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/* mm block type */
typedef struct _zend_mm_block_info {
    size_t _size;   /* block的大小*/
    size_t _prev;   /* 计算前一个块有用到*/
} zend_mm_block_info;

typedef struct _zend_mm_block {
    zend_mm_block_info info;
} zend_mm_block;

typedef struct _zend_mm_small_free_block {  /* 双向链表 */
    zend_mm_block_info info;
    struct _zend_mm_free_block *prev_free_block;    /* 前一个块 */
    struct _zend_mm_free_block *next_free_block;    /* 后一个块 */
} zend_mm_small_free_block; /* 小的空闲块*/

typedef struct _zend_mm_free_block {    /* 双向链表 + 树结构 */
    zend_mm_block_info info;
    struct _zend_mm_free_block *prev_free_block;    /* 前一个块 */
    struct _zend_mm_free_block *next_free_block;    /* 后一个块 */

    struct _zend_mm_free_block **parent;    /* 父结点 */
    struct _zend_mm_free_block *child[2];   /* 两个子结点*/
} zend_mm_free_block;

struct _zend_mm_heap {
    int                 use_zend_alloc; /* 是否使用zend内存管理器 */
    void               *(*_malloc)(size_t); /* 内存分配函数*/
    void                (*_free)(void*);    /* 内存释放函数*/
    void               *(*_realloc)(void*, size_t);
    size_t              free_bitmap;    /* 小块空闲内存标识 */
    size_t              large_free_bitmap;  /* 大块空闲内存标识*/
    size_t              block_size;     /* 一次内存分配的段大小，即ZEND_MM_SEG_SIZE指定的大小，默认为ZEND_MM_SEG_SIZE   (256 * 1024)*/
    size_t              compact_size;   /* 压缩操作边界值，为ZEND_MM_COMPACT指定大小，默认为 2 * 1024 * 1024*/
    zend_mm_segment    *segments_list;  /* 段指针列表 */
    zend_mm_storage    *storage;    /* 所调用的存储层 */
    size_t              real_size;  /* 堆的真实大小 */
    size_t              real_peak;  /* 堆真实大小的峰值 */
    size_t              limit;  /* 堆的内存边界 */
    size_t              size;   /* 堆大小 */
    size_t              peak;   /* 堆大小的峰值*/
    size_t              reserve_size;   /* 备用堆大小*/
    void               *reserve;    /* 备用堆 */
    int                 overflow;   /* 内存溢出数*/
    int                 internal;
#if ZEND_MM_CACHE
    unsigned int        cached; /* 已缓存大小 */
    zend_mm_free_block *cache[ZEND_MM_NUM_BUCKETS]; /* 缓存数组/
#endif
    zend_mm_free_block *free_buckets[ZEND_MM_NUM_BUCKETS*2];    /* 小块内存数组，相当索引的角色 */
    zend_mm_free_block *large_free_buckets[ZEND_MM_NUM_BUCKETS];    /* 大块内存数组，相当索引的角色 */
    zend_mm_free_block *rest_buckets[2];    /* 剩余内存数组*/
#if ZEND_MM_CACHE_STAT
	struct {
		int count;
		int max_count;
		int hit;
		int miss;
	} cache_stat[ZEND_MM_NUM_BUCKETS+1];
#endif

};
/* Heaps with user defined storage */
typedef struct _zend_mm_storage zend_mm_storage;

typedef struct _zend_mm_segment {
	size_t	size;
	struct _zend_mm_segment *next_segment;
} zend_mm_segment;

typedef struct _zend_mm_mem_handlers {
	const char *name;
	zend_mm_storage* (*init)(void *params);
	void (*dtor)(zend_mm_storage *storage);
	zend_mm_segment* (*_alloc)(zend_mm_storage *storage, size_t size);
	zend_mm_segment* (*_realloc)(zend_mm_storage *storage, zend_mm_segment *ptr, size_t size);
	void (*_free)(zend_mm_storage *storage, zend_mm_segment *ptr);
} zend_mm_mem_handlers;

struct _zend_mm_storage {
	const zend_mm_mem_handlers *handlers;
	void *data;
};

更的内存相关内容介绍，可以参考：http://www.php-internal.com/