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* Copyright 2012 Facebook, Inc.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
// Functions to provide smarter use of jemalloc, if jemalloc is being used.
// If using fbstring from libstdc++, then just define stub code
// here to typedef the fbstring type into the folly namespace.
// This provides backwards compatibility for code that explicitly
// includes and uses fbstring.
#if defined(_GLIBCXX_USE_FB) && !defined(_LIBSTDCXX_FBSTRING)
#include <string>
namespace folly {
using std::goodMallocSize;
using std::jemallocMinInPlaceExpandable;
using std::usingJEMalloc;
using std::smartRealloc;
using std::checkedMalloc;
using std::checkedCalloc;
using std::checkedRealloc;
#else // !defined(_GLIBCXX_USE_FB) || defined(_LIBSTDCXX_FBSTRING)
#pragma GCC system_header
#include "folly-config.h"
// for malloc_usable_size
// NOTE: FreeBSD 9 doesn't have malloc.h. It's defitions
// are found in stdlib.h.
#include <malloc.h>
#include <stdlib.h>
#include <cassert>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <new>
#include <bits/functexcept.h>
* Declare rallocm() and malloc_usable_size() as weak symbols. It
* will be provided by jemalloc if we are using jemalloc, or it will
* be NULL if we are using another malloc implementation.
extern "C" int rallocm(void**, size_t*, size_t, size_t, int)
* normally provided by jemalloc. We define them so that we don't have to
* include jemalloc.h, in case the program is built without jemalloc support.
#define ALLOCM_ERR_OOM 1
#define ALLOCM_ZERO 64
#define ALLOCM_NO_MOVE 128
#define ALLOCM_LG_ALIGN(la) (la)
namespace std _GLIBCXX_VISIBILITY(default) {
namespace folly {
* Determine if we are using jemalloc or not.
inline bool usingJEMalloc() {
return rallocm != NULL;
* For jemalloc's size classes, see
inline size_t goodMallocSize(size_t minSize) {
if (!usingJEMalloc()) {
// Not using jemalloc - no smarts
return minSize;
if (minSize <= 64) {
// Choose smallest allocation to be 64 bytes - no tripping over
// cache line boundaries, and small string optimization takes care
// of short strings anyway.
return 64;
if (minSize <= 512) {
// Round up to the next multiple of 64; we don't want to trip over
// cache line boundaries.
return (minSize + 63) & ~size_t(63);
if (minSize <= 3840) {
// Round up to the next multiple of 256
return (minSize + 255) & ~size_t(255);
if (minSize <= 4072 * 1024) {
// Round up to the next multiple of 4KB
return (minSize + 4095) & ~size_t(4095);
// Holy Moly
// Round up to the next multiple of 4MB
return (minSize + 4194303) & ~size_t(4194303);
// We always request "good" sizes for allocation, so jemalloc can
// never grow in place small blocks; they're already occupied to the
// brim. Blocks larger than or equal to 4096 bytes can in fact be
// expanded in place, and this constant reflects that.
static const size_t jemallocMinInPlaceExpandable = 4096;
* Trivial wrappers around malloc, calloc, realloc that check for allocation
* failure and throw std::bad_alloc in that case.
inline void* checkedMalloc(size_t size) {
void* p = malloc(size);
if (!p) std::__throw_bad_alloc();
return p;
inline void* checkedCalloc(size_t n, size_t size) {
void* p = calloc(n, size);
if (!p) std::__throw_bad_alloc();
return p;
inline void* checkedRealloc(void* ptr, size_t size) {
void* p = realloc(ptr, size);
if (!p) std::__throw_bad_alloc();
return p;
* This function tries to reallocate a buffer of which only the first
* currentSize bytes are used. The problem with using realloc is that
* if currentSize is relatively small _and_ if realloc decides it
* needs to move the memory chunk to a new buffer, then realloc ends
* up copying data that is not used. It's impossible to hook into
* GNU's malloc to figure whether expansion will occur in-place or as
* a malloc-copy-free troika. (If an expand_in_place primitive would
* be available, smartRealloc would use it.) As things stand, this
* routine just tries to call realloc() (thus benefitting of potential
* copy-free coalescing) unless there's too much slack memory.
inline void* smartRealloc(void* p,
const size_t currentSize,
const size_t currentCapacity,
const size_t newCapacity) {
assert(currentSize <= currentCapacity &&
currentCapacity < newCapacity);
if (usingJEMalloc()) {
// using jemalloc's API. Don't forget that jemalloc can never grow
// in place blocks smaller than 4096 bytes.
if (currentCapacity >= jemallocMinInPlaceExpandable &&
rallocm(&p, NULL, newCapacity, 0, ALLOCM_NO_MOVE) == ALLOCM_SUCCESS) {
// Managed to expand in place
return p;
// Cannot expand; must move
auto const result = checkedMalloc(newCapacity);
std::memcpy(result, p, currentSize);
return result;
// No jemalloc no honey
auto const slack = currentCapacity - currentSize;
if (slack * 2 > currentSize) {
// Too much slack, malloc-copy-free cycle:
auto const result = checkedMalloc(newCapacity);
std::memcpy(result, p, currentSize);
return result;
// If there's not too much slack, we realloc in hope of coalescing
return checkedRealloc(p, newCapacity);
} // folly
#endif // !defined(_GLIBCXX_USE_FB) || defined(_LIBSTDCXX_FBSTRING)
#endif // FOLLY_MALLOC_H_
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