAreaEnd() - page_extra_;
+  }
+
+  int object_size_in_bytes() { return object_size_in_bytes_; }
+
+  // Give a fixed sized block of memory to the space's free list.
+  void Free(Address start) {
+    free_list_.Free(start);
+    accounting_stats_.DeallocateBytes(object_size_in_bytes_);
+  }
+
+  // Prepares for a mark-compact GC.
+  virtual void PrepareForMarkCompact(bool will_compact);
+
+  // Updates the allocation pointer to the relocation top after a mark-compact
+  // collection.
+  virtual void MCCommitRelocationInfo();
+
+#ifdef DEBUG
+  // Reports statistic info of the space
+  void ReportStatistics();
+
+  // Dump the remembered sets in the space to stdout.
+  void PrintRSet();
+#endif
+
+ protected:
+  // Virtual function in the superclass.  Slow path of AllocateRaw.
+  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 size of objects in this space.
+  int object_size_in_bytes_;
+
+  // The name of this space.
+  const char* name_;
+
+  // The space's free list.
+  FixedSizeFreeList free_list_;
+};
+
+
+// -----------------------------------------------------------------------------
+// Old space for all map objects
+
+class MapSpace : public FixedSpace {
+ public:
+  // Creates a map space object with a maximum capacity.
+  MapSpace(int max_capacity, AllocationSpace id)
+      : FixedSpace(max_capacity, id, Map::kSize, "map") {}
+
+  // 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]; }
+
+  // Constants.
+  static const int kMaxMapPageIndex = (1 << MapWord::kMapPageIndexBits) - 1;
+
+ protected:
+#ifdef DEBUG
+  virtual void VerifyObject(HeapObject* obj);
+#endif
+
+ private:
+  // An array of page start address in a map space.
+  Address page_addresses_[kMaxMapPageIndex + 1];
+
+ public:
+  TRACK_MEMORY("MapSpace")
+};
+
+
+// -----------------------------------------------------------------------------
+// Old space for all global object property cell objects
+
+class CellSpace : public FixedSpace {
+ public:
+  // Creates a property cell space object with a maximum capacity.
+  CellSpace(int max_capacity, AllocationSpace id)
+      : FixedSpace(max_capacity, id, JSGlobalPropertyCell::kSize, "cell") {}
+
+ protected:
+#ifdef DEBUG
+  virtual void VerifyObject(HeapObject* obj);
+#endif
+
+ public:
+  TRACK_MEMORY("CellSpace")
+};
+
+
+// -----------------------------------------------------------------------------
+// Large objects ( > Page::kMaxHeapObjectSize ) are allocated and managed by
+// the large object space. A large object is allocated from OS heap with
+// extra padding bytes (Page::kPageSize + Page::kObjectStartOffset).
+// 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 and possibly extra remembered set words) bytes after the object
+  // area start of that page. The allocated chunk size is set in the output
+  // parameter chunk_size.
+  static LargeObjectChunk* New(int size_in_bytes,
+                               size_t* chunk_size,
+                               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); }
+
+  // Accessors for the fields of the chunk.
+  LargeObjectChunk* next() { return next_; }
+  void set_next(LargeObjectChunk* chunk) { next_ = chunk; }
+
+  size_t size() { return size_; }
+  void set_size(size_t size_in_bytes) { size_ = size_in_bytes; }
+
+  // Returns the object in this chunk.
+  inline HeapObject* GetObject();
+
+  // Given a requested size (including any extra remembered set words),
+  // 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 (not
+  // including any extra remembered set words).  Used by
+  // LargeObjectSpace::Available.  Note that this can overestimate the size
+  // of object that will fit in a chunk---if the object requires extra
+  // remembered set words (eg, for large fixed arrays), the actual object
+  // size for the chunk will be smaller than reported by this function.
+  static int ObjectSizeFor(int 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 size of this chunk.
+  size_t size_;
+
+ public:
+  TRACK_MEMORY("LargeObjectChunk")
+};
+
+
+class LargeObjectSpace : public Space {
+ public:
+  explicit LargeObjectSpace(AllocationSpace id);
+  virtual ~LargeObjectSpace() {}
+
+  // Initializes internal data structures.
+  bool Setup();
+
+  // Releases internal resources, frees objects in this space.
+  void TearDown();
+
+  // Allocates a (non-FixedArray, non-Code) large object.
+  Object* AllocateRaw(int size_in_bytes);
+  // Allocates a large Code object.
+  Object* AllocateRawCode(int size_in_bytes);
+  // Allocates a large FixedArray.
+  Object* AllocateRawFixedArray(int size_in_bytes);
+
+  // Available bytes for objects in this space, not including any extra
+  // remembered set words.
+  int Available() {
+    return LargeObjectChunk::ObjectSizeFor(MemoryAllocator::Available());
+  }
+
+  virtual int Size() {
+    return size_;
+  }
+
+  int PageCount() {
+    return page_count_;
+  }
+
+  // Finds an object for a given address, returns Failure::Exception()
+  // if it is not found. The function iterates through all objects in this
+  // space, may be slow.
+  Object* FindObject(Address a);
+
+  // Clears remembered sets.
+  void ClearRSet();
+
+  // Iterates objects whose remembered set bits are set.
+  void IterateRSet(ObjectSlotCallback func);
+
+  // Frees unmarked objects.
+  void FreeUnmarkedObjects();
+
+  // Checks whether a heap object is in this space; O(1).
+  bool Contains(HeapObject* obj);
+
+  // Checks whether the space is empty.
+  bool IsEmpty() { return first_chunk_ == NULL; }
+
+#ifdef ENABLE_HEAP_PROTECTION
+  // Protect/unprotect the space by marking it read-only/writable.
+  void Protect();
+  void Unprotect();
+#endif
+
+#ifdef DEBUG
+  virtual void Verify();
+  virtual void Print();
+  void ReportStatistics();
+  void CollectCodeStatistics();
+  // Dump the remembered sets in the space to stdout.
+  void PrintRSet();
+#endif
+  // Checks whether an address is in the object area in this space.  It
+  // iterates all objects in the space. May be slow.
+  bool SlowContains(Address addr) { return !FindObject(addr)->IsFailure(); }
+
+ private:
+  // The head of the linked list of large object chunks.
+  LargeObjectChunk* first_chunk_;
+  int size_;  // allocated bytes
+  int page_count_;  // number of chunks
+
+
+  // Shared implementation of AllocateRaw, AllocateRawCode and
+  // AllocateRawFixedArray.
+  Object* AllocateRawInternal(int requested_size,
+                              int object_size,
+                              Executability executable);
+
+  // Returns the number of extra bytes (rounded up to the nearest full word)
+  // required for extra_object_bytes of extra pointers (in bytes).
+  static inline int ExtraRSetBytesFor(int extra_object_bytes);
+
+  friend class LargeObjectIterator;
+
+ public:
+  TRACK_MEMORY("LargeObjectSpace")
+};
+
+
+class LargeObjectIterator: public ObjectIterator {
+ public:
+  explicit LargeObjectIterator(LargeObjectSpace* space);
+  LargeObjectIterator(LargeObjectSpace* space, HeapObjectCallback size_func);
+
+  bool has_next() { return current_ != NULL; }
+  HeapObject* next();
+
+  // implementation of ObjectIterator.
+  virtual bool has_next_object() { return has_next(); }
+  virtual HeapObject* next_object() { return next(); }
+
+ private:
+  LargeObjectChunk* current_;
+  HeapObjectCallback size_func_;
+};
+
+
+} }  // namespace v8::internal
+
+#endif  // V8_SPACES_H_