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FastMalloc.cpp
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FastMalloc.cpp
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// Copyright (c) 2005, 2007, Google Inc.
// All rights reserved.
// Copyright (C) 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// ---
// Author: Sanjay Ghemawat <opensource@google.com>
//
// A malloc that uses a per-thread cache to satisfy small malloc requests.
// (The time for malloc/free of a small object drops from 300 ns to 50 ns.)
//
// See doc/tcmalloc.html for a high-level
// description of how this malloc works.
//
// SYNCHRONIZATION
// 1. The thread-specific lists are accessed without acquiring any locks.
// This is safe because each such list is only accessed by one thread.
// 2. We have a lock per central free-list, and hold it while manipulating
// the central free list for a particular size.
// 3. The central page allocator is protected by "pageheap_lock".
// 4. The pagemap (which maps from page-number to descriptor),
// can be read without holding any locks, and written while holding
// the "pageheap_lock".
// 5. To improve performance, a subset of the information one can get
// from the pagemap is cached in a data structure, pagemap_cache_,
// that atomically reads and writes its entries. This cache can be
// read and written without locking.
//
// This multi-threaded access to the pagemap is safe for fairly
// subtle reasons. We basically assume that when an object X is
// allocated by thread A and deallocated by thread B, there must
// have been appropriate synchronization in the handoff of object
// X from thread A to thread B. The same logic applies to pagemap_cache_.
//
// THE PAGEID-TO-SIZECLASS CACHE
// Hot PageID-to-sizeclass mappings are held by pagemap_cache_. If this cache
// returns 0 for a particular PageID then that means "no information," not that
// the sizeclass is 0. The cache may have stale information for pages that do
// not hold the beginning of any free()'able object. Staleness is eliminated
// in Populate() for pages with sizeclass > 0 objects, and in do_malloc() and
// do_memalign() for all other relevant pages.
//
// TODO: Bias reclamation to larger addresses
// TODO: implement mallinfo/mallopt
// TODO: Better testing
//
// 9/28/2003 (new page-level allocator replaces ptmalloc2):
// * malloc/free of small objects goes from ~300 ns to ~50 ns.
// * allocation of a reasonably complicated struct
// goes from about 1100 ns to about 300 ns.
#include "config.h"
#include "FastMalloc.h"
#include "Assertions.h"
#if ENABLE(JSC_MULTIPLE_THREADS)
#include <pthread.h>
#endif
#include <Availability.h>
#ifndef NO_TCMALLOC_SAMPLES
#ifdef WTF_CHANGES
#define NO_TCMALLOC_SAMPLES
#endif
#endif
#if !defined(USE_SYSTEM_MALLOC) && defined(NDEBUG)
#define FORCE_SYSTEM_MALLOC 0
#else
#define FORCE_SYSTEM_MALLOC 1
#endif
#define TCMALLOC_TRACK_DECOMMITED_SPANS (HAVE(VIRTUALALLOC))
#ifndef NDEBUG
namespace WTF {
#if ENABLE(JSC_MULTIPLE_THREADS)
static pthread_key_t isForbiddenKey;
static pthread_once_t isForbiddenKeyOnce = PTHREAD_ONCE_INIT;
static void initializeIsForbiddenKey()
{
pthread_key_create(&isForbiddenKey, 0);
}
static bool isForbidden()
{
pthread_once(&isForbiddenKeyOnce, initializeIsForbiddenKey);
return !!pthread_getspecific(isForbiddenKey);
}
void fastMallocForbid()
{
pthread_once(&isForbiddenKeyOnce, initializeIsForbiddenKey);
pthread_setspecific(isForbiddenKey, &isForbiddenKey);
}
void fastMallocAllow()
{
pthread_once(&isForbiddenKeyOnce, initializeIsForbiddenKey);
pthread_setspecific(isForbiddenKey, 0);
}
#else
static bool staticIsForbidden;
static bool isForbidden()
{
return staticIsForbidden;
}
void fastMallocForbid()
{
staticIsForbidden = true;
}
void fastMallocAllow()
{
staticIsForbidden = false;
}
#endif // ENABLE(JSC_MULTIPLE_THREADS)
} // namespace WTF
#endif // NDEBUG
#include <string.h>
namespace WTF {
void* fastZeroedMalloc(size_t n)
{
void* result = fastMalloc(n);
memset(result, 0, n);
return result;
}
void* tryFastZeroedMalloc(size_t n)
{
void* result = tryFastMalloc(n);
if (!result)
return 0;
memset(result, 0, n);
return result;
}
} // namespace WTF
#if FORCE_SYSTEM_MALLOC
#include <stdlib.h>
#if !PLATFORM(WIN_OS)
#include <pthread.h>
#else
#include "windows.h"
#endif
namespace WTF {
void* tryFastMalloc(size_t n)
{
ASSERT(!isForbidden());
return malloc(n);
}
void* fastMalloc(size_t n)
{
ASSERT(!isForbidden());
void* result = malloc(n);
if (!result)
CRASH();
return result;
}
void* tryFastCalloc(size_t n_elements, size_t element_size)
{
ASSERT(!isForbidden());
return calloc(n_elements, element_size);
}
void* fastCalloc(size_t n_elements, size_t element_size)
{
ASSERT(!isForbidden());
void* result = calloc(n_elements, element_size);
if (!result)
CRASH();
return result;
}
void fastFree(void* p)
{
ASSERT(!isForbidden());
free(p);
}
void* tryFastRealloc(void* p, size_t n)
{
ASSERT(!isForbidden());
return realloc(p, n);
}
void* fastRealloc(void* p, size_t n)
{
ASSERT(!isForbidden());
void* result = realloc(p, n);
if (!result)
CRASH();
return result;
}
void releaseFastMallocFreeMemory() { }
FastMallocStatistics fastMallocStatistics()
{
FastMallocStatistics statistics = { 0, 0, 0, 0 };
return statistics;
}
} // namespace WTF
#if PLATFORM(DARWIN)
// This symbol is present in the JavaScriptCore exports file even when FastMalloc is disabled.
// It will never be used in this case, so it's type and value are less interesting than its presence.
extern "C" const int jscore_fastmalloc_introspection = 0;
#endif
#else // FORCE_SYSTEM_MALLOC
#if HAVE(STDINT_H)
#include <stdint.h>
#elif HAVE(INTTYPES_H)
#include <inttypes.h>
#else
#include <sys/types.h>
#endif
#include "AlwaysInline.h"
#include "Assertions.h"
#include "TCPackedCache.h"
#include "TCPageMap.h"
#include "TCSpinLock.h"
#include "TCSystemAlloc.h"
#include <algorithm>
#include <errno.h>
#include <new>
#include <pthread.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#if COMPILER(MSVC)
#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>
#endif
#if WTF_CHANGES
#if PLATFORM(DARWIN)
#include "MallocZoneSupport.h"
#include <wtf/HashSet.h>
#endif
#ifndef PRIuS
#define PRIuS "zu"
#endif
// Calling pthread_getspecific through a global function pointer is faster than a normal
// call to the function on Mac OS X, and it's used in performance-critical code. So we
// use a function pointer. But that's not necessarily faster on other platforms, and we had
// problems with this technique on Windows, so we'll do this only on Mac OS X.
#if PLATFORM(DARWIN)
static void* (*pthread_getspecific_function_pointer)(pthread_key_t) = pthread_getspecific;
#define pthread_getspecific(key) pthread_getspecific_function_pointer(key)
#endif
#define DEFINE_VARIABLE(type, name, value, meaning) \
namespace FLAG__namespace_do_not_use_directly_use_DECLARE_##type##_instead { \
type FLAGS_##name(value); \
char FLAGS_no##name; \
} \
using FLAG__namespace_do_not_use_directly_use_DECLARE_##type##_instead::FLAGS_##name
#define DEFINE_int64(name, value, meaning) \
DEFINE_VARIABLE(int64_t, name, value, meaning)
#define DEFINE_double(name, value, meaning) \
DEFINE_VARIABLE(double, name, value, meaning)
namespace WTF {
#define malloc fastMalloc
#define calloc fastCalloc
#define free fastFree
#define realloc fastRealloc
#define MESSAGE LOG_ERROR
#define CHECK_CONDITION ASSERT
#if PLATFORM(DARWIN)
class TCMalloc_PageHeap;
class TCMalloc_ThreadCache;
class TCMalloc_Central_FreeListPadded;
class FastMallocZone {
public:
static void init();
static kern_return_t enumerate(task_t, void*, unsigned typeMmask, vm_address_t zoneAddress, memory_reader_t, vm_range_recorder_t);
static size_t goodSize(malloc_zone_t*, size_t size) { return size; }
static boolean_t check(malloc_zone_t*) { return true; }
static void print(malloc_zone_t*, boolean_t) { }
static void log(malloc_zone_t*, void*) { }
static void forceLock(malloc_zone_t*) { }
static void forceUnlock(malloc_zone_t*) { }
static void statistics(malloc_zone_t*, malloc_statistics_t* stats) { memset(stats, 0, sizeof(malloc_statistics_t)); }
private:
FastMallocZone(TCMalloc_PageHeap*, TCMalloc_ThreadCache**, TCMalloc_Central_FreeListPadded*);
static size_t size(malloc_zone_t*, const void*);
static void* zoneMalloc(malloc_zone_t*, size_t);
static void* zoneCalloc(malloc_zone_t*, size_t numItems, size_t size);
static void zoneFree(malloc_zone_t*, void*);
static void* zoneRealloc(malloc_zone_t*, void*, size_t);
static void* zoneValloc(malloc_zone_t*, size_t) { LOG_ERROR("valloc is not supported"); return 0; }
static void zoneDestroy(malloc_zone_t*) { }
malloc_zone_t m_zone;
TCMalloc_PageHeap* m_pageHeap;
TCMalloc_ThreadCache** m_threadHeaps;
TCMalloc_Central_FreeListPadded* m_centralCaches;
};
#endif
#endif
#ifndef WTF_CHANGES
// This #ifdef should almost never be set. Set NO_TCMALLOC_SAMPLES if
// you're porting to a system where you really can't get a stacktrace.
#ifdef NO_TCMALLOC_SAMPLES
// We use #define so code compiles even if you #include stacktrace.h somehow.
# define GetStackTrace(stack, depth, skip) (0)
#else
# include <google/stacktrace.h>
#endif
#endif
// Even if we have support for thread-local storage in the compiler
// and linker, the OS may not support it. We need to check that at
// runtime. Right now, we have to keep a manual set of "bad" OSes.
#if defined(HAVE_TLS)
static bool kernel_supports_tls = false; // be conservative
static inline bool KernelSupportsTLS() {
return kernel_supports_tls;
}
# if !HAVE_DECL_UNAME // if too old for uname, probably too old for TLS
static void CheckIfKernelSupportsTLS() {
kernel_supports_tls = false;
}
# else
# include <sys/utsname.h> // DECL_UNAME checked for <sys/utsname.h> too
static void CheckIfKernelSupportsTLS() {
struct utsname buf;
if (uname(&buf) != 0) { // should be impossible
MESSAGE("uname failed assuming no TLS support (errno=%d)\n", errno);
kernel_supports_tls = false;
} else if (strcasecmp(buf.sysname, "linux") == 0) {
// The linux case: the first kernel to support TLS was 2.6.0
if (buf.release[0] < '2' && buf.release[1] == '.') // 0.x or 1.x
kernel_supports_tls = false;
else if (buf.release[0] == '2' && buf.release[1] == '.' &&
buf.release[2] >= '0' && buf.release[2] < '6' &&
buf.release[3] == '.') // 2.0 - 2.5
kernel_supports_tls = false;
else
kernel_supports_tls = true;
} else { // some other kernel, we'll be optimisitic
kernel_supports_tls = true;
}
// TODO(csilvers): VLOG(1) the tls status once we support RAW_VLOG
}
# endif // HAVE_DECL_UNAME
#endif // HAVE_TLS
// __THROW is defined in glibc systems. It means, counter-intuitively,
// "This function will never throw an exception." It's an optional
// optimization tool, but we may need to use it to match glibc prototypes.
#ifndef __THROW // I guess we're not on a glibc system
# define __THROW // __THROW is just an optimization, so ok to make it ""
#endif
//-------------------------------------------------------------------
// Configuration
//-------------------------------------------------------------------
// Not all possible combinations of the following parameters make
// sense. In particular, if kMaxSize increases, you may have to
// increase kNumClasses as well.
static const size_t kPageShift = 12;
static const size_t kPageSize = 1 << kPageShift;
static const size_t kMaxSize = 8u * kPageSize;
static const size_t kAlignShift = 3;
static const size_t kAlignment = 1 << kAlignShift;
static const size_t kNumClasses = 68;
// Allocates a big block of memory for the pagemap once we reach more than
// 128MB
static const size_t kPageMapBigAllocationThreshold = 128 << 20;
// Minimum number of pages to fetch from system at a time. Must be
// significantly bigger than kBlockSize to amortize system-call
// overhead, and also to reduce external fragementation. Also, we
// should keep this value big because various incarnations of Linux
// have small limits on the number of mmap() regions per
// address-space.
static const size_t kMinSystemAlloc = 1 << (20 - kPageShift);
// Number of objects to move between a per-thread list and a central
// list in one shot. We want this to be not too small so we can
// amortize the lock overhead for accessing the central list. Making
// it too big may temporarily cause unnecessary memory wastage in the
// per-thread free list until the scavenger cleans up the list.
static int num_objects_to_move[kNumClasses];
// Maximum length we allow a per-thread free-list to have before we
// move objects from it into the corresponding central free-list. We
// want this big to avoid locking the central free-list too often. It
// should not hurt to make this list somewhat big because the
// scavenging code will shrink it down when its contents are not in use.
static const int kMaxFreeListLength = 256;
// Lower and upper bounds on the per-thread cache sizes
static const size_t kMinThreadCacheSize = kMaxSize * 2;
static const size_t kMaxThreadCacheSize = 512 * 1024;
// Default bound on the total amount of thread caches
static const size_t kDefaultOverallThreadCacheSize = 16 << 20;
// For all span-lengths < kMaxPages we keep an exact-size list.
// REQUIRED: kMaxPages >= kMinSystemAlloc;
static const size_t kMaxPages = kMinSystemAlloc;
/* The smallest prime > 2^n */
static int primes_list[] = {
// Small values might cause high rates of sampling
// and hence commented out.
// 2, 5, 11, 17, 37, 67, 131, 257,
// 521, 1031, 2053, 4099, 8209, 16411,
32771, 65537, 131101, 262147, 524309, 1048583,
2097169, 4194319, 8388617, 16777259, 33554467 };
// Twice the approximate gap between sampling actions.
// I.e., we take one sample approximately once every
// tcmalloc_sample_parameter/2
// bytes of allocation, i.e., ~ once every 128KB.
// Must be a prime number.
#ifdef NO_TCMALLOC_SAMPLES
DEFINE_int64(tcmalloc_sample_parameter, 0,
"Unused: code is compiled with NO_TCMALLOC_SAMPLES");
static size_t sample_period = 0;
#else
DEFINE_int64(tcmalloc_sample_parameter, 262147,
"Twice the approximate gap between sampling actions."
" Must be a prime number. Otherwise will be rounded up to a "
" larger prime number");
static size_t sample_period = 262147;
#endif
// Protects sample_period above
static SpinLock sample_period_lock = SPINLOCK_INITIALIZER;
// Parameters for controlling how fast memory is returned to the OS.
DEFINE_double(tcmalloc_release_rate, 1,
"Rate at which we release unused memory to the system. "
"Zero means we never release memory back to the system. "
"Increase this flag to return memory faster; decrease it "
"to return memory slower. Reasonable rates are in the "
"range [0,10]");
//-------------------------------------------------------------------
// Mapping from size to size_class and vice versa
//-------------------------------------------------------------------
// Sizes <= 1024 have an alignment >= 8. So for such sizes we have an
// array indexed by ceil(size/8). Sizes > 1024 have an alignment >= 128.
// So for these larger sizes we have an array indexed by ceil(size/128).
//
// We flatten both logical arrays into one physical array and use
// arithmetic to compute an appropriate index. The constants used by
// ClassIndex() were selected to make the flattening work.
//
// Examples:
// Size Expression Index
// -------------------------------------------------------
// 0 (0 + 7) / 8 0
// 1 (1 + 7) / 8 1
// ...
// 1024 (1024 + 7) / 8 128
// 1025 (1025 + 127 + (120<<7)) / 128 129
// ...
// 32768 (32768 + 127 + (120<<7)) / 128 376
static const size_t kMaxSmallSize = 1024;
static const int shift_amount[2] = { 3, 7 }; // For divides by 8 or 128
static const int add_amount[2] = { 7, 127 + (120 << 7) };
static unsigned char class_array[377];
// Compute index of the class_array[] entry for a given size
static inline int ClassIndex(size_t s) {
const int i = (s > kMaxSmallSize);
return static_cast<int>((s + add_amount[i]) >> shift_amount[i]);
}
// Mapping from size class to max size storable in that class
static size_t class_to_size[kNumClasses];
// Mapping from size class to number of pages to allocate at a time
static size_t class_to_pages[kNumClasses];
// TransferCache is used to cache transfers of num_objects_to_move[size_class]
// back and forth between thread caches and the central cache for a given size
// class.
struct TCEntry {
void *head; // Head of chain of objects.
void *tail; // Tail of chain of objects.
};
// A central cache freelist can have anywhere from 0 to kNumTransferEntries
// slots to put link list chains into. To keep memory usage bounded the total
// number of TCEntries across size classes is fixed. Currently each size
// class is initially given one TCEntry which also means that the maximum any
// one class can have is kNumClasses.
static const int kNumTransferEntries = kNumClasses;
// Note: the following only works for "n"s that fit in 32-bits, but
// that is fine since we only use it for small sizes.
static inline int LgFloor(size_t n) {
int log = 0;
for (int i = 4; i >= 0; --i) {
int shift = (1 << i);
size_t x = n >> shift;
if (x != 0) {
n = x;
log += shift;
}
}
ASSERT(n == 1);
return log;
}
// Some very basic linked list functions for dealing with using void * as
// storage.
static inline void *SLL_Next(void *t) {
return *(reinterpret_cast<void**>(t));
}
static inline void SLL_SetNext(void *t, void *n) {
*(reinterpret_cast<void**>(t)) = n;
}
static inline void SLL_Push(void **list, void *element) {
SLL_SetNext(element, *list);
*list = element;
}
static inline void *SLL_Pop(void **list) {
void *result = *list;
*list = SLL_Next(*list);
return result;
}
// Remove N elements from a linked list to which head points. head will be
// modified to point to the new head. start and end will point to the first
// and last nodes of the range. Note that end will point to NULL after this
// function is called.
static inline void SLL_PopRange(void **head, int N, void **start, void **end) {
if (N == 0) {
*start = NULL;
*end = NULL;
return;
}
void *tmp = *head;
for (int i = 1; i < N; ++i) {
tmp = SLL_Next(tmp);
}
*start = *head;
*end = tmp;
*head = SLL_Next(tmp);
// Unlink range from list.
SLL_SetNext(tmp, NULL);
}
static inline void SLL_PushRange(void **head, void *start, void *end) {
if (!start) return;
SLL_SetNext(end, *head);
*head = start;
}
static inline size_t SLL_Size(void *head) {
int count = 0;
while (head) {
count++;
head = SLL_Next(head);
}
return count;
}
// Setup helper functions.
static ALWAYS_INLINE size_t SizeClass(size_t size) {
return class_array[ClassIndex(size)];
}
// Get the byte-size for a specified class
static ALWAYS_INLINE size_t ByteSizeForClass(size_t cl) {
return class_to_size[cl];
}
static int NumMoveSize(size_t size) {
if (size == 0) return 0;
// Use approx 64k transfers between thread and central caches.
int num = static_cast<int>(64.0 * 1024.0 / size);
if (num < 2) num = 2;
// Clamp well below kMaxFreeListLength to avoid ping pong between central
// and thread caches.
if (num > static_cast<int>(0.8 * kMaxFreeListLength))
num = static_cast<int>(0.8 * kMaxFreeListLength);
// Also, avoid bringing in too many objects into small object free
// lists. There are lots of such lists, and if we allow each one to
// fetch too many at a time, we end up having to scavenge too often
// (especially when there are lots of threads and each thread gets a
// small allowance for its thread cache).
//
// TODO: Make thread cache free list sizes dynamic so that we do not
// have to equally divide a fixed resource amongst lots of threads.
if (num > 32) num = 32;
return num;
}
// Initialize the mapping arrays
static void InitSizeClasses() {
// Do some sanity checking on add_amount[]/shift_amount[]/class_array[]
if (ClassIndex(0) < 0) {
MESSAGE("Invalid class index %d for size 0\n", ClassIndex(0));
CRASH();
}
if (static_cast<size_t>(ClassIndex(kMaxSize)) >= sizeof(class_array)) {
MESSAGE("Invalid class index %d for kMaxSize\n", ClassIndex(kMaxSize));
CRASH();
}
// Compute the size classes we want to use
size_t sc = 1; // Next size class to assign
unsigned char alignshift = kAlignShift;
int last_lg = -1;
for (size_t size = kAlignment; size <= kMaxSize; size += (1 << alignshift)) {
int lg = LgFloor(size);
if (lg > last_lg) {
// Increase alignment every so often.
//
// Since we double the alignment every time size doubles and
// size >= 128, this means that space wasted due to alignment is
// at most 16/128 i.e., 12.5%. Plus we cap the alignment at 256
// bytes, so the space wasted as a percentage starts falling for
// sizes > 2K.
if ((lg >= 7) && (alignshift < 8)) {
alignshift++;
}
last_lg = lg;
}
// Allocate enough pages so leftover is less than 1/8 of total.
// This bounds wasted space to at most 12.5%.
size_t psize = kPageSize;
while ((psize % size) > (psize >> 3)) {
psize += kPageSize;
}
const size_t my_pages = psize >> kPageShift;
if (sc > 1 && my_pages == class_to_pages[sc-1]) {
// See if we can merge this into the previous class without
// increasing the fragmentation of the previous class.
const size_t my_objects = (my_pages << kPageShift) / size;
const size_t prev_objects = (class_to_pages[sc-1] << kPageShift)
/ class_to_size[sc-1];
if (my_objects == prev_objects) {
// Adjust last class to include this size
class_to_size[sc-1] = size;
continue;
}
}
// Add new class
class_to_pages[sc] = my_pages;
class_to_size[sc] = size;
sc++;
}
if (sc != kNumClasses) {
MESSAGE("wrong number of size classes: found %" PRIuS " instead of %d\n",
sc, int(kNumClasses));
CRASH();
}
// Initialize the mapping arrays
int next_size = 0;
for (unsigned char c = 1; c < kNumClasses; c++) {
const size_t max_size_in_class = class_to_size[c];
for (size_t s = next_size; s <= max_size_in_class; s += kAlignment) {
class_array[ClassIndex(s)] = c;
}
next_size = static_cast<int>(max_size_in_class + kAlignment);
}
// Double-check sizes just to be safe
for (size_t size = 0; size <= kMaxSize; size++) {
const size_t sc = SizeClass(size);
if (sc == 0) {
MESSAGE("Bad size class %" PRIuS " for %" PRIuS "\n", sc, size);
CRASH();
}
if (sc > 1 && size <= class_to_size[sc-1]) {
MESSAGE("Allocating unnecessarily large class %" PRIuS " for %" PRIuS
"\n", sc, size);
CRASH();
}
if (sc >= kNumClasses) {
MESSAGE("Bad size class %" PRIuS " for %" PRIuS "\n", sc, size);
CRASH();
}
const size_t s = class_to_size[sc];
if (size > s) {
MESSAGE("Bad size %" PRIuS " for %" PRIuS " (sc = %" PRIuS ")\n", s, size, sc);
CRASH();
}
if (s == 0) {
MESSAGE("Bad size %" PRIuS " for %" PRIuS " (sc = %" PRIuS ")\n", s, size, sc);
CRASH();
}
}
// Initialize the num_objects_to_move array.
for (size_t cl = 1; cl < kNumClasses; ++cl) {
num_objects_to_move[cl] = NumMoveSize(ByteSizeForClass(cl));
}
#ifndef WTF_CHANGES
if (false) {
// Dump class sizes and maximum external wastage per size class
for (size_t cl = 1; cl < kNumClasses; ++cl) {
const int alloc_size = class_to_pages[cl] << kPageShift;
const int alloc_objs = alloc_size / class_to_size[cl];
const int min_used = (class_to_size[cl-1] + 1) * alloc_objs;
const int max_waste = alloc_size - min_used;
MESSAGE("SC %3d [ %8d .. %8d ] from %8d ; %2.0f%% maxwaste\n",
int(cl),
int(class_to_size[cl-1] + 1),
int(class_to_size[cl]),
int(class_to_pages[cl] << kPageShift),
max_waste * 100.0 / alloc_size
);
}
}
#endif
}
// -------------------------------------------------------------------------
// Simple allocator for objects of a specified type. External locking
// is required before accessing one of these objects.
// -------------------------------------------------------------------------
// Metadata allocator -- keeps stats about how many bytes allocated
static uint64_t metadata_system_bytes = 0;
static void* MetaDataAlloc(size_t bytes) {
void* result = TCMalloc_SystemAlloc(bytes, 0);
if (result != NULL) {
metadata_system_bytes += bytes;
}
return result;
}
template <class T>
class PageHeapAllocator {
private:
// How much to allocate from system at a time
static const size_t kAllocIncrement = 32 << 10;
// Aligned size of T
static const size_t kAlignedSize
= (((sizeof(T) + kAlignment - 1) / kAlignment) * kAlignment);
// Free area from which to carve new objects
char* free_area_;
size_t free_avail_;
// Free list of already carved objects
void* free_list_;
// Number of allocated but unfreed objects
int inuse_;
public:
void Init() {
ASSERT(kAlignedSize <= kAllocIncrement);
inuse_ = 0;
free_area_ = NULL;
free_avail_ = 0;
free_list_ = NULL;
}
T* New() {
// Consult free list
void* result;
if (free_list_ != NULL) {
result = free_list_;
free_list_ = *(reinterpret_cast<void**>(result));
} else {
if (free_avail_ < kAlignedSize) {
// Need more room
free_area_ = reinterpret_cast<char*>(MetaDataAlloc(kAllocIncrement));
if (free_area_ == NULL) CRASH();
free_avail_ = kAllocIncrement;
}
result = free_area_;
free_area_ += kAlignedSize;
free_avail_ -= kAlignedSize;
}
inuse_++;
return reinterpret_cast<T*>(result);
}
void Delete(T* p) {
*(reinterpret_cast<void**>(p)) = free_list_;
free_list_ = p;
inuse_--;
}
int inuse() const { return inuse_; }
};
// -------------------------------------------------------------------------
// Span - a contiguous run of pages
// -------------------------------------------------------------------------
// Type that can hold a page number
typedef uintptr_t PageID;
// Type that can hold the length of a run of pages
typedef uintptr_t Length;
static const Length kMaxValidPages = (~static_cast<Length>(0)) >> kPageShift;
// Convert byte size into pages. This won't overflow, but may return
// an unreasonably large value if bytes is huge enough.
static inline Length pages(size_t bytes) {
return (bytes >> kPageShift) +
((bytes & (kPageSize - 1)) > 0 ? 1 : 0);
}
// Convert a user size into the number of bytes that will actually be
// allocated
static size_t AllocationSize(size_t bytes) {
if (bytes > kMaxSize) {
// Large object: we allocate an integral number of pages
ASSERT(bytes <= (kMaxValidPages << kPageShift));
return pages(bytes) << kPageShift;
} else {
// Small object: find the size class to which it belongs
return ByteSizeForClass(SizeClass(bytes));
}
}
// Information kept for a span (a contiguous run of pages).
struct Span {
PageID start; // Starting page number
Length length; // Number of pages in span
Span* next; // Used when in link list
Span* prev; // Used when in link list
void* objects; // Linked list of free objects
unsigned int free : 1; // Is the span free
#ifndef NO_TCMALLOC_SAMPLES
unsigned int sample : 1; // Sampled object?
#endif
unsigned int sizeclass : 8; // Size-class for small objects (or 0)
unsigned int refcount : 11; // Number of non-free objects
bool decommitted : 1;
#undef SPAN_HISTORY
#ifdef SPAN_HISTORY
// For debugging, we can keep a log events per span
int nexthistory;
char history[64];
int value[64];
#endif
};
#if TCMALLOC_TRACK_DECOMMITED_SPANS
#define ASSERT_SPAN_COMMITTED(span) ASSERT(!span->decommitted)
#else
#define ASSERT_SPAN_COMMITTED(span)
#endif
#ifdef SPAN_HISTORY
void Event(Span* span, char op, int v = 0) {
span->history[span->nexthistory] = op;
span->value[span->nexthistory] = v;
span->nexthistory++;
if (span->nexthistory == sizeof(span->history)) span->nexthistory = 0;
}
#else
#define Event(s,o,v) ((void) 0)
#endif
// Allocator/deallocator for spans
static PageHeapAllocator<Span> span_allocator;
static Span* NewSpan(PageID p, Length len) {
Span* result = span_allocator.New();
memset(result, 0, sizeof(*result));
result->start = p;
result->length = len;
#ifdef SPAN_HISTORY
result->nexthistory = 0;
#endif
return result;
}
static inline void DeleteSpan(Span* span) {
#ifndef NDEBUG
// In debug mode, trash the contents of deleted Spans
memset(span, 0x3f, sizeof(*span));
#endif
span_allocator.Delete(span);
}
// -------------------------------------------------------------------------
// Doubly linked list of spans.
// -------------------------------------------------------------------------
static inline void DLL_Init(Span* list) {
list->next = list;
list->prev = list;
}
static inline void DLL_Remove(Span* span) {
span->prev->next = span->next;
span->next->prev = span->prev;
span->prev = NULL;
span->next = NULL;
}
static ALWAYS_INLINE bool DLL_IsEmpty(const Span* list) {
return list->next == list;
}
static int DLL_Length(const Span* list) {
int result = 0;
for (Span* s = list->next; s != list; s = s->next) {
result++;
}
return result;
}
#if 0 /* Not needed at the moment -- causes compiler warnings if not used */
static void DLL_Print(const char* label, const Span* list) {
MESSAGE("%-10s %p:", label, list);
for (const Span* s = list->next; s != list; s = s->next) {
MESSAGE(" <%p,%u,%u>", s, s->start, s->length);
}
MESSAGE("\n");
}
#endif