Redis source code analysis: Memory Management

Source code version: redis 2.4.4

Redis memory-related functions are stored in zmalloc. h zmalloc. C.

Redis can use tcmalloc and 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

#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

Simple Encapsulation
Void * zmalloc (size_t size );
Void * zcalloc (size_t size );
Void * zrealloc (void * PTR, size_t size );
Void zfree (void * PTR );
Simple encapsulation of malloc, calloc, realloc, and free
Analyze zmalloc and zfree

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}

In addition to the specified memory size, prefix_size is also allocated.
The memory pattern is as follows:

Real_ptr returned when applying for memory

#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 records the total memory currently allocated

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 ()*/
Secure zmalloc is required when threaded virtual memory I/O is used.

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 returns the memory currently used by the process for memory clearing. For example:

Zmalloc_used_memory ()> server. maxmemory // compare with the configured maximum memory ....

Zmalloc_get_rss () is used to calculate the actual physical memory used by the Process