gecko-dev/memory/build/mozjemalloc.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// Portions of this file were originally under the following license:
//
// Copyright (C) 2006-2008 Jason Evans <jasone@FreeBSD.org>.
// All rights reserved.
// Copyright (C) 2007-2017 Mozilla Foundation.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice(s), this list of conditions and the following disclaimer as
//    the first lines of this file unmodified other than the possible
//    addition of one or more copyright notices.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice(s), this list of conditions and the following disclaimer in
//    the documentation and/or other materials provided with the
//    distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 HOLDER(S) 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.
//
// *****************************************************************************
//
// This allocator implementation is designed to provide scalable performance
// for multi-threaded programs on multi-processor systems.  The following
// features are included for this purpose:
//
//   + Multiple arenas are used if there are multiple CPUs, which reduces lock
//     contention and cache sloshing.
//
//   + Cache line sharing between arenas is avoided for internal data
//     structures.
//
//   + Memory is managed in chunks and runs (chunks can be split into runs),
//     rather than as individual pages.  This provides a constant-time
//     mechanism for associating allocations with particular arenas.
//
// Allocation requests are rounded up to the nearest size class, and no record
// of the original request size is maintained.  Allocations are broken into
// categories according to size class.  Assuming runtime defaults, 4 kB pages
// and a 16 byte quantum on a 32-bit system, the size classes in each category
// are as follows:
//
//   |=====================================|
//   | Category | Subcategory    |    Size |
//   |=====================================|
//   | Small    | Tiny           |       4 |
//   |          |                |       8 |
//   |          |----------------+---------|
//   |          | Quantum-spaced |      16 |
//   |          |                |      32 |
//   |          |                |      48 |
//   |          |                |     ... |
//   |          |                |     480 |
//   |          |                |     496 |
//   |          |                |     512 |
//   |          |----------------+---------|
//   |          | Sub-page       |    1 kB |
//   |          |                |    2 kB |
//   |=====================================|
//   | Large                     |    4 kB |
//   |                           |    8 kB |
//   |                           |   12 kB |
//   |                           |     ... |
//   |                           | 1012 kB |
//   |                           | 1016 kB |
//   |                           | 1020 kB |
//   |=====================================|
//   | Huge                      |    1 MB |
//   |                           |    2 MB |
//   |                           |    3 MB |
//   |                           |     ... |
//   |=====================================|
//
// NOTE: Due to Mozilla bug 691003, we cannot reserve less than one word for an
// allocation on Linux or Mac.  So on 32-bit *nix, the smallest bucket size is
// 4 bytes, and on 64-bit, the smallest bucket size is 8 bytes.
//
// A different mechanism is used for each category:
//
//   Small : Each size class is segregated into its own set of runs.  Each run
//           maintains a bitmap of which regions are free/allocated.
//
//   Large : Each allocation is backed by a dedicated run.  Metadata are stored
//           in the associated arena chunk header maps.
//
//   Huge : Each allocation is backed by a dedicated contiguous set of chunks.
//          Metadata are stored in a separate red-black tree.
//
// *****************************************************************************

#include "mozmemory_wrap.h"
#include "mozjemalloc.h"
#include "mozjemalloc_types.h"

#include <cstring>
#include <cerrno>
#ifdef XP_WIN
#include <io.h>
#include <windows.h>
#else
#include <sys/mman.h>
#include <unistd.h>
#endif
#ifdef XP_DARWIN
#include <libkern/OSAtomic.h>
#include <mach/mach_init.h>
#include <mach/vm_map.h>
#endif

#include "mozilla/Atomics.h"
#include "mozilla/Alignment.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/CheckedInt.h"
#include "mozilla/DoublyLinkedList.h"
#include "mozilla/Likely.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Sprintf.h"
// Note: MozTaggedAnonymousMmap() could call an LD_PRELOADed mmap
// instead of the one defined here; use only MozTagAnonymousMemory().
#include "mozilla/TaggedAnonymousMemory.h"
#include "mozilla/ThreadLocal.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/Unused.h"
#include "mozilla/fallible.h"
#include "rb.h"
#include "Mutex.h"
#include "Utils.h"

using namespace mozilla;

// On Linux, we use madvise(MADV_DONTNEED) to release memory back to the
// operating system.  If we release 1MB of live pages with MADV_DONTNEED, our
// RSS will decrease by 1MB (almost) immediately.
//
// On Mac, we use madvise(MADV_FREE).  Unlike MADV_DONTNEED on Linux, MADV_FREE
// on Mac doesn't cause the OS to release the specified pages immediately; the
// OS keeps them in our process until the machine comes under memory pressure.
//
// It's therefore difficult to measure the process's RSS on Mac, since, in the
// absence of memory pressure, the contribution from the heap to RSS will not
// decrease due to our madvise calls.
//
// We therefore define MALLOC_DOUBLE_PURGE on Mac.  This causes jemalloc to
// track which pages have been MADV_FREE'd.  You can then call
// jemalloc_purge_freed_pages(), which will force the OS to release those
// MADV_FREE'd pages, making the process's RSS reflect its true memory usage.
//
// The jemalloc_purge_freed_pages definition in memory/build/mozmemory.h needs
// to be adjusted if MALLOC_DOUBLE_PURGE is ever enabled on Linux.

#ifdef XP_DARWIN
#define MALLOC_DOUBLE_PURGE
#endif

#ifdef XP_WIN
#define MALLOC_DECOMMIT
#endif

// When MALLOC_STATIC_PAGESIZE is defined, the page size is fixed at
// compile-time for better performance, as opposed to determined at
// runtime. Some platforms can have different page sizes at runtime
// depending on kernel configuration, so they are opted out by default.
// Debug builds are opted out too, for test coverage.
#ifndef MOZ_DEBUG
#if !defined(__ia64__) && !defined(__sparc__) && !defined(__mips__) &&         \
  !defined(__aarch64__)
#define MALLOC_STATIC_PAGESIZE 1
#endif
#endif

#ifdef XP_WIN
#define STDERR_FILENO 2

// Implement getenv without using malloc.
static char mozillaMallocOptionsBuf[64];

#define getenv xgetenv
static char*
getenv(const char* name)
{

  if (GetEnvironmentVariableA(
        name, mozillaMallocOptionsBuf, sizeof(mozillaMallocOptionsBuf)) > 0) {
    return mozillaMallocOptionsBuf;
  }

  return nullptr;
}
#endif

#ifndef XP_WIN
#ifndef MADV_FREE
#define MADV_FREE MADV_DONTNEED
#endif
#endif

// Some tools, such as /dev/dsp wrappers, LD_PRELOAD libraries that
// happen to override mmap() and call dlsym() from their overridden
// mmap(). The problem is that dlsym() calls malloc(), and this ends
// up in a dead lock in jemalloc.
// On these systems, we prefer to directly use the system call.
// We do that for Linux systems and kfreebsd with GNU userland.
// Note sanity checks are not done (alignment of offset, ...) because
// the uses of mmap are pretty limited, in jemalloc.
//
// On Alpha, glibc has a bug that prevents syscall() to work for system
// calls with 6 arguments.
#if (defined(XP_LINUX) && !defined(__alpha__)) ||                              \
  (defined(__FreeBSD_kernel__) && defined(__GLIBC__))
#include <sys/syscall.h>
#if defined(SYS_mmap) || defined(SYS_mmap2)
static inline void*
_mmap(void* addr, size_t length, int prot, int flags, int fd, off_t offset)
{
// S390 only passes one argument to the mmap system call, which is a
// pointer to a structure containing the arguments.
#ifdef __s390__
  struct
  {
    void* addr;
    size_t length;
    long prot;
    long flags;
    long fd;
    off_t offset;
  } args = { addr, length, prot, flags, fd, offset };
  return (void*)syscall(SYS_mmap, &args);
#else
#if defined(ANDROID) && defined(__aarch64__) && defined(SYS_mmap2)
// Android NDK defines SYS_mmap2 for AArch64 despite it not supporting mmap2.
#undef SYS_mmap2
#endif
#ifdef SYS_mmap2
  return (void*)syscall(SYS_mmap2, addr, length, prot, flags, fd, offset >> 12);
#else
  return (void*)syscall(SYS_mmap, addr, length, prot, flags, fd, offset);
#endif
#endif
}
#define mmap _mmap
#define munmap(a, l) syscall(SYS_munmap, a, l)
#endif
#endif

// ***************************************************************************
// Structures for chunk headers for chunks used for non-huge allocations.

struct arena_t;

// Each element of the chunk map corresponds to one page within the chunk.
struct arena_chunk_map_t
{
  // Linkage for run trees.  There are two disjoint uses:
  //
  // 1) arena_t's tree or available runs.
  // 2) arena_run_t conceptually uses this linkage for in-use non-full
  //    runs, rather than directly embedding linkage.
  RedBlackTreeNode<arena_chunk_map_t> link;

  // Run address (or size) and various flags are stored together.  The bit
  // layout looks like (assuming 32-bit system):
  //
  //   ???????? ???????? ????---- -mckdzla
  //
  // ? : Unallocated: Run address for first/last pages, unset for internal
  //                  pages.
  //     Small: Run address.
  //     Large: Run size for first page, unset for trailing pages.
  // - : Unused.
  // m : MADV_FREE/MADV_DONTNEED'ed?
  // c : decommitted?
  // k : key?
  // d : dirty?
  // z : zeroed?
  // l : large?
  // a : allocated?
  //
  // Following are example bit patterns for the three types of runs.
  //
  // r : run address
  // s : run size
  // x : don't care
  // - : 0
  // [cdzla] : bit set
  //
  //   Unallocated:
  //     ssssssss ssssssss ssss---- --c-----
  //     xxxxxxxx xxxxxxxx xxxx---- ----d---
  //     ssssssss ssssssss ssss---- -----z--
  //
  //   Small:
  //     rrrrrrrr rrrrrrrr rrrr---- -------a
  //     rrrrrrrr rrrrrrrr rrrr---- -------a
  //     rrrrrrrr rrrrrrrr rrrr---- -------a
  //
  //   Large:
  //     ssssssss ssssssss ssss---- ------la
  //     -------- -------- -------- ------la
  //     -------- -------- -------- ------la
  size_t bits;

// Note that CHUNK_MAP_DECOMMITTED's meaning varies depending on whether
// MALLOC_DECOMMIT and MALLOC_DOUBLE_PURGE are defined.
//
// If MALLOC_DECOMMIT is defined, a page which is CHUNK_MAP_DECOMMITTED must be
// re-committed with pages_commit() before it may be touched.  If
// MALLOC_DECOMMIT is defined, MALLOC_DOUBLE_PURGE may not be defined.
//
// If neither MALLOC_DECOMMIT nor MALLOC_DOUBLE_PURGE is defined, pages which
// are madvised (with either MADV_DONTNEED or MADV_FREE) are marked with
// CHUNK_MAP_MADVISED.
//
// Otherwise, if MALLOC_DECOMMIT is not defined and MALLOC_DOUBLE_PURGE is
// defined, then a page which is madvised is marked as CHUNK_MAP_MADVISED.
// When it's finally freed with jemalloc_purge_freed_pages, the page is marked
// as CHUNK_MAP_DECOMMITTED.
#define CHUNK_MAP_MADVISED ((size_t)0x40U)
#define CHUNK_MAP_DECOMMITTED ((size_t)0x20U)
#define CHUNK_MAP_MADVISED_OR_DECOMMITTED                                      \
  (CHUNK_MAP_MADVISED | CHUNK_MAP_DECOMMITTED)
#define CHUNK_MAP_KEY ((size_t)0x10U)
#define CHUNK_MAP_DIRTY ((size_t)0x08U)
#define CHUNK_MAP_ZEROED ((size_t)0x04U)
#define CHUNK_MAP_LARGE ((size_t)0x02U)
#define CHUNK_MAP_ALLOCATED ((size_t)0x01U)
};

// Arena chunk header.
struct arena_chunk_t
{
  // Arena that owns the chunk.
  arena_t* arena;

  // Linkage for the arena's tree of dirty chunks.
  RedBlackTreeNode<arena_chunk_t> link_dirty;

#ifdef MALLOC_DOUBLE_PURGE
  // If we're double-purging, we maintain a linked list of chunks which
  // have pages which have been madvise(MADV_FREE)'d but not explicitly
  // purged.
  //
  // We're currently lazy and don't remove a chunk from this list when
  // all its madvised pages are recommitted.
  DoublyLinkedListElement<arena_chunk_t> chunks_madvised_elem;
#endif

  // Number of dirty pages.
  size_t ndirty;

  // Map of pages within chunk that keeps track of free/large/small.
  arena_chunk_map_t map[1]; // Dynamically sized.
};

// ***************************************************************************
// Constants defining allocator size classes and behavior.

// Maximum size of L1 cache line.  This is used to avoid cache line aliasing,
// so over-estimates are okay (up to a point), but under-estimates will
// negatively affect performance.
static const size_t kCacheLineSize = 64;

// Smallest size class to support.  On Windows the smallest allocation size
// must be 8 bytes on 32-bit, 16 bytes on 64-bit.  On Linux and Mac, even
// malloc(1) must reserve a word's worth of memory (see Mozilla bug 691003).
#ifdef XP_WIN
static const size_t kMinTinyClass = sizeof(void*) * 2;
#else
static const size_t kMinTinyClass = sizeof(void*);
#endif

// Maximum tiny size class.
static const size_t kMaxTinyClass = 8;

// Amount (quantum) separating quantum-spaced size classes.
static const size_t kQuantum = 16;
static const size_t kQuantumMask = kQuantum - 1;

// Smallest quantum-spaced size classes. It could actually also be labelled a
// tiny allocation, and is spaced as such from the largest tiny size class.
// Tiny classes being powers of 2, this is twice as large as the largest of
// them.
static const size_t kMinQuantumClass = kMaxTinyClass * 2;

// Largest quantum-spaced size classes.
static const size_t kMaxQuantumClass = 512;

static_assert(kMaxQuantumClass % kQuantum == 0,
              "kMaxQuantumClass is not a multiple of kQuantum");

// Number of (2^n)-spaced tiny classes.
static const size_t kNumTinyClasses =
  LOG2(kMinQuantumClass) - LOG2(kMinTinyClass);

// Number of quantum-spaced classes.
static const size_t kNumQuantumClasses = kMaxQuantumClass / kQuantum;

// Size and alignment of memory chunks that are allocated by the OS's virtual
// memory system.
static const size_t kChunkSize = 1_MiB;
static const size_t kChunkSizeMask = kChunkSize - 1;

#ifdef MALLOC_STATIC_PAGESIZE
// VM page size. It must divide the runtime CPU page size or the code
// will abort.
// Platform specific page size conditions copied from js/public/HeapAPI.h
#if (defined(SOLARIS) || defined(__FreeBSD__)) &&                              \
  (defined(__sparc) || defined(__sparcv9) || defined(__ia64))
static const size_t gPageSize = 8_KiB;
#elif defined(__powerpc64__)
static const size_t gPageSize = 64_KiB;
#else
static const size_t gPageSize = 4_KiB;
#endif

#else
static size_t gPageSize;
#endif

#ifdef MALLOC_STATIC_PAGESIZE
#define DECLARE_GLOBAL(type, name)
#define DEFINE_GLOBALS
#define END_GLOBALS
#define DEFINE_GLOBAL(type) static const type
#define GLOBAL_LOG2 LOG2
#define GLOBAL_ASSERT_HELPER1(x) static_assert(x, #x)
#define GLOBAL_ASSERT_HELPER2(x, y) static_assert(x, y)
#define GLOBAL_ASSERT(...)                                                     \
  MACRO_CALL(                                                                  \
    MOZ_PASTE_PREFIX_AND_ARG_COUNT(GLOBAL_ASSERT_HELPER, __VA_ARGS__),         \
    (__VA_ARGS__))
#else
#define DECLARE_GLOBAL(type, name) static type name;
#define DEFINE_GLOBALS                                                         \
  static void DefineGlobals()                                                  \
  {
#define END_GLOBALS }
#define DEFINE_GLOBAL(type)
#define GLOBAL_LOG2 FloorLog2
#define GLOBAL_ASSERT MOZ_RELEASE_ASSERT
#endif

DECLARE_GLOBAL(size_t, gMaxSubPageClass)
DECLARE_GLOBAL(uint8_t, gNumSubPageClasses)
DECLARE_GLOBAL(uint8_t, gPageSize2Pow)
DECLARE_GLOBAL(size_t, gPageSizeMask)
DECLARE_GLOBAL(size_t, gChunkNumPages)
DECLARE_GLOBAL(size_t, gChunkHeaderNumPages)
DECLARE_GLOBAL(size_t, gMaxLargeClass)

DEFINE_GLOBALS
// Largest sub-page size class.
DEFINE_GLOBAL(size_t) gMaxSubPageClass = gPageSize / 2;

// Max size class for bins.
#define gMaxBinClass gMaxSubPageClass

// Number of (2^n)-spaced sub-page bins.
DEFINE_GLOBAL(uint8_t)
gNumSubPageClasses = GLOBAL_LOG2(gMaxSubPageClass) - LOG2(kMaxQuantumClass);

DEFINE_GLOBAL(uint8_t) gPageSize2Pow = GLOBAL_LOG2(gPageSize);
DEFINE_GLOBAL(size_t) gPageSizeMask = gPageSize - 1;

// Number of pages in a chunk.
DEFINE_GLOBAL(size_t) gChunkNumPages = kChunkSize >> gPageSize2Pow;

// Number of pages necessary for a chunk header.
DEFINE_GLOBAL(size_t)
gChunkHeaderNumPages =
  ((sizeof(arena_chunk_t) + sizeof(arena_chunk_map_t) * (gChunkNumPages - 1) +
    gPageSizeMask) &
   ~gPageSizeMask) >>
  gPageSize2Pow;

// Max size class for arenas.
DEFINE_GLOBAL(size_t)
gMaxLargeClass = kChunkSize - (gChunkHeaderNumPages << gPageSize2Pow);

// Various sanity checks that regard configuration.
GLOBAL_ASSERT(1ULL << gPageSize2Pow == gPageSize,
              "Page size is not a power of two");
GLOBAL_ASSERT(kQuantum >= sizeof(void*));
GLOBAL_ASSERT(kQuantum <= gPageSize);
GLOBAL_ASSERT(kChunkSize >= gPageSize);
GLOBAL_ASSERT(kQuantum * 4 <= kChunkSize);
END_GLOBALS

// Recycle at most 128 MiB of chunks. This means we retain at most
// 6.25% of the process address space on a 32-bit OS for later use.
static const size_t gRecycleLimit = 128_MiB;

// The current amount of recycled bytes, updated atomically.
static Atomic<size_t, ReleaseAcquire> gRecycledSize;

// Maximum number of dirty pages per arena.
#define DIRTY_MAX_DEFAULT (1U << 8)

static size_t opt_dirty_max = DIRTY_MAX_DEFAULT;

// Return the smallest chunk multiple that is >= s.
#define CHUNK_CEILING(s) (((s) + kChunkSizeMask) & ~kChunkSizeMask)

// Return the smallest cacheline multiple that is >= s.
#define CACHELINE_CEILING(s)                                                   \
  (((s) + (kCacheLineSize - 1)) & ~(kCacheLineSize - 1))

// Return the smallest quantum multiple that is >= a.
#define QUANTUM_CEILING(a) (((a) + (kQuantumMask)) & ~(kQuantumMask))

// Return the smallest pagesize multiple that is >= s.
#define PAGE_CEILING(s) (((s) + gPageSizeMask) & ~gPageSizeMask)

// ***************************************************************************
// MALLOC_DECOMMIT and MALLOC_DOUBLE_PURGE are mutually exclusive.
#if defined(MALLOC_DECOMMIT) && defined(MALLOC_DOUBLE_PURGE)
#error MALLOC_DECOMMIT and MALLOC_DOUBLE_PURGE are mutually exclusive.
#endif

static void*
base_alloc(size_t aSize);

// Set to true once the allocator has been initialized.
static Atomic<bool> malloc_initialized(false);

static StaticMutex gInitLock;

// ***************************************************************************
// Statistics data structures.

struct arena_stats_t
{
  // Number of bytes currently mapped.
  size_t mapped;

  // Current number of committed pages.
  size_t committed;

  // Per-size-category statistics.
  size_t allocated_small;

  size_t allocated_large;
};

// ***************************************************************************
// Extent data structures.

enum ChunkType
{
  UNKNOWN_CHUNK,
  ZEROED_CHUNK,   // chunk only contains zeroes.
  ARENA_CHUNK,    // used to back arena runs created by arena_t::AllocRun.
  HUGE_CHUNK,     // used to back huge allocations (e.g. arena_t::MallocHuge).
  RECYCLED_CHUNK, // chunk has been stored for future use by chunk_recycle.
};

// Tree of extents.
struct extent_node_t
{
  // Linkage for the size/address-ordered tree.
  RedBlackTreeNode<extent_node_t> mLinkBySize;

  // Linkage for the address-ordered tree.
  RedBlackTreeNode<extent_node_t> mLinkByAddr;

  // Pointer to the extent that this tree node is responsible for.
  void* mAddr;

  // Total region size.
  size_t mSize;

  union {
    // What type of chunk is there; used for chunk recycling.
    ChunkType mChunkType;

    // A pointer to the associated arena, for huge allocations.
    arena_t* mArena;
  };
};

struct ExtentTreeSzTrait
{
  static RedBlackTreeNode<extent_node_t>& GetTreeNode(extent_node_t* aThis)
  {
    return aThis->mLinkBySize;
  }

  static inline Order Compare(extent_node_t* aNode, extent_node_t* aOther)
  {
    Order ret = CompareInt(aNode->mSize, aOther->mSize);
    return (ret != Order::eEqual) ? ret
                                  : CompareAddr(aNode->mAddr, aOther->mAddr);
  }
};

struct ExtentTreeTrait
{
  static RedBlackTreeNode<extent_node_t>& GetTreeNode(extent_node_t* aThis)
  {
    return aThis->mLinkByAddr;
  }

  static inline Order Compare(extent_node_t* aNode, extent_node_t* aOther)
  {
    return CompareAddr(aNode->mAddr, aOther->mAddr);
  }
};

struct ExtentTreeBoundsTrait : public ExtentTreeTrait
{
  static inline Order Compare(extent_node_t* aKey, extent_node_t* aNode)
  {
    uintptr_t key_addr = reinterpret_cast<uintptr_t>(aKey->mAddr);
    uintptr_t node_addr = reinterpret_cast<uintptr_t>(aNode->mAddr);
    size_t node_size = aNode->mSize;

    // Is aKey within aNode?
    if (node_addr <= key_addr && key_addr < node_addr + node_size) {
      return Order::eEqual;
    }

    return CompareAddr(aKey->mAddr, aNode->mAddr);
  }
};

// Describe size classes to which allocations are rounded up to.
// TODO: add large and huge types when the arena allocation code
// changes in a way that allows it to be beneficial.
class SizeClass
{
public:
  enum ClassType
  {
    Tiny,
    Quantum,
    SubPage,
    Large,
  };

  explicit inline SizeClass(size_t aSize)
  {
    if (aSize <= kMaxTinyClass) {
      mType = Tiny;
      mSize = std::max(RoundUpPow2(aSize), kMinTinyClass);
    } else if (aSize <= kMaxQuantumClass) {
      mType = Quantum;
      mSize = QUANTUM_CEILING(aSize);
    } else if (aSize <= gMaxSubPageClass) {
      mType = SubPage;
      mSize = RoundUpPow2(aSize);
    } else if (aSize <= gMaxLargeClass) {
      mType = Large;
      mSize = PAGE_CEILING(aSize);
    } else {
      MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Invalid size");
    }
  }

  SizeClass& operator=(const SizeClass& aOther) = default;

  bool operator==(const SizeClass& aOther) { return aOther.mSize == mSize; }

  size_t Size() { return mSize; }

  ClassType Type() { return mType; }

  SizeClass Next() { return SizeClass(mSize + 1); }

private:
  ClassType mType;
  size_t mSize;
};

// ***************************************************************************
// Radix tree data structures.
//
// The number of bits passed to the template is the number of significant bits
// in an address to do a radix lookup with.
//
// An address is looked up by splitting it in kBitsPerLevel bit chunks, except
// the most significant bits, where the bit chunk is kBitsAtLevel1 which can be
// different if Bits is not a multiple of kBitsPerLevel.
//
// With e.g. sizeof(void*)=4, Bits=16 and kBitsPerLevel=8, an address is split
// like the following:
// 0x12345678 -> mRoot[0x12][0x34]
template<size_t Bits>
class AddressRadixTree
{
// Size of each radix tree node (as a power of 2).
// This impacts tree depth.
#ifdef HAVE_64BIT_BUILD
  static const size_t kNodeSize = kCacheLineSize;
#else
  static const size_t kNodeSize = 16_KiB;
#endif
  static const size_t kBitsPerLevel = LOG2(kNodeSize) - LOG2(sizeof(void*));
  static const size_t kBitsAtLevel1 =
    (Bits % kBitsPerLevel) ? Bits % kBitsPerLevel : kBitsPerLevel;
  static const size_t kHeight = (Bits + kBitsPerLevel - 1) / kBitsPerLevel;
  static_assert(kBitsAtLevel1 + (kHeight - 1) * kBitsPerLevel == Bits,
                "AddressRadixTree parameters don't work out");

  Mutex mLock;
  void** mRoot;

public:
  bool Init();

  inline void* Get(void* aAddr);

  // Returns whether the value was properly set.
  inline bool Set(void* aAddr, void* aValue);

  inline bool Unset(void* aAddr) { return Set(aAddr, nullptr); }

private:
  inline void** GetSlot(void* aAddr, bool aCreate = false);
};

// ***************************************************************************
// Arena data structures.

struct arena_bin_t;

struct ArenaChunkMapLink
{
  static RedBlackTreeNode<arena_chunk_map_t>& GetTreeNode(
    arena_chunk_map_t* aThis)
  {
    return aThis->link;
  }
};

struct ArenaRunTreeTrait : public ArenaChunkMapLink
{
  static inline Order Compare(arena_chunk_map_t* aNode,
                              arena_chunk_map_t* aOther)
  {
    MOZ_ASSERT(aNode);
    MOZ_ASSERT(aOther);
    return CompareAddr(aNode, aOther);
  }
};

struct ArenaAvailTreeTrait : public ArenaChunkMapLink
{
  static inline Order Compare(arena_chunk_map_t* aNode,
                              arena_chunk_map_t* aOther)
  {
    size_t size1 = aNode->bits & ~gPageSizeMask;
    size_t size2 = aOther->bits & ~gPageSizeMask;
    Order ret = CompareInt(size1, size2);
    return (ret != Order::eEqual)
             ? ret
             : CompareAddr((aNode->bits & CHUNK_MAP_KEY) ? nullptr : aNode,
                           aOther);
  }
};

struct ArenaDirtyChunkTrait
{
  static RedBlackTreeNode<arena_chunk_t>& GetTreeNode(arena_chunk_t* aThis)
  {
    return aThis->link_dirty;
  }

  static inline Order Compare(arena_chunk_t* aNode, arena_chunk_t* aOther)
  {
    MOZ_ASSERT(aNode);
    MOZ_ASSERT(aOther);
    return CompareAddr(aNode, aOther);
  }
};

#ifdef MALLOC_DOUBLE_PURGE
namespace mozilla {

template<>
struct GetDoublyLinkedListElement<arena_chunk_t>
{
  static DoublyLinkedListElement<arena_chunk_t>& Get(arena_chunk_t* aThis)
  {
    return aThis->chunks_madvised_elem;
  }
};
}
#endif

struct arena_run_t
{
#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  uint32_t mMagic;
#define ARENA_RUN_MAGIC 0x384adf93

  // On 64-bit platforms, having the arena_bin_t pointer following
  // the mMagic field means there's padding between both fields, making
  // the run header larger than necessary.
  // But when MOZ_DIAGNOSTIC_ASSERT_ENABLED is not set, starting the
  // header with this field followed by the arena_bin_t pointer yields
  // the same padding. We do want the mMagic field to appear first, so
  // depending whether MOZ_DIAGNOSTIC_ASSERT_ENABLED is set or not, we
  // move some field to avoid padding.

  // Number of free regions in run.
  unsigned mNumFree;
#endif

  // Bin this run is associated with.
  arena_bin_t* mBin;

  // Index of first element that might have a free region.
  unsigned mRegionsMinElement;

#if !defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  // Number of free regions in run.
  unsigned mNumFree;
#endif

  // Bitmask of in-use regions (0: in use, 1: free).
  unsigned mRegionsMask[1]; // Dynamically sized.
};

struct arena_bin_t
{
  // Current run being used to service allocations of this bin's size
  // class.
  arena_run_t* mCurrentRun;

  // Tree of non-full runs.  This tree is used when looking for an
  // existing run when mCurrentRun is no longer usable.  We choose the
  // non-full run that is lowest in memory; this policy tends to keep
  // objects packed well, and it can also help reduce the number of
  // almost-empty chunks.
  RedBlackTree<arena_chunk_map_t, ArenaRunTreeTrait> mNonFullRuns;

  // Bin's size class.
  size_t mSizeClass;

  // Total size of a run for this bin's size class.
  size_t mRunSize;

  // Total number of regions in a run for this bin's size class.
  uint32_t mRunNumRegions;

  // Number of elements in a run's mRegionsMask for this bin's size class.
  uint32_t mRunNumRegionsMask;

  // Offset of first region in a run for this bin's size class.
  uint32_t mRunFirstRegionOffset;

  // Current number of runs in this bin, full or otherwise.
  unsigned long mNumRuns;

  // Amount of overhead runs are allowed to have.
  static constexpr double kRunOverhead = 1.6_percent;
  static constexpr double kRunRelaxedOverhead = 2.4_percent;

  // Initialize a bin for the given size class.
  // The generated run sizes, for a page size of 4 KiB, are:
  //   size|run       size|run       size|run       size|run
  //  class|size     class|size     class|size     class|size
  //     4   4 KiB      8   4 KiB     16   4 KiB     32   4 KiB
  //    48   4 KiB     64   4 KiB     80   4 KiB     96   4 KiB
  //   112   4 KiB    128   8 KiB    144   4 KiB    160   8 KiB
  //   176   4 KiB    192   4 KiB    208   8 KiB    224   4 KiB
  //   240   4 KiB    256  16 KiB    272   4 KiB    288   4 KiB
  //   304  12 KiB    320  12 KiB    336   4 KiB    352   8 KiB
  //   368   4 KiB    384   8 KiB    400  20 KiB    416  16 KiB
  //   432  12 KiB    448   4 KiB    464  16 KiB    480   8 KiB
  //   496  20 KiB    512  32 KiB   1024  64 KiB   2048 128 KiB
  inline void Init(SizeClass aSizeClass);
};

struct arena_t
{
#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  uint32_t mMagic;
#define ARENA_MAGIC 0x947d3d24
#endif

  arena_id_t mId;
  // Linkage for the tree of arenas by id.
  RedBlackTreeNode<arena_t> mLink;

  // All operations on this arena require that lock be locked.
  Mutex mLock;

  arena_stats_t mStats;

private:
  // Tree of dirty-page-containing chunks this arena manages.
  RedBlackTree<arena_chunk_t, ArenaDirtyChunkTrait> mChunksDirty;

#ifdef MALLOC_DOUBLE_PURGE
  // Head of a linked list of MADV_FREE'd-page-containing chunks this
  // arena manages.
  DoublyLinkedList<arena_chunk_t> mChunksMAdvised;
#endif

  // In order to avoid rapid chunk allocation/deallocation when an arena
  // oscillates right on the cusp of needing a new chunk, cache the most
  // recently freed chunk.  The spare is left in the arena's chunk trees
  // until it is deleted.
  //
  // There is one spare chunk per arena, rather than one spare total, in
  // order to avoid interactions between multiple threads that could make
  // a single spare inadequate.
  arena_chunk_t* mSpare;

public:
  // Current count of pages within unused runs that are potentially
  // dirty, and for which madvise(... MADV_FREE) has not been called.  By
  // tracking this, we can institute a limit on how much dirty unused
  // memory is mapped for each arena.
  size_t mNumDirty;

  // Maximum value allowed for mNumDirty.
  size_t mMaxDirty;

private:
  // Size/address-ordered tree of this arena's available runs.  This tree
  // is used for first-best-fit run allocation.
  RedBlackTree<arena_chunk_map_t, ArenaAvailTreeTrait> mRunsAvail;

public:
  // mBins is used to store rings of free regions of the following sizes,
  // assuming a 16-byte quantum, 4kB pagesize, and default MALLOC_OPTIONS.
  //
  //   mBins[i] | size |
  //   --------+------+
  //        0  |    2 |
  //        1  |    4 |
  //        2  |    8 |
  //   --------+------+
  //        3  |   16 |
  //        4  |   32 |
  //        5  |   48 |
  //        6  |   64 |
  //           :      :
  //           :      :
  //       33  |  496 |
  //       34  |  512 |
  //   --------+------+
  //       35  | 1024 |
  //       36  | 2048 |
  //   --------+------+
  arena_bin_t mBins[1]; // Dynamically sized.

  explicit arena_t(arena_params_t* aParams);

private:
  void InitChunk(arena_chunk_t* aChunk, bool aZeroed);

  void DeallocChunk(arena_chunk_t* aChunk);

  arena_run_t* AllocRun(size_t aSize, bool aLarge, bool aZero);

  void DallocRun(arena_run_t* aRun, bool aDirty);

  MOZ_MUST_USE bool SplitRun(arena_run_t* aRun,
                             size_t aSize,
                             bool aLarge,
                             bool aZero);

  void TrimRunHead(arena_chunk_t* aChunk,
                   arena_run_t* aRun,
                   size_t aOldSize,
                   size_t aNewSize);

  void TrimRunTail(arena_chunk_t* aChunk,
                   arena_run_t* aRun,
                   size_t aOldSize,
                   size_t aNewSize,
                   bool dirty);

  arena_run_t* GetNonFullBinRun(arena_bin_t* aBin);

  inline void* MallocSmall(size_t aSize, bool aZero);

  void* MallocLarge(size_t aSize, bool aZero);

  void* MallocHuge(size_t aSize, bool aZero);

  void* PallocLarge(size_t aAlignment, size_t aSize, size_t aAllocSize);

  void* PallocHuge(size_t aSize, size_t aAlignment, bool aZero);

  void RallocShrinkLarge(arena_chunk_t* aChunk,
                         void* aPtr,
                         size_t aSize,
                         size_t aOldSize);

  bool RallocGrowLarge(arena_chunk_t* aChunk,
                       void* aPtr,
                       size_t aSize,
                       size_t aOldSize);

  void* RallocSmallOrLarge(void* aPtr, size_t aSize, size_t aOldSize);

  void* RallocHuge(void* aPtr, size_t aSize, size_t aOldSize);

public:
  inline void* Malloc(size_t aSize, bool aZero);

  void* Palloc(size_t aAlignment, size_t aSize);

  inline void DallocSmall(arena_chunk_t* aChunk,
                          void* aPtr,
                          arena_chunk_map_t* aMapElm);

  void DallocLarge(arena_chunk_t* aChunk, void* aPtr);

  void* Ralloc(void* aPtr, size_t aSize, size_t aOldSize);

  void Purge(bool aAll);

  void HardPurge();

  void* operator new(size_t aCount) = delete;

  void* operator new(size_t aCount, const fallible_t&)
#if !defined(_MSC_VER) || defined(_CPPUNWIND)
    noexcept
#endif
  {
    MOZ_ASSERT(aCount == sizeof(arena_t));
    // Allocate enough space for trailing bins.
    return base_alloc(
      aCount + (sizeof(arena_bin_t) * (kNumTinyClasses + kNumQuantumClasses +
                                       gNumSubPageClasses - 1)));
  }

  void operator delete(void*) = delete;
};

struct ArenaTreeTrait
{
  static RedBlackTreeNode<arena_t>& GetTreeNode(arena_t* aThis)
  {
    return aThis->mLink;
  }

  static inline Order Compare(arena_t* aNode, arena_t* aOther)
  {
    MOZ_ASSERT(aNode);
    MOZ_ASSERT(aOther);
    return CompareInt(aNode->mId, aOther->mId);
  }
};

// Bookkeeping for all the arenas used by the allocator.
// Arenas are separated in two categories:
// - "private" arenas, used through the moz_arena_* API
// - all the other arenas: the default arena, and thread-local arenas,
//   used by the standard API.
class ArenaCollection
{
public:
  bool Init()
  {
    mArenas.Init();
    mPrivateArenas.Init();
    arena_params_t params;
    // The main arena allows more dirty pages than the default for other arenas.
    params.mMaxDirty = opt_dirty_max;
    mDefaultArena =
      mLock.Init() ? CreateArena(/* IsPrivate = */ false, &params) : nullptr;
    return bool(mDefaultArena);
  }

  inline arena_t* GetById(arena_id_t aArenaId, bool aIsPrivate);

  arena_t* CreateArena(bool aIsPrivate, arena_params_t* aParams);

  void DisposeArena(arena_t* aArena)
  {
    MutexAutoLock lock(mLock);
    (mPrivateArenas.Search(aArena) ? mPrivateArenas : mArenas).Remove(aArena);
    // The arena is leaked, and remaining allocations in it still are alive
    // until they are freed. After that, the arena will be empty but still
    // taking have at least a chunk taking address space. TODO: bug 1364359.
  }

  using Tree = RedBlackTree<arena_t, ArenaTreeTrait>;

  struct Iterator : Tree::Iterator
  {
    explicit Iterator(Tree* aTree, Tree* aSecondTree)
      : Tree::Iterator(aTree)
      , mNextTree(aSecondTree)
    {
    }

    Item<Iterator> begin()
    {
      return Item<Iterator>(this, *Tree::Iterator::begin());
    }

    Item<Iterator> end() { return Item<Iterator>(this, nullptr); }

    Tree::TreeNode* Next()
    {
      Tree::TreeNode* result = Tree::Iterator::Next();
      if (!result && mNextTree) {
        new (this) Iterator(mNextTree, nullptr);
        result = reinterpret_cast<Tree::TreeNode*>(*Tree::Iterator::begin());
      }
      return result;
    }

  private:
    Tree* mNextTree;
  };

  Iterator iter() { return Iterator(&mArenas, &mPrivateArenas); }

  inline arena_t* GetDefault() { return mDefaultArena; }

  Mutex mLock;

private:
  arena_t* mDefaultArena;
  arena_id_t mLastArenaId;
  Tree mArenas;
  Tree mPrivateArenas;
};

static ArenaCollection gArenas;

// ******
// Chunks.
static AddressRadixTree<(sizeof(void*) << 3) - LOG2(kChunkSize)> gChunkRTree;

// Protects chunk-related data structures.
static Mutex chunks_mtx;

// Trees of chunks that were previously allocated (trees differ only in node
// ordering).  These are used when allocating chunks, in an attempt to re-use
// address space.  Depending on function, different tree orderings are needed,
// which is why there are two trees with the same contents.
static RedBlackTree<extent_node_t, ExtentTreeSzTrait> gChunksBySize;
static RedBlackTree<extent_node_t, ExtentTreeTrait> gChunksByAddress;

// Protects huge allocation-related data structures.
static Mutex huge_mtx;

// Tree of chunks that are stand-alone huge allocations.
static RedBlackTree<extent_node_t, ExtentTreeTrait> huge;

// Huge allocation statistics.
static size_t huge_allocated;
static size_t huge_mapped;

// **************************
// base (internal allocation).

// Current pages that are being used for internal memory allocations.  These
// pages are carved up in cacheline-size quanta, so that there is no chance of
// false cache line sharing.

static void* base_pages;
static void* base_next_addr;
static void* base_next_decommitted;
static void* base_past_addr; // Addr immediately past base_pages.
static extent_node_t* base_nodes;
static Mutex base_mtx;
static size_t base_mapped;
static size_t base_committed;

// ******
// Arenas.

// The arena associated with the current thread (per
// jemalloc_thread_local_arena) On OSX, __thread/thread_local circles back
// calling malloc to allocate storage on first access on each thread, which
// leads to an infinite loop, but pthread-based TLS somehow doesn't have this
// problem.
#if !defined(XP_DARWIN)
static MOZ_THREAD_LOCAL(arena_t*) thread_arena;
#else
static detail::ThreadLocal<arena_t*, detail::ThreadLocalKeyStorage>
  thread_arena;
#endif

// *****************************
// Runtime configuration options.

const uint8_t kAllocJunk = 0xe4;
const uint8_t kAllocPoison = 0xe5;

#ifdef MOZ_DEBUG
static bool opt_junk = true;
static bool opt_zero = false;
#else
static const bool opt_junk = false;
static const bool opt_zero = false;
#endif

// ***************************************************************************
// Begin forward declarations.

static void*
chunk_alloc(size_t aSize,
            size_t aAlignment,
            bool aBase,
            bool* aZeroed = nullptr);
static void
chunk_dealloc(void* aChunk, size_t aSize, ChunkType aType);
static void
chunk_ensure_zero(void* aPtr, size_t aSize, bool aZeroed);
static void
huge_dalloc(void* aPtr, arena_t* aArena);
static bool
malloc_init_hard();

#ifdef XP_DARWIN
#define FORK_HOOK extern "C"
#else
#define FORK_HOOK static
#endif
FORK_HOOK void
_malloc_prefork(void);
FORK_HOOK void
_malloc_postfork_parent(void);
FORK_HOOK void
_malloc_postfork_child(void);

// End forward declarations.
// ***************************************************************************

// FreeBSD's pthreads implementation calls malloc(3), so the malloc
// implementation has to take pains to avoid infinite recursion during
// initialization.
// Returns whether the allocator was successfully initialized.
static inline bool
malloc_init()
{

  if (malloc_initialized == false) {
    return malloc_init_hard();
  }

  return true;
}

static void
_malloc_message(const char* p)
{
#if !defined(XP_WIN)
#define _write write
#endif
  // Pretend to check _write() errors to suppress gcc warnings about
  // warn_unused_result annotations in some versions of glibc headers.
  if (_write(STDERR_FILENO, p, (unsigned int)strlen(p)) < 0) {
    return;
  }
}

template<typename... Args>
static void
_malloc_message(const char* p, Args... args)
{
  _malloc_message(p);
  _malloc_message(args...);
}

#ifdef ANDROID
// Android's pthread.h does not declare pthread_atfork() until SDK 21.
extern "C" MOZ_EXPORT int
pthread_atfork(void (*)(void), void (*)(void), void (*)(void));
#endif

// ***************************************************************************
// Begin Utility functions/macros.

// Return the chunk address for allocation address a.
static inline arena_chunk_t*
GetChunkForPtr(const void* aPtr)
{
  return (arena_chunk_t*)(uintptr_t(aPtr) & ~kChunkSizeMask);
}

// Return the chunk offset of address a.
static inline size_t
GetChunkOffsetForPtr(const void* aPtr)
{
  return (size_t)(uintptr_t(aPtr) & kChunkSizeMask);
}

static inline const char*
_getprogname(void)
{

  return "<jemalloc>";
}

// Fill the given range of memory with zeroes or junk depending on opt_junk and
// opt_zero. Callers can force filling with zeroes through the aForceZero
// argument.
static inline void
ApplyZeroOrJunk(void* aPtr, size_t aSize)
{
  if (opt_junk) {
    memset(aPtr, kAllocJunk, aSize);
  } else if (opt_zero) {
    memset(aPtr, 0, aSize);
  }
}

// ***************************************************************************

static inline void
pages_decommit(void* aAddr, size_t aSize)
{
#ifdef XP_WIN
  // The region starting at addr may have been allocated in multiple calls
  // to VirtualAlloc and recycled, so decommitting the entire region in one
  // go may not be valid. However, since we allocate at least a chunk at a
  // time, we may touch any region in chunksized increments.
  size_t pages_size = std::min(aSize, kChunkSize - GetChunkOffsetForPtr(aAddr));
  while (aSize > 0) {
    if (!VirtualFree(aAddr, pages_size, MEM_DECOMMIT)) {
      MOZ_CRASH();
    }
    aAddr = (void*)((uintptr_t)aAddr + pages_size);
    aSize -= pages_size;
    pages_size = std::min(aSize, kChunkSize);
  }
#else
  if (mmap(
        aAddr, aSize, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, -1, 0) ==
      MAP_FAILED) {
    MOZ_CRASH();
  }
  MozTagAnonymousMemory(aAddr, aSize, "jemalloc-decommitted");
#endif
}

// Commit pages. Returns whether pages were committed.
MOZ_MUST_USE static inline bool
pages_commit(void* aAddr, size_t aSize)
{
#ifdef XP_WIN
  // The region starting at addr may have been allocated in multiple calls
  // to VirtualAlloc and recycled, so committing the entire region in one
  // go may not be valid. However, since we allocate at least a chunk at a
  // time, we may touch any region in chunksized increments.
  size_t pages_size = std::min(aSize, kChunkSize - GetChunkOffsetForPtr(aAddr));
  while (aSize > 0) {
    if (!VirtualAlloc(aAddr, pages_size, MEM_COMMIT, PAGE_READWRITE)) {
      return false;
    }
    aAddr = (void*)((uintptr_t)aAddr + pages_size);
    aSize -= pages_size;
    pages_size = std::min(aSize, kChunkSize);
  }
#else
  if (mmap(aAddr,
           aSize,
           PROT_READ | PROT_WRITE,
           MAP_FIXED | MAP_PRIVATE | MAP_ANON,
           -1,
           0) == MAP_FAILED) {
    return false;
  }
  MozTagAnonymousMemory(aAddr, aSize, "jemalloc");
#endif
  return true;
}

static bool
base_pages_alloc(size_t minsize)
{
  size_t csize;
  size_t pminsize;

  MOZ_ASSERT(minsize != 0);
  csize = CHUNK_CEILING(minsize);
  base_pages = chunk_alloc(csize, kChunkSize, true);
  if (!base_pages) {
    return true;
  }
  base_next_addr = base_pages;
  base_past_addr = (void*)((uintptr_t)base_pages + csize);
  // Leave enough pages for minsize committed, since otherwise they would
  // have to be immediately recommitted.
  pminsize = PAGE_CEILING(minsize);
  base_next_decommitted = (void*)((uintptr_t)base_pages + pminsize);
#if defined(MALLOC_DECOMMIT)
  if (pminsize < csize) {
    pages_decommit(base_next_decommitted, csize - pminsize);
  }
#endif
  base_mapped += csize;
  base_committed += pminsize;

  return false;
}

static void*
base_alloc(size_t aSize)
{
  void* ret;
  size_t csize;

  // Round size up to nearest multiple of the cacheline size.
  csize = CACHELINE_CEILING(aSize);

  MutexAutoLock lock(base_mtx);
  // Make sure there's enough space for the allocation.
  if ((uintptr_t)base_next_addr + csize > (uintptr_t)base_past_addr) {
    if (base_pages_alloc(csize)) {
      return nullptr;
    }
  }
  // Allocate.
  ret = base_next_addr;
  base_next_addr = (void*)((uintptr_t)base_next_addr + csize);
  // Make sure enough pages are committed for the new allocation.
  if ((uintptr_t)base_next_addr > (uintptr_t)base_next_decommitted) {
    void* pbase_next_addr = (void*)(PAGE_CEILING((uintptr_t)base_next_addr));

#ifdef MALLOC_DECOMMIT
    if (!pages_commit(base_next_decommitted,
                      (uintptr_t)pbase_next_addr -
                        (uintptr_t)base_next_decommitted)) {
      return nullptr;
    }
#endif
    base_next_decommitted = pbase_next_addr;
    base_committed +=
      (uintptr_t)pbase_next_addr - (uintptr_t)base_next_decommitted;
  }

  return ret;
}

static void*
base_calloc(size_t aNumber, size_t aSize)
{
  void* ret = base_alloc(aNumber * aSize);
  if (ret) {
    memset(ret, 0, aNumber * aSize);
  }
  return ret;
}

static extent_node_t*
base_node_alloc(void)
{
  extent_node_t* ret;

  base_mtx.Lock();
  if (base_nodes) {
    ret = base_nodes;
    base_nodes = *(extent_node_t**)ret;
    base_mtx.Unlock();
  } else {
    base_mtx.Unlock();
    ret = (extent_node_t*)base_alloc(sizeof(extent_node_t));
  }

  return ret;
}

static void
base_node_dealloc(extent_node_t* aNode)
{
  MutexAutoLock lock(base_mtx);
  *(extent_node_t**)aNode = base_nodes;
  base_nodes = aNode;
}

struct BaseNodeFreePolicy
{
  void operator()(extent_node_t* aPtr) { base_node_dealloc(aPtr); }
};

using UniqueBaseNode = UniquePtr<extent_node_t, BaseNodeFreePolicy>;

// End Utility functions/macros.
// ***************************************************************************
// Begin chunk management functions.

#ifdef XP_WIN

static void*
pages_map(void* aAddr, size_t aSize)
{
  void* ret = nullptr;
  ret = VirtualAlloc(aAddr, aSize, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
  return ret;
}

static void
pages_unmap(void* aAddr, size_t aSize)
{
  if (VirtualFree(aAddr, 0, MEM_RELEASE) == 0) {
    _malloc_message(_getprogname(), ": (malloc) Error in VirtualFree()\n");
  }
}
#else

static void
pages_unmap(void* aAddr, size_t aSize)
{
  if (munmap(aAddr, aSize) == -1) {
    char buf[64];

    if (strerror_r(errno, buf, sizeof(buf)) == 0) {
      _malloc_message(
        _getprogname(), ": (malloc) Error in munmap(): ", buf, "\n");
    }
  }
}

static void*
pages_map(void* aAddr, size_t aSize)
{
  void* ret;
#if defined(__ia64__) ||                                                       \
  (defined(__sparc__) && defined(__arch64__) && defined(__linux__))
  // The JS engine assumes that all allocated pointers have their high 17 bits
  // clear, which ia64's mmap doesn't support directly. However, we can emulate
  // it by passing mmap an "addr" parameter with those bits clear. The mmap will
  // return that address, or the nearest available memory above that address,
  // providing a near-guarantee that those bits are clear. If they are not, we
  // return nullptr below to indicate out-of-memory.
  //
  // The addr is chosen as 0x0000070000000000, which still allows about 120TB of
  // virtual address space.
  //
  // See Bug 589735 for more information.
  bool check_placement = true;
  if (!aAddr) {
    aAddr = (void*)0x0000070000000000;
    check_placement = false;
  }
#endif

#if defined(__sparc__) && defined(__arch64__) && defined(__linux__)
  const uintptr_t start = 0x0000070000000000ULL;
  const uintptr_t end = 0x0000800000000000ULL;

  // Copied from js/src/gc/Memory.cpp and adapted for this source
  uintptr_t hint;
  void* region = MAP_FAILED;
  for (hint = start; region == MAP_FAILED && hint + aSize <= end;
       hint += kChunkSize) {
    region = mmap((void*)hint,
                  aSize,
                  PROT_READ | PROT_WRITE,
                  MAP_PRIVATE | MAP_ANON,
                  -1,
                  0);
    if (region != MAP_FAILED) {
      if (((size_t)region + (aSize - 1)) & 0xffff800000000000) {
        if (munmap(region, aSize)) {
          MOZ_ASSERT(errno == ENOMEM);
        }
        region = MAP_FAILED;
      }
    }
  }
  ret = region;
#else
  // We don't use MAP_FIXED here, because it can cause the *replacement*
  // of existing mappings, and we only want to create new mappings.
  ret =
    mmap(aAddr, aSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
  MOZ_ASSERT(ret);
#endif
  if (ret == MAP_FAILED) {
    ret = nullptr;
  }
#if defined(__ia64__) ||                                                       \
  (defined(__sparc__) && defined(__arch64__) && defined(__linux__))
  // If the allocated memory doesn't have its upper 17 bits clear, consider it
  // as out of memory.
  else if ((long long)ret & 0xffff800000000000) {
    munmap(ret, aSize);
    ret = nullptr;
  }
  // If the caller requested a specific memory location, verify that's what mmap
  // returned.
  else if (check_placement && ret != aAddr) {
#else
  else if (aAddr && ret != aAddr) {
#endif
    // We succeeded in mapping memory, but not in the right place.
    pages_unmap(ret, aSize);
    ret = nullptr;
  }
  if (ret) {
    MozTagAnonymousMemory(ret, aSize, "jemalloc");
  }

#if defined(__ia64__) ||                                                       \
  (defined(__sparc__) && defined(__arch64__) && defined(__linux__))
  MOZ_ASSERT(!ret || (!check_placement && ret) ||
             (check_placement && ret == aAddr));
#else
  MOZ_ASSERT(!ret || (!aAddr && ret != aAddr) || (aAddr && ret == aAddr));
#endif
  return ret;
}
#endif

#ifdef XP_DARWIN
#define VM_COPY_MIN (gPageSize * 32)
static inline void
pages_copy(void* dest, const void* src, size_t n)
{

  MOZ_ASSERT((void*)((uintptr_t)dest & ~gPageSizeMask) == dest);
  MOZ_ASSERT(n >= VM_COPY_MIN);
  MOZ_ASSERT((void*)((uintptr_t)src & ~gPageSizeMask) == src);

  vm_copy(
    mach_task_self(), (vm_address_t)src, (vm_size_t)n, (vm_address_t)dest);
}
#endif

template<size_t Bits>
bool
AddressRadixTree<Bits>::Init()
{
  mLock.Init();
  mRoot = (void**)base_calloc(1 << kBitsAtLevel1, sizeof(void*));
  return mRoot;
}

template<size_t Bits>
void**
AddressRadixTree<Bits>::GetSlot(void* aKey, bool aCreate)
{
  uintptr_t key = reinterpret_cast<uintptr_t>(aKey);
  uintptr_t subkey;
  unsigned i, lshift, height, bits;
  void** node;
  void** child;

  for (i = lshift = 0, height = kHeight, node = mRoot; i < height - 1;
       i++, lshift += bits, node = child) {
    bits = i ? kBitsPerLevel : kBitsAtLevel1;
    subkey = (key << lshift) >> ((sizeof(void*) << 3) - bits);
    child = (void**)node[subkey];
    if (!child && aCreate) {
      child = (void**)base_calloc(1 << kBitsPerLevel, sizeof(void*));
      if (child) {
        node[subkey] = child;
      }
    }
    if (!child) {
      return nullptr;
    }
  }

  // node is a leaf, so it contains values rather than node
  // pointers.
  bits = i ? kBitsPerLevel : kBitsAtLevel1;
  subkey = (key << lshift) >> ((sizeof(void*) << 3) - bits);
  return &node[subkey];
}

template<size_t Bits>
void*
AddressRadixTree<Bits>::Get(void* aKey)
{
  void* ret = nullptr;

  void** slot = GetSlot(aKey);

  if (slot) {
    ret = *slot;
  }
#ifdef MOZ_DEBUG
  MutexAutoLock lock(mLock);

  // Suppose that it were possible for a jemalloc-allocated chunk to be
  // munmap()ped, followed by a different allocator in another thread re-using
  // overlapping virtual memory, all without invalidating the cached rtree
  // value.  The result would be a false positive (the rtree would claim that
  // jemalloc owns memory that it had actually discarded).  I don't think this
  // scenario is possible, but the following assertion is a prudent sanity
  // check.
  if (!slot) {
    // In case a slot has been created in the meantime.
    slot = GetSlot(aKey);
  }
  if (slot) {
    // The MutexAutoLock above should act as a memory barrier, forcing
    // the compiler to emit a new read instruction for *slot.
    MOZ_ASSERT(ret == *slot);
  } else {
    MOZ_ASSERT(ret == nullptr);
  }
#endif
  return ret;
}

template<size_t Bits>
bool
AddressRadixTree<Bits>::Set(void* aKey, void* aValue)
{
  MutexAutoLock lock(mLock);
  void** slot = GetSlot(aKey, /* create = */ true);
  if (slot) {
    *slot = aValue;
  }
  return slot;
}

// pages_trim, chunk_alloc_mmap_slow and chunk_alloc_mmap were cherry-picked
// from upstream jemalloc 3.4.1 to fix Mozilla bug 956501.

// Return the offset between a and the nearest aligned address at or below a.
#define ALIGNMENT_ADDR2OFFSET(a, alignment)                                    \
  ((size_t)((uintptr_t)(a) & (alignment - 1)))

// Return the smallest alignment multiple that is >= s.
#define ALIGNMENT_CEILING(s, alignment)                                        \
  (((s) + (alignment - 1)) & (~(alignment - 1)))

static void*
pages_trim(void* addr, size_t alloc_size, size_t leadsize, size_t size)
{
  void* ret = (void*)((uintptr_t)addr + leadsize);

  MOZ_ASSERT(alloc_size >= leadsize + size);
#ifdef XP_WIN
  {
    void* new_addr;

    pages_unmap(addr, alloc_size);
    new_addr = pages_map(ret, size);
    if (new_addr == ret) {
      return ret;
    }
    if (new_addr) {
      pages_unmap(new_addr, size);
    }
    return nullptr;
  }
#else
  {
    size_t trailsize = alloc_size - leadsize - size;

    if (leadsize != 0) {
      pages_unmap(addr, leadsize);
    }
    if (trailsize != 0) {
      pages_unmap((void*)((uintptr_t)ret + size), trailsize);
    }
    return ret;
  }
#endif
}

static void*
chunk_alloc_mmap_slow(size_t size, size_t alignment)
{
  void *ret, *pages;
  size_t alloc_size, leadsize;

  alloc_size = size + alignment - gPageSize;
  // Beware size_t wrap-around.
  if (alloc_size < size) {
    return nullptr;
  }
  do {
    pages = pages_map(nullptr, alloc_size);
    if (!pages) {
      return nullptr;
    }
    leadsize =
      ALIGNMENT_CEILING((uintptr_t)pages, alignment) - (uintptr_t)pages;
    ret = pages_trim(pages, alloc_size, leadsize, size);
  } while (!ret);

  MOZ_ASSERT(ret);
  return ret;
}

static void*
chunk_alloc_mmap(size_t size, size_t alignment)
{
  void* ret;
  size_t offset;

  // Ideally, there would be a way to specify alignment to mmap() (like
  // NetBSD has), but in the absence of such a feature, we have to work
  // hard to efficiently create aligned mappings. The reliable, but
  // slow method is to create a mapping that is over-sized, then trim the
  // excess. However, that always results in one or two calls to
  // pages_unmap().
  //
  // Optimistically try mapping precisely the right amount before falling
  // back to the slow method, with the expectation that the optimistic
  // approach works most of the time.
  ret = pages_map(nullptr, size);
  if (!ret) {
    return nullptr;
  }
  offset = ALIGNMENT_ADDR2OFFSET(ret, alignment);
  if (offset != 0) {
    pages_unmap(ret, size);
    return chunk_alloc_mmap_slow(size, alignment);
  }

  MOZ_ASSERT(ret);
  return ret;
}

// Purge and release the pages in the chunk of length `length` at `addr` to
// the OS.
// Returns whether the pages are guaranteed to be full of zeroes when the
// function returns.
// The force_zero argument explicitly requests that the memory is guaranteed
// to be full of zeroes when the function returns.
static bool
pages_purge(void* addr, size_t length, bool force_zero)
{
#ifdef MALLOC_DECOMMIT
  pages_decommit(addr, length);
  return true;
#else
#ifndef XP_LINUX
  if (force_zero) {
    memset(addr, 0, length);
  }
#endif
#ifdef XP_WIN
  // The region starting at addr may have been allocated in multiple calls
  // to VirtualAlloc and recycled, so resetting the entire region in one
  // go may not be valid. However, since we allocate at least a chunk at a
  // time, we may touch any region in chunksized increments.
  size_t pages_size = std::min(length, kChunkSize - GetChunkOffsetForPtr(addr));
  while (length > 0) {
    VirtualAlloc(addr, pages_size, MEM_RESET, PAGE_READWRITE);
    addr = (void*)((uintptr_t)addr + pages_size);
    length -= pages_size;
    pages_size = std::min(length, kChunkSize);
  }
  return force_zero;
#else
#ifdef XP_LINUX
#define JEMALLOC_MADV_PURGE MADV_DONTNEED
#define JEMALLOC_MADV_ZEROS true
#else // FreeBSD and Darwin.
#define JEMALLOC_MADV_PURGE MADV_FREE
#define JEMALLOC_MADV_ZEROS force_zero
#endif
  int err = madvise(addr, length, JEMALLOC_MADV_PURGE);
  return JEMALLOC_MADV_ZEROS && err == 0;
#undef JEMALLOC_MADV_PURGE
#undef JEMALLOC_MADV_ZEROS
#endif
#endif
}

static void*
chunk_recycle(size_t aSize, size_t aAlignment, bool* aZeroed)
{
  extent_node_t key;

  size_t alloc_size = aSize + aAlignment - kChunkSize;
  // Beware size_t wrap-around.
  if (alloc_size < aSize) {
    return nullptr;
  }
  key.mAddr = nullptr;
  key.mSize = alloc_size;
  chunks_mtx.Lock();
  extent_node_t* node = gChunksBySize.SearchOrNext(&key);
  if (!node) {
    chunks_mtx.Unlock();
    return nullptr;
  }
  size_t leadsize = ALIGNMENT_CEILING((uintptr_t)node->mAddr, aAlignment) -
                    (uintptr_t)node->mAddr;
  MOZ_ASSERT(node->mSize >= leadsize + aSize);
  size_t trailsize = node->mSize - leadsize - aSize;
  void* ret = (void*)((uintptr_t)node->mAddr + leadsize);
  ChunkType chunk_type = node->mChunkType;
  if (aZeroed) {
    *aZeroed = (chunk_type == ZEROED_CHUNK);
  }
  // Remove node from the tree.
  gChunksBySize.Remove(node);
  gChunksByAddress.Remove(node);
  if (leadsize != 0) {
    // Insert the leading space as a smaller chunk.
    node->mSize = leadsize;
    gChunksBySize.Insert(node);
    gChunksByAddress.Insert(node);
    node = nullptr;
  }
  if (trailsize != 0) {
    // Insert the trailing space as a smaller chunk.
    if (!node) {
      // An additional node is required, but
      // base_node_alloc() can cause a new base chunk to be
      // allocated.  Drop chunks_mtx in order to avoid
      // deadlock, and if node allocation fails, deallocate
      // the result before returning an error.
      chunks_mtx.Unlock();
      node = base_node_alloc();
      if (!node) {
        chunk_dealloc(ret, aSize, chunk_type);
        return nullptr;
      }
      chunks_mtx.Lock();
    }
    node->mAddr = (void*)((uintptr_t)(ret) + aSize);
    node->mSize = trailsize;
    node->mChunkType = chunk_type;
    gChunksBySize.Insert(node);
    gChunksByAddress.Insert(node);
    node = nullptr;
  }

  gRecycledSize -= aSize;

  chunks_mtx.Unlock();

  if (node) {
    base_node_dealloc(node);
  }
#ifdef MALLOC_DECOMMIT
  if (!pages_commit(ret, aSize)) {
    return nullptr;
  }
  // pages_commit is guaranteed to zero the chunk.
  if (aZeroed) {
    *aZeroed = true;
  }
#endif
  return ret;
}

#ifdef XP_WIN
// On Windows, calls to VirtualAlloc and VirtualFree must be matched, making it
// awkward to recycle allocations of varying sizes. Therefore we only allow
// recycling when the size equals the chunksize, unless deallocation is entirely
// disabled.
#define CAN_RECYCLE(size) (size == kChunkSize)
#else
#define CAN_RECYCLE(size) true
#endif

// Allocates `size` bytes of system memory aligned for `alignment`.
// `base` indicates whether the memory will be used for the base allocator
// (e.g. base_alloc).
// `zeroed` is an outvalue that returns whether the allocated memory is
// guaranteed to be full of zeroes. It can be omitted when the caller doesn't
// care about the result.
static void*
chunk_alloc(size_t aSize, size_t aAlignment, bool aBase, bool* aZeroed)
{
  void* ret = nullptr;

  MOZ_ASSERT(aSize != 0);
  MOZ_ASSERT((aSize & kChunkSizeMask) == 0);
  MOZ_ASSERT(aAlignment != 0);
  MOZ_ASSERT((aAlignment & kChunkSizeMask) == 0);

  // Base allocations can't be fulfilled by recycling because of
  // possible deadlock or infinite recursion.
  if (CAN_RECYCLE(aSize) && !aBase) {
    ret = chunk_recycle(aSize, aAlignment, aZeroed);
  }
  if (!ret) {
    ret = chunk_alloc_mmap(aSize, aAlignment);
    if (aZeroed) {
      *aZeroed = true;
    }
  }
  if (ret && !aBase) {
    if (!gChunkRTree.Set(ret, ret)) {
      chunk_dealloc(ret, aSize, UNKNOWN_CHUNK);
      return nullptr;
    }
  }

  MOZ_ASSERT(GetChunkOffsetForPtr(ret) == 0);
  return ret;
}

static void
chunk_ensure_zero(void* aPtr, size_t aSize, bool aZeroed)
{
  if (aZeroed == false) {
    memset(aPtr, 0, aSize);
  }
#ifdef MOZ_DEBUG
  else {
    size_t i;
    size_t* p = (size_t*)(uintptr_t)aPtr;

    for (i = 0; i < aSize / sizeof(size_t); i++) {
      MOZ_ASSERT(p[i] == 0);
    }
  }
#endif
}

static void
chunk_record(void* aChunk, size_t aSize, ChunkType aType)
{
  extent_node_t key;

  if (aType != ZEROED_CHUNK) {
    if (pages_purge(aChunk, aSize, aType == HUGE_CHUNK)) {
      aType = ZEROED_CHUNK;
    }
  }

  // Allocate a node before acquiring chunks_mtx even though it might not
  // be needed, because base_node_alloc() may cause a new base chunk to
  // be allocated, which could cause deadlock if chunks_mtx were already
  // held.
  UniqueBaseNode xnode(base_node_alloc());
  // Use xprev to implement conditional deferred deallocation of prev.
  UniqueBaseNode xprev;

  // RAII deallocates xnode and xprev defined above after unlocking
  // in order to avoid potential dead-locks
  MutexAutoLock lock(chunks_mtx);
  key.mAddr = (void*)((uintptr_t)aChunk + aSize);
  extent_node_t* node = gChunksByAddress.SearchOrNext(&key);
  // Try to coalesce forward.
  if (node && node->mAddr == key.mAddr) {
    // Coalesce chunk with the following address range.  This does
    // not change the position within gChunksByAddress, so only
    // remove/insert from/into gChunksBySize.
    gChunksBySize.Remove(node);
    node->mAddr = aChunk;
    node->mSize += aSize;
    if (node->mChunkType != aType) {
      node->mChunkType = RECYCLED_CHUNK;
    }
    gChunksBySize.Insert(node);
  } else {
    // Coalescing forward failed, so insert a new node.
    if (!xnode) {
      // base_node_alloc() failed, which is an exceedingly
      // unlikely failure.  Leak chunk; its pages have
      // already been purged, so this is only a virtual
      // memory leak.
      return;
    }
    node = xnode.release();
    node->mAddr = aChunk;
    node->mSize = aSize;
    node->mChunkType = aType;
    gChunksByAddress.Insert(node);
    gChunksBySize.Insert(node);
  }

  // Try to coalesce backward.
  extent_node_t* prev = gChunksByAddress.Prev(node);
  if (prev && (void*)((uintptr_t)prev->mAddr + prev->mSize) == aChunk) {
    // Coalesce chunk with the previous address range.  This does
    // not change the position within gChunksByAddress, so only
    // remove/insert node from/into gChunksBySize.
    gChunksBySize.Remove(prev);
    gChunksByAddress.Remove(prev);

    gChunksBySize.Remove(node);
    node->mAddr = prev->mAddr;
    node->mSize += prev->mSize;
    if (node->mChunkType != prev->mChunkType) {
      node->mChunkType = RECYCLED_CHUNK;
    }
    gChunksBySize.Insert(node);

    xprev.reset(prev);
  }

  gRecycledSize += aSize;
}

static void
chunk_dealloc(void* aChunk, size_t aSize, ChunkType aType)
{
  MOZ_ASSERT(aChunk);
  MOZ_ASSERT(GetChunkOffsetForPtr(aChunk) == 0);
  MOZ_ASSERT(aSize != 0);
  MOZ_ASSERT((aSize & kChunkSizeMask) == 0);

  gChunkRTree.Unset(aChunk);

  if (CAN_RECYCLE(aSize)) {
    size_t recycled_so_far = gRecycledSize;
    // In case some race condition put us above the limit.
    if (recycled_so_far < gRecycleLimit) {
      size_t recycle_remaining = gRecycleLimit - recycled_so_far;
      size_t to_recycle;
      if (aSize > recycle_remaining) {
        to_recycle = recycle_remaining;
        // Drop pages that would overflow the recycle limit
        pages_trim(aChunk, aSize, 0, to_recycle);
      } else {
        to_recycle = aSize;
      }
      chunk_record(aChunk, to_recycle, aType);
      return;
    }
  }

  pages_unmap(aChunk, aSize);
}

#undef CAN_RECYCLE

// End chunk management functions.
// ***************************************************************************
// Begin arena.

static inline arena_t*
thread_local_arena(bool enabled)
{
  arena_t* arena;

  if (enabled) {
    // The arena will essentially be leaked if this function is
    // called with `false`, but it doesn't matter at the moment.
    // because in practice nothing actually calls this function
    // with `false`, except maybe at shutdown.
    arena =
      gArenas.CreateArena(/* IsPrivate = */ false, /* Params = */ nullptr);
  } else {
    arena = gArenas.GetDefault();
  }
  thread_arena.set(arena);
  return arena;
}

template<>
inline void
MozJemalloc::jemalloc_thread_local_arena(bool aEnabled)
{
  if (malloc_init()) {
    thread_local_arena(aEnabled);
  }
}

// Choose an arena based on a per-thread value.
static inline arena_t*
choose_arena(size_t size)
{
  arena_t* ret = nullptr;

  // We can only use TLS if this is a PIC library, since for the static
  // library version, libc's malloc is used by TLS allocation, which
  // introduces a bootstrapping issue.

  if (size > kMaxQuantumClass) {
    // Force the default arena for larger allocations.
    ret = gArenas.GetDefault();
  } else {
    // Check TLS to see if our thread has requested a pinned arena.
    ret = thread_arena.get();
    if (!ret) {
      // Nothing in TLS. Pin this thread to the default arena.
      ret = thread_local_arena(false);
    }
  }

  MOZ_DIAGNOSTIC_ASSERT(ret);
  return ret;
}

static inline void*
arena_run_reg_alloc(arena_run_t* run, arena_bin_t* bin)
{
  void* ret;
  unsigned i, mask, bit, regind;

  MOZ_DIAGNOSTIC_ASSERT(run->mMagic == ARENA_RUN_MAGIC);
  MOZ_ASSERT(run->mRegionsMinElement < bin->mRunNumRegionsMask);

  // Move the first check outside the loop, so that run->mRegionsMinElement can
  // be updated unconditionally, without the possibility of updating it
  // multiple times.
  i = run->mRegionsMinElement;
  mask = run->mRegionsMask[i];
  if (mask != 0) {
    // Usable allocation found.
    bit = CountTrailingZeroes32(mask);

    regind = ((i << (LOG2(sizeof(int)) + 3)) + bit);
    MOZ_ASSERT(regind < bin->mRunNumRegions);
    ret = (void*)(((uintptr_t)run) + bin->mRunFirstRegionOffset +
                  (bin->mSizeClass * regind));

    // Clear bit.
    mask ^= (1U << bit);
    run->mRegionsMask[i] = mask;

    return ret;
  }

  for (i++; i < bin->mRunNumRegionsMask; i++) {
    mask = run->mRegionsMask[i];
    if (mask != 0) {
      // Usable allocation found.
      bit = CountTrailingZeroes32(mask);

      regind = ((i << (LOG2(sizeof(int)) + 3)) + bit);
      MOZ_ASSERT(regind < bin->mRunNumRegions);
      ret = (void*)(((uintptr_t)run) + bin->mRunFirstRegionOffset +
                    (bin->mSizeClass * regind));

      // Clear bit.
      mask ^= (1U << bit);
      run->mRegionsMask[i] = mask;

      // Make a note that nothing before this element
      // contains a free region.
      run->mRegionsMinElement = i; // Low payoff: + (mask == 0);

      return ret;
    }
  }
  // Not reached.
  MOZ_DIAGNOSTIC_ASSERT(0);
  return nullptr;
}

static inline void
arena_run_reg_dalloc(arena_run_t* run, arena_bin_t* bin, void* ptr, size_t size)
{
// To divide by a number D that is not a power of two we multiply
// by (2^21 / D) and then right shift by 21 positions.
//
//   X / D
//
// becomes
//
//   (X * size_invs[(D / kQuantum) - 3]) >> SIZE_INV_SHIFT

#define SIZE_INV_SHIFT 21
#define SIZE_INV(s) (((1U << SIZE_INV_SHIFT) / (s * kQuantum)) + 1)
  // clang-format off
  static const unsigned size_invs[] = {
    SIZE_INV(3),
    SIZE_INV(4), SIZE_INV(5), SIZE_INV(6), SIZE_INV(7),
    SIZE_INV(8), SIZE_INV(9), SIZE_INV(10), SIZE_INV(11),
    SIZE_INV(12),SIZE_INV(13), SIZE_INV(14), SIZE_INV(15),
    SIZE_INV(16),SIZE_INV(17), SIZE_INV(18), SIZE_INV(19),
    SIZE_INV(20),SIZE_INV(21), SIZE_INV(22), SIZE_INV(23),
    SIZE_INV(24),SIZE_INV(25), SIZE_INV(26), SIZE_INV(27),
    SIZE_INV(28),SIZE_INV(29), SIZE_INV(30), SIZE_INV(31)
  };
  // clang-format on
  unsigned diff, regind, elm, bit;

  MOZ_DIAGNOSTIC_ASSERT(run->mMagic == ARENA_RUN_MAGIC);
  static_assert(((sizeof(size_invs)) / sizeof(unsigned)) + 3 >=
                  kNumQuantumClasses,
                "size_invs doesn't have enough values");

  // Avoid doing division with a variable divisor if possible.  Using
  // actual division here can reduce allocator throughput by over 20%!
  diff =
    (unsigned)((uintptr_t)ptr - (uintptr_t)run - bin->mRunFirstRegionOffset);
  if (mozilla::IsPowerOfTwo(size)) {
    regind = diff >> FloorLog2(size);
  } else if (size <= ((sizeof(size_invs) / sizeof(unsigned)) * kQuantum) + 2) {
    regind = size_invs[(size / kQuantum) - 3] * diff;
    regind >>= SIZE_INV_SHIFT;
  } else {
    // size_invs isn't large enough to handle this size class, so
    // calculate regind using actual division.  This only happens
    // if the user increases small_max via the 'S' runtime
    // configuration option.
    regind = diff / size;
  };
  MOZ_DIAGNOSTIC_ASSERT(diff == regind * size);
  MOZ_DIAGNOSTIC_ASSERT(regind < bin->mRunNumRegions);

  elm = regind >> (LOG2(sizeof(int)) + 3);
  if (elm < run->mRegionsMinElement) {
    run->mRegionsMinElement = elm;
  }
  bit = regind - (elm << (LOG2(sizeof(int)) + 3));
  MOZ_DIAGNOSTIC_ASSERT((run->mRegionsMask[elm] & (1U << bit)) == 0);
  run->mRegionsMask[elm] |= (1U << bit);
#undef SIZE_INV
#undef SIZE_INV_SHIFT
}

bool
arena_t::SplitRun(arena_run_t* aRun, size_t aSize, bool aLarge, bool aZero)
{
  arena_chunk_t* chunk;
  size_t old_ndirty, run_ind, total_pages, need_pages, rem_pages, i;

  chunk = GetChunkForPtr(aRun);
  old_ndirty = chunk->ndirty;
  run_ind = (unsigned)((uintptr_t(aRun) - uintptr_t(chunk)) >> gPageSize2Pow);
  total_pages = (chunk->map[run_ind].bits & ~gPageSizeMask) >> gPageSize2Pow;
  need_pages = (aSize >> gPageSize2Pow);
  MOZ_ASSERT(need_pages > 0);
  MOZ_ASSERT(need_pages <= total_pages);
  rem_pages = total_pages - need_pages;

  for (i = 0; i < need_pages; i++) {
    // Commit decommitted pages if necessary.  If a decommitted
    // page is encountered, commit all needed adjacent decommitted
    // pages in one operation, in order to reduce system call
    // overhead.
    if (chunk->map[run_ind + i].bits & CHUNK_MAP_MADVISED_OR_DECOMMITTED) {
      size_t j;

      // Advance i+j to just past the index of the last page
      // to commit.  Clear CHUNK_MAP_DECOMMITTED and
      // CHUNK_MAP_MADVISED along the way.
      for (j = 0; i + j < need_pages && (chunk->map[run_ind + i + j].bits &
                                         CHUNK_MAP_MADVISED_OR_DECOMMITTED);
           j++) {
        // DECOMMITTED and MADVISED are mutually exclusive.
        MOZ_ASSERT(!(chunk->map[run_ind + i + j].bits & CHUNK_MAP_DECOMMITTED &&
                     chunk->map[run_ind + i + j].bits & CHUNK_MAP_MADVISED));

        chunk->map[run_ind + i + j].bits &= ~CHUNK_MAP_MADVISED_OR_DECOMMITTED;
      }

#ifdef MALLOC_DECOMMIT
      bool committed = pages_commit(
        (void*)(uintptr_t(chunk) + ((run_ind + i) << gPageSize2Pow)),
        j << gPageSize2Pow);
      // pages_commit zeroes pages, so mark them as such if it succeeded.
      // That's checked further below to avoid manually zeroing the pages.
      for (size_t k = 0; k < j; k++) {
        chunk->map[run_ind + i + k].bits |=
          committed ? CHUNK_MAP_ZEROED : CHUNK_MAP_DECOMMITTED;
      }
      if (!committed) {
        return false;
      }
#endif

      mStats.committed += j;
    }
  }

  mRunsAvail.Remove(&chunk->map[run_ind]);

  // Keep track of trailing unused pages for later use.
  if (rem_pages > 0) {
    chunk->map[run_ind + need_pages].bits =
      (rem_pages << gPageSize2Pow) |
      (chunk->map[run_ind + need_pages].bits & gPageSizeMask);
    chunk->map[run_ind + total_pages - 1].bits =
      (rem_pages << gPageSize2Pow) |
      (chunk->map[run_ind + total_pages - 1].bits & gPageSizeMask);
    mRunsAvail.Insert(&chunk->map[run_ind + need_pages]);
  }

  for (i = 0; i < need_pages; i++) {
    // Zero if necessary.
    if (aZero) {
      if ((chunk->map[run_ind + i].bits & CHUNK_MAP_ZEROED) == 0) {
        memset((void*)(uintptr_t(chunk) + ((run_ind + i) << gPageSize2Pow)),
               0,
               gPageSize);
        // CHUNK_MAP_ZEROED is cleared below.
      }
    }

    // Update dirty page accounting.
    if (chunk->map[run_ind + i].bits & CHUNK_MAP_DIRTY) {
      chunk->ndirty--;
      mNumDirty--;
      // CHUNK_MAP_DIRTY is cleared below.
    }

    // Initialize the chunk map.
    if (aLarge) {
      chunk->map[run_ind + i].bits = CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;
    } else {
      chunk->map[run_ind + i].bits = size_t(aRun) | CHUNK_MAP_ALLOCATED;
    }
  }

  // Set the run size only in the first element for large runs.  This is
  // primarily a debugging aid, since the lack of size info for trailing
  // pages only matters if the application tries to operate on an
  // interior pointer.
  if (aLarge) {
    chunk->map[run_ind].bits |= aSize;
  }

  if (chunk->ndirty == 0 && old_ndirty > 0) {
    mChunksDirty.Remove(chunk);
  }
  return true;
}

void
arena_t::InitChunk(arena_chunk_t* aChunk, bool aZeroed)
{
  size_t i;
  // WARNING: The following relies on !aZeroed meaning "used to be an arena
  // chunk".
  // When the chunk we're initializating as an arena chunk is zeroed, we
  // mark all runs are decommitted and zeroed.
  // When it is not, which we can assume means it's a recycled arena chunk,
  // all it can contain is an arena chunk header (which we're overwriting),
  // and zeroed or poisoned memory (because a recycled arena chunk will
  // have been emptied before being recycled). In that case, we can get
  // away with reusing the chunk as-is, marking all runs as madvised.

  size_t flags =
    aZeroed ? CHUNK_MAP_DECOMMITTED | CHUNK_MAP_ZEROED : CHUNK_MAP_MADVISED;

  mStats.mapped += kChunkSize;

  aChunk->arena = this;

  // Claim that no pages are in use, since the header is merely overhead.
  aChunk->ndirty = 0;

  // Initialize the map to contain one maximal free untouched run.
#ifdef MALLOC_DECOMMIT
  arena_run_t* run =
    (arena_run_t*)(uintptr_t(aChunk) + (gChunkHeaderNumPages << gPageSize2Pow));
#endif

  for (i = 0; i < gChunkHeaderNumPages; i++) {
    aChunk->map[i].bits = 0;
  }
  aChunk->map[i].bits = gMaxLargeClass | flags;
  for (i++; i < gChunkNumPages - 1; i++) {
    aChunk->map[i].bits = flags;
  }
  aChunk->map[gChunkNumPages - 1].bits = gMaxLargeClass | flags;

#ifdef MALLOC_DECOMMIT
  // Start out decommitted, in order to force a closer correspondence
  // between dirty pages and committed untouched pages.
  pages_decommit(run, gMaxLargeClass);
#endif
  mStats.committed += gChunkHeaderNumPages;

  // Insert the run into the tree of available runs.
  mRunsAvail.Insert(&aChunk->map[gChunkHeaderNumPages]);

#ifdef MALLOC_DOUBLE_PURGE
  new (&aChunk->chunks_madvised_elem) DoublyLinkedListElement<arena_chunk_t>();
#endif
}

void
arena_t::DeallocChunk(arena_chunk_t* aChunk)
{
  if (mSpare) {
    if (mSpare->ndirty > 0) {
      aChunk->arena->mChunksDirty.Remove(mSpare);
      mNumDirty -= mSpare->ndirty;
      mStats.committed -= mSpare->ndirty;
    }

#ifdef MALLOC_DOUBLE_PURGE
    if (mChunksMAdvised.ElementProbablyInList(mSpare)) {
      mChunksMAdvised.remove(mSpare);
    }
#endif

    chunk_dealloc((void*)mSpare, kChunkSize, ARENA_CHUNK);
    mStats.mapped -= kChunkSize;
    mStats.committed -= gChunkHeaderNumPages;
  }

  // Remove run from the tree of available runs, so that the arena does not use
  // it. Dirty page flushing only uses the tree of dirty chunks, so leaving this
  // chunk in the chunks_* trees is sufficient for that purpose.
  mRunsAvail.Remove(&aChunk->map[gChunkHeaderNumPages]);

  mSpare = aChunk;
}

arena_run_t*
arena_t::AllocRun(size_t aSize, bool aLarge, bool aZero)
{
  arena_run_t* run;
  arena_chunk_map_t* mapelm;
  arena_chunk_map_t key;

  MOZ_ASSERT(aSize <= gMaxLargeClass);
  MOZ_ASSERT((aSize & gPageSizeMask) == 0);

  // Search the arena's chunks for the lowest best fit.
  key.bits = aSize | CHUNK_MAP_KEY;
  mapelm = mRunsAvail.SearchOrNext(&key);
  if (mapelm) {
    arena_chunk_t* chunk = GetChunkForPtr(mapelm);
    size_t pageind =
      (uintptr_t(mapelm) - uintptr_t(chunk->map)) / sizeof(arena_chunk_map_t);

    run = (arena_run_t*)(uintptr_t(chunk) + (pageind << gPageSize2Pow));
  } else if (mSpare) {
    // Use the spare.
    arena_chunk_t* chunk = mSpare;
    mSpare = nullptr;
    run = (arena_run_t*)(uintptr_t(chunk) +
                         (gChunkHeaderNumPages << gPageSize2Pow));
    // Insert the run into the tree of available runs.
    mRunsAvail.Insert(&chunk->map[gChunkHeaderNumPages]);
  } else {
    // No usable runs.  Create a new chunk from which to allocate
    // the run.
    bool zeroed;
    arena_chunk_t* chunk =
      (arena_chunk_t*)chunk_alloc(kChunkSize, kChunkSize, false, &zeroed);
    if (!chunk) {
      return nullptr;
    }

    InitChunk(chunk, zeroed);
    run = (arena_run_t*)(uintptr_t(chunk) +
                         (gChunkHeaderNumPages << gPageSize2Pow));
  }
  // Update page map.
  return SplitRun(run, aSize, aLarge, aZero) ? run : nullptr;
}

void
arena_t::Purge(bool aAll)
{
  arena_chunk_t* chunk;
  size_t i, npages;
  // If all is set purge all dirty pages.
  size_t dirty_max = aAll ? 1 : mMaxDirty;
#ifdef MOZ_DEBUG
  size_t ndirty = 0;
  for (auto chunk : mChunksDirty.iter()) {
    ndirty += chunk->ndirty;
  }
  MOZ_ASSERT(ndirty == mNumDirty);
#endif
  MOZ_DIAGNOSTIC_ASSERT(aAll || (mNumDirty > mMaxDirty));

  // Iterate downward through chunks until enough dirty memory has been
  // purged.  Terminate as soon as possible in order to minimize the
  // number of system calls, even if a chunk has only been partially
  // purged.
  while (mNumDirty > (dirty_max >> 1)) {
#ifdef MALLOC_DOUBLE_PURGE
    bool madvised = false;
#endif
    chunk = mChunksDirty.Last();
    MOZ_DIAGNOSTIC_ASSERT(chunk);

    for (i = gChunkNumPages - 1; chunk->ndirty > 0; i--) {
      MOZ_DIAGNOSTIC_ASSERT(i >= gChunkHeaderNumPages);

      if (chunk->map[i].bits & CHUNK_MAP_DIRTY) {
#ifdef MALLOC_DECOMMIT
        const size_t free_operation = CHUNK_MAP_DECOMMITTED;
#else
        const size_t free_operation = CHUNK_MAP_MADVISED;
#endif
        MOZ_ASSERT((chunk->map[i].bits & CHUNK_MAP_MADVISED_OR_DECOMMITTED) ==
                   0);
        chunk->map[i].bits ^= free_operation | CHUNK_MAP_DIRTY;
        // Find adjacent dirty run(s).
        for (npages = 1; i > gChunkHeaderNumPages &&
                         (chunk->map[i - 1].bits & CHUNK_MAP_DIRTY);
             npages++) {
          i--;
          MOZ_ASSERT((chunk->map[i].bits & CHUNK_MAP_MADVISED_OR_DECOMMITTED) ==
                     0);
          chunk->map[i].bits ^= free_operation | CHUNK_MAP_DIRTY;
        }
        chunk->ndirty -= npages;
        mNumDirty -= npages;

#ifdef MALLOC_DECOMMIT
        pages_decommit((void*)(uintptr_t(chunk) + (i << gPageSize2Pow)),
                       (npages << gPageSize2Pow));
#endif
        mStats.committed -= npages;

#ifndef MALLOC_DECOMMIT
        madvise((void*)(uintptr_t(chunk) + (i << gPageSize2Pow)),
                (npages << gPageSize2Pow),
                MADV_FREE);
#ifdef MALLOC_DOUBLE_PURGE
        madvised = true;
#endif
#endif
        if (mNumDirty <= (dirty_max >> 1)) {
          break;
        }
      }
    }

    if (chunk->ndirty == 0) {
      mChunksDirty.Remove(chunk);
    }
#ifdef MALLOC_DOUBLE_PURGE
    if (madvised) {
      // The chunk might already be in the list, but this
      // makes sure it's at the front.
      if (mChunksMAdvised.ElementProbablyInList(chunk)) {
        mChunksMAdvised.remove(chunk);
      }
      mChunksMAdvised.pushFront(chunk);
    }
#endif
  }
}

void
arena_t::DallocRun(arena_run_t* aRun, bool aDirty)
{
  arena_chunk_t* chunk;
  size_t size, run_ind, run_pages;

  chunk = GetChunkForPtr(aRun);
  run_ind = (size_t)((uintptr_t(aRun) - uintptr_t(chunk)) >> gPageSize2Pow);
  MOZ_DIAGNOSTIC_ASSERT(run_ind >= gChunkHeaderNumPages);
  MOZ_DIAGNOSTIC_ASSERT(run_ind < gChunkNumPages);
  if ((chunk->map[run_ind].bits & CHUNK_MAP_LARGE) != 0) {
    size = chunk->map[run_ind].bits & ~gPageSizeMask;
  } else {
    size = aRun->mBin->mRunSize;
  }
  run_pages = (size >> gPageSize2Pow);

  // Mark pages as unallocated in the chunk map.
  if (aDirty) {
    size_t i;

    for (i = 0; i < run_pages; i++) {
      MOZ_DIAGNOSTIC_ASSERT((chunk->map[run_ind + i].bits & CHUNK_MAP_DIRTY) ==
                            0);
      chunk->map[run_ind + i].bits = CHUNK_MAP_DIRTY;
    }

    if (chunk->ndirty == 0) {
      mChunksDirty.Insert(chunk);
    }
    chunk->ndirty += run_pages;
    mNumDirty += run_pages;
  } else {
    size_t i;

    for (i = 0; i < run_pages; i++) {
      chunk->map[run_ind + i].bits &= ~(CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED);
    }
  }
  chunk->map[run_ind].bits = size | (chunk->map[run_ind].bits & gPageSizeMask);
  chunk->map[run_ind + run_pages - 1].bits =
    size | (chunk->map[run_ind + run_pages - 1].bits & gPageSizeMask);

  // Try to coalesce forward.
  if (run_ind + run_pages < gChunkNumPages &&
      (chunk->map[run_ind + run_pages].bits & CHUNK_MAP_ALLOCATED) == 0) {
    size_t nrun_size = chunk->map[run_ind + run_pages].bits & ~gPageSizeMask;

    // Remove successor from tree of available runs; the coalesced run is
    // inserted later.
    mRunsAvail.Remove(&chunk->map[run_ind + run_pages]);

    size += nrun_size;
    run_pages = size >> gPageSize2Pow;

    MOZ_DIAGNOSTIC_ASSERT(
      (chunk->map[run_ind + run_pages - 1].bits & ~gPageSizeMask) == nrun_size);
    chunk->map[run_ind].bits =
      size | (chunk->map[run_ind].bits & gPageSizeMask);
    chunk->map[run_ind + run_pages - 1].bits =
      size | (chunk->map[run_ind + run_pages - 1].bits & gPageSizeMask);
  }

  // Try to coalesce backward.
  if (run_ind > gChunkHeaderNumPages &&
      (chunk->map[run_ind - 1].bits & CHUNK_MAP_ALLOCATED) == 0) {
    size_t prun_size = chunk->map[run_ind - 1].bits & ~gPageSizeMask;

    run_ind -= prun_size >> gPageSize2Pow;

    // Remove predecessor from tree of available runs; the coalesced run is
    // inserted later.
    mRunsAvail.Remove(&chunk->map[run_ind]);

    size += prun_size;
    run_pages = size >> gPageSize2Pow;

    MOZ_DIAGNOSTIC_ASSERT((chunk->map[run_ind].bits & ~gPageSizeMask) ==
                          prun_size);
    chunk->map[run_ind].bits =
      size | (chunk->map[run_ind].bits & gPageSizeMask);
    chunk->map[run_ind + run_pages - 1].bits =
      size | (chunk->map[run_ind + run_pages - 1].bits & gPageSizeMask);
  }

  // Insert into tree of available runs, now that coalescing is complete.
  mRunsAvail.Insert(&chunk->map[run_ind]);

  // Deallocate chunk if it is now completely unused.
  if ((chunk->map[gChunkHeaderNumPages].bits &
       (~gPageSizeMask | CHUNK_MAP_ALLOCATED)) == gMaxLargeClass) {
    DeallocChunk(chunk);
  }

  // Enforce mMaxDirty.
  if (mNumDirty > mMaxDirty) {
    Purge(false);
  }
}

void
arena_t::TrimRunHead(arena_chunk_t* aChunk,
                     arena_run_t* aRun,
                     size_t aOldSize,
                     size_t aNewSize)
{
  size_t pageind = (uintptr_t(aRun) - uintptr_t(aChunk)) >> gPageSize2Pow;
  size_t head_npages = (aOldSize - aNewSize) >> gPageSize2Pow;

  MOZ_ASSERT(aOldSize > aNewSize);

  // Update the chunk map so that arena_t::RunDalloc() can treat the
  // leading run as separately allocated.
  aChunk->map[pageind].bits =
    (aOldSize - aNewSize) | CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;
  aChunk->map[pageind + head_npages].bits =
    aNewSize | CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;

  DallocRun(aRun, false);
}

void
arena_t::TrimRunTail(arena_chunk_t* aChunk,
                     arena_run_t* aRun,
                     size_t aOldSize,
                     size_t aNewSize,
                     bool aDirty)
{
  size_t pageind = (uintptr_t(aRun) - uintptr_t(aChunk)) >> gPageSize2Pow;
  size_t npages = aNewSize >> gPageSize2Pow;

  MOZ_ASSERT(aOldSize > aNewSize);

  // Update the chunk map so that arena_t::RunDalloc() can treat the
  // trailing run as separately allocated.
  aChunk->map[pageind].bits = aNewSize | CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;
  aChunk->map[pageind + npages].bits =
    (aOldSize - aNewSize) | CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;

  DallocRun((arena_run_t*)(uintptr_t(aRun) + aNewSize), aDirty);
}

arena_run_t*
arena_t::GetNonFullBinRun(arena_bin_t* aBin)
{
  arena_chunk_map_t* mapelm;
  arena_run_t* run;
  unsigned i, remainder;

  // Look for a usable run.
  mapelm = aBin->mNonFullRuns.First();
  if (mapelm) {
    // run is guaranteed to have available space.
    aBin->mNonFullRuns.Remove(mapelm);
    run = (arena_run_t*)(mapelm->bits & ~gPageSizeMask);
    return run;
  }
  // No existing runs have any space available.

  // Allocate a new run.
  run = AllocRun(aBin->mRunSize, false, false);
  if (!run) {
    return nullptr;
  }
  // Don't initialize if a race in arena_t::RunAlloc() allowed an existing
  // run to become usable.
  if (run == aBin->mCurrentRun) {
    return run;
  }

  // Initialize run internals.
  run->mBin = aBin;

  for (i = 0; i < aBin->mRunNumRegionsMask - 1; i++) {
    run->mRegionsMask[i] = UINT_MAX;
  }
  remainder = aBin->mRunNumRegions & ((1U << (LOG2(sizeof(int)) + 3)) - 1);
  if (remainder == 0) {
    run->mRegionsMask[i] = UINT_MAX;
  } else {
    // The last element has spare bits that need to be unset.
    run->mRegionsMask[i] =
      (UINT_MAX >> ((1U << (LOG2(sizeof(int)) + 3)) - remainder));
  }

  run->mRegionsMinElement = 0;

  run->mNumFree = aBin->mRunNumRegions;
#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  run->mMagic = ARENA_RUN_MAGIC;
#endif

  aBin->mNumRuns++;
  return run;
}

void
arena_bin_t::Init(SizeClass aSizeClass)
{
  size_t try_run_size;
  unsigned try_nregs, try_mask_nelms, try_reg0_offset;
  // Size of the run header, excluding mRegionsMask.
  static const size_t kFixedHeaderSize = offsetof(arena_run_t, mRegionsMask);

  MOZ_ASSERT(aSizeClass.Size() <= gMaxBinClass);

  try_run_size = gPageSize;

  mCurrentRun = nullptr;
  mNonFullRuns.Init();
  mSizeClass = aSizeClass.Size();
  mNumRuns = 0;

  // mRunSize expansion loop.
  while (true) {
    try_nregs = ((try_run_size - kFixedHeaderSize) / mSizeClass) +
                1; // Counter-act try_nregs-- in loop.

    // The do..while loop iteratively reduces the number of regions until
    // the run header and the regions no longer overlap.  A closed formula
    // would be quite messy, since there is an interdependency between the
    // header's mask length and the number of regions.
    do {
      try_nregs--;
      try_mask_nelms =
        (try_nregs >> (LOG2(sizeof(int)) + 3)) +
        ((try_nregs & ((1U << (LOG2(sizeof(int)) + 3)) - 1)) ? 1 : 0);
      try_reg0_offset = try_run_size - (try_nregs * mSizeClass);
    } while (kFixedHeaderSize + (sizeof(unsigned) * try_mask_nelms) >
             try_reg0_offset);

    // Don't allow runs larger than the largest possible large size class.
    if (try_run_size > gMaxLargeClass) {
      break;
    }

    // Try to keep the run overhead below kRunOverhead.
    if (Fraction(try_reg0_offset, try_run_size) <= kRunOverhead) {
      break;
    }

    // If the overhead is larger than the size class, it means the size class
    // is small and doesn't align very well with the header. It's desirable to
    // have smaller run sizes for them, so relax the overhead requirement.
    if (try_reg0_offset > mSizeClass) {
      if (Fraction(try_reg0_offset, try_run_size) <= kRunRelaxedOverhead) {
        break;
      }
    }

    // The run header includes one bit per region of the given size. For sizes
    // small enough, the number of regions is large enough that growing the run
    // size barely moves the needle for the overhead because of all those bits.
    // For example, for a size of 8 bytes, adding 4KiB to the run size adds
    // close to 512 bits to the header, which is 64 bytes.
    // With such overhead, there is no way to get to the wanted overhead above,
    // so we give up if the required size for mRegionsMask more than doubles the
    // size of the run header.
    if (try_mask_nelms * sizeof(unsigned) >= kFixedHeaderSize) {
      break;
    }

    // Try more aggressive settings.
    try_run_size += gPageSize;
  }

  MOZ_ASSERT(kFixedHeaderSize + (sizeof(unsigned) * try_mask_nelms) <=
             try_reg0_offset);
  MOZ_ASSERT((try_mask_nelms << (LOG2(sizeof(int)) + 3)) >= try_nregs);

  // Copy final settings.
  mRunSize = try_run_size;
  mRunNumRegions = try_nregs;
  mRunNumRegionsMask = try_mask_nelms;
  mRunFirstRegionOffset = try_reg0_offset;
}

void*
arena_t::MallocSmall(size_t aSize, bool aZero)
{
  void* ret;
  arena_bin_t* bin;
  arena_run_t* run;
  SizeClass sizeClass(aSize);
  aSize = sizeClass.Size();

  switch (sizeClass.Type()) {
    case SizeClass::Tiny:
      bin = &mBins[FloorLog2(aSize / kMinTinyClass)];
      break;
    case SizeClass::Quantum:
      bin = &mBins[kNumTinyClasses + (aSize / kQuantum) - 1];
      break;
    case SizeClass::SubPage:
      bin = &mBins[kNumTinyClasses + kNumQuantumClasses +
                   (FloorLog2(aSize / kMaxQuantumClass) - 1)];
      break;
    default:
      MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected size class type");
  }
  MOZ_DIAGNOSTIC_ASSERT(aSize == bin->mSizeClass);

  {
    MutexAutoLock lock(mLock);
    run = bin->mCurrentRun;
    if (MOZ_UNLIKELY(!run || run->mNumFree == 0)) {
      run = bin->mCurrentRun = GetNonFullBinRun(bin);
    }
    if (MOZ_UNLIKELY(!run)) {
      return nullptr;
    }
    MOZ_DIAGNOSTIC_ASSERT(run->mMagic == ARENA_RUN_MAGIC);
    MOZ_DIAGNOSTIC_ASSERT(run->mNumFree > 0);
    ret = arena_run_reg_alloc(run, bin);
    MOZ_DIAGNOSTIC_ASSERT(ret);
    run->mNumFree--;
    if (!ret) {
      return nullptr;
    }

    mStats.allocated_small += aSize;
  }

  if (!aZero) {
    ApplyZeroOrJunk(ret, aSize);
  } else {
    memset(ret, 0, aSize);
  }

  return ret;
}

void*
arena_t::MallocLarge(size_t aSize, bool aZero)
{
  void* ret;

  // Large allocation.
  aSize = PAGE_CEILING(aSize);

  {
    MutexAutoLock lock(mLock);
    ret = AllocRun(aSize, true, aZero);
    if (!ret) {
      return nullptr;
    }
    mStats.allocated_large += aSize;
  }

  if (!aZero) {
    ApplyZeroOrJunk(ret, aSize);
  }

  return ret;
}

void*
arena_t::Malloc(size_t aSize, bool aZero)
{
  MOZ_DIAGNOSTIC_ASSERT(mMagic == ARENA_MAGIC);
  MOZ_ASSERT(aSize != 0);

  if (aSize <= gMaxBinClass) {
    return MallocSmall(aSize, aZero);
  }
  if (aSize <= gMaxLargeClass) {
    return MallocLarge(aSize, aZero);
  }
  return MallocHuge(aSize, aZero);
}

// Only handles large allocations that require more than page alignment.
void*
arena_t::PallocLarge(size_t aAlignment, size_t aSize, size_t aAllocSize)
{
  void* ret;
  size_t offset;
  arena_chunk_t* chunk;

  MOZ_ASSERT((aSize & gPageSizeMask) == 0);
  MOZ_ASSERT((aAlignment & gPageSizeMask) == 0);

  {
    MutexAutoLock lock(mLock);
    ret = AllocRun(aAllocSize, true, false);
    if (!ret) {
      return nullptr;
    }

    chunk = GetChunkForPtr(ret);

    offset = uintptr_t(ret) & (aAlignment - 1);
    MOZ_ASSERT((offset & gPageSizeMask) == 0);
    MOZ_ASSERT(offset < aAllocSize);
    if (offset == 0) {
      TrimRunTail(chunk, (arena_run_t*)ret, aAllocSize, aSize, false);
    } else {
      size_t leadsize, trailsize;

      leadsize = aAlignment - offset;
      if (leadsize > 0) {
        TrimRunHead(
          chunk, (arena_run_t*)ret, aAllocSize, aAllocSize - leadsize);
        ret = (void*)(uintptr_t(ret) + leadsize);
      }

      trailsize = aAllocSize - leadsize - aSize;
      if (trailsize != 0) {
        // Trim trailing space.
        MOZ_ASSERT(trailsize < aAllocSize);
        TrimRunTail(chunk, (arena_run_t*)ret, aSize + trailsize, aSize, false);
      }
    }

    mStats.allocated_large += aSize;
  }

  ApplyZeroOrJunk(ret, aSize);
  return ret;
}

void*
arena_t::Palloc(size_t aAlignment, size_t aSize)
{
  void* ret;
  size_t ceil_size;

  // Round size up to the nearest multiple of alignment.
  //
  // This done, we can take advantage of the fact that for each small
  // size class, every object is aligned at the smallest power of two
  // that is non-zero in the base two representation of the size.  For
  // example:
  //
  //   Size |   Base 2 | Minimum alignment
  //   -----+----------+------------------
  //     96 |  1100000 |  32
  //    144 | 10100000 |  32
  //    192 | 11000000 |  64
  //
  // Depending on runtime settings, it is possible that arena_malloc()
  // will further round up to a power of two, but that never causes
  // correctness issues.
  ceil_size = ALIGNMENT_CEILING(aSize, aAlignment);

  // (ceil_size < aSize) protects against the combination of maximal
  // alignment and size greater than maximal alignment.
  if (ceil_size < aSize) {
    // size_t overflow.
    return nullptr;
  }

  if (ceil_size <= gPageSize ||
      (aAlignment <= gPageSize && ceil_size <= gMaxLargeClass)) {
    ret = Malloc(ceil_size, false);
  } else {
    size_t run_size;

    // We can't achieve sub-page alignment, so round up alignment
    // permanently; it makes later calculations simpler.
    aAlignment = PAGE_CEILING(aAlignment);
    ceil_size = PAGE_CEILING(aSize);

    // (ceil_size < aSize) protects against very large sizes within
    // pagesize of SIZE_T_MAX.
    //
    // (ceil_size + aAlignment < ceil_size) protects against the
    // combination of maximal alignment and ceil_size large enough
    // to cause overflow.  This is similar to the first overflow
    // check above, but it needs to be repeated due to the new
    // ceil_size value, which may now be *equal* to maximal
    // alignment, whereas before we only detected overflow if the
    // original size was *greater* than maximal alignment.
    if (ceil_size < aSize || ceil_size + aAlignment < ceil_size) {
      // size_t overflow.
      return nullptr;
    }

    // Calculate the size of the over-size run that arena_palloc()
    // would need to allocate in order to guarantee the alignment.
    if (ceil_size >= aAlignment) {
      run_size = ceil_size + aAlignment - gPageSize;
    } else {
      // It is possible that (aAlignment << 1) will cause
      // overflow, but it doesn't matter because we also
      // subtract pagesize, which in the case of overflow
      // leaves us with a very large run_size.  That causes
      // the first conditional below to fail, which means
      // that the bogus run_size value never gets used for
      // anything important.
      run_size = (aAlignment << 1) - gPageSize;
    }

    if (run_size <= gMaxLargeClass) {
      ret = PallocLarge(aAlignment, ceil_size, run_size);
    } else if (aAlignment <= kChunkSize) {
      ret = MallocHuge(ceil_size, false);
    } else {
      ret = PallocHuge(ceil_size, aAlignment, false);
    }
  }

  MOZ_ASSERT((uintptr_t(ret) & (aAlignment - 1)) == 0);
  return ret;
}

// Return the size of the allocation pointed to by ptr.
static size_t
arena_salloc(const void* ptr)
{
  size_t ret;
  arena_chunk_t* chunk;
  size_t pageind, mapbits;

  MOZ_ASSERT(ptr);
  MOZ_ASSERT(GetChunkOffsetForPtr(ptr) != 0);

  chunk = GetChunkForPtr(ptr);
  pageind = (((uintptr_t)ptr - (uintptr_t)chunk) >> gPageSize2Pow);
  mapbits = chunk->map[pageind].bits;
  MOZ_DIAGNOSTIC_ASSERT((mapbits & CHUNK_MAP_ALLOCATED) != 0);
  if ((mapbits & CHUNK_MAP_LARGE) == 0) {
    arena_run_t* run = (arena_run_t*)(mapbits & ~gPageSizeMask);
    MOZ_DIAGNOSTIC_ASSERT(run->mMagic == ARENA_RUN_MAGIC);
    ret = run->mBin->mSizeClass;
  } else {
    ret = mapbits & ~gPageSizeMask;
    MOZ_DIAGNOSTIC_ASSERT(ret != 0);
  }

  return ret;
}

class AllocInfo
{
public:
  template<bool Validate = false>
  static inline AllocInfo Get(const void* aPtr)
  {
    // If the allocator is not initialized, the pointer can't belong to it.
    if (Validate && malloc_initialized == false) {
      return AllocInfo();
    }

    auto chunk = GetChunkForPtr(aPtr);
    if (Validate) {
      if (!chunk || !gChunkRTree.Get(chunk)) {
        return AllocInfo();
      }
    }

    if (chunk != aPtr) {
      MOZ_DIAGNOSTIC_ASSERT(chunk->arena->mMagic == ARENA_MAGIC);
      return AllocInfo(arena_salloc(aPtr), chunk);
    }

    extent_node_t key;

    // Huge allocation
    key.mAddr = chunk;
    MutexAutoLock lock(huge_mtx);
    extent_node_t* node = huge.Search(&key);
    if (Validate && !node) {
      return AllocInfo();
    }
    return AllocInfo(node->mSize, node);
  }

  // Validate ptr before assuming that it points to an allocation.  Currently,
  // the following validation is performed:
  //
  // + Check that ptr is not nullptr.
  //
  // + Check that ptr lies within a mapped chunk.
  static inline AllocInfo GetValidated(const void* aPtr)
  {
    return Get<true>(aPtr);
  }

  AllocInfo()
    : mSize(0)
    , mChunk(nullptr)
  {
  }

  explicit AllocInfo(size_t aSize, arena_chunk_t* aChunk)
    : mSize(aSize)
    , mChunk(aChunk)
  {
    MOZ_ASSERT(mSize <= gMaxLargeClass);
  }

  explicit AllocInfo(size_t aSize, extent_node_t* aNode)
    : mSize(aSize)
    , mNode(aNode)
  {
    MOZ_ASSERT(mSize > gMaxLargeClass);
  }

  size_t Size() { return mSize; }

  arena_t* Arena()
  {
    return (mSize <= gMaxLargeClass) ? mChunk->arena : mNode->mArena;
  }

private:
  size_t mSize;
  union {
    // Pointer to the chunk associated with the allocation for small
    // and large allocations.
    arena_chunk_t* mChunk;

    // Pointer to the extent node for huge allocations.
    extent_node_t* mNode;
  };
};

template<>
inline void
MozJemalloc::jemalloc_ptr_info(const void* aPtr, jemalloc_ptr_info_t* aInfo)
{
  arena_chunk_t* chunk = GetChunkForPtr(aPtr);

  // Is the pointer null, or within one chunk's size of null?
  // Alternatively, if the allocator is not initialized yet, the pointer
  // can't be known.
  if (!chunk || !malloc_initialized) {
    *aInfo = { TagUnknown, nullptr, 0 };
    return;
  }

  // Look for huge allocations before looking for |chunk| in gChunkRTree.
  // This is necessary because |chunk| won't be in gChunkRTree if it's
  // the second or subsequent chunk in a huge allocation.
  extent_node_t* node;
  extent_node_t key;
  {
    MutexAutoLock lock(huge_mtx);
    key.mAddr = const_cast<void*>(aPtr);
    node =
      reinterpret_cast<RedBlackTree<extent_node_t, ExtentTreeBoundsTrait>*>(
        &huge)
        ->Search(&key);
    if (node) {
      *aInfo = { TagLiveHuge, node->mAddr, node->mSize };
      return;
    }
  }

  // It's not a huge allocation. Check if we have a known chunk.
  if (!gChunkRTree.Get(chunk)) {
    *aInfo = { TagUnknown, nullptr, 0 };
    return;
  }

  MOZ_DIAGNOSTIC_ASSERT(chunk->arena->mMagic == ARENA_MAGIC);

  // Get the page number within the chunk.
  size_t pageind = (((uintptr_t)aPtr - (uintptr_t)chunk) >> gPageSize2Pow);
  if (pageind < gChunkHeaderNumPages) {
    // Within the chunk header.
    *aInfo = { TagUnknown, nullptr, 0 };
    return;
  }

  size_t mapbits = chunk->map[pageind].bits;

  if (!(mapbits & CHUNK_MAP_ALLOCATED)) {
    PtrInfoTag tag = TagFreedPageDirty;
    if (mapbits & CHUNK_MAP_DIRTY) {
      tag = TagFreedPageDirty;
    } else if (mapbits & CHUNK_MAP_DECOMMITTED) {
      tag = TagFreedPageDecommitted;
    } else if (mapbits & CHUNK_MAP_MADVISED) {
      tag = TagFreedPageMadvised;
    } else if (mapbits & CHUNK_MAP_ZEROED) {
      tag = TagFreedPageZeroed;
    } else {
      MOZ_CRASH();
    }

    void* pageaddr = (void*)(uintptr_t(aPtr) & ~gPageSizeMask);
    *aInfo = { tag, pageaddr, gPageSize };
    return;
  }

  if (mapbits & CHUNK_MAP_LARGE) {
    // It's a large allocation. Only the first page of a large
    // allocation contains its size, so if the address is not in
    // the first page, scan back to find the allocation size.
    size_t size;
    while (true) {
      size = mapbits & ~gPageSizeMask;
      if (size != 0) {
        break;
      }

      // The following two return paths shouldn't occur in
      // practice unless there is heap corruption.
      pageind--;
      MOZ_DIAGNOSTIC_ASSERT(pageind >= gChunkHeaderNumPages);
      if (pageind < gChunkHeaderNumPages) {
        *aInfo = { TagUnknown, nullptr, 0 };
        return;
      }

      mapbits = chunk->map[pageind].bits;
      MOZ_DIAGNOSTIC_ASSERT(mapbits & CHUNK_MAP_LARGE);
      if (!(mapbits & CHUNK_MAP_LARGE)) {
        *aInfo = { TagUnknown, nullptr, 0 };
        return;
      }
    }

    void* addr = ((char*)chunk) + (pageind << gPageSize2Pow);
    *aInfo = { TagLiveLarge, addr, size };
    return;
  }

  // It must be a small allocation.
  auto run = (arena_run_t*)(mapbits & ~gPageSizeMask);
  MOZ_DIAGNOSTIC_ASSERT(run->mMagic == ARENA_RUN_MAGIC);

  // The allocation size is stored in the run metadata.
  size_t size = run->mBin->mSizeClass;

  // Address of the first possible pointer in the run after its headers.
  uintptr_t reg0_addr = (uintptr_t)run + run->mBin->mRunFirstRegionOffset;
  if (aPtr < (void*)reg0_addr) {
    // In the run header.
    *aInfo = { TagUnknown, nullptr, 0 };
    return;
  }

  // Position in the run.
  unsigned regind = ((uintptr_t)aPtr - reg0_addr) / size;

  // Pointer to the allocation's base address.
  void* addr = (void*)(reg0_addr + regind * size);

  // Check if the allocation has been freed.
  unsigned elm = regind >> (LOG2(sizeof(int)) + 3);
  unsigned bit = regind - (elm << (LOG2(sizeof(int)) + 3));
  PtrInfoTag tag =
    ((run->mRegionsMask[elm] & (1U << bit))) ? TagFreedSmall : TagLiveSmall;

  *aInfo = { tag, addr, size };
}

namespace Debug {
// Helper for debuggers. We don't want it to be inlined and optimized out.
MOZ_NEVER_INLINE jemalloc_ptr_info_t*
jemalloc_ptr_info(const void* aPtr)
{
  static jemalloc_ptr_info_t info;
  MozJemalloc::jemalloc_ptr_info(aPtr, &info);
  return &info;
}
}

void
arena_t::DallocSmall(arena_chunk_t* aChunk,
                     void* aPtr,
                     arena_chunk_map_t* aMapElm)
{
  arena_run_t* run;
  arena_bin_t* bin;
  size_t size;

  run = (arena_run_t*)(aMapElm->bits & ~gPageSizeMask);
  MOZ_DIAGNOSTIC_ASSERT(run->mMagic == ARENA_RUN_MAGIC);
  bin = run->mBin;
  size = bin->mSizeClass;
  MOZ_DIAGNOSTIC_ASSERT(uintptr_t(aPtr) >=
                        uintptr_t(run) + bin->mRunFirstRegionOffset);
  MOZ_DIAGNOSTIC_ASSERT(
    (uintptr_t(aPtr) - (uintptr_t(run) + bin->mRunFirstRegionOffset)) % size ==
    0);

  memset(aPtr, kAllocPoison, size);

  arena_run_reg_dalloc(run, bin, aPtr, size);
  run->mNumFree++;

  if (run->mNumFree == bin->mRunNumRegions) {
    // Deallocate run.
    if (run == bin->mCurrentRun) {
      bin->mCurrentRun = nullptr;
    } else if (bin->mRunNumRegions != 1) {
      size_t run_pageind =
        (uintptr_t(run) - uintptr_t(aChunk)) >> gPageSize2Pow;
      arena_chunk_map_t* run_mapelm = &aChunk->map[run_pageind];

      // This block's conditional is necessary because if the
      // run only contains one region, then it never gets
      // inserted into the non-full runs tree.
      MOZ_DIAGNOSTIC_ASSERT(bin->mNonFullRuns.Search(run_mapelm) == run_mapelm);
      bin->mNonFullRuns.Remove(run_mapelm);
    }
#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
    run->mMagic = 0;
#endif
    DallocRun(run, true);
    bin->mNumRuns--;
  } else if (run->mNumFree == 1 && run != bin->mCurrentRun) {
    // Make sure that bin->mCurrentRun always refers to the lowest
    // non-full run, if one exists.
    if (!bin->mCurrentRun) {
      bin->mCurrentRun = run;
    } else if (uintptr_t(run) < uintptr_t(bin->mCurrentRun)) {
      // Switch mCurrentRun.
      if (bin->mCurrentRun->mNumFree > 0) {
        arena_chunk_t* runcur_chunk = GetChunkForPtr(bin->mCurrentRun);
        size_t runcur_pageind =
          (uintptr_t(bin->mCurrentRun) - uintptr_t(runcur_chunk)) >>
          gPageSize2Pow;
        arena_chunk_map_t* runcur_mapelm = &runcur_chunk->map[runcur_pageind];

        // Insert runcur.
        MOZ_DIAGNOSTIC_ASSERT(!bin->mNonFullRuns.Search(runcur_mapelm));
        bin->mNonFullRuns.Insert(runcur_mapelm);
      }
      bin->mCurrentRun = run;
    } else {
      size_t run_pageind =
        (uintptr_t(run) - uintptr_t(aChunk)) >> gPageSize2Pow;
      arena_chunk_map_t* run_mapelm = &aChunk->map[run_pageind];

      MOZ_DIAGNOSTIC_ASSERT(bin->mNonFullRuns.Search(run_mapelm) == nullptr);
      bin->mNonFullRuns.Insert(run_mapelm);
    }
  }
  mStats.allocated_small -= size;
}

void
arena_t::DallocLarge(arena_chunk_t* aChunk, void* aPtr)
{
  MOZ_DIAGNOSTIC_ASSERT((uintptr_t(aPtr) & gPageSizeMask) == 0);
  size_t pageind = (uintptr_t(aPtr) - uintptr_t(aChunk)) >> gPageSize2Pow;
  size_t size = aChunk->map[pageind].bits & ~gPageSizeMask;

  memset(aPtr, kAllocPoison, size);
  mStats.allocated_large -= size;

  DallocRun((arena_run_t*)aPtr, true);
}

static inline void
arena_dalloc(void* aPtr, size_t aOffset, arena_t* aArena)
{
  MOZ_ASSERT(aPtr);
  MOZ_ASSERT(aOffset != 0);
  MOZ_ASSERT(GetChunkOffsetForPtr(aPtr) == aOffset);

  auto chunk = (arena_chunk_t*)((uintptr_t)aPtr - aOffset);
  auto arena = chunk->arena;
  MOZ_ASSERT(arena);
  MOZ_DIAGNOSTIC_ASSERT(arena->mMagic == ARENA_MAGIC);
  MOZ_RELEASE_ASSERT(!aArena || arena == aArena);

  MutexAutoLock lock(arena->mLock);
  size_t pageind = aOffset >> gPageSize2Pow;
  arena_chunk_map_t* mapelm = &chunk->map[pageind];
  MOZ_DIAGNOSTIC_ASSERT((mapelm->bits & CHUNK_MAP_ALLOCATED) != 0);
  if ((mapelm->bits & CHUNK_MAP_LARGE) == 0) {
    // Small allocation.
    arena->DallocSmall(chunk, aPtr, mapelm);
  } else {
    // Large allocation.
    arena->DallocLarge(chunk, aPtr);
  }
}

static inline void
idalloc(void* ptr, arena_t* aArena)
{
  size_t offset;

  MOZ_ASSERT(ptr);

  offset = GetChunkOffsetForPtr(ptr);
  if (offset != 0) {
    arena_dalloc(ptr, offset, aArena);
  } else {
    huge_dalloc(ptr, aArena);
  }
}

void
arena_t::RallocShrinkLarge(arena_chunk_t* aChunk,
                           void* aPtr,
                           size_t aSize,
                           size_t aOldSize)
{
  MOZ_ASSERT(aSize < aOldSize);

  // Shrink the run, and make trailing pages available for other
  // allocations.
  MutexAutoLock lock(mLock);
  TrimRunTail(aChunk, (arena_run_t*)aPtr, aOldSize, aSize, true);
  mStats.allocated_large -= aOldSize - aSize;
}

// Returns whether reallocation was successful.
bool
arena_t::RallocGrowLarge(arena_chunk_t* aChunk,
                         void* aPtr,
                         size_t aSize,
                         size_t aOldSize)
{
  size_t pageind = (uintptr_t(aPtr) - uintptr_t(aChunk)) >> gPageSize2Pow;
  size_t npages = aOldSize >> gPageSize2Pow;

  MutexAutoLock lock(mLock);
  MOZ_DIAGNOSTIC_ASSERT(aOldSize ==
                        (aChunk->map[pageind].bits & ~gPageSizeMask));

  // Try to extend the run.
  MOZ_ASSERT(aSize > aOldSize);
  if (pageind + npages < gChunkNumPages &&
      (aChunk->map[pageind + npages].bits & CHUNK_MAP_ALLOCATED) == 0 &&
      (aChunk->map[pageind + npages].bits & ~gPageSizeMask) >=
        aSize - aOldSize) {
    // The next run is available and sufficiently large.  Split the
    // following run, then merge the first part with the existing
    // allocation.
    if (!SplitRun((arena_run_t*)(uintptr_t(aChunk) +
                                 ((pageind + npages) << gPageSize2Pow)),
                  aSize - aOldSize,
                  true,
                  false)) {
      return false;
    }

    aChunk->map[pageind].bits = aSize | CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;
    aChunk->map[pageind + npages].bits = CHUNK_MAP_LARGE | CHUNK_MAP_ALLOCATED;

    mStats.allocated_large += aSize - aOldSize;
    return true;
  }

  return false;
}

void*
arena_t::RallocSmallOrLarge(void* aPtr, size_t aSize, size_t aOldSize)
{
  void* ret;
  size_t copysize;
  SizeClass sizeClass(aSize);

  // Try to avoid moving the allocation.
  if (aOldSize <= gMaxLargeClass && sizeClass.Size() == aOldSize) {
    if (aSize < aOldSize) {
      memset((void*)(uintptr_t(aPtr) + aSize), kAllocPoison, aOldSize - aSize);
    }
    return aPtr;
  }
  if (sizeClass.Type() == SizeClass::Large && aOldSize > gMaxBinClass &&
      aOldSize <= gMaxLargeClass) {
    arena_chunk_t* chunk = GetChunkForPtr(aPtr);
    if (sizeClass.Size() < aOldSize) {
      // Fill before shrinking in order to avoid a race.
      memset((void*)((uintptr_t)aPtr + aSize), kAllocPoison, aOldSize - aSize);
      RallocShrinkLarge(chunk, aPtr, sizeClass.Size(), aOldSize);
      return aPtr;
    }
    if (RallocGrowLarge(chunk, aPtr, sizeClass.Size(), aOldSize)) {
      ApplyZeroOrJunk((void*)((uintptr_t)aPtr + aOldSize), aSize - aOldSize);
      return aPtr;
    }
  }

  // If we get here, then aSize and aOldSize are different enough that we
  // need to move the object.  In that case, fall back to allocating new
  // space and copying.
  ret = Malloc(aSize, false);
  if (!ret) {
    return nullptr;
  }

  // Junk/zero-filling were already done by arena_t::Malloc().
  copysize = (aSize < aOldSize) ? aSize : aOldSize;
#ifdef VM_COPY_MIN
  if (copysize >= VM_COPY_MIN) {
    pages_copy(ret, aPtr, copysize);
  } else
#endif
  {
    memcpy(ret, aPtr, copysize);
  }
  idalloc(aPtr, this);
  return ret;
}

void*
arena_t::Ralloc(void* aPtr, size_t aSize, size_t aOldSize)
{
  MOZ_DIAGNOSTIC_ASSERT(mMagic == ARENA_MAGIC);
  MOZ_ASSERT(aPtr);
  MOZ_ASSERT(aSize != 0);

  return (aSize <= gMaxLargeClass) ? RallocSmallOrLarge(aPtr, aSize, aOldSize)
                                   : RallocHuge(aPtr, aSize, aOldSize);
}

arena_t::arena_t(arena_params_t* aParams)
{
  unsigned i;

  MOZ_RELEASE_ASSERT(mLock.Init());

  memset(&mLink, 0, sizeof(mLink));
  memset(&mStats, 0, sizeof(arena_stats_t));

  // Initialize chunks.
  mChunksDirty.Init();
#ifdef MALLOC_DOUBLE_PURGE
  new (&mChunksMAdvised) DoublyLinkedList<arena_chunk_t>();
#endif
  mSpare = nullptr;

  mNumDirty = 0;

  // The default maximum amount of dirty pages allowed on arenas is a fraction
  // of opt_dirty_max.
  mMaxDirty =
    (aParams && aParams->mMaxDirty) ? aParams->mMaxDirty : (opt_dirty_max / 8);

  mRunsAvail.Init();

  // Initialize bins.
  SizeClass sizeClass(1);

  for (i = 0;; i++) {
    arena_bin_t& bin = mBins[i];
    bin.Init(sizeClass);

    // SizeClass doesn't want sizes larger than gMaxSubPageClass for now.
    if (sizeClass.Size() == gMaxSubPageClass) {
      break;
    }
    sizeClass = sizeClass.Next();
  }
  MOZ_ASSERT(i ==
             kNumTinyClasses + kNumQuantumClasses + gNumSubPageClasses - 1);

#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  mMagic = ARENA_MAGIC;
#endif
}

arena_t*
ArenaCollection::CreateArena(bool aIsPrivate, arena_params_t* aParams)
{
  fallible_t fallible;
  arena_t* ret = new (fallible) arena_t(aParams);
  if (!ret) {
    // Only reached if there is an OOM error.

    // OOM here is quite inconvenient to propagate, since dealing with it
    // would require a check for failure in the fast path.  Instead, punt
    // by using the first arena.
    // In practice, this is an extremely unlikely failure.
    _malloc_message(_getprogname(), ": (malloc) Error initializing arena\n");

    return mDefaultArena;
  }

  MutexAutoLock lock(mLock);

  // TODO: Use random Ids.
  ret->mId = mLastArenaId++;
  (aIsPrivate ? mPrivateArenas : mArenas).Insert(ret);
  return ret;
}

// End arena.
// ***************************************************************************
// Begin general internal functions.

void*
arena_t::MallocHuge(size_t aSize, bool aZero)
{
  return PallocHuge(aSize, kChunkSize, aZero);
}

void*
arena_t::PallocHuge(size_t aSize, size_t aAlignment, bool aZero)
{
  void* ret;
  size_t csize;
  size_t psize;
  extent_node_t* node;
  bool zeroed;

  // Allocate one or more contiguous chunks for this request.
  csize = CHUNK_CEILING(aSize);
  if (csize == 0) {
    // size is large enough to cause size_t wrap-around.
    return nullptr;
  }

  // Allocate an extent node with which to track the chunk.
  node = base_node_alloc();
  if (!node) {
    return nullptr;
  }

  ret = chunk_alloc(csize, aAlignment, false, &zeroed);
  if (!ret) {
    base_node_dealloc(node);
    return nullptr;
  }
  if (aZero) {
    chunk_ensure_zero(ret, csize, zeroed);
  }

  // Insert node into huge.
  node->mAddr = ret;
  psize = PAGE_CEILING(aSize);
  node->mSize = psize;
  node->mArena = this;

  {
    MutexAutoLock lock(huge_mtx);
    huge.Insert(node);

    // Although we allocated space for csize bytes, we indicate that we've
    // allocated only psize bytes.
    //
    // If DECOMMIT is defined, this is a reasonable thing to do, since
    // we'll explicitly decommit the bytes in excess of psize.
    //
    // If DECOMMIT is not defined, then we're relying on the OS to be lazy
    // about how it allocates physical pages to mappings.  If we never
    // touch the pages in excess of psize, the OS won't allocate a physical
    // page, and we won't use more than psize bytes of physical memory.
    //
    // A correct program will only touch memory in excess of how much it
    // requested if it first calls malloc_usable_size and finds out how
    // much space it has to play with.  But because we set node->mSize =
    // psize above, malloc_usable_size will return psize, not csize, and
    // the program will (hopefully) never touch bytes in excess of psize.
    // Thus those bytes won't take up space in physical memory, and we can
    // reasonably claim we never "allocated" them in the first place.
    huge_allocated += psize;
    huge_mapped += csize;
  }

#ifdef MALLOC_DECOMMIT
  if (csize - psize > 0) {
    pages_decommit((void*)((uintptr_t)ret + psize), csize - psize);
  }
#endif

  if (!aZero) {
#ifdef MALLOC_DECOMMIT
    ApplyZeroOrJunk(ret, psize);
#else
    ApplyZeroOrJunk(ret, csize);
#endif
  }

  return ret;
}

void*
arena_t::RallocHuge(void* aPtr, size_t aSize, size_t aOldSize)
{
  void* ret;
  size_t copysize;

  // Avoid moving the allocation if the size class would not change.
  if (aOldSize > gMaxLargeClass &&
      CHUNK_CEILING(aSize) == CHUNK_CEILING(aOldSize)) {
    size_t psize = PAGE_CEILING(aSize);
    if (aSize < aOldSize) {
      memset((void*)((uintptr_t)aPtr + aSize), kAllocPoison, aOldSize - aSize);
    }
#ifdef MALLOC_DECOMMIT
    if (psize < aOldSize) {
      extent_node_t key;

      pages_decommit((void*)((uintptr_t)aPtr + psize), aOldSize - psize);

      // Update recorded size.
      MutexAutoLock lock(huge_mtx);
      key.mAddr = const_cast<void*>(aPtr);
      extent_node_t* node = huge.Search(&key);
      MOZ_ASSERT(node);
      MOZ_ASSERT(node->mSize == aOldSize);
      MOZ_RELEASE_ASSERT(node->mArena == this);
      huge_allocated -= aOldSize - psize;
      // No need to change huge_mapped, because we didn't (un)map anything.
      node->mSize = psize;
    } else if (psize > aOldSize) {
      if (!pages_commit((void*)((uintptr_t)aPtr + aOldSize),
                        psize - aOldSize)) {
        return nullptr;
      }
    }
#endif

    // Although we don't have to commit or decommit anything if
    // DECOMMIT is not defined and the size class didn't change, we
    // do need to update the recorded size if the size increased,
    // so malloc_usable_size doesn't return a value smaller than
    // what was requested via realloc().
    if (psize > aOldSize) {
      // Update recorded size.
      extent_node_t key;
      MutexAutoLock lock(huge_mtx);
      key.mAddr = const_cast<void*>(aPtr);
      extent_node_t* node = huge.Search(&key);
      MOZ_ASSERT(node);
      MOZ_ASSERT(node->mSize == aOldSize);
      MOZ_RELEASE_ASSERT(node->mArena == this);
      huge_allocated += psize - aOldSize;
      // No need to change huge_mapped, because we didn't
      // (un)map anything.
      node->mSize = psize;
    }

    if (aSize > aOldSize) {
      ApplyZeroOrJunk((void*)((uintptr_t)aPtr + aOldSize), aSize - aOldSize);
    }
    return aPtr;
  }

  // If we get here, then aSize and aOldSize are different enough that we
  // need to use a different size class.  In that case, fall back to
  // allocating new space and copying.
  ret = MallocHuge(aSize, false);
  if (!ret) {
    return nullptr;
  }

  copysize = (aSize < aOldSize) ? aSize : aOldSize;
#ifdef VM_COPY_MIN
  if (copysize >= VM_COPY_MIN) {
    pages_copy(ret, aPtr, copysize);
  } else
#endif
  {
    memcpy(ret, aPtr, copysize);
  }
  idalloc(aPtr, this);
  return ret;
}

static void
huge_dalloc(void* aPtr, arena_t* aArena)
{
  extent_node_t* node;
  {
    extent_node_t key;
    MutexAutoLock lock(huge_mtx);

    // Extract from tree of huge allocations.
    key.mAddr = aPtr;
    node = huge.Search(&key);
    MOZ_ASSERT(node);
    MOZ_ASSERT(node->mAddr == aPtr);
    MOZ_RELEASE_ASSERT(!aArena || node->mArena == aArena);
    huge.Remove(node);

    huge_allocated -= node->mSize;
    huge_mapped -= CHUNK_CEILING(node->mSize);
  }

  // Unmap chunk.
  chunk_dealloc(node->mAddr, CHUNK_CEILING(node->mSize), HUGE_CHUNK);

  base_node_dealloc(node);
}

static size_t
GetKernelPageSize()
{
  static size_t kernel_page_size = ([]() {
#ifdef XP_WIN
    SYSTEM_INFO info;
    GetSystemInfo(&info);
    return info.dwPageSize;
#else
    long result = sysconf(_SC_PAGESIZE);
    MOZ_ASSERT(result != -1);
    return result;
#endif
  })();
  return kernel_page_size;
}

// Returns whether the allocator was successfully initialized.
static bool
malloc_init_hard()
{
  unsigned i;
  const char* opts;
  long result;

  AutoLock<StaticMutex> lock(gInitLock);

  if (malloc_initialized) {
    // Another thread initialized the allocator before this one
    // acquired gInitLock.
    return true;
  }

  if (!thread_arena.init()) {
    return true;
  }

  // Get page size and number of CPUs
  result = GetKernelPageSize();
  // We assume that the page size is a power of 2.
  MOZ_ASSERT(((result - 1) & result) == 0);
#ifdef MALLOC_STATIC_PAGESIZE
  if (gPageSize % (size_t)result) {
    _malloc_message(
      _getprogname(),
      "Compile-time page size does not divide the runtime one.\n");
    MOZ_CRASH();
  }
#else
  gPageSize = (size_t)result;
  DefineGlobals();
#endif

  // Get runtime configuration.
  if ((opts = getenv("MALLOC_OPTIONS"))) {
    for (i = 0; opts[i] != '\0'; i++) {
      unsigned j, nreps;
      bool nseen;

      // Parse repetition count, if any.
      for (nreps = 0, nseen = false;; i++, nseen = true) {
        switch (opts[i]) {
          case '0':
          case '1':
          case '2':
          case '3':
          case '4':
          case '5':
          case '6':
          case '7':
          case '8':
          case '9':
            nreps *= 10;
            nreps += opts[i] - '0';
            break;
          default:
            goto MALLOC_OUT;
        }
      }
    MALLOC_OUT:
      if (nseen == false) {
        nreps = 1;
      }

      for (j = 0; j < nreps; j++) {
        switch (opts[i]) {
          case 'f':
            opt_dirty_max >>= 1;
            break;
          case 'F':
            if (opt_dirty_max == 0) {
              opt_dirty_max = 1;
            } else if ((opt_dirty_max << 1) != 0) {
              opt_dirty_max <<= 1;
            }
            break;
#ifdef MOZ_DEBUG
          case 'j':
            opt_junk = false;
            break;
          case 'J':
            opt_junk = true;
            break;
#endif
#ifdef MOZ_DEBUG
          case 'z':
            opt_zero = false;
            break;
          case 'Z':
            opt_zero = true;
            break;
#endif
          default: {
            char cbuf[2];

            cbuf[0] = opts[i];
            cbuf[1] = '\0';
            _malloc_message(_getprogname(),
                            ": (malloc) Unsupported character "
                            "in malloc options: '",
                            cbuf,
                            "'\n");
          }
        }
      }
    }
  }

  gRecycledSize = 0;

  // Initialize chunks data.
  chunks_mtx.Init();
  gChunksBySize.Init();
  gChunksByAddress.Init();

  // Initialize huge allocation data.
  huge_mtx.Init();
  huge.Init();
  huge_allocated = 0;
  huge_mapped = 0;

  // Initialize base allocation data structures.
  base_mapped = 0;
  base_committed = 0;
  base_nodes = nullptr;
  base_mtx.Init();

  // Initialize arenas collection here.
  if (!gArenas.Init()) {
    return false;
  }

  // Assign the default arena to the initial thread.
  thread_arena.set(gArenas.GetDefault());

  if (!gChunkRTree.Init()) {
    return false;
  }

  malloc_initialized = true;

  // Dummy call so that the function is not removed by dead-code elimination
  Debug::jemalloc_ptr_info(nullptr);

#if !defined(XP_WIN) && !defined(XP_DARWIN)
  // Prevent potential deadlock on malloc locks after fork.
  pthread_atfork(
    _malloc_prefork, _malloc_postfork_parent, _malloc_postfork_child);
#endif

  return true;
}

// End general internal functions.
// ***************************************************************************
// Begin malloc(3)-compatible functions.

// The BaseAllocator class is a helper class that implements the base allocator
// functions (malloc, calloc, realloc, free, memalign) for a given arena,
// or an appropriately chosen arena (per choose_arena()) when none is given.
struct BaseAllocator
{
#define MALLOC_DECL(name, return_type, ...)                                    \
  inline return_type name(__VA_ARGS__);

#define MALLOC_FUNCS MALLOC_FUNCS_MALLOC_BASE
#include "malloc_decls.h"

  explicit BaseAllocator(arena_t* aArena)
    : mArena(aArena)
  {
  }

private:
  arena_t* mArena;
};

#define MALLOC_DECL(name, return_type, ...)                                    \
  template<>                                                                   \
  inline return_type MozJemalloc::name(ARGS_HELPER(TYPED_ARGS, ##__VA_ARGS__)) \
  {                                                                            \
    BaseAllocator allocator(nullptr);                                          \
    return allocator.name(ARGS_HELPER(ARGS, ##__VA_ARGS__));                   \
  }
#define MALLOC_FUNCS MALLOC_FUNCS_MALLOC_BASE
#include "malloc_decls.h"

inline void*
BaseAllocator::malloc(size_t aSize)
{
  void* ret;
  arena_t* arena;

  if (!malloc_init()) {
    ret = nullptr;
    goto RETURN;
  }

  if (aSize == 0) {
    aSize = 1;
  }
  arena = mArena ? mArena : choose_arena(aSize);
  ret = arena->Malloc(aSize, /* zero = */ false);

RETURN:
  if (!ret) {
    errno = ENOMEM;
  }

  return ret;
}

inline void*
BaseAllocator::memalign(size_t aAlignment, size_t aSize)
{
  MOZ_ASSERT(((aAlignment - 1) & aAlignment) == 0);

  if (!malloc_init()) {
    return nullptr;
  }

  if (aSize == 0) {
    aSize = 1;
  }

  aAlignment = aAlignment < sizeof(void*) ? sizeof(void*) : aAlignment;
  arena_t* arena = mArena ? mArena : choose_arena(aSize);
  return arena->Palloc(aAlignment, aSize);
}

inline void*
BaseAllocator::calloc(size_t aNum, size_t aSize)
{
  void* ret;

  if (malloc_init()) {
    CheckedInt<size_t> checkedSize = CheckedInt<size_t>(aNum) * aSize;
    if (checkedSize.isValid()) {
      size_t allocSize = checkedSize.value();
      if (allocSize == 0) {
        allocSize = 1;
      }
      arena_t* arena = mArena ? mArena : choose_arena(allocSize);
      ret = arena->Malloc(allocSize, /* zero = */ true);
    } else {
      ret = nullptr;
    }
  } else {
    ret = nullptr;
  }

  if (!ret) {
    errno = ENOMEM;
  }

  return ret;
}

inline void*
BaseAllocator::realloc(void* aPtr, size_t aSize)
{
  void* ret;

  if (aSize == 0) {
    aSize = 1;
  }

  if (aPtr) {
    MOZ_RELEASE_ASSERT(malloc_initialized);

    auto info = AllocInfo::Get(aPtr);
    auto arena = info.Arena();
    MOZ_RELEASE_ASSERT(!mArena || arena == mArena);
    ret = arena->Ralloc(aPtr, aSize, info.Size());

    if (!ret) {
      errno = ENOMEM;
    }
  } else {
    if (!malloc_init()) {
      ret = nullptr;
    } else {
      arena_t* arena = mArena ? mArena : choose_arena(aSize);
      ret = arena->Malloc(aSize, /* zero = */ false);
    }

    if (!ret) {
      errno = ENOMEM;
    }
  }

  return ret;
}

inline void
BaseAllocator::free(void* aPtr)
{
  size_t offset;

  // A version of idalloc that checks for nullptr pointer.
  offset = GetChunkOffsetForPtr(aPtr);
  if (offset != 0) {
    MOZ_RELEASE_ASSERT(malloc_initialized);
    arena_dalloc(aPtr, offset, mArena);
  } else if (aPtr) {
    MOZ_RELEASE_ASSERT(malloc_initialized);
    huge_dalloc(aPtr, mArena);
  }
}

template<void* (*memalign)(size_t, size_t)>
struct AlignedAllocator
{
  static inline int posix_memalign(void** aMemPtr,
                                   size_t aAlignment,
                                   size_t aSize)
  {
    void* result;

    // alignment must be a power of two and a multiple of sizeof(void*)
    if (((aAlignment - 1) & aAlignment) != 0 || aAlignment < sizeof(void*)) {
      return EINVAL;
    }

    // The 0-->1 size promotion is done in the memalign() call below
    result = memalign(aAlignment, aSize);

    if (!result) {
      return ENOMEM;
    }

    *aMemPtr = result;
    return 0;
  }

  static inline void* aligned_alloc(size_t aAlignment, size_t aSize)
  {
    if (aSize % aAlignment) {
      return nullptr;
    }
    return memalign(aAlignment, aSize);
  }

  static inline void* valloc(size_t aSize)
  {
    return memalign(GetKernelPageSize(), aSize);
  }
};

template<>
inline int
MozJemalloc::posix_memalign(void** aMemPtr, size_t aAlignment, size_t aSize)
{
  return AlignedAllocator<memalign>::posix_memalign(aMemPtr, aAlignment, aSize);
}

template<>
inline void*
MozJemalloc::aligned_alloc(size_t aAlignment, size_t aSize)
{
  return AlignedAllocator<memalign>::aligned_alloc(aAlignment, aSize);
}

template<>
inline void*
MozJemalloc::valloc(size_t aSize)
{
  return AlignedAllocator<memalign>::valloc(aSize);
}

// End malloc(3)-compatible functions.
// ***************************************************************************
// Begin non-standard functions.

// This was added by Mozilla for use by SQLite.
template<>
inline size_t
MozJemalloc::malloc_good_size(size_t aSize)
{
  if (aSize <= gMaxLargeClass) {
    // Small or large
    aSize = SizeClass(aSize).Size();
  } else {
    // Huge.  We use PAGE_CEILING to get psize, instead of using
    // CHUNK_CEILING to get csize.  This ensures that this
    // malloc_usable_size(malloc(n)) always matches
    // malloc_good_size(n).
    aSize = PAGE_CEILING(aSize);
  }
  return aSize;
}

template<>
inline size_t
MozJemalloc::malloc_usable_size(usable_ptr_t aPtr)
{
  return AllocInfo::GetValidated(aPtr).Size();
}

template<>
inline void
MozJemalloc::jemalloc_stats(jemalloc_stats_t* aStats)
{
  size_t non_arena_mapped, chunk_header_size;

  if (!aStats) {
    return;
  }
  if (!malloc_init()) {
    memset(aStats, 0, sizeof(*aStats));
    return;
  }

  // Gather runtime settings.
  aStats->opt_junk = opt_junk;
  aStats->opt_zero = opt_zero;
  aStats->quantum = kQuantum;
  aStats->small_max = kMaxQuantumClass;
  aStats->large_max = gMaxLargeClass;
  aStats->chunksize = kChunkSize;
  aStats->page_size = gPageSize;
  aStats->dirty_max = opt_dirty_max;

  // Gather current memory usage statistics.
  aStats->narenas = 0;
  aStats->mapped = 0;
  aStats->allocated = 0;
  aStats->waste = 0;
  aStats->page_cache = 0;
  aStats->bookkeeping = 0;
  aStats->bin_unused = 0;

  non_arena_mapped = 0;

  // Get huge mapped/allocated.
  {
    MutexAutoLock lock(huge_mtx);
    non_arena_mapped += huge_mapped;
    aStats->allocated += huge_allocated;
    MOZ_ASSERT(huge_mapped >= huge_allocated);
  }

  // Get base mapped/allocated.
  {
    MutexAutoLock lock(base_mtx);
    non_arena_mapped += base_mapped;
    aStats->bookkeeping += base_committed;
    MOZ_ASSERT(base_mapped >= base_committed);
  }

  gArenas.mLock.Lock();
  // Iterate over arenas.
  for (auto arena : gArenas.iter()) {
    size_t arena_mapped, arena_allocated, arena_committed, arena_dirty, j,
      arena_unused, arena_headers;
    arena_run_t* run;

    arena_headers = 0;
    arena_unused = 0;

    {
      MutexAutoLock lock(arena->mLock);

      arena_mapped = arena->mStats.mapped;

      // "committed" counts dirty and allocated memory.
      arena_committed = arena->mStats.committed << gPageSize2Pow;

      arena_allocated =
        arena->mStats.allocated_small + arena->mStats.allocated_large;

      arena_dirty = arena->mNumDirty << gPageSize2Pow;

      for (j = 0; j < kNumTinyClasses + kNumQuantumClasses + gNumSubPageClasses;
           j++) {
        arena_bin_t* bin = &arena->mBins[j];
        size_t bin_unused = 0;

        for (auto mapelm : bin->mNonFullRuns.iter()) {
          run = (arena_run_t*)(mapelm->bits & ~gPageSizeMask);
          bin_unused += run->mNumFree * bin->mSizeClass;
        }

        if (bin->mCurrentRun) {
          bin_unused += bin->mCurrentRun->mNumFree * bin->mSizeClass;
        }

        arena_unused += bin_unused;
        arena_headers += bin->mNumRuns * bin->mRunFirstRegionOffset;
      }
    }

    MOZ_ASSERT(arena_mapped >= arena_committed);
    MOZ_ASSERT(arena_committed >= arena_allocated + arena_dirty);

    // "waste" is committed memory that is neither dirty nor
    // allocated.
    aStats->mapped += arena_mapped;
    aStats->allocated += arena_allocated;
    aStats->page_cache += arena_dirty;
    aStats->waste += arena_committed - arena_allocated - arena_dirty -
                     arena_unused - arena_headers;
    aStats->bin_unused += arena_unused;
    aStats->bookkeeping += arena_headers;
    aStats->narenas++;
  }
  gArenas.mLock.Unlock();

  // Account for arena chunk headers in bookkeeping rather than waste.
  chunk_header_size =
    ((aStats->mapped / aStats->chunksize) * gChunkHeaderNumPages)
    << gPageSize2Pow;

  aStats->mapped += non_arena_mapped;
  aStats->bookkeeping += chunk_header_size;
  aStats->waste -= chunk_header_size;

  MOZ_ASSERT(aStats->mapped >= aStats->allocated + aStats->waste +
                                 aStats->page_cache + aStats->bookkeeping);
}

#ifdef MALLOC_DOUBLE_PURGE

// Explicitly remove all of this chunk's MADV_FREE'd pages from memory.
static void
hard_purge_chunk(arena_chunk_t* aChunk)
{
  // See similar logic in arena_t::Purge().
  for (size_t i = gChunkHeaderNumPages; i < gChunkNumPages; i++) {
    // Find all adjacent pages with CHUNK_MAP_MADVISED set.
    size_t npages;
    for (npages = 0; aChunk->map[i + npages].bits & CHUNK_MAP_MADVISED &&
                     i + npages < gChunkNumPages;
         npages++) {
      // Turn off the chunk's MADV_FREED bit and turn on its
      // DECOMMITTED bit.
      MOZ_DIAGNOSTIC_ASSERT(
        !(aChunk->map[i + npages].bits & CHUNK_MAP_DECOMMITTED));
      aChunk->map[i + npages].bits ^= CHUNK_MAP_MADVISED_OR_DECOMMITTED;
    }

    // We could use mincore to find out which pages are actually
    // present, but it's not clear that's better.
    if (npages > 0) {
      pages_decommit(((char*)aChunk) + (i << gPageSize2Pow),
                     npages << gPageSize2Pow);
      Unused << pages_commit(((char*)aChunk) + (i << gPageSize2Pow),
                             npages << gPageSize2Pow);
    }
    i += npages;
  }
}

// Explicitly remove all of this arena's MADV_FREE'd pages from memory.
void
arena_t::HardPurge()
{
  MutexAutoLock lock(mLock);

  while (!mChunksMAdvised.isEmpty()) {
    arena_chunk_t* chunk = mChunksMAdvised.popFront();
    hard_purge_chunk(chunk);
  }
}

template<>
inline void
MozJemalloc::jemalloc_purge_freed_pages()
{
  if (malloc_initialized) {
    MutexAutoLock lock(gArenas.mLock);
    for (auto arena : gArenas.iter()) {
      arena->HardPurge();
    }
  }
}

#else // !defined MALLOC_DOUBLE_PURGE

template<>
inline void
MozJemalloc::jemalloc_purge_freed_pages()
{
  // Do nothing.
}

#endif // defined MALLOC_DOUBLE_PURGE

template<>
inline void
MozJemalloc::jemalloc_free_dirty_pages(void)
{
  if (malloc_initialized) {
    MutexAutoLock lock(gArenas.mLock);
    for (auto arena : gArenas.iter()) {
      MutexAutoLock arena_lock(arena->mLock);
      arena->Purge(true);
    }
  }
}

inline arena_t*
ArenaCollection::GetById(arena_id_t aArenaId, bool aIsPrivate)
{
  if (!malloc_initialized) {
    return nullptr;
  }
  // Use AlignedStorage2 to avoid running the arena_t constructor, while
  // we only need it as a placeholder for mId.
  mozilla::AlignedStorage2<arena_t> key;
  key.addr()->mId = aArenaId;
  MutexAutoLock lock(mLock);
  arena_t* result = (aIsPrivate ? mPrivateArenas : mArenas).Search(key.addr());
  MOZ_RELEASE_ASSERT(result);
  return result;
}

#ifdef NIGHTLY_BUILD
template<>
inline arena_id_t
MozJemalloc::moz_create_arena_with_params(arena_params_t* aParams)
{
  if (malloc_init()) {
    arena_t* arena = gArenas.CreateArena(/* IsPrivate = */ true, aParams);
    return arena->mId;
  }
  return 0;
}

template<>
inline void
MozJemalloc::moz_dispose_arena(arena_id_t aArenaId)
{
  arena_t* arena = gArenas.GetById(aArenaId, /* IsPrivate = */ true);
  MOZ_RELEASE_ASSERT(arena);
  gArenas.DisposeArena(arena);
}

#define MALLOC_DECL(name, return_type, ...)                                    \
  template<>                                                                   \
  inline return_type MozJemalloc::moz_arena_##name(                            \
    arena_id_t aArenaId, ARGS_HELPER(TYPED_ARGS, ##__VA_ARGS__))               \
  {                                                                            \
    BaseAllocator allocator(                                                   \
      gArenas.GetById(aArenaId, /* IsPrivate = */ true));                      \
    return allocator.name(ARGS_HELPER(ARGS, ##__VA_ARGS__));                   \
  }
#define MALLOC_FUNCS MALLOC_FUNCS_MALLOC_BASE
#include "malloc_decls.h"

#else

#define MALLOC_DECL(name, return_type, ...)                                    \
  template<>                                                                   \
  inline return_type MozJemalloc::name(ARGS_HELPER(TYPED_ARGS, ##__VA_ARGS__)) \
  {                                                                            \
    return DummyArenaAllocator<MozJemalloc>::name(                             \
      ARGS_HELPER(ARGS, ##__VA_ARGS__));                                       \
  }
#define MALLOC_FUNCS MALLOC_FUNCS_ARENA
#include "malloc_decls.h"

#endif

// End non-standard functions.
// ***************************************************************************
// Begin library-private functions, used by threading libraries for protection
// of malloc during fork().  These functions are only called if the program is
// running in threaded mode, so there is no need to check whether the program
// is threaded here.
#ifndef XP_DARWIN
static
#endif
  void
  _malloc_prefork(void)
{
  // Acquire all mutexes in a safe order.
  gArenas.mLock.Lock();

  for (auto arena : gArenas.iter()) {
    arena->mLock.Lock();
  }

  base_mtx.Lock();

  huge_mtx.Lock();
}

#ifndef XP_DARWIN
static
#endif
  void
  _malloc_postfork_parent(void)
{
  // Release all mutexes, now that fork() has completed.
  huge_mtx.Unlock();

  base_mtx.Unlock();

  for (auto arena : gArenas.iter()) {
    arena->mLock.Unlock();
  }

  gArenas.mLock.Unlock();
}

#ifndef XP_DARWIN
static
#endif
  void
  _malloc_postfork_child(void)
{
  // Reinitialize all mutexes, now that fork() has completed.
  huge_mtx.Init();

  base_mtx.Init();

  for (auto arena : gArenas.iter()) {
    arena->mLock.Init();
  }

  gArenas.mLock.Init();
}

// End library-private functions.
// ***************************************************************************
#ifdef MOZ_REPLACE_MALLOC
// Windows doesn't come with weak imports as they are possible with
// LD_PRELOAD or DYLD_INSERT_LIBRARIES on Linux/OSX. On this platform,
// the replacement functions are defined as variable pointers to the
// function resolved with GetProcAddress() instead of weak definitions
// of functions. On Android, the same needs to happen as well, because
// the Android linker doesn't handle weak linking with non LD_PRELOADed
// libraries, but LD_PRELOADing is not very convenient on Android, with
// the zygote.
#ifdef XP_DARWIN
#define MOZ_REPLACE_WEAK __attribute__((weak_import))
#elif defined(XP_WIN) || defined(ANDROID)
#define MOZ_DYNAMIC_REPLACE_INIT
#define replace_init replace_init_decl
#elif defined(__GNUC__)
#define MOZ_REPLACE_WEAK __attribute__((weak))
#endif

#include "replace_malloc.h"

#define MALLOC_DECL(name, return_type, ...) MozJemalloc::name,

static malloc_table_t gReplaceMallocTable = {
#include "malloc_decls.h"
};

#ifdef MOZ_DYNAMIC_REPLACE_INIT
#undef replace_init
typedef decltype(replace_init_decl) replace_init_impl_t;
static replace_init_impl_t* replace_init = nullptr;
#endif

#ifdef XP_WIN
typedef HMODULE replace_malloc_handle_t;

static replace_malloc_handle_t
replace_malloc_handle()
{
  char replace_malloc_lib[1024];
  if (GetEnvironmentVariableA("MOZ_REPLACE_MALLOC_LIB",
                              replace_malloc_lib,
                              sizeof(replace_malloc_lib)) > 0) {
    return LoadLibraryA(replace_malloc_lib);
  }
  return nullptr;
}

#define REPLACE_MALLOC_GET_INIT_FUNC(handle)                                   \
  (replace_init_impl_t*)GetProcAddress(handle, "replace_init")

#elif defined(ANDROID)
#include <dlfcn.h>

typedef void* replace_malloc_handle_t;

static replace_malloc_handle_t
replace_malloc_handle()
{
  const char* replace_malloc_lib = getenv("MOZ_REPLACE_MALLOC_LIB");
  if (replace_malloc_lib && *replace_malloc_lib) {
    return dlopen(replace_malloc_lib, RTLD_LAZY);
  }
  return nullptr;
}

#define REPLACE_MALLOC_GET_INIT_FUNC(handle)                                   \
  (replace_init_impl_t*)dlsym(handle, "replace_init")

#endif

static void
replace_malloc_init_funcs();

#ifdef MOZ_REPLACE_MALLOC_STATIC
extern "C" void
logalloc_init(malloc_table_t*, ReplaceMallocBridge**);

extern "C" void
dmd_init(malloc_table_t*, ReplaceMallocBridge**);
#endif

bool
Equals(malloc_table_t& aTable1, malloc_table_t& aTable2)
{
  return memcmp(&aTable1, &aTable2, sizeof(malloc_table_t)) == 0;
}

// Below is the malloc implementation overriding jemalloc and calling the
// replacement functions if they exist.
static bool gReplaceMallocInitialized = false;
static ReplaceMallocBridge* gReplaceMallocBridge = nullptr;
static void
init()
{
#ifdef MOZ_REPLACE_MALLOC_STATIC
  malloc_table_t initialTable = gReplaceMallocTable;
#endif

#ifdef MOZ_DYNAMIC_REPLACE_INIT
  replace_malloc_handle_t handle = replace_malloc_handle();
  if (handle) {
    replace_init = REPLACE_MALLOC_GET_INIT_FUNC(handle);
  }
#endif

  // Set this *before* calling replace_init, otherwise if replace_init calls
  // malloc() we'll get an infinite loop.
  gReplaceMallocInitialized = true;
  if (replace_init) {
    replace_init(&gReplaceMallocTable, &gReplaceMallocBridge);
  }
#ifdef MOZ_REPLACE_MALLOC_STATIC
  if (Equals(initialTable, gReplaceMallocTable)) {
    logalloc_init(&gReplaceMallocTable, &gReplaceMallocBridge);
  }
#ifdef MOZ_DMD
  if (Equals(initialTable, gReplaceMallocTable)) {
    dmd_init(&gReplaceMallocTable, &gReplaceMallocBridge);
  }
#endif
#endif
  replace_malloc_init_funcs();
}

#define MALLOC_DECL(name, return_type, ...)                                    \
  template<>                                                                   \
  inline return_type ReplaceMalloc::name(                                      \
    ARGS_HELPER(TYPED_ARGS, ##__VA_ARGS__))                                    \
  {                                                                            \
    if (MOZ_UNLIKELY(!gReplaceMallocInitialized)) {                            \
      init();                                                                  \
    }                                                                          \
    return gReplaceMallocTable.name(ARGS_HELPER(ARGS, ##__VA_ARGS__));         \
  }
#include "malloc_decls.h"

MOZ_JEMALLOC_API struct ReplaceMallocBridge*
get_bridge(void)
{
  if (MOZ_UNLIKELY(!gReplaceMallocInitialized)) {
    init();
  }
  return gReplaceMallocBridge;
}

// posix_memalign, aligned_alloc, memalign and valloc all implement some kind
// of aligned memory allocation. For convenience, a replace-malloc library can
// skip defining replace_posix_memalign, replace_aligned_alloc and
// replace_valloc, and default implementations will be automatically derived
// from replace_memalign.
static void
replace_malloc_init_funcs()
{
  if (gReplaceMallocTable.posix_memalign == MozJemalloc::posix_memalign &&
      gReplaceMallocTable.memalign != MozJemalloc::memalign) {
    gReplaceMallocTable.posix_memalign =
      AlignedAllocator<ReplaceMalloc::memalign>::posix_memalign;
  }
  if (gReplaceMallocTable.aligned_alloc == MozJemalloc::aligned_alloc &&
      gReplaceMallocTable.memalign != MozJemalloc::memalign) {
    gReplaceMallocTable.aligned_alloc =
      AlignedAllocator<ReplaceMalloc::memalign>::aligned_alloc;
  }
  if (gReplaceMallocTable.valloc == MozJemalloc::valloc &&
      gReplaceMallocTable.memalign != MozJemalloc::memalign) {
    gReplaceMallocTable.valloc =
      AlignedAllocator<ReplaceMalloc::memalign>::valloc;
  }
  if (gReplaceMallocTable.moz_create_arena_with_params ==
        MozJemalloc::moz_create_arena_with_params &&
      gReplaceMallocTable.malloc != MozJemalloc::malloc) {
#define MALLOC_DECL(name, ...)                                                 \
  gReplaceMallocTable.name = DummyArenaAllocator<ReplaceMalloc>::name;
#define MALLOC_FUNCS MALLOC_FUNCS_ARENA
#include "malloc_decls.h"
  }
}

#endif // MOZ_REPLACE_MALLOC
  // ***************************************************************************
  // Definition of all the _impl functions

#define GENERIC_MALLOC_DECL2(name, name_impl, return_type, ...)                \
  return_type name_impl(ARGS_HELPER(TYPED_ARGS, ##__VA_ARGS__))                \
  {                                                                            \
    return DefaultMalloc::name(ARGS_HELPER(ARGS, ##__VA_ARGS__));              \
  }

#define GENERIC_MALLOC_DECL(name, return_type, ...)                            \
  GENERIC_MALLOC_DECL2(name, name##_impl, return_type, ##__VA_ARGS__)

#define MALLOC_DECL(...)                                                       \
  MOZ_MEMORY_API MACRO_CALL(GENERIC_MALLOC_DECL, (__VA_ARGS__))
#define MALLOC_FUNCS MALLOC_FUNCS_MALLOC
#include "malloc_decls.h"

#undef GENERIC_MALLOC_DECL
#define GENERIC_MALLOC_DECL(name, return_type, ...)                            \
  GENERIC_MALLOC_DECL2(name, name, return_type, ##__VA_ARGS__)

#define MALLOC_DECL(...)                                                       \
  MOZ_JEMALLOC_API MACRO_CALL(GENERIC_MALLOC_DECL, (__VA_ARGS__))
#define MALLOC_FUNCS (MALLOC_FUNCS_JEMALLOC | MALLOC_FUNCS_ARENA)
#include "malloc_decls.h"
  // ***************************************************************************

#ifdef HAVE_DLOPEN
#include <dlfcn.h>
#endif

#if defined(__GLIBC__) && !defined(__UCLIBC__)
// glibc provides the RTLD_DEEPBIND flag for dlopen which can make it possible
// to inconsistently reference libc's malloc(3)-compatible functions
// (bug 493541).
//
// These definitions interpose hooks in glibc.  The functions are actually
// passed an extra argument for the caller return address, which will be
// ignored.

extern "C" {
MOZ_EXPORT void (*__free_hook)(void*) = free_impl;
MOZ_EXPORT void* (*__malloc_hook)(size_t) = malloc_impl;
MOZ_EXPORT void* (*__realloc_hook)(void*, size_t) = realloc_impl;
MOZ_EXPORT void* (*__memalign_hook)(size_t, size_t) = memalign_impl;
}

#elif defined(RTLD_DEEPBIND)
// XXX On systems that support RTLD_GROUP or DF_1_GROUP, do their
// implementations permit similar inconsistencies?  Should STV_SINGLETON
// visibility be used for interposition where available?
#error "Interposing malloc is unsafe on this system without libc malloc hooks."
#endif

#ifdef XP_WIN
void*
_recalloc(void* aPtr, size_t aCount, size_t aSize)
{
  size_t oldsize = aPtr ? AllocInfo::Get(aPtr).Size() : 0;
  CheckedInt<size_t> checkedSize = CheckedInt<size_t>(aCount) * aSize;

  if (!checkedSize.isValid()) {
    return nullptr;
  }

  size_t newsize = checkedSize.value();

  // In order for all trailing bytes to be zeroed, the caller needs to
  // use calloc(), followed by recalloc().  However, the current calloc()
  // implementation only zeros the bytes requested, so if recalloc() is
  // to work 100% correctly, calloc() will need to change to zero
  // trailing bytes.
  aPtr = DefaultMalloc::realloc(aPtr, newsize);
  if (aPtr && oldsize < newsize) {
    memset((void*)((uintptr_t)aPtr + oldsize), 0, newsize - oldsize);
  }

  return aPtr;
}

// This impl of _expand doesn't ever actually expand or shrink blocks: it
// simply replies that you may continue using a shrunk block.
void*
_expand(void* aPtr, size_t newsize)
{
  if (AllocInfo::Get(aPtr).Size() >= newsize) {
    return aPtr;
  }

  return nullptr;
}

size_t
_msize(void* aPtr)
{
  return DefaultMalloc::malloc_usable_size(aPtr);
}
#endif