2 * Copyright 2012 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 // Functions to provide smarter use of jemalloc, if jemalloc is being used.
18 // http://www.canonware.com/download/jemalloc/jemalloc-latest/doc/jemalloc.html
20 #ifndef FOLLY_MALLOC_H_
21 #define FOLLY_MALLOC_H_
23 // If using fbstring from libstdc++, then just define stub code
24 // here to typedef the fbstring type into the folly namespace.
25 // This provides backwards compatibility for code that explicitly
26 // includes and uses fbstring.
27 #if defined(_GLIBCXX_USE_FB) && !defined(_LIBSTDCXX_FBSTRING)
31 using std::goodMallocSize;
32 using std::jemallocMinInPlaceExpandable;
33 using std::usingJEMalloc;
34 using std::smartRealloc;
37 #else // !defined(_GLIBCXX_USE_FB) || defined(_LIBSTDCXX_FBSTRING)
39 #ifdef _LIBSTDCXX_FBSTRING
40 #pragma GCC system_header
41 #define FOLLY_HAVE_MALLOC_H 1
43 #include "folly-config.h"
46 // for malloc_usable_size
47 // NOTE: FreeBSD 9 doesn't have malloc.h. It's defitions
48 // are found in stdlib.h.
49 #ifdef FOLLY_HAVE_MALLOC_H
61 * Declare rallocm() and malloc_usable_size() as weak symbols. It
62 * will be provided by jemalloc if we are using jemalloc, or it will
63 * be NULL if we are using another malloc implementation.
65 extern "C" int rallocm(void**, size_t*, size_t, size_t, int)
66 __attribute__((weak));
69 * Define the ALLOCM_SUCCESS, ALLOCM_ZERO, and ALLOCM_NO_MOVE constants
70 * normally provided by jemalloc. We define them so that we don't have to
71 * include jemalloc.h, in case the program is built without jemalloc support.
73 #ifndef ALLOCM_SUCCESS
74 #define ALLOCM_SUCCESS 0
75 #define ALLOCM_ERR_OOM 1
76 #define ALLOCM_ERR_NOT_MOVED 2
78 #define ALLOCM_ZERO 64
79 #define ALLOCM_NO_MOVE 128
82 #ifdef _LIBSTDCXX_FBSTRING
83 namespace std _GLIBCXX_VISIBILITY(default) {
84 _GLIBCXX_BEGIN_NAMESPACE_VERSION
91 * Determine if we are using jemalloc or not.
93 inline bool usingJEMalloc() {
94 return rallocm != NULL;
98 * For jemalloc's size classes, see
99 * http://www.canonware.com/download/jemalloc/jemalloc-latest/doc/jemalloc.html
101 inline size_t goodMallocSize(size_t minSize) {
102 if (!usingJEMalloc()) {
103 // Not using jemalloc - no smarts
107 // Choose smallest allocation to be 64 bytes - no tripping over
108 // cache line boundaries, and small string optimization takes care
109 // of short strings anyway.
112 if (minSize <= 512) {
113 // Round up to the next multiple of 64; we don't want to trip over
114 // cache line boundaries.
115 return (minSize + 63) & ~size_t(63);
117 if (minSize <= 3840) {
118 // Round up to the next multiple of 256
119 return (minSize + 255) & ~size_t(255);
121 if (minSize <= 4072 * 1024) {
122 // Round up to the next multiple of 4KB
123 return (minSize + 4095) & ~size_t(4095);
126 // Round up to the next multiple of 4MB
127 return (minSize + 4194303) & ~size_t(4194303);
130 // We always request "good" sizes for allocation, so jemalloc can
131 // never grow in place small blocks; they're already occupied to the
132 // brim. Blocks larger than or equal to 4096 bytes can in fact be
133 // expanded in place, and this constant reflects that.
134 static const size_t jemallocMinInPlaceExpandable = 4096;
137 * This function tries to reallocate a buffer of which only the first
138 * currentSize bytes are used. The problem with using realloc is that
139 * if currentSize is relatively small _and_ if realloc decides it
140 * needs to move the memory chunk to a new buffer, then realloc ends
141 * up copying data that is not used. It's impossible to hook into
142 * GNU's malloc to figure whether expansion will occur in-place or as
143 * a malloc-copy-free troika. (If an expand_in_place primitive would
144 * be available, smartRealloc would use it.) As things stand, this
145 * routine just tries to call realloc() (thus benefitting of potential
146 * copy-free coalescing) unless there's too much slack memory.
148 inline void* smartRealloc(void* p,
149 const size_t currentSize,
150 const size_t currentCapacity,
151 const size_t newCapacity) {
153 assert(currentSize <= currentCapacity &&
154 currentCapacity < newCapacity);
156 if (usingJEMalloc()) {
157 // using jemalloc's API. Don't forget that jemalloc can never grow
158 // in place blocks smaller than 4096 bytes.
159 if (currentCapacity >= jemallocMinInPlaceExpandable &&
160 rallocm(&p, NULL, newCapacity, 0, ALLOCM_NO_MOVE) == ALLOCM_SUCCESS) {
161 // Managed to expand in place
164 // Cannot expand; must move
165 auto const result = malloc(newCapacity);
166 std::memcpy(result, p, currentSize);
171 // No jemalloc no honey
172 auto const slack = currentCapacity - currentSize;
173 if (slack * 2 > currentSize) {
174 // Too much slack, malloc-copy-free cycle:
175 auto const result = malloc(newCapacity);
176 std::memcpy(result, p, currentSize);
180 // If there's not too much slack, we realloc in hope of coalescing
181 return realloc(p, newCapacity);
184 #ifdef _LIBSTDCXX_FBSTRING
185 _GLIBCXX_END_NAMESPACE_VERSION
190 #endif // !defined(_GLIBCXX_USE_FB) || defined(_LIBSTDCXX_FBSTRING)
192 #endif // FOLLY_MALLOC_H_