fastmalloc.cpp

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  if (result != NULL) {
    metadata_system_bytes += bytes;
  }
  return result;
}

template <class T>
class PageHeapAllocator {
 private:
  // How much to allocate from system at a time
  static const size_t kAllocIncrement = 32 << 10;

  // Aligned size of T
  static const size_t kAlignedSize
  = (((sizeof(T) + kAlignment - 1) / kAlignment) * kAlignment);

  // Free area from which to carve new objects
  char* free_area_;
  size_t free_avail_;

  // Linked list of all regions allocated by this allocator
  void* allocated_regions_;

  // Free list of already carved objects
  void* free_list_;

  // Number of allocated but unfreed objects
  int inuse_;

 public:
  void Init() {
    ASSERT(kAlignedSize <= kAllocIncrement);
    inuse_ = 0;
    allocated_regions_ = 0;
    free_area_ = NULL;
    free_avail_ = 0;
    free_list_ = NULL;
  }

  T* New() {
    // Consult free list
    void* result;
    if (free_list_ != NULL) {
      result = free_list_;
      free_list_ = *(reinterpret_cast<void**>(result));
    } else {
      if (free_avail_ < kAlignedSize) {
        // Need more room
        char* new_allocation = reinterpret_cast<char*>(MetaDataAlloc(kAllocIncrement));
        if (!new_allocation)
          CRASH();

        *(void**)new_allocation = allocated_regions_;
        allocated_regions_ = new_allocation;
        free_area_ = new_allocation + kAlignedSize;
        free_avail_ = kAllocIncrement - kAlignedSize;
      }
      result = free_area_;
      free_area_ += kAlignedSize;
      free_avail_ -= kAlignedSize;
    }
    inuse_++;
    return reinterpret_cast<T*>(result);
  }

  void Delete(T* p) {
    *(reinterpret_cast<void**>(p)) = free_list_;
    free_list_ = p;
    inuse_--;
  }

  int inuse() const { return inuse_; }

#if defined(WTF_CHANGES) && PLATFORM(DARWIN)
  template <class Recorder>
  void recordAdministrativeRegions(Recorder& recorder, const RemoteMemoryReader& reader)
  {
      vm_address_t adminAllocation = reinterpret_cast<vm_address_t>(allocated_regions_);
      while (adminAllocation) {
          recorder.recordRegion(adminAllocation, kAllocIncrement);
          adminAllocation = *reader(reinterpret_cast<vm_address_t*>(adminAllocation));
      }
  }
#endif
};

// -------------------------------------------------------------------------
// Span - a contiguous run of pages
// -------------------------------------------------------------------------

// Type that can hold a page number
typedef uintptr_t PageID;

// Type that can hold the length of a run of pages
typedef uintptr_t Length;

static const Length kMaxValidPages = (~static_cast<Length>(0)) >> kPageShift;

// Convert byte size into pages.  This won't overflow, but may return
// an unreasonably large value if bytes is huge enough.
static inline Length pages(size_t bytes) {
  return (bytes >> kPageShift) +
      ((bytes & (kPageSize - 1)) > 0 ? 1 : 0);
}

// Convert a user size into the number of bytes that will actually be
// allocated
static size_t AllocationSize(size_t bytes) {
  if (bytes > kMaxSize) {
    // Large object: we allocate an integral number of pages
    ASSERT(bytes <= (kMaxValidPages << kPageShift));
    return pages(bytes) << kPageShift;
  } else {
    // Small object: find the size class to which it belongs
    return ByteSizeForClass(SizeClass(bytes));
  }
}

// Information kept for a span (a contiguous run of pages).
struct Span {
  PageID        start;          // Starting page number
  Length        length;         // Number of pages in span
  Span*         next;           // Used when in link list
  Span*         prev;           // Used when in link list
  void*         objects;        // Linked list of free objects
  unsigned int  free : 1;       // Is the span free
#ifndef NO_TCMALLOC_SAMPLES
  unsigned int  sample : 1;     // Sampled object?
#endif
  unsigned int  sizeclass : 8;  // Size-class for small objects (or 0)
  unsigned int  refcount : 11;  // Number of non-free objects
  bool decommitted : 1;

#undef SPAN_HISTORY
#ifdef SPAN_HISTORY
  // For debugging, we can keep a log events per span
  int nexthistory;
  char history[64];
  int value[64];
#endif
};

#if TCMALLOC_TRACK_DECOMMITED_SPANS
#define ASSERT_SPAN_COMMITTED(span) ASSERT(!span->decommitted)
#else
#define ASSERT_SPAN_COMMITTED(span)
#endif

#ifdef SPAN_HISTORY
void Event(Span* span, char op, int v = 0) {
  span->history[span->nexthistory] = op;
  span->value[span->nexthistory] = v;
  span->nexthistory++;
  if (span->nexthistory == sizeof(span->history)) span->nexthistory = 0;
}
#else
#define Event(s,o,v) ((void) 0)
#endif

// Allocator/deallocator for spans
static PageHeapAllocator<Span> span_allocator;
static Span* NewSpan(PageID p, Length len) {
  Span* result = span_allocator.New();
  memset(result, 0, sizeof(*result));
  result->start = p;
  result->length = len;
#ifdef SPAN_HISTORY
  result->nexthistory = 0;
#endif
  return result;
}

static inline void DeleteSpan(Span* span) {
#ifndef NDEBUG
  // In debug mode, trash the contents of deleted Spans
  memset(span, 0x3f, sizeof(*span));
#endif
  span_allocator.Delete(span);
}

// -------------------------------------------------------------------------
// Doubly linked list of spans.
// -------------------------------------------------------------------------

static inline void DLL_Init(Span* list) {
  list->next = list;
  list->prev = list;
}

static inline void DLL_Remove(Span* span) {
  span->prev->next = span->next;
  span->next->prev = span->prev;
  span->prev = NULL;
  span->next = NULL;
}

static ALWAYS_INLINE bool DLL_IsEmpty(const Span* list) {
  return list->next == list;
}

static int DLL_Length(const Span* list) {
  int result = 0;
  for (Span* s = list->next; s != list; s = s->next) {
    result++;
  }
  return result;
}

#if 0 /* Not needed at the moment -- causes compiler warnings if not used */
static void DLL_Print(const char* label, const Span* list) {
  MESSAGE("%-10s %p:", label, list);
  for (const Span* s = list->next; s != list; s = s->next) {
    MESSAGE(" <%p,%u,%u>", s, s->start, s->length);
  }
  MESSAGE("\n");
}
#endif

static inline void DLL_Prepend(Span* list, Span* span) {
  ASSERT(span->next == NULL);
  ASSERT(span->prev == NULL);
  span->next = list->next;
  span->prev = list;
  list->next->prev = span;
  list->next = span;
}

// -------------------------------------------------------------------------
// Stack traces kept for sampled allocations
//   The following state is protected by pageheap_lock_.
// -------------------------------------------------------------------------

// size/depth are made the same size as a pointer so that some generic
// code below can conveniently cast them back and forth to void*.
static const int kMaxStackDepth = 31;
struct StackTrace {
  uintptr_t size;          // Size of object
  uintptr_t depth;         // Number of PC values stored in array below
  void*     stack[kMaxStackDepth];
};
static PageHeapAllocator<StackTrace> stacktrace_allocator;
static Span sampled_objects;

// -------------------------------------------------------------------------
// Map from page-id to per-page data
// -------------------------------------------------------------------------

// We use PageMap2<> for 32-bit and PageMap3<> for 64-bit machines.
// We also use a simple one-level cache for hot PageID-to-sizeclass mappings,
// because sometimes the sizeclass is all the information we need.

// Selector class -- general selector uses 3-level map
template <int BITS> class MapSelector {
 public:
  typedef TCMalloc_PageMap3<BITS-kPageShift> Type;
  typedef PackedCache<BITS, uint64_t> CacheType;
};

#if defined(WTF_CHANGES)
#if PLATFORM(X86_64)
// On all known X86-64 platforms, the upper 16 bits are always unused and therefore 
// can be excluded from the PageMap key.
// See http://en.wikipedia.org/wiki/X86-64#Virtual_address_space_details

static const size_t kBitsUnusedOn64Bit = 16;
#else
static const size_t kBitsUnusedOn64Bit = 0;
#endif

// A three-level map for 64-bit machines
template <> class MapSelector<64> {
 public:
  typedef TCMalloc_PageMap3<64 - kPageShift - kBitsUnusedOn64Bit> Type;
  typedef PackedCache<64, uint64_t> CacheType;
};
#endif

// A two-level map for 32-bit machines
template <> class MapSelector<32> {
 public:
  typedef TCMalloc_PageMap2<32 - kPageShift> Type;
  typedef PackedCache<32 - kPageShift, uint16_t> CacheType;
};

// -------------------------------------------------------------------------
// Page-level allocator
//  * Eager coalescing
//
// Heap for page-level allocation.  We allow allocating and freeing a
// contiguous runs of pages (called a "span").
// -------------------------------------------------------------------------

class TCMalloc_PageHeap {
 public:
  void init();

  // Allocate a run of "n" pages.  Returns zero if out of memory.
  Span* New(Length n);

  // Delete the span "[p, p+n-1]".
  // REQUIRES: span was returned by earlier call to New() and
  //           has not yet been deleted.
  void Delete(Span* span);

  // Mark an allocated span as being used for small objects of the
  // specified size-class.
  // REQUIRES: span was returned by an earlier call to New()
  //           and has not yet been deleted.
  void RegisterSizeClass(Span* span, size_t sc);

  // Split an allocated span into two spans: one of length "n" pages
  // followed by another span of length "span->length - n" pages.
  // Modifies "*span" to point to the first span of length "n" pages.
  // Returns a pointer to the second span.
  //
  // REQUIRES: "0 < n < span->length"
  // REQUIRES: !span->free
  // REQUIRES: span->sizeclass == 0
  Span* Split(Span* span, Length n);

  // Return the descriptor for the specified page.
  inline Span* GetDescriptor(PageID p) const {
    return reinterpret_cast<Span*>(pagemap_.get(p));
  }

#ifdef WTF_CHANGES
  inline Span* GetDescriptorEnsureSafe(PageID p)
  {
      pagemap_.Ensure(p, 1);
      return GetDescriptor(p);
  }
    
  size_t ReturnedBytes() const;
#endif

  // Dump state to stderr
#ifndef WTF_CHANGES
  void Dump(TCMalloc_Printer* out);
#endif

  // Return number of bytes allocated from system
  inline uint64_t SystemBytes() const { return system_bytes_; }

  // Return number of free bytes in heap
  uint64_t FreeBytes() const {
    return (static_cast<uint64_t>(free_pages_) << kPageShift);
  }

  bool Check();
  bool CheckList(Span* list, Length min_pages, Length max_pages);

  // Release all pages on the free list for reuse by the OS:
  void ReleaseFreePages();

  // Return 0 if we have no information, or else the correct sizeclass for p.
  // Reads and writes to pagemap_cache_ do not require locking.
  // The entries are 64 bits on 64-bit hardware and 16 bits on
  // 32-bit hardware, and we don't mind raciness as long as each read of
  // an entry yields a valid entry, not a partially updated entry.
  size_t GetSizeClassIfCached(PageID p) const {
    return pagemap_cache_.GetOrDefault(p, 0);
  }
  void CacheSizeClass(PageID p, size_t cl) const { pagemap_cache_.Put(p, cl); }

 private:
  // Pick the appropriate map and cache types based on pointer size
  typedef MapSelector<8*sizeof(uintptr_t)>::Type PageMap;
  typedef MapSelector<8*sizeof(uintptr_t)>::CacheType PageMapCache;
  PageMap pagemap_;
  mutable PageMapCache pagemap_cache_;

  // We segregate spans of a given size into two circular linked
  // lists: one for normal spans, and one for spans whose memory
  // has been returned to the system.
  struct SpanList {
    Span        normal;
    Span        returned;
  };

  // List of free spans of length >= kMaxPages
  SpanList large_;

  // Array mapping from span length to a doubly linked list of free spans
  SpanList free_[kMaxPages];

  // Number of pages kept in free lists
  uintptr_t free_pages_;

  // Bytes allocated from system
  uint64_t system_bytes_;

  bool GrowHeap(Length n);

  // REQUIRES   span->length >= n
  // Remove span from its free list, and move any leftover part of
  // span into appropriate free lists.  Also update "span" to have
  // length exactly "n" and mark it as non-free so it can be returned
  // to the client.
  //
  // "released" is true iff "span" was found on a "returned" list.
  void Carve(Span* span, Length n, bool released);

  void RecordSpan(Span* span) {