memcached内存管理的一些小小的变化
原来的看这里：
http://blog.developers.api.sina.com.cn/?p=124
http://basiccoder.com/memcached-memory-mamagement.html
在slabs.c中原来的slabclass_t如下：
typedef struct { unsigned int size; /* sizes of items */ unsigned int perslab; /* how many items per slab */ void **slots; /* list of item ptrs */ unsigned int sl_total; /* size of previous array */ unsigned int sl_curr; /* first free slot */ void *end_page_ptr; /* pointer to next free item at end of page, or 0 */ unsigned int end_page_free; /* number of items remaining at end of last alloced page */ unsigned int slabs; /* how many slabs were allocated for this class */ void **slab_list; /* array of slab pointers */ unsigned int list_size; /* size of prev array */ unsigned int killing; /* index+1 of dying slab, or zero if none */ size_t requested; /* The number of requested bytes */ } slabclass_t; static slabclass_t slabclass[MAX_NUMBER_OF_SLAB_CLASSES];
而现在在官网上新下载的源码slabclass_t的结构如下：
typedef struct {
unsigned int size; /* sizes of items */
unsigned int perslab; /* how many items per slab */
void *slots; /* list of item ptrs */
unsigned int sl_curr; /* total free items in list */
unsigned int slabs; /* how many slabs were allocated for this class */
void **slab_list; /* array of slab pointers */
unsigned int list_size; /* size of prev array */
unsigned int killing; /* index+1 of dying slab, or zero if none */
size_t requested; /* The number of requested bytes */
} slabclass_t;
主要是少了end_page_ptr和end_page_free这2个字段。
在以前end_page_ptr是指向新分配的slab上未使用的chunk的。而现在少了这个就意味着，现在不需要这个了，因为新slab刚分配内存后就会直接通过do_slab_free放到slot中，这样就不需要区分slab和slot了，可能管理起来会方便点吧。
代码如下：
static int grow_slab_list (const unsigned int id) {
slabclass_t *p = &slabclass[id];
if (p->slabs == p->list_size) {
size_t new_size = (p->list_size != 0) ? p->list_size * 2 : 16;
void *new_list = realloc(p->slab_list, new_size * sizeof(void *));
if (new_list == 0) return 0;
p->list_size = new_size;
p->slab_list = new_list;
}
return 1;
}
static void split_slab_page_into_freelist(char *ptr, const unsigned int id) {
slabclass_t *p = &slabclass[id];
int x;
for (x = 0; x < p->perslab; x++) {
do_slabs_free(ptr, 0, id);
ptr += p->size;
}
}
static int do_slabs_newslab(const unsigned int id) {
slabclass_t *p = &slabclass[id];
int len = settings.slab_reassign ? settings.item_size_max
: p->size * p->perslab;
char *ptr;
if ((mem_limit && mem_malloced + len > mem_limit && p->slabs > 0) ||
(grow_slab_list(id) == 0) ||
((ptr = memory_allocate((size_t)len)) == 0)) {
MEMCACHED_SLABS_SLABCLASS_ALLOCATE_FAILED(id);
return 0;
}
memset(ptr, 0, (size_t)len);
split_slab_page_into_freelist(ptr, id);
p->slab_list[p->slabs++] = ptr;
mem_malloced += len;
MEMCACHED_SLABS_SLABCLASS_ALLOCATE(id);
return 1;
}