Redis 内存管理 源码分析

要想了解redis底层的内存管理是如何进行的，直接看源码绝对是一个很好的选择

下面是我添加了详细注释的源码，需要注意的是，为了便于源码分析，我把redis为了弥补平台差异的那部分代码删了，只需要知道有这个东西便好

下面我会贴上两份源码：一份是我自己的，有删减添加了注释的，一部分是原生的，可以做个参考对照

redis内存管理部分的源码在zmalloc.h文件和zmalloc.c文件

推荐文章：

https://www.cnblogs.com/likui360/p/5272443.html

https://www.cnblogs.com/likui360/p/5272975.html

http://wiki.jikexueyuan.com/project/redis/memory-data-management.html

我的源码

zmalloc.h：

#ifndef __ZMALLOC_H
#define __ZMALLOC_H

#define __xstr(s) __str(s)
#define __str(s) #s

#ifndef ZMALLOC_LIB
#define ZMALLOC_LIB "libc"
#endif

/*
  CPU一次性能读取数据的二进制位数称为字长，也就是我们通常所说的32位系统（字长4个字节）、64位系统（字长8个字节）的由来。

  所谓的8字节对齐，就是指变量的起始地址是8的倍数。

  比如程序运行时（CPU）在读取long型数据的时候，只需要一个总线周期，时间更短，

  如果不是8字节对齐的则需要两个总线周期才能读完数据。

  本文中我提到的8字节对齐是针对64位系统而言的，如果是32位系统那么就是4字节对齐。

  实际上Redis源码中的字节对齐是软编码，而非硬编码。

  里面多用sizeof(long)或sizeof(size_t)来表示。

  size_t（gcc中其值为long unsigned int）和long的长度是一样的，

  long的长度就是计算机的字长。

  这样在未来的系统中如果字长（long的大小）不是8个字节了，该段代码依然能保证相应代码可用。

*/

/**
Redis内存模型:

|--------|:代表8个字节大小

| 头部   |            实际内存              |
|--------|--------|--------|--------|--------|
         ^
         |
         ptr:实际返回的地址

上面的内存模型说明了两个问题：

1.内存对齐,都是8个字节的，可以提高cpu响应速度

2.返回的实际地址不包括头部

ps:从左到右内存地址是增加的,默认大端模式

*/
//============ API ==================//

//封装malloc,申请内存
void *zmalloc(size_t size);

//封装calloc,不再支持按块成倍申请
void *zcalloc(size_t size);

//封装realloc,内存扩展
void *zrealloc(void *ptr, size_t size);

//封装free,内存释放，释放时会更新已经使用的内存值，如果在多线程下没有开启安全模式，可能会出现并发错误
void zfree(void *ptr);

//复制一个字符串,为字符串在堆分配内存
char *zstrdup(const char *s);

//获取已经使用的内存大小
size_t zmalloc_used_memory(void);

//设置内存管理为多线程安全模式，设置之后在更新使用内存大小时会使用mutex进行互斥操作
void zmalloc_enable_thread_safeness(void);

//设置内存异常时的回调函数
void zmalloc_set_oom_handler(void (*oom_handler)(size_t));

//内存碎片率,驻留在物理内存中的内存/总分配的物理内存
float zmalloc_get_fragmentation_ratio(size_t rss);

//获取进程可使用的所有内存大小
size_t zmalloc_get_rss(void);

//获得private_dirty字段
size_t zmalloc_get_private_dirty(void);

//用这个释放内存时，不会更新使用内存变量的值。
void zlibc_free(void *ptr);

//获取内内存块总体大小
size_t zmalloc_size(void *ptr);

#endif /* __ZMALLOC_H */

/*
1.malloc函数和calloc函数的区别

  void *malloc(unsigned int size) 在内存中分配一个大小为size的连续空间

  void* calloc（unsigned int num，unsigned int size）在内存中分配num个size大小的内存空间

  调用malloc后内存中的数据是随机的垃圾数据

  调用calloc后内存中的数据是0，因为calloc会自动清零

2.redis为了方便管理内存，在分配一块内存之后，会将内存大小size插入内存头部，size所占内存大小固定

3.Redis允许使用四种内存管理策略:jemalloc,tcmalloc,苹果系统自带的malloc，其他系统自带的malloc

  当存在前面三种策略的时候，就选择前面三种，第四种是没有选择的选择

  jemalloc是freebsd操作系统自带的内存分配策略，具有速度快，多线程优化的特点

  tcmalloc是谷歌开发的，里面集成了很多内存分配的测试工具

  这二者的性能不分伯仲

4.Redis很多对象都是共享的，可以节约内存

5.memory aware【内存感知】

  Redis能随时高性能的感知所使用的内存总量，实时的获取Redis所使用的内存的大小，从而随时感知内存

  实现方式：
      每次分配/释放内存时都更新一个全局的内存使用值

6.内存对齐，比如5位补齐为8位,CPU访问对齐内存仅仅需要一次,访问非对齐内存需要2次，内存对齐可以提高cpu的访问速率

*/

 

zmalloc.c:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include "zmalloc.h"

//记录已经使用的内存大小
static size_t used_memory = ;

//线程安全开关
static int zmalloc_thread_safe = ;

//互斥锁，如果开启了线程安全，而编译器又不支持原子操作函数，则需要互斥锁来完成代码互斥操作
pthread_mutex_t used_memory_mutex = PTHREAD_MUTEX_INITIALIZER;

//头部长度
#define PREFIX_SIZE (sizeof(size_t))

//以线程安全的方式 增加 内存已使用 变量
#define update_zmalloc_stat_add(__n) do { \
    pthread_mutex_lock(&used_memory_mutex); \
    used_memory += (__n); \
    pthread_mutex_unlock(&used_memory_mutex); \
} while()

//以线程安全的方式 减小 内存已使用 变量

#define update_zmalloc_stat_sub(__n) do { \
    pthread_mutex_lock(&used_memory_mutex); \
    used_memory -= (__n); \
    pthread_mutex_unlock(&used_memory_mutex); \
} while()

//增加 已经使用的内存大小,函数内确定是否以线程安全的模式运行
#define update_zmalloc_stat_alloc(__n) do { \
    size_t _n = (__n); \
    if (_n&(sizeof(long)-)) _n += sizeof(long)-(_n&(sizeof(long)-));/*手动内存补齐*/ \
    if (zmalloc_thread_safe) { \
        update_zmalloc_stat_add(_n); \
    } else { \
        used_memory += _n; \
    } \
} while()

//减小 已经使用的内存大小,函数内确定是否以线程安全的模式运行
#define update_zmalloc_stat_free(__n) do { \
    size_t _n = (__n); \
    if (_n&(sizeof(long)-)) _n += sizeof(long)-(_n&(sizeof(long)-)); /*手动内存补齐*/ \
    if (zmalloc_thread_safe) { \
        update_zmalloc_stat_sub(_n); \
    } else { \
        used_memory -= _n; \
    } \
} while()

//释放内存，不会更改 已使用内存变量
void zlibc_free(void *ptr)
{
    free(ptr);
}

//打印错误信息并且终止程序 OOM:out of memory
static void zmalloc_default_oom(size_t size)
{
    fprintf(stderr, "zmalloc: Out of memory trying to allocate %zu bytes\n",
            size);
    fflush(stderr);
    abort();
}

//设置OMM时的回调函数
static void (*zmalloc_oom_handler)(size_t) = zmalloc_default_oom;

//申请size大小的连续内存空间，返回一个指向该空间的指针
void *zmalloc(size_t size)
{
    //申请内存空间，预留了PREFIX_SIZE这样一小段空间
    void *ptr = malloc(size+PREFIX_SIZE);

    //oom out of memory
    if (!ptr) zmalloc_oom_handler(size); // 如果分配不成功,那么说明内存用尽

    //把内存大小存储在头部
    *((size_t*)ptr) = size;

    //更新已经使用的内存大小
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);

    //返回指向该内存空间实际地址的指针，该指针不指向存放内存大小的内存头部
    return (char*)ptr+PREFIX_SIZE;
}

//内存申请
void *zcalloc(size_t size)
{
    //不再支持按倍数分配内存
    void *ptr = calloc(, size+PREFIX_SIZE);

    //内存分配失败，调用回调函数
    if (!ptr) zmalloc_oom_handler(size);

    *((size_t*)ptr) = size;

    //更改已经使用的内存大小
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);

    //返回指向该内存块的指针
    return (char*)ptr+PREFIX_SIZE;
}

//指定的内存扩展为size大小，返回扩展后的内存块指针
void *zrealloc(void *ptr, size_t size)
{
    void *realptr;
    size_t oldsize;
    void *newptr;

    //原内存为空，则直接申请
    if (ptr == NULL) return zmalloc(size);

    //实际内存地址指针(包含头部)
    realptr = (char*)ptr-PREFIX_SIZE;

    //实际内存大小(包含头部)
    oldsize = *((size_t*)realptr);

    //其实zrealloc底层还是封装了realloc,将原内存扩展为size+PREFIX_SIZE大小
    newptr = realloc(realptr,size+PREFIX_SIZE);

    //内存扩展失败，进行回调
    if (!newptr) zmalloc_oom_handler(size);

    //新内存块大小记录在内存头部
    *((size_t*)newptr) = size;

    //修改已使用的内存大小
    update_zmalloc_stat_free(oldsize);
    update_zmalloc_stat_alloc(size);

    //返回指针指向扩展后的内存块(不包含头部)
    return (char*)newptr+PREFIX_SIZE;
}

//返回指定内存块的大小(不包括头部)
size_t zmalloc_size(void *ptr)
{
    //指向实际内存块(包含头部)
    void *realptr = (char*)ptr-PREFIX_SIZE;

    //实际内存块大小
    size_t size = *((size_t*)realptr);

    //内存对齐，比如5位补齐为8位,CPU访问对齐内存仅仅需要一次,访问非对齐内存需要2次，内存对齐可以提高cpu的访问速率
    if (size&(sizeof(long)-)) size += sizeof(long)-(size&(sizeof(long)-));

    //返回内存大小(不包括头部)
    return size+PREFIX_SIZE;
}

//释放内存，会更改 已使用的内存变量
void zfree(void *ptr)
{
    /*释放内存之前要先获得包含头部内存的实际内存地址，才能避免头部内存的内存泄漏*/
    void *realptr;
    size_t oldsize;

    //空内存 直接返回
    if (ptr == NULL) return;

    //指向实际内存(包含内存头部)
    realptr = (char*)ptr-PREFIX_SIZE;

    //实际内存大小
    oldsize = *((size_t*)realptr);

    //更改已使用的内存变量
    update_zmalloc_stat_free(oldsize+PREFIX_SIZE);

    //释放
    free(realptr);

}

//复制字符串
char *zstrdup(const char *s)
{
    size_t l = strlen(s)+;
    char *p = zmalloc(l);
    memcpy(p,s,l);
    return p;
}

//获得已使用的内存空间
size_t zmalloc_used_memory(void)
{
    size_t um;

    //线程不安全的情况 加锁
    if (zmalloc_thread_safe)
    {
        pthread_mutex_lock(&used_memory_mutex);
        um = used_memory;
        pthread_mutex_unlock(&used_memory_mutex);

    }
    else
    {
        um = used_memory;
    }

    return um;
}

//启动线程安全的开关,保证线程安全
void zmalloc_enable_thread_safeness(void)
{
    zmalloc_thread_safe = ;
}

//设置OMM的回调函数
void zmalloc_set_oom_handler(void (*oom_handler)(size_t))
{
    zmalloc_oom_handler = oom_handler;
}

//下面几个函数深究起来意义不大

//获取进程可使用的所有内存大小
size_t zmalloc_get_rss(void)
{
    //很多东西我注释掉了.....
    return zmalloc_used_memory();
}

//内存碎片率
float zmalloc_get_fragmentation_ratio(size_t rss)
{
    return (float)rss/zmalloc_used_memory();
}

//获得private_dirty字段
size_t zmalloc_get_private_dirty(void)
{
    return ;
}

原生源码:

zmalloc.h：

/* zmalloc - total amount of allocated memory aware version of malloc()
 *
 * Copyright (c) 2009-2010, Salvatore Sanfilippo <antirez at gmail dot com>
 * 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 Redis 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.
 */

#ifndef __ZMALLOC_H
#define __ZMALLOC_H

/* Double expansion needed for stringification of macro values. */
#define __xstr(s) __str(s)
#define __str(s) #s

#if defined(USE_TCMALLOC)
#define ZMALLOC_LIB ("tcmalloc-" __xstr(TC_VERSION_MAJOR) "." __xstr(TC_VERSION_MINOR))
#include <google/tcmalloc.h>
#if (TC_VERSION_MAJOR == 1 && TC_VERSION_MINOR >= 6) || (TC_VERSION_MAJOR > 1)
#define HAVE_MALLOC_SIZE 1
#define zmalloc_size(p) tc_malloc_size(p)
#else
#error "Newer version of tcmalloc required"
#endif

#elif defined(USE_JEMALLOC)
#define ZMALLOC_LIB ("jemalloc-" __xstr(JEMALLOC_VERSION_MAJOR) "." __xstr(JEMALLOC_VERSION_MINOR) "." __xstr(JEMALLOC_VERSION_BUGFIX))
#include <jemalloc/jemalloc.h>
#if (JEMALLOC_VERSION_MAJOR == 2 && JEMALLOC_VERSION_MINOR >= 1) || (JEMALLOC_VERSION_MAJOR > 2)
#define HAVE_MALLOC_SIZE 1
#define zmalloc_size(p) je_malloc_usable_size(p)
#else
#error "Newer version of jemalloc required"
#endif

#elif defined(__APPLE__)
#include <malloc/malloc.h>
#define HAVE_MALLOC_SIZE 1
#define zmalloc_size(p) malloc_size(p)
#endif

#ifndef ZMALLOC_LIB
#define ZMALLOC_LIB "libc"
#endif

void *zmalloc(size_t size);
void *zcalloc(size_t size);
void *zrealloc(void *ptr, size_t size);
void zfree(void *ptr);
char *zstrdup(const char *s);
size_t zmalloc_used_memory(void);
void zmalloc_enable_thread_safeness(void);
void zmalloc_set_oom_handler(void (*oom_handler)(size_t));
float zmalloc_get_fragmentation_ratio(size_t rss);
size_t zmalloc_get_rss(void);
size_t zmalloc_get_private_dirty(void);
void zlibc_free(void *ptr);

#ifndef HAVE_MALLOC_SIZE
size_t zmalloc_size(void *ptr);
#endif

#endif /* __ZMALLOC_H */

zmalloc.c:

/* zmalloc - total amount of allocated memory aware version of malloc()
 *
 * Copyright (c) 2009-2010, Salvatore Sanfilippo <antirez at gmail dot com>
 * 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 Redis 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.
 */

#include <stdio.h>
#include <stdlib.h>

/* This function provide us access to the original libc free(). This is useful
 * for instance to free results obtained by backtrace_symbols(). We need
 * to define this function before including zmalloc.h that may shadow the
 * free implementation if we use jemalloc or another non standard allocator. */
void zlibc_free(void *ptr) {
    free(ptr);
}

#include <string.h>
#include <pthread.h>
#include "config.h"
#include "zmalloc.h"

#ifdef HAVE_MALLOC_SIZE
#define PREFIX_SIZE (0)
#else
#if defined(__sun) || defined(__sparc) || defined(__sparc__)
#define PREFIX_SIZE (sizeof(long long))
#else
#define PREFIX_SIZE (sizeof(size_t))
#endif
#endif

/* Explicitly override malloc/free etc when using tcmalloc. */
#if defined(USE_TCMALLOC)
#define malloc(size) tc_malloc(size)
#define calloc(count,size) tc_calloc(count,size)
#define realloc(ptr,size) tc_realloc(ptr,size)
#define free(ptr) tc_free(ptr)
#elif defined(USE_JEMALLOC)
#define malloc(size) je_malloc(size)
#define calloc(count,size) je_calloc(count,size)
#define realloc(ptr,size) je_realloc(ptr,size)
#define free(ptr) je_free(ptr)
#endif

#ifdef HAVE_ATOMIC
#define update_zmalloc_stat_add(__n) __sync_add_and_fetch(&used_memory, (__n))
#define update_zmalloc_stat_sub(__n) __sync_sub_and_fetch(&used_memory, (__n))
#else
#define update_zmalloc_stat_add(__n) do { \
    pthread_mutex_lock(&used_memory_mutex); \
    used_memory += (__n); \
    pthread_mutex_unlock(&used_memory_mutex); \
} while()

#define update_zmalloc_stat_sub(__n) do { \
    pthread_mutex_lock(&used_memory_mutex); \
    used_memory -= (__n); \
    pthread_mutex_unlock(&used_memory_mutex); \
} while()

#endif

#define update_zmalloc_stat_alloc(__n) do { \
    size_t _n = (__n); \
    if (_n&(sizeof(long)-)) _n += sizeof(long)-(_n&(sizeof(long)-)); \
    if (zmalloc_thread_safe) { \
        update_zmalloc_stat_add(_n); \
    } else { \
        used_memory += _n; \
    } \
} while()

#define update_zmalloc_stat_free(__n) do { \
    size_t _n = (__n); \
    if (_n&(sizeof(long)-)) _n += sizeof(long)-(_n&(sizeof(long)-)); \
    if (zmalloc_thread_safe) { \
        update_zmalloc_stat_sub(_n); \
    } else { \
        used_memory -= _n; \
    } \
} while()

static size_t used_memory = ;
static int zmalloc_thread_safe = ;
pthread_mutex_t used_memory_mutex = PTHREAD_MUTEX_INITIALIZER;

static void zmalloc_default_oom(size_t size) {
    fprintf(stderr, "zmalloc: Out of memory trying to allocate %zu bytes\n",
        size);
    fflush(stderr);
    abort();
}

static void (*zmalloc_oom_handler)(size_t) = zmalloc_default_oom;

void *zmalloc(size_t size) {
    void *ptr = malloc(size+PREFIX_SIZE);

    if (!ptr) zmalloc_oom_handler(size);
#ifdef HAVE_MALLOC_SIZE
    update_zmalloc_stat_alloc(zmalloc_size(ptr));
    return ptr;
#else
    *((size_t*)ptr) = size;
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);
    return (char*)ptr+PREFIX_SIZE;
#endif
}

void *zcalloc(size_t size) {
    void *ptr = calloc(, size+PREFIX_SIZE);

    if (!ptr) zmalloc_oom_handler(size);
#ifdef HAVE_MALLOC_SIZE
    update_zmalloc_stat_alloc(zmalloc_size(ptr));
    return ptr;
#else
    *((size_t*)ptr) = size;
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);
    return (char*)ptr+PREFIX_SIZE;
#endif
}

void *zrealloc(void *ptr, size_t size) {
#ifndef HAVE_MALLOC_SIZE
    void *realptr;
#endif
    size_t oldsize;
    void *newptr;

    if (ptr == NULL) return zmalloc(size);
#ifdef HAVE_MALLOC_SIZE
    oldsize = zmalloc_size(ptr);
    newptr = realloc(ptr,size);
    if (!newptr) zmalloc_oom_handler(size);

    update_zmalloc_stat_free(oldsize);
    update_zmalloc_stat_alloc(zmalloc_size(newptr));
    return newptr;
#else
    realptr = (char*)ptr-PREFIX_SIZE;
    oldsize = *((size_t*)realptr);
    newptr = realloc(realptr,size+PREFIX_SIZE);
    if (!newptr) zmalloc_oom_handler(size);

    *((size_t*)newptr) = size;
    update_zmalloc_stat_free(oldsize);
    update_zmalloc_stat_alloc(size);
    return (char*)newptr+PREFIX_SIZE;
#endif
}

/* Provide zmalloc_size() for systems where this function is not provided by
 * malloc itself, given that in that case we store a header with this
 * information as the first bytes of every allocation. */
#ifndef HAVE_MALLOC_SIZE
size_t zmalloc_size(void *ptr) {
    void *realptr = (char*)ptr-PREFIX_SIZE;
    size_t size = *((size_t*)realptr);
    /* Assume at least that all the allocations are padded at sizeof(long) by
     * the underlying allocator. */
    if (size&(sizeof(long)-)) size += sizeof(long)-(size&(sizeof(long)-));
    return size+PREFIX_SIZE;
}
#endif

void zfree(void *ptr) {
#ifndef HAVE_MALLOC_SIZE
    void *realptr;
    size_t oldsize;
#endif

    if (ptr == NULL) return;
#ifdef HAVE_MALLOC_SIZE
    update_zmalloc_stat_free(zmalloc_size(ptr));
    free(ptr);
#else
    realptr = (char*)ptr-PREFIX_SIZE;
    oldsize = *((size_t*)realptr);
    update_zmalloc_stat_free(oldsize+PREFIX_SIZE);
    free(realptr);
#endif
}

char *zstrdup(const char *s) {
    size_t l = strlen(s)+;
    char *p = zmalloc(l);

    memcpy(p,s,l);
    return p;
}

size_t zmalloc_used_memory(void) {
    size_t um;

    if (zmalloc_thread_safe) {
#ifdef HAVE_ATOMIC
        um = __sync_add_and_fetch(&used_memory, );
#else
        pthread_mutex_lock(&used_memory_mutex);
        um = used_memory;
        pthread_mutex_unlock(&used_memory_mutex);
#endif
    }
    else {
        um = used_memory;
    }

    return um;
}

void zmalloc_enable_thread_safeness(void) {
    zmalloc_thread_safe = ;
}

void zmalloc_set_oom_handler(void (*oom_handler)(size_t)) {
    zmalloc_oom_handler = oom_handler;
}

/* Get the RSS information in an OS-specific way.
 *
 * WARNING: the function zmalloc_get_rss() is not designed to be fast
 * and may not be called in the busy loops where Redis tries to release
 * memory expiring or swapping out objects.
 *
 * For this kind of "fast RSS reporting" usages use instead the
 * function RedisEstimateRSS() that is a much faster (and less precise)
 * version of the function. */

#if defined(HAVE_PROC_STAT)
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

size_t zmalloc_get_rss(void) {
    int page = sysconf(_SC_PAGESIZE);
    size_t rss;
    char buf[];
    char filename[];
    int fd, count;
    char *p, *x;

    snprintf(filename,,"/proc/%d/stat",getpid());
    if ((fd = open(filename,O_RDONLY)) == -) return ;
    if (read(fd,buf,) <= ) {
        close(fd);
        return ;
    }
    close(fd);

    p = buf;
    count = ; /* RSS is the 24th field in /proc/<pid>/stat */
    while(p && count--) {
        p = strchr(p,' ');
        if (p) p++;
    }
    if (!p) return ;
    x = strchr(p,' ');
    if (!x) return ;
    *x = '\0';

    rss = strtoll(p,NULL,);
    rss *= page;
    return rss;
}
#elif defined(HAVE_TASKINFO)
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <mach/task.h>
#include <mach/mach_init.h>

size_t zmalloc_get_rss(void) {
    task_t task = MACH_PORT_NULL;
    struct task_basic_info t_info;
    mach_msg_type_number_t t_info_count = TASK_BASIC_INFO_COUNT;

    if (task_for_pid(current_task(), getpid(), &task) != KERN_SUCCESS)
        return ;
    task_info(task, TASK_BASIC_INFO, (task_info_t)&t_info, &t_info_count);

    return t_info.resident_size;
}
#else
size_t zmalloc_get_rss(void) {
    /* If we can't get the RSS in an OS-specific way for this system just
     * return the memory usage we estimated in zmalloc()..
     *
     * Fragmentation will appear to be always 1 (no fragmentation)
     * of course... */
    return zmalloc_used_memory();
}
#endif

/* Fragmentation = RSS / allocated-bytes */
float zmalloc_get_fragmentation_ratio(size_t rss) {
    return (float)rss/zmalloc_used_memory();
}

#if defined(HAVE_PROC_SMAPS)
size_t zmalloc_get_private_dirty(void) {
    char line[];
    size_t pd = ;
    FILE *fp = fopen("/proc/self/smaps","r");

    if (!fp) return ;
    while(fgets(line,sizeof(line),fp) != NULL) {
        if (strncmp(line,"Private_Dirty:",) == ) {
            char *p = strchr(line,'k');
            if (p) {
                *p = '\0';
                pd += strtol(line+,NULL,) * ;
            }
        }
    }
    fclose(fp);
    return pd;
}
#else
size_t zmalloc_get_private_dirty(void) {
    return ;
}
#endif