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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_SPACES_H_
#define V8_SPACES_H_
#include "src/allocation.h"
#include "src/base/atomicops.h"
#include "src/hashmap.h"
#include "src/list.h"
#include "src/log.h"
#include "src/platform/mutex.h"
#include "src/utils.h"
namespace v8 {
namespace internal {
class Isolate;
// -----------------------------------------------------------------------------
// 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 and an 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. Pages in large object space
// may be larger than the page size.
// 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 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 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.
#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::kMaxRegularHeapObjectSize))
#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;
class Space;
class FreeList;
class MemoryChunk;
class MarkBit {
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_;
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_);
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 {
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 {
CellPrinter() : seq_start(0), seq_type(0), seq_length(0) { }
void Print(uint32_t pos, uint32_t cell) {
if (cell == seq_type) {
if (IsSeq(cell)) {
seq_start = pos;
seq_length = 0;
seq_type = cell;
PrintF("%d: ", pos);
void Flush() {
if (seq_length > 0) {
PrintF("%d: %dx%d\n",
seq_type == 0 ? 0 : 1,
seq_length * kBitsPerCell);
seq_length = 0;
static bool IsSeq(uint32_t cell) { return cell == 0 || cell == 0xFFFFFFFF; }
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]);
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 accommodate
// any heap object.
class MemoryChunk {
// 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(Heap* heap, Address addr);
Address address() { return reinterpret_cast<Address>(this); }
bool is_valid() { return address() != NULL; }
MemoryChunk* next_chunk() const {
return reinterpret_cast<MemoryChunk*>(base::Acquire_Load(&next_chunk_));
MemoryChunk* prev_chunk() const {
return reinterpret_cast<MemoryChunk*>(base::Acquire_Load(&prev_chunk_));
void set_next_chunk(MemoryChunk* next) {
base::Release_Store(&next_chunk_, reinterpret_cast<base::AtomicWord>(next));
void set_prev_chunk(MemoryChunk* prev) {
base::Release_Store(&prev_chunk_, reinterpret_cast<base::AtomicWord>(prev));
Space* owner() const {
if ((reinterpret_cast<intptr_t>(owner_) & kFailureTagMask) ==
kFailureTag) {
return reinterpret_cast<Space*>(reinterpret_cast<intptr_t>(owner_) -
} 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) ==
VirtualMemory* reserved_memory() {
return &reservation_;
void InitializeReservedMemory() {
void set_reserved_memory(VirtualMemory* reservation) {
bool scan_on_scavenge() { return IsFlagSet(SCAN_ON_SCAVENGE); }
void initialize_scan_on_scavenge(bool scan) {
if (scan) {
} else {
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;
bool Contains(Address addr) {
return addr >= area_start() && addr < area_end();
// 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 >= area_start() && addr <= area_end();
// Every n write barrier invocations we go to runtime even though
// we could have handled it in generated code. This lets us check
// whether we have hit the limit and should do some more marking.
static const int kWriteBarrierCounterGranularity = 500;
enum MemoryChunkFlags {
IN_FROM_SPACE, // Mutually exclusive with IN_TO_SPACE.
IN_TO_SPACE, // All pages in new space has one of these two set.
// 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.
// Large objects can have a progress bar in their page header. These object
// are scanned in increments and will be kept black while being scanned.
// Even if the mutator writes to them they will be kept black and a white
// to grey transition is performed in the value.
// Last flag, keep at bottom.
static const int kPointersToHereAreInterestingMask =
static const int kPointersFromHereAreInterestingMask =
static const int kEvacuationCandidateMask =
static const int kSkipEvacuationSlotsRecordingMask =
(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) {
} else {
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_; }
// PARALLEL_SWEEPING_DONE - The page state when sweeping is complete or
// sweeping must not be performed on that page.
// PARALLEL_SWEEPING_FINALIZE - A sweeper thread is done sweeping this
// page and will not touch the page memory anymore.
// PARALLEL_SWEEPING_IN_PROGRESS - This page is currently swept by a
// sweeper thread.
// PARALLEL_SWEEPING_PENDING - This page is ready for parallel sweeping.
enum ParallelSweepingState {
ParallelSweepingState parallel_sweeping() {
return static_cast<ParallelSweepingState>(
void set_parallel_sweeping(ParallelSweepingState state) {
base::Release_Store(&parallel_sweeping_, state);
bool TryParallelSweeping() {
return base::Acquire_CompareAndSwap(
&parallel_sweeping_, PARALLEL_SWEEPING_PENDING,
// Manage live byte count (count of bytes known to be live,
// because they are marked black).
void ResetLiveBytes() {
if (FLAG_gc_verbose) {
static_cast<void*>(this), live_byte_count_);
live_byte_count_ = 0;
void IncrementLiveBytes(int by) {
if (FLAG_gc_verbose) {
static_cast<void*>(this), live_byte_count_,
((by < 0) ? '-' : '+'), ((by < 0) ? -by : by),
live_byte_count_ + by);
live_byte_count_ += by;
ASSERT_LE(static_cast<unsigned>(live_byte_count_), size_);
int LiveBytes() {
ASSERT(static_cast<unsigned>(live_byte_count_) <= size_);
return live_byte_count_;
int write_barrier_counter() {
return static_cast<int>(write_barrier_counter_);
void set_write_barrier_counter(int counter) {
write_barrier_counter_ = counter;
int progress_bar() {
return progress_bar_;
void set_progress_bar(int progress_bar) {
progress_bar_ = progress_bar;
void ResetProgressBar() {
if (IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
bool IsLeftOfProgressBar(Object** slot) {
Address slot_address = reinterpret_cast<Address>(slot);
ASSERT(slot_address > this->address());
return (slot_address - (this->address() + kObjectStartOffset)) <
static void IncrementLiveBytesFromGC(Address address, int by) {
static void IncrementLiveBytesFromMutator(Address address, int by);
static const intptr_t kAlignment =
(static_cast<uintptr_t>(1) << kPageSizeBits);
static const intptr_t kAlignmentMask = kAlignment - 1;
static const intptr_t kSizeOffset = 0;
static const intptr_t kLiveBytesOffset =
kSizeOffset + kPointerSize + kPointerSize + kPointerSize +
kPointerSize + kPointerSize +
kPointerSize + kPointerSize + kPointerSize + kIntSize;
static const size_t kSlotsBufferOffset = kLiveBytesOffset + kIntSize;
static const size_t kWriteBarrierCounterOffset =
kSlotsBufferOffset + kPointerSize + kPointerSize;
static const size_t kHeaderSize = kWriteBarrierCounterOffset + kPointerSize +
kIntSize + kIntSize + kPointerSize +
5 * kPointerSize +
kPointerSize + kPointerSize;
static const int kBodyOffset =
CODE_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_; }
void set_size(size_t size) {
size_ = size;
void SetArea(Address area_start, Address area_end) {
area_start_ = area_start;
area_end_ = area_end;
Executability executable() {
bool ContainsOnlyData() {
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;
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);
void ClearEvacuationCandidate() {
ASSERT(slots_buffer_ == NULL);
Address area_start() { return area_start_; }
Address area_end() { return area_end_; }
int area_size() {
return static_cast<int>(area_end() - area_start());
bool CommitArea(size_t requested);
// Approximate amount of physical memory committed for this chunk.
size_t CommittedPhysicalMemory() {
return high_water_mark_;
static inline void UpdateHighWaterMark(Address mark);
size_t size_;
intptr_t flags_;
// Start and end of allocatable memory on this chunk.
Address area_start_;
Address area_end_;
// 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_;
intptr_t write_barrier_counter_;
// Used by the incremental marker to keep track of the scanning progress in
// large objects that have a progress bar and are scanned in increments.
int progress_bar_;
// Assuming the initial allocation on a page is sequential,
// count highest number of bytes ever allocated on the page.
int high_water_mark_;
base::AtomicWord parallel_sweeping_;
// PagedSpace free-list statistics.
intptr_t available_in_small_free_list_;
intptr_t available_in_medium_free_list_;
intptr_t available_in_large_free_list_;
intptr_t available_in_huge_free_list_;
intptr_t non_available_small_blocks_;
static MemoryChunk* Initialize(Heap* heap,
Address base,
size_t size,
Address area_start,
Address area_end,
Executability executable,
Space* owner);
// next_chunk_ holds a pointer of type MemoryChunk
base::AtomicWord next_chunk_;
// prev_chunk_ holds a pointer of type MemoryChunk
base::AtomicWord prev_chunk_;
friend class MemoryAllocator;
STATIC_ASSERT(sizeof(MemoryChunk) <= MemoryChunk::kHeaderSize);
// -----------------------------------------------------------------------------
// A page is a memory chunk of a size 1MB. Large object pages may be larger.
// 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 MemoryChunk {
// Returns the page containing a given address. The address ranges
// from [page_addr .. page_addr + kPageSize[
// 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);
// 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);
return p;
// 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);
// Checks whether an address is page aligned.
static bool IsAlignedToPageSize(Address a) {
return 0 == (OffsetFrom(a) & kPageAlignmentMask);
// Returns the offset of a given address to this page.
INLINE(int Offset(Address a)) {
int offset = static_cast<int>(a - address());
return offset;
// Returns the address for a given offset to the this page.
Address OffsetToAddress(int offset) {
return address() + offset;
// ---------------------------------------------------------------------
// Page size in bytes. This must be a multiple of the OS page size.
static const int kPageSize = 1 << kPageSizeBits;
// Maximum object size that fits in a page. Objects larger than that size
// are allocated in large object space and are never moved in memory. This
// also applies to new space allocation, since objects are never migrated
// from new space to large object space. Takes double alignment into account.
static const int kMaxRegularHeapObjectSize = kPageSize - kObjectStartOffset;
// Page size mask.
static const intptr_t kPageAlignmentMask = (1 << kPageSizeBits) - 1;
inline void ClearGCFields();
static inline Page* Initialize(Heap* heap,
MemoryChunk* chunk,
Executability executable,
PagedSpace* owner);
void InitializeAsAnchor(PagedSpace* owner);
bool WasSweptPrecisely() { return IsFlagSet(WAS_SWEPT_PRECISELY); }
bool WasSweptConservatively() { return IsFlagSet(WAS_SWEPT_CONSERVATIVELY); }
bool WasSwept() { return WasSweptPrecisely() || WasSweptConservatively(); }
void MarkSweptPrecisely() { SetFlag(WAS_SWEPT_PRECISELY); }
void MarkSweptConservatively() { SetFlag(WAS_SWEPT_CONSERVATIVELY); }
void ClearSweptPrecisely() { ClearFlag(WAS_SWEPT_PRECISELY); }
void ClearSweptConservatively() { ClearFlag(WAS_SWEPT_CONSERVATIVELY); }
void ResetFreeListStatistics();
type name() { return name##_; } \
void set_##name(type name) { name##_ = name; } \
void add_##name(type name) { name##_ += name; }
FRAGMENTATION_STATS_ACCESSORS(intptr_t, non_available_small_blocks)
FRAGMENTATION_STATS_ACCESSORS(intptr_t, available_in_small_free_list)
FRAGMENTATION_STATS_ACCESSORS(intptr_t, available_in_medium_free_list)
FRAGMENTATION_STATS_ACCESSORS(intptr_t, available_in_large_free_list)
FRAGMENTATION_STATS_ACCESSORS(intptr_t, available_in_huge_free_list)
#ifdef DEBUG
void Print();
#endif // DEBUG
friend class MemoryAllocator;
STATIC_ASSERT(sizeof(Page) <= MemoryChunk::kHeaderSize);
class LargePage : public MemoryChunk {
HeapObject* GetObject() {
return HeapObject::FromAddress(area_start());
inline LargePage* next_page() const {
return static_cast<LargePage*>(next_chunk());
inline void set_next_page(LargePage* page) {
static inline LargePage* Initialize(Heap* heap, MemoryChunk* chunk);
friend class MemoryAllocator;
STATIC_ASSERT(sizeof(LargePage) <= MemoryChunk::kHeaderSize);
// ----------------------------------------------------------------------------
// Space is the abstract superclass for all allocation spaces.
class Space : public Malloced {
Space(Heap* heap, AllocationSpace id, Executability executable)
: heap_(heap), id_(id), executable_(executable) {}
virtual ~Space() {}
Heap* heap() const { return heap_; }
// Does the space need executable memory?
Executability executable() { return executable_; }
// Identity used in error reporting.
AllocationSpace identity() { return id_; }
// Returns allocated size.
virtual intptr_t Size() = 0;
// Returns size of objects. Can differ from the allocated size
// (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;
Heap* heap_;
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 {
explicit CodeRange(Isolate* isolate);
~CodeRange() { TearDown(); }
// 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.
bool SetUp(size_t requested_size);
// Frees the range of virtual memory, and frees the data structures used to
// manage it.
void TearDown();
bool valid() { return code_range_ != NULL; }
Address start() {
return static_cast<Address>(code_range_->address());
bool contains(Address address) {
if (!valid()) 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.
MUST_USE_RESULT Address AllocateRawMemory(const size_t requested_size,
const size_t commit_size,
size_t* allocated);
bool CommitRawMemory(Address start, size_t length);
bool UncommitRawMemory(Address start, size_t length);
void FreeRawMemory(Address buf, size_t length);
Isolate* isolate_;
// The reserved range of virtual memory that all code objects are put in.
VirtualMemory* code_range_;
// Plain old data class, just a struct plus a constructor.
class FreeBlock {
FreeBlock(Address start_arg, size_t 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) {
ASSERT(IsAddressAligned(start, MemoryChunk::kAlignment));
ASSERT(size >= static_cast<size_t>(Page::kPageSize));
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.
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.
List<FreeBlock> allocation_list_;
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, returns false.
bool GetNextAllocationBlock(size_t requested);
// Compares the start addresses of two free blocks.
static int CompareFreeBlockAddress(const FreeBlock* left,
const FreeBlock* right);
class SkipList {
SkipList() {
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();
list->AddObject(addr, size);
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 allocated and deallocates pages for the paged heap spaces and large
// pages for large object space.
// Each space has to manage it's own pages.
class MemoryAllocator {
explicit MemoryAllocator(Isolate* isolate);
// Initializes its internal bookkeeping structures.
// Max capacity of the total space and executable memory limit.
bool SetUp(intptr_t max_capacity, intptr_t capacity_executable);
void TearDown();
Page* AllocatePage(
intptr_t size, PagedSpace* owner, Executability executable);
LargePage* AllocateLargePage(
intptr_t object_size, Space* owner, Executability executable);
void Free(MemoryChunk* chunk);
// Returns the maximum available bytes of heaps.
intptr_t Available() { return capacity_ < size_ ? 0 : capacity_ - size_; }
// Returns allocated spaces in bytes.
intptr_t Size() { return size_; }
// Returns the maximum available executable bytes of heaps.
intptr_t AvailableExecutable() {
if (capacity_executable_ < size_executable_) return 0;
return capacity_executable_ - size_executable_;
// Returns allocated executable spaces in bytes.
intptr_t SizeExecutable() { return size_executable_; }
// Returns maximum available bytes that the old space can have.
intptr_t MaxAvailable() {
return (Available() / Page::kPageSize) * Page::kMaxRegularHeapObjectSize;
// Returns an indication of whether a pointer is in a space that has
// been allocated by this MemoryAllocator.
V8_INLINE bool IsOutsideAllocatedSpace(const void* address) const {
return address < lowest_ever_allocated_ ||
address >= highest_ever_allocated_;
#ifdef DEBUG
// Reports statistic info of the space.
void ReportStatistics();
// Returns a MemoryChunk in which the memory region from commit_area_size to
// reserve_area_size of the chunk area is reserved but not committed, it
// could be committed later by calling MemoryChunk::CommitArea.
MemoryChunk* AllocateChunk(intptr_t reserve_area_size,
intptr_t commit_area_size,
Executability executable,
Space* space);
Address ReserveAlignedMemory(size_t requested,
size_t alignment,
VirtualMemory* controller);
Address AllocateAlignedMemory(size_t reserve_size,
size_t commit_size,
size_t alignment,
Executability executable,
VirtualMemory* controller);
bool CommitMemory(Address addr, size_t size, Executability executable);
void FreeMemory(VirtualMemory* reservation, Executability executable);
void FreeMemory(Address addr, size_t size, Executability executable);
// 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);
// 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);
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);
static int CodePageGuardStartOffset();
static int CodePageGuardSize();
static int CodePageAreaStartOffset();
static int CodePageAreaEndOffset();
static int CodePageAreaSize() {
return CodePageAreaEndOffset() - CodePageAreaStartOffset();
MUST_USE_RESULT bool CommitExecutableMemory(VirtualMemory* vm,
Address start,
size_t commit_size,
size_t reserved_size);
Isolate* isolate_;
// Maximum space size in bytes.
size_t capacity_;
// Maximum subset of capacity_ that can be executable
size_t capacity_executable_;
// Allocated space size in bytes.
size_t size_;
// Allocated executable space size in bytes.
size_t size_executable_;
// We keep the lowest and highest addresses allocated as a quick way
// of determining that pointers are outside the heap. The estimate is
// conservative, i.e. not all addrsses in 'allocated' space are allocated
// to our heap. The range is [lowest, highest[, inclusive on the low end
// and exclusive on the high end.
void* lowest_ever_allocated_;
void* highest_ever_allocated_;
struct MemoryAllocationCallbackRegistration {
MemoryAllocationCallbackRegistration(MemoryAllocationCallback callback,
ObjectSpace space,
AllocationAction action)
: callback(callback), space(space), action(action) {
MemoryAllocationCallback callback;
ObjectSpace space;
AllocationAction action;
// A List of callback that are triggered when memory is allocated or free'd
// 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.
Page* InitializePagesInChunk(int chunk_id, int pages_in_chunk,
PagedSpace* owner);
void UpdateAllocatedSpaceLimits(void* low, void* high) {
lowest_ever_allocated_ = Min(lowest_ever_allocated_, low);
highest_ever_allocated_ = Max(highest_ever_allocated_, high);
// -----------------------------------------------------------------------------
// Interface for heap object iterator to be implemented by all object space
// object iterators.
// NOTE: The space specific object iterators also implements the own next()
// method which is used to avoid using virtual functions
// iterating a specific space.
class ObjectIterator : public Malloced {
virtual ~ObjectIterator() { }
virtual HeapObject* next_object() = 0;
// -----------------------------------------------------------------------------
// Heap object iterator in new/old/map spaces.
// 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.
// 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 {
// 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(Page* page, HeapObjectCallback size_func);
// 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;
virtual HeapObject* next_object() {
return Next();
enum PageMode { kOnePageOnly, kAllPagesInSpace };
Address cur_addr_; // Current iteration point.
Address cur_end_; // End iteration point.
HeapObjectCallback size_func_; // Size function or NULL.
PagedSpace* space_;
PageMode page_mode_;
// Fast (inlined) path of next().
inline HeapObject* FromCurrentPage();
// Slow path of next(), goes into the next page. Returns false if the
// iteration has ended.
bool AdvanceToNextPage();
// Initializes fields.
inline void Initialize(PagedSpace* owner,
Address start,
Address end,
PageMode mode,
HeapObjectCallback size_func);
// -----------------------------------------------------------------------------
// A PageIterator iterates the pages in a paged space.
class PageIterator BASE_EMBEDDED {
explicit inline PageIterator(PagedSpace* space);
inline bool has_next();
inline Page* next();
PagedSpace* space_;
Page* 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.
Page* next_page_;
// -----------------------------------------------------------------------------
// 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 {
AllocationInfo() : top_(NULL), limit_(NULL) {
INLINE(void set_top(Address top)) {
(reinterpret_cast<intptr_t>(top) & HeapObjectTagMask()) == 0);
top_ = top;
INLINE(Address top()) const {
(reinterpret_cast<intptr_t>(top_) & HeapObjectTagMask()) == 0);
return top_;
Address* top_address() {
return &top_;
INLINE(void set_limit(Address limit)) {
SLOW_ASSERT(limit == NULL ||
(reinterpret_cast<intptr_t>(limit) & HeapObjectTagMask()) == 0);
limit_ = limit;
INLINE(Address limit()) const {
SLOW_ASSERT(limit_ == NULL ||
(reinterpret_cast<intptr_t>(limit_) & HeapObjectTagMask()) == 0);
return limit_;
Address* limit_address() {
return &limit_;
#ifdef DEBUG
bool VerifyPagedAllocation() {
return (Page::FromAllocationTop(top_) == Page::FromAllocationTop(limit_))
&& (top_ <= limit_);
// Current allocation top.
Address top_;
// Current allocation limit.
Address limit_;
// An abstraction of the accounting statistics of a page-structured space.
// The 'capacity' of a space is the number of object-area bytes (i.e., 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 (e.g. 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 {
AllocationStats() { Clear(); }
// Zero out all the allocation statistics (i.e., no capacity).
void Clear() {
capacity_ = 0;
max_capacity_ = 0;
size_ = 0;
waste_ = 0;
void ClearSizeWaste() {
size_ = capacity_;
waste_ = 0;
// Reset the allocation statistics (i.e., available = capacity with no
// wasted or allocated bytes).
void Reset() {
size_ = 0;
waste_ = 0;
// Accessors for the allocation statistics.
intptr_t Capacity() { return capacity_; }
intptr_t MaxCapacity() { return max_capacity_; }
intptr_t Size() { return size_; }
intptr_t Waste() { return waste_; }
// 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;
size_ += size_in_bytes;
if (capacity_ > max_capacity_) {
max_capacity_ = capacity_;
ASSERT(size_ >= 0);
// Shrink the space by removing available bytes. Since shrinking is done
// during sweeping, bytes have been marked as being in use (part of the size)
// and are hereby freed.
void ShrinkSpace(int size_in_bytes) {
capacity_ -= size_in_bytes;
size_ -= size_in_bytes;
ASSERT(size_ >= 0);
// Allocate from available bytes (available -> size).
void AllocateBytes(intptr_t 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;
ASSERT(size_ >= 0);
// Waste free bytes (available -> waste).
void WasteBytes(int size_in_bytes) {
size_ -= size_in_bytes;
waste_ += size_in_bytes;
ASSERT(size_ >= 0);
intptr_t capacity_;
intptr_t max_capacity_;
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 {
// 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();
static inline FreeListNode* cast(Object* object) {
return reinterpret_cast<FreeListNode*>(object);
static const int kNextOffset = POINTER_SIZE_ALIGN(FreeSpace::kHeaderSize);
// The free list category holds a pointer to the top element and a pointer to
// the end element of the linked list of free memory blocks.
class FreeListCategory {
FreeListCategory() :
available_(0) {}
intptr_t Concatenate(FreeListCategory* category);
void Reset();
void Free(FreeListNode* node, int size_in_bytes);
FreeListNode* PickNodeFromList(int *node_size);
FreeListNode* PickNodeFromList(int size_in_bytes, int *node_size);
intptr_t EvictFreeListItemsInList(Page* p);
bool ContainsPageFreeListItemsInList(Page* p);
void RepairFreeList(Heap* heap);
FreeListNode* top() const {
return reinterpret_cast<FreeListNode*>(base::NoBarrier_Load(&top_));
void set_top(FreeListNode* top) {
base::NoBarrier_Store(&top_, reinterpret_cast<base::AtomicWord>(top));
FreeListNode** GetEndAddress() { return &end_; }
FreeListNode* end() const { return end_; }
void set_end(FreeListNode* end) { end_ = end; }
int* GetAvailableAddress() { return &available_; }
int available() const { return available_; }
void set_available(int available) { available_ = available; }
Mutex* mutex() { return &mutex_; }
bool IsEmpty() {
return top() == 0;
#ifdef DEBUG
intptr_t SumFreeList();
int FreeListLength();
// top_ points to the top FreeListNode* in the free list category.
base::AtomicWord top_;
FreeListNode* end_;
Mutex mutex_;
// Total available bytes in all blocks of this free list category.
int available_;
// 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 {
explicit FreeList(PagedSpace* owner);
intptr_t Concatenate(FreeList* free_list);
// Clear the free list.
void Reset();
// Return the number of bytes available on the free list.
intptr_t available() {
return small_list_.available() + medium_list_.available() +
large_list_.available() + huge_list_.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,
// i.e., 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);
bool IsEmpty() {
return small_list_.IsEmpty() && medium_list_.IsEmpty() &&
large_list_.IsEmpty() && huge_list_.IsEmpty();
#ifdef DEBUG
void Zap();
intptr_t SumFreeLists();
bool IsVeryLong();
// Used after booting the VM.
void RepairLists(Heap* heap);
intptr_t EvictFreeListItems(Page* p);
bool ContainsPageFreeListItems(Page* p);
FreeListCategory* small_list() { return &small_list_; }
FreeListCategory* medium_list() { return &medium_list_; }
FreeListCategory* large_list() { return &large_list_; }
FreeListCategory* huge_list() { return &huge_list_; }
// The size range of blocks, in bytes.
static const int kMinBlockSize = 3 * kPointerSize;
static const int kMaxBlockSize = Page::kMaxRegularHeapObjectSize;
FreeListNode* FindNodeFor(int size_in_bytes, int* node_size);
PagedSpace* owner_;
Heap* heap_;
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;
FreeListCategory small_list_;
FreeListCategory medium_list_;
FreeListCategory large_list_;
FreeListCategory huge_list_;
class AllocationResult {
// Implicit constructor from Object*.
AllocationResult(Object* object) : object_(object), // NOLINT
retry_space_(INVALID_SPACE) { }
AllocationResult() : object_(NULL),
retry_space_(INVALID_SPACE) { }
static inline AllocationResult Retry(AllocationSpace space = NEW_SPACE) {
return AllocationResult(space);
inline bool IsRetry() { return retry_space_ != INVALID_SPACE; }
template <typename T>
bool To(T** obj) {
if (IsRetry()) return false;
*obj = T::cast(object_);
return true;
Object* ToObjectChecked() {
return object_;
AllocationSpace RetrySpace() {
return retry_space_;
explicit AllocationResult(AllocationSpace space) : object_(NULL),
retry_space_(space) { }
Object* object_;
AllocationSpace retry_space_;
class PagedSpace : public Space {
// Creates a space with a maximum capacity, and an id.
PagedSpace(Heap* heap,
intptr_t 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();
// 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 a Smi 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);
// During boot the free_space_map is created, and afterwards we may need
// to write it into the free list nodes that were already created.
void RepairFreeListsAfterBoot();
// Prepares for a mark-compact GC.
void PrepareForMarkCompact();
// 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(); }
// The maximum amount of memory ever committed for this space.
intptr_t MaximumCommittedMemory() { return accounting_stats_.MaxCapacity(); }
// Approximate amount of physical memory committed for this space.
size_t CommittedPhysicalMemory();
struct SizeStats {
intptr_t Total() {
return small_size_ + medium_size_ + large_size_ + huge_size_;
intptr_t small_size_;
intptr_t medium_size_;
intptr_t large_size_;
intptr_t huge_size_;
void ObtainFreeListStatistics(Page* p, SizeStats* sizes);
void ResetFreeListStatistics();
// 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() {
// Increases the number of available bytes of that space.
void AddToAccountingStats(intptr_t bytes) {
// 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
// concurrent 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(); }
// As size, but the bytes in lazily swept pages are estimated and the bytes
// in the current linear allocation area are not included.
virtual intptr_t SizeOfObjects();
// 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; }
Address limit() { return allocation_info_.limit(); }
// The allocation top address.
Address* allocation_top_address() {
return allocation_info_.top_address();
// The allocation limit address.
Address* allocation_limit_address() {
return allocation_info_.limit_address();
// Allocate the requested number of bytes in the space if possible, return a
// failure object if not.
MUST_USE_RESULT inline AllocationResult AllocateRaw(int size_in_bytes);
// 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;
void ResetFreeList() {
// Set space allocation info.
void SetTopAndLimit(Address top, Address limit) {
ASSERT(top == limit ||
Page::FromAddress(top) == Page::FromAddress(limit - 1));
// Empty space allocation info, returning unused area to free list.
void EmptyAllocationInfo() {
// Mark the old linear allocation area with a free space map so it can be
// skipped when scanning the heap.
int old_linear_size = static_cast<int>(limit() - top());
Free(top(), old_linear_size);
SetTopAndLimit(NULL, NULL);
void Allocate(int bytes) {
void IncreaseCapacity(int size);
// Releases an unused page and shrinks the space.
void ReleasePage(Page* page);
// The dummy page that anchors the linked list of pages.
Page* anchor() { return &anchor_; }
// 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) {}
#ifdef DEBUG
// Print meta info and objects in this space.
virtual void Print();
// Reports statistics for the space
void ReportStatistics();
// Report code object related statistics
void CollectCodeStatistics();
static void ReportCodeStatistics(Isolate* isolate);
static void ResetCodeStatistics(Isolate* isolate);
bool was_swept_conservatively() { return was_swept_conservatively_; }
void set_was_swept_conservatively(bool b) { was_swept_conservatively_ = b; }
// Evacuation candidates are swept by evacuator. Needs to return a valid
// result before _and_ after evacuation has finished.
static bool ShouldBeSweptBySweeperThreads(Page* p) {
return !p->IsEvacuationCandidate() &&
!p->IsFlagSet(Page::RESCAN_ON_EVACUATION) &&
void IncrementUnsweptFreeBytes(intptr_t by) {
unswept_free_bytes_ += by;
void IncreaseUnsweptFreeBytes(Page* p) {
unswept_free_bytes_ += (p->area_size() - p->LiveBytes());
void DecrementUnsweptFreeBytes(intptr_t by) {
unswept_free_bytes_ -= by;
void DecreaseUnsweptFreeBytes(Page* p) {
unswept_free_bytes_ -= (p->area_size() - p->LiveBytes());
void ResetUnsweptFreeBytes() {
unswept_free_bytes_ = 0;
// This function tries to steal size_in_bytes memory from the sweeper threads
// free-lists. If it does not succeed stealing enough memory, it will wait
// for the sweeper threads to finish sweeping.
// It returns true when sweeping is completed and false otherwise.
bool EnsureSweeperProgress(intptr_t size_in_bytes);
void set_end_of_unswept_pages(Page* page) {
end_of_unswept_pages_ = page;
Page* end_of_unswept_pages() {
return end_of_unswept_pages_;
Page* FirstPage() { return anchor_.next_page(); }
Page* LastPage() { return anchor_.prev_page(); }
void EvictEvacuationCandidatesFromFreeLists();
bool CanExpand();
// Returns the number of total pages in this space.
int CountTotalPages();
// Return size of allocatable area on a page in this space.
inline int AreaSize() {
return area_size_;
FreeList* free_list() { return &free_list_; }
int area_size_;
// Maximum capacity of this space.
intptr_t max_capacity_;
intptr_t SizeOfFirstPage();
// Accounting information for this space.
AllocationStats accounting_stats_;
// The dummy page that anchors the double linked list of pages.
Page anchor_;
// The space's free list.
FreeList free_list_;
// Normal allocation information.
AllocationInfo allocation_info_;
bool was_swept_conservatively_;
// The number of free bytes which could be reclaimed by advancing the
// concurrent sweeper threads. This is only an estimation because concurrent
// sweeping is done conservatively.
intptr_t unswept_free_bytes_;
// The sweeper threads iterate over the list of pointer and data space pages
// and sweep these pages concurrently. They will stop sweeping after the
// end_of_unswept_pages_ page.
Page* end_of_unswept_pages_;
// Expands the space by allocating a fixed number of pages. Returns false if
// it cannot allocate requested number of pages from OS, or if the hard heap
// size limit has been hit.
bool Expand();
// Generic fast case allocation function that tries linear allocation at the
// address denoted by top in allocation_info_.
inline HeapObject* AllocateLinearly(int size_in_bytes);
WaitForSweeperThreadsAndRetryAllocation(int size_in_bytes);
// Slow path of AllocateRaw. This function is space-dependent.
MUST_USE_RESULT HeapObject* SlowAllocateRaw(int size_in_bytes);
friend class PageIterator;
friend class MarkCompactCollector;
class NumberAndSizeInfo BASE_EMBEDDED {
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;
int number_;
int bytes_;
// HistogramInfo class for recording a single "bar" of a histogram. This
// class is used for collecting statistics to print to the log file.
class HistogramInfo: public NumberAndSizeInfo {
HistogramInfo() : NumberAndSizeInfo() {}
const char* name() { return name_; }
void set_name(const char* name) { name_ = name; }
const char* name_;
enum SemiSpaceId {
kFromSpace = 0,
kToSpace = 1
class SemiSpace;
class NewSpacePage : public MemoryChunk {
// GC related flags copied from from-space to to-space when
// flipping semispaces.
static const intptr_t kCopyOnFlipFlagsMask =
(1 << MemoryChunk::SCAN_ON_SCAVENGE);
static const int kAreaSize = Page::kMaxRegularHeapObjectSize;
inline NewSpacePage* next_page() const {
return static_cast<NewSpacePage*>(next_chunk());
inline void set_next_page(NewSpacePage* page) {
inline NewSpacePage* prev_page() const {
return static_cast<NewSpacePage*>(prev_chunk());
inline void set_prev_page(NewSpacePage* 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) &
NewSpacePage* page = reinterpret_cast<NewSpacePage*>(page_start);
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);
// Checks if address1 and address2 are on the same new space page.
static inline bool OnSamePage(Address address1, Address address2) {
return NewSpacePage::FromAddress(address1) ==
// Create a NewSpacePage object that is only used as anchor
// for the doubly-linked list of real pages.
explicit NewSpacePage(SemiSpace* 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 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 {
// Constructor.
SemiSpace(Heap* heap, SemiSpaceId semispace)
current_page_(NULL) { }
// Sets up the semispace using the given chunk.
void 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 semispace to the new capacity. The new capacity
// requested must be larger than the current capacity and less than
// the maximum 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 first page of the space.
Address space_start() {
ASSERT(anchor_.next_page() != &anchor_);
return anchor_.next_page()->area_start();
// Returns the start address of the current page of the space.
Address page_low() {
return current_page_->area_start();
// Returns one past the end address of the space.
Address space_end() {
return anchor_.prev_page()->area_end();
// Returns one past the end address of the current page of the space.
Address page_high() {
return current_page_->area_end();
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);
// 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_;
// If we don't have these here then SemiSpace will be abstract. However
// they should never be called.
virtual intptr_t Size() {
return 0;
bool is_committed() { return committed_; }
bool Commit();
bool Uncommit();
NewSpacePage* first_page() { return anchor_.next_page(); }
NewSpacePage* current_page() { return current_page_; }
virtual void Verify();
#ifdef DEBUG
virtual void Print();
// 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);
// Do nothing.
inline static void AssertValidRange(Address from, Address to) {}
// 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_; }
SemiSpaceId id() { return id_; }
static void Swap(SemiSpace* from, SemiSpace* to);
// Returns the maximum amount of memory ever committed by the semi space.
size_t MaximumCommittedMemory() { return maximum_committed_; }
// Approximate amount of physical memory committed for this space.
size_t CommittedPhysicalMemory();
// 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);
// Updates Capacity and MaximumCommitted based on new capacity.
void SetCapacity(int new_capacity);
NewSpacePage* anchor() { return &anchor_; }
// The current and maximum capacity of the space.
int capacity_;
int maximum_capacity_;
int initial_capacity_;
intptr_t maximum_committed_;
// 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_;
SemiSpaceId id_;
NewSpacePage anchor_;
NewSpacePage* current_page_;
friend class SemiSpaceIterator;
friend class NewSpacePageIterator;
// 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 {
// 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() {
if (current_ == limit_) return NULL;
if (NewSpacePage::IsAtEnd(current_)) {
NewSpacePage* page = NewSpacePage::FromLimit(current_);
page = page->next_page();
current_ = page->area_start();
if (current_ == limit_) return NULL;
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 HeapObject* next_object() { return Next(); }
void Initialize(Address start,
Address end,
HeapObjectCallback size_func);
// The current iteration point.
Address current_;
// The end of iteration.
Address limit_;
// The callback function.
HeapObjectCallback size_func_;
// -----------------------------------------------------------------------------
// A PageIterator iterates the pages in a semi-space.
class NewSpacePageIterator BASE_EMBEDDED {
// 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();
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
// forwards most functions to the appropriate semispace.
class NewSpace : public Space {
// Constructor.
explicit NewSpace(Heap* heap)
to_space_(heap, kToSpace),
from_space_(heap, kFromSpace),
inline_allocation_limit_step_(0) {}
// Sets up the new space using the given chunk.
bool SetUp(int reserved_semispace_size_, int max_semi_space_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) {
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 pages_used_ * NewSpacePage::kAreaSize +
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() {
SLOW_ASSERT(to_space_.Capacity() == from_space_.Capacity());
return (to_space_.Capacity() / Page::kPageSize) * NewSpacePage::kAreaSize;
// Return the current capacity of a semispace.
intptr_t Capacity() {
ASSERT(to_space_.Capacity() == from_space_.Capacity());
return to_space_.Capacity();
// Return the total amount of memory committed for new space.
intptr_t CommittedMemory() {
if (from_space_.is_committed()) return 2 * Capacity();
return Capacity();
// Return the total amount of memory committed for new space.
intptr_t MaximumCommittedMemory() {
return to_space_.MaximumCommittedMemory() +
// Approximate amount of physical memory committed for this space.
size_t CommittedPhysicalMemory();
// Return the available bytes without growing.
intptr_t Available() {
return Capacity() - Size();
// Return the maximum capacity of a semispace.
int MaximumCapacity() {
ASSERT(to_space_.MaximumCapacity() == from_space_.MaximumCapacity());
return to_space_.MaximumCapacity();
bool IsAtMaximumCapacity() {
return Capacity() == 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() {
void set_top(Address top) {
// Return the address of the allocation pointer limit in the active semispace.
Address limit() {
return allocation_info_.limit();
// Return the address of the first object in the active semispace.
Address bottom() { return to_space_.space_start(); }
// 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_; }
INLINE(uint32_t AddressToMarkbitIndex(Address 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 address.
Address* allocation_top_address() {
return allocation_info_.top_address();
// The allocation limit address.
Address* allocation_limit_address() {
return allocation_info_.limit_address();
MUST_USE_RESULT INLINE(AllocationResult AllocateRaw(int size_in_bytes));
// Reset the allocation pointer to the beginning of the active semispace.
void ResetAllocationInfo();
void UpdateInlineAllocationLimit(int size_in_bytes);
void LowerInlineAllocationLimit(intptr_t step) {
inline_allocation_limit_step_ = step;
top_on_previous_step_ =;
// 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(); }
// 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);
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).
inline bool ToSpaceContains(Object* o) { return to_space_.Contains(o); }
inline bool FromSpaceContains(Object* o) { return from_space_.Contains(o); }
// 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();
// Verify the active semispace.
virtual void Verify();
#ifdef DEBUG
// Print the active semispace.
virtual void Print() { to_space_.Print(); }
// 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);
// 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();
inline intptr_t inline_allocation_limit_step() {
return inline_allocation_limit_step_;
SemiSpace* active_space() { return &to_space_; }
// 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_;
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_;
// 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_;
MUST_USE_RESULT AllocationResult SlowAllocateRaw(int size_in_bytes);
friend class SemiSpaceIterator;
// -----------------------------------------------------------------------------
// Old object space (excluding map objects)
class OldSpace : public PagedSpace {
// Creates an old space object with a given maximum capacity.
// The constructor does not allocate pages from OS.
OldSpace(Heap* heap,
intptr_t max_capacity,
AllocationSpace id,
Executability executable)
: PagedSpace(heap, max_capacity, id, executable) {
// For contiguous spaces, top should be in the space (or at the end) and limit
// should be the end of the space.
SLOW_ASSERT((space).page_low() <= (info).top() \
&& (info).top() <= (space).page_high() \
&& (info).limit() <= (space).page_high())
// -----------------------------------------------------------------------------
// Old space for all map objects
class MapSpace : public PagedSpace {
// Creates a map space object with a maximum capacity.
MapSpace(Heap* heap, intptr_t max_capacity, AllocationSpace id)
: PagedSpace(heap, max_capacity, id, NOT_EXECUTABLE),
max_map_space_pages_(kMaxMapPageIndex - 1) {
// Given an index, returns the page address.
// TODO(1600): this limit is artifical just to keep code compilable
static const int kMaxMapPageIndex = 1 << 16;
virtual int RoundSizeDownToObjectAlignment(int size) {
if (IsPowerOf2(Map::kSize)) {
return RoundDown(size, Map::kSize);
} else {
return (size / Map::kSize) * Map::kSize;
virtual void VerifyObject(HeapObject* obj);
static const int kMapsPerPage = Page::kMaxRegularHeapObjectSize / Map::kSize;
// Do map space compaction if there is a page gap.
int CompactionThreshold() {
return kMapsPerPage * (max_map_space_pages_ - 1);
const int max_map_space_pages_;
// -----------------------------------------------------------------------------
// Old space for simple property cell objects
class CellSpace : public PagedSpace {
// Creates a property cell space object with a maximum capacity.
CellSpace(Heap* heap, intptr_t max_capacity, AllocationSpace id)
: PagedSpace(heap, max_capacity, id, NOT_EXECUTABLE) {
virtual int RoundSizeDownToObjectAlignment(int size) {
if (IsPowerOf2(Cell::kSize)) {
return RoundDown(size, Cell::kSize);
} else {
return (size / Cell::kSize) * Cell::kSize;
virtual void VerifyObject(HeapObject* obj);
// -----------------------------------------------------------------------------
// Old space for all global object property cell objects
class PropertyCellSpace : public PagedSpace {
// Creates a property cell space object with a maximum capacity.
PropertyCellSpace(Heap* heap, intptr_t max_capacity,
AllocationSpace id)
: PagedSpace(heap, max_capacity, id, NOT_EXECUTABLE) {
virtual int RoundSizeDownToObjectAlignment(int size) {
if (IsPowerOf2(PropertyCell::kSize)) {
return RoundDown(size, PropertyCell::kSize);
} else {
return (size / PropertyCell::kSize) * PropertyCell::kSize;