slabs 内存分配原理

前段时间，看过slabs内存分配的代码。

代码看过容易忘记，把看的用图记下来，方便后面自己看。

具体实现可以阅读代码：http://code.google.com/p/squirrel-message-queue/

                                           或者 http://code.google.com/p/memcached/

                                           slabs.c

 

#define POWER_SMALLEST 3#define POWER_LARGEST  20#define POWER_BLOCK 1048576/* powers-of-2 allocation structures */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;static slabclass_t slabclass[POWER_LARGEST+1];static unsigned int mem_limit = 0;static unsigned int mem_malloced = 0;unsigned int slabs_clsid(unsigned int size) {    int res = 1;    if(size==0)        return 0;    size--;    while(size >>= 1)        res++;    if (res < POWER_SMALLEST)         res = POWER_SMALLEST;    if (res > POWER_LARGEST)        res = 0;    return res;}void slabs_init(unsigned int limit) {    int i;    int size=1;    mem_limit = limit;    for(i=0; i<=POWER_LARGEST; i++, size*=2) {        slabclass[i].size = size;        slabclass[i].perslab = POWER_BLOCK / size;        slabclass[i].slots = 0;        slabclass[i].sl_curr = slabclass[i].sl_total = slabclass[i].slabs = 0;        slabclass[i].end_page_ptr = 0;        slabclass[i].end_page_free = 0;        slabclass[i].slab_list = 0;        slabclass[i].list_size = 0;        slabclass[i].killing = 0;    }}static int grow_slab_list (unsigned int id) {     slabclass_t *p = &slabclass[id];    if (p->slabs == p->list_size) {        unsigned int new_size =  p->list_size ? 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;}int slabs_newslab(unsigned int id) {    slabclass_t *p = &slabclass[id];    int num = p->perslab;    int len = POWER_BLOCK;    char *ptr;    if (mem_limit && mem_malloced + len > mem_limit)        return 0;    if (! grow_slab_list(id)) return 0;       ptr = malloc(len);    if (ptr == 0) return 0;    memset(ptr, 0, len);    p->end_page_ptr = ptr;    p->end_page_free = num;    p->slab_list[p->slabs++] = ptr;    mem_malloced += len;    return 1;}void *slabs_alloc(unsigned int size) {    slabclass_t *p;    unsigned char id = slabs_clsid(size);    if (id < POWER_SMALLEST || id > POWER_LARGEST)        return 0;    p = &slabclass[id];#ifdef USE_SYSTEM_MALLOC    if (mem_limit && mem_malloced + size > mem_limit)        return 0;    mem_malloced += size;    return malloc(size);#endif        /* fail unless we have space at the end of a recently allocated page,       we have something on our freelist, or we could allocate a new page */    if (! (p->end_page_ptr || p->sl_curr || slabs_newslab(id)))        return 0;    /* return off our freelist, if we have one */    if (p->sl_curr)        return p->slots[--p->sl_curr];    /* if we recently allocated a whole page, return from that */    if (p->end_page_ptr) {        void *ptr = p->end_page_ptr;        if (--p->end_page_free) {            p->end_page_ptr += p->size;        } else {            p->end_page_ptr = 0;        }        return ptr;    }    return 0;  /* shouldn't ever get here */}void slabs_free(void *ptr, unsigned int size) {    unsigned char id = slabs_clsid(size);    slabclass_t *p;    if (id < POWER_SMALLEST || id > POWER_LARGEST)        return;    p = &slabclass[id];#ifdef USE_SYSTEM_MALLOC    mem_malloced -= size;    free(ptr);    return;#endif    if (p->sl_curr == p->sl_total) { /* need more space on the free list */        int new_size = p->sl_total ? p->sl_total*2 : 16;  /* 16 is arbitrary */        void **new_slots = realloc(p->slots, new_size*sizeof(void *));        if (new_slots == 0)            return;        p->slots = new_slots;        p->sl_total = new_size;    }    p->slots[p->sl_curr++] = ptr;    return;}char* slabs_stats(int *buflen) {    int i, total;    char *buf = (char*) malloc(8192);    char *bufcurr = buf;    *buflen = 0;    if (!buf) return 0;    total = 0;    for(i = POWER_SMALLEST; i <= POWER_LARGEST; i++) {        slabclass_t *p = &slabclass[i];        if (p->slabs) {            unsigned int perslab, slabs;            slabs = p->slabs;            perslab = p->perslab;            bufcurr += sprintf(bufcurr, "STAT %d:chunk_size %u\r\n", i, p->size);            bufcurr += sprintf(bufcurr, "STAT %d:chunks_per_page %u\r\n", i, perslab);            bufcurr += sprintf(bufcurr, "STAT %d:total_pages %u\r\n", i, slabs);            bufcurr += sprintf(bufcurr, "STAT %d:total_chunks %u\r\n", i, slabs*perslab);            bufcurr += sprintf(bufcurr, "STAT %d:used_chunks %u\r\n", i, slabs*perslab - p->sl_curr);            bufcurr += sprintf(bufcurr, "STAT %d:free_chunks %u\r\n", i, p->sl_curr);            bufcurr += sprintf(bufcurr, "STAT %d:free_chunks_end %u\r\n", i, p->end_page_free);            total++;        }    }    bufcurr += sprintf(bufcurr, "STAT active_slabs %d\r\nSTAT total_malloced %u", total, mem_malloced);    *buflen = bufcurr - buf;        return buf;}