Redis源碼分析：記憶體管理

源碼版本：redis 2.4.4

redis記憶體相關函數都放在zmalloc.h zmalloc.c中

redis中可以使用tcmalloc、jemalloc
Makefile：

ifeq ($(USE_TCMALLOC),yes)  ALLOC_DEP=  ALLOC_LINK=-ltcmalloc  ALLOC_FLAGS=-DUSE_TCMALLOCendififeq ($(USE_JEMALLOC),yes)  ALLOC_DEP=../deps/jemalloc/lib/libjemalloc.a  ALLOC_LINK=$(ALLOC_DEP) -ldl  ALLOC_FLAGS=-DUSE_JEMALLOC -I../deps/jemalloc/includeendif

zmalloc.c中

#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

簡單封裝
void *zmalloc(size_t size);
void *zcalloc(size_t size);
void *zrealloc(void *ptr, size_t size);
void zfree(void *ptr);
分別對malloc、calloc、realloc、free做了簡單封裝
對zmalloc和zfree做分析

void *zmalloc(size_t size) {    void *ptr = malloc(size+PREFIX_SIZE);    if (!ptr) zmalloc_oom(size);#ifdef HAVE_MALLOC_SIZE    update_zmalloc_stat_alloc(zmalloc_size(ptr),size);    return ptr;#else    *((size_t*)ptr) = size;    update_zmalloc_stat_alloc(size+PREFIX_SIZE,size);    return (char*)ptr+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}

除了分配給指定大小的記憶體之外，還分配了PREFIX_SIZE
記憶體格局如下：

申請記憶體返回Real_ptr

#define update_zmalloc_stat_alloc(__n,__size) do { \    size_t _n = (__n); \    if (_n&(sizeof(long)-1)) _n += sizeof(long)-(_n&(sizeof(long)-1)); \    if (zmalloc_thread_safe) { \        pthread_mutex_lock(&used_memory_mutex);  \        used_memory += _n; \        pthread_mutex_unlock(&used_memory_mutex); \    } else { \        used_memory += _n; \    } \} while(0)#define update_zmalloc_stat_free(__n) do { \    size_t _n = (__n); \    if (_n&(sizeof(long)-1)) _n += sizeof(long)-(_n&(sizeof(long)-1)); \    if (zmalloc_thread_safe) { \        pthread_mutex_lock(&used_memory_mutex);  \        used_memory -= _n; \        pthread_mutex_unlock(&used_memory_mutex); \    } else { \        used_memory -= _n; \    } \} while(0)

used_memory記錄當前分配的總記憶體

在定義了 int vm_max_threads; /* Max number of I/O threads running at the same time */
    if (server.vm_max_threads != 0)
        zmalloc_enable_thread_safeness(); /* we need thread safe zmalloc() */
在使用Threaded Virtual Memory I/O的時候，需要安全的zmalloc

size_t zmalloc_used_memory(void) {    size_t um;    if (zmalloc_thread_safe) pthread_mutex_lock(&used_memory_mutex);    um = used_memory;    if (zmalloc_thread_safe) pthread_mutex_unlock(&used_memory_mutex);    return um;}

zmalloc_used_memory返回進程當前使用的記憶體，用以做相應的清記憶體操作，eg：

zmalloc_used_memory() > server.maxmemory //和配置的最大記憶體比較....

zmalloc_get_rss()用來計算進程實際使用實體記憶體