memcache的内存管理探微

slab分配器：http://blog.****.net/luotuo44/article/details/42737181

hash操作  ：http://blog.****.net/luotuo44/article/details/42773231

lru操作     ：http://blog.****.net/luotuo44/article/details/42869325

配置参数   ：http://blog.****.net/luotuo44/article/details/42672913

核心结构体

typedef struct _stritem {
    struct _stritem *next;
    struct _stritem *prev;
    struct _stritem *h_next;    /* hash chain next */
    rel_time_t      time;       /* least recent access */
    rel_time_t      exptime;    /* expire time */
    int             nbytes;     /* size of data */
    unsigned short  refcount;
    uint8_t         nsuffix;    /* length of flags-and-length string */
    uint8_t         it_flags;   /* ITEM_* above */
    uint8_t         slabs_clsid;/* which slab class we're in */
    uint8_t         nkey;       /* key length, w/terminating null and padding */
    uint64_t        cas_id;     /* the CAS identifier */
    void * end[];
    /* then null-terminated key */
    /* then " flags length\r\n" (no terminating null) */
    /* then data with terminating \r\n (no terminating null; it's binary!) */
} item;

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 */
} slabclass_t;