Nginx内存池源码剖析

能看出来Nginx小块内存和大块内存分界线就是一个页面4k（x86）

#define NGX_MAX_ALLOC_FROM_POOL  (ngx_pagesize - 1)//能分配的最大内存#define NGX_DEFAULT_POOL_SIZE    (16 * 1024)//默认池的大小 16k#define NGX_POOL_ALIGNMENT       16//字节对齐
#define NGX_MIN_POOL_SIZE                     //最小的大小                                 \ngx_align((sizeof(ngx_pool_t) + 2 * sizeof(ngx_pool_large_t)),            \NGX_POOL_ALIGNMENT)

进到ngx_align看到其实就是调整倍数，和SGI STL的做法是一样的

他的数据成员和函数

typedef void (*ngx_pool_cleanup_pt)(void *data);typedef struct ngx_pool_cleanup_s  ngx_pool_cleanup_t;struct ngx_pool_cleanup_s {ngx_pool_cleanup_pt   handler;void                 *data;ngx_pool_cleanup_t   *next;
};typedef struct ngx_pool_large_s  ngx_pool_large_t;struct ngx_pool_large_s {ngx_pool_large_t     *next;void                 *alloc;
};typedef struct {u_char               *last;u_char               *end;ngx_pool_t           *next;ngx_uint_t            failed;//记录分配失败的次数<4后面写死了
} ngx_pool_data_t;struct ngx_pool_s {ngx_pool_data_t       d;size_t                max;ngx_pool_t           *current;ngx_chain_t          *chain;ngx_pool_large_t     *large;ngx_pool_cleanup_t   *cleanup;ngx_log_t            *log;
};typedef struct {ngx_fd_t              fd;u_char               *name;ngx_log_t            *log;
} ngx_pool_cleanup_file_t;ngx_pool_t *ngx_create_pool(size_t size, ngx_log_t *log);//创建内存池
void ngx_destroy_pool(ngx_pool_t *pool);
void ngx_reset_pool(ngx_pool_t *pool);void *ngx_palloc(ngx_pool_t *pool, size_t size);//分配内存
void *ngx_pnalloc(ngx_pool_t *pool, size_t size);
void *ngx_pcalloc(ngx_pool_t *pool, size_t size);
void *ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment);
ngx_int_t ngx_pfree(ngx_pool_t *pool, void *p);ngx_pool_cleanup_t *ngx_pool_cleanup_add(ngx_pool_t *p, size_t size);
void ngx_pool_run_cleanup_file(ngx_pool_t *p, ngx_fd_t fd);
void ngx_pool_cleanup_file(void *data);
void ngx_pool_delete_file(void *data);

创建内存池Create

ngx_pool_t *
ngx_create_pool(size_t size, ngx_log_t *log)
{ngx_pool_t  *p;p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log);//根据用户指定size大小内存对齐，不同平台if (p == NULL) {return NULL;}//初始化p->d.last = (u_char *) p + sizeof(ngx_pool_t);//指向除ngx_pool_t结构的头信息之后的位置p->d.end = (u_char *) p + size;//指向内存池的末尾p->d.next = NULL;p->d.failed = 0;size = size - sizeof(ngx_pool_t);//内存池能使用的大小，size-头部信息p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;//4095	开辟比一个页面小就用size，比一个页面大就用一个页面				p->current = p;//指向内存起始地址p->chain = NULL;p->large = NULL;p->cleanup = NULL;p->log = log;//日志return p;
}

分配内存

当分配小块内存的时候，如果剩的还够分配 

static ngx_inline void *
ngx_palloc_small(ngx_pool_t *pool, size_t size, ngx_uint_t align)
{u_char      *m;ngx_pool_t  *p;p = pool->current;do {m = p->d.last;//可分配内存的地址if (align) {m = ngx_align_ptr(m, NGX_ALIGNMENT);//根据平台 调整倍数}if ((size_t) (p->d.end - m) >= size) {//剩余的大于要申请的sizep->d.last = m + size;//把m指针偏移个size字节return m;}p = p->d.next;} while (p);return ngx_palloc_block(pool, size);
}

当剩的不够分配了进入 return ngx_palloc_block(pool, size);

我们看看ngx_palloc_block

第二块内存块之后的里面头信息就不用存max，large那些了，只存用于分配内存的last next那些指针

static void *
ngx_palloc_block(ngx_pool_t *pool, size_t size)
{u_char      *m;size_t       psize;ngx_pool_t  *p, *new;psize = (size_t) (pool->d.end - (u_char *) pool);//计算要再分配的内存块大小//又开辟一块空间m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log);if (m == NULL) {return NULL;}//指向新内存块new = (ngx_pool_t *) m;new->d.end = m + psize;new->d.next = NULL;new->d.failed = 0;m += sizeof(ngx_pool_data_t);//头只存ngx_pool_data_t的成员m = ngx_align_ptr(m, NGX_ALIGNMENT);new->d.last = m + size;//分配出去，指向剩的内存起始地址for (p = pool->current; p->d.next; p = p->d.next) {if (p->d.failed++ > 4) {//当前块内存一直不够分配pool->current = p->d.next; //去下一个内存块}}p->d.next = new;//新生成的内存块接到原来的内存块后面return m;
}

下面看看要是分配大块内存>4k，nginx怎么分配的

整理逻辑就是先malloc把内存分配出来，然后遍历large链表找大块内存的头信息，看看哪个里面是空的被free了，如果找到了就把新分配的内存地址填进去就行，但是遍历了三个还没找到，那就不找了直接退出，利用小块内存分配移动last指针把大小内存头信息分配出来，然后把刚刚分配大块内存填进去就行。nginx处处体现了效率，就看三下，没有就用小块，因为小块的效率高，直接移动指针就行

static void *
ngx_palloc_large(ngx_pool_t *pool, size_t size)
{void              *p;ngx_uint_t         n;ngx_pool_large_t  *large;p = ngx_alloc(size, pool->log);//调mallocif (p == NULL) {return NULL;}n = 0;//遍历链表for (large = pool->large; large; large = large->next) {if (large->alloc == NULL) {large->alloc = p;return p;}if (n++ > 3) {break;}}large = ngx_palloc_small(pool, sizeof(ngx_pool_large_t), 1);//通过小块内存把large头分配进去if (large == NULL) {ngx_free(p);return NULL;}large->alloc = p;//大块内存起始地址large->next = pool->large;//头插 连接起来pool->large = large;return p;
}

Nginx对于大块内存提供了free函数

ngx_int_t
ngx_pfree(ngx_pool_t *pool, void *p)//释放大块内存，小块不释放
{ngx_pool_large_t  *l;for (l = pool->large; l; l = l->next) {if (p == l->alloc) {ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,"free: %p", l->alloc);ngx_free(l->alloc);l->alloc = NULL;return NGX_OK;}}return NGX_DECLINED;
}

对于小块内存没有提供释放函数

所以小块内存的释放只能用reset重置整个内存池，nginx源码重置里面对于小块内存的处理有点浪费，他全部按照第一块内存那样处理了，但是第二块往后小块内存的头部信息都没有ngx_pool_s这个结构里的成员了，所以更好的应该分别处理

void
ngx_reset_pool(ngx_pool_t *pool)//内存池重置
{ngx_pool_t        *p;ngx_pool_large_t  *l;for (l = pool->large; l; l = l->next) {//大块if (l->alloc) {ngx_free(l->alloc);}}/* for (p = pool; p; p = p->d.next) {//小块p->d.last = (u_char *) p + sizeof(ngx_pool_t);p->d.failed = 0;}*/  这块nginx源码自己写的//下面我改的处理小块内存//处理第一个内存块p=pool;p->d.last = (u_char *) p + sizeof(ngx_pool_t);p->d.failed = 0;//处理第二个开始到剩下的for (p = p->d.next; p; p = p->d.next) {//小块p->d.last = (u_char *) p + sizeof(ngx_pool_data_t);p->d.failed = 0;}pool->current = pool;pool->chain = NULL;pool->large = NULL;
}

对于内存池外部资源的释放

在小块内存内存池创建个clean头信息，开辟完之后把这一块内存起始地址返回回来

void
ngx_destroy_pool(ngx_pool_t *pool)
{ngx_pool_t          *p, *n;ngx_pool_large_t    *l;ngx_pool_cleanup_t  *c;for (c = pool->cleanup; c; c = c->next) {if (c->handler) {ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,"run cleanup: %p", c);c->handler(c->data);}}ngx_pool_cleanup_t *
ngx_pool_cleanup_add(ngx_pool_t *p, size_t size)
{ngx_pool_cleanup_t  *c;c = ngx_palloc(p, sizeof(ngx_pool_cleanup_t));//头信息，小块内存开辟if (c == NULL) {return NULL;}if (size) {c->data = ngx_palloc(p, size);if (c->data == NULL) {return NULL;}} else {c->data = NULL;}c->handler = NULL;c->next = p->cleanup;p->cleanup = c;ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, p->log, 0, "add cleanup: %p", c);return c;
}

整个释放流程，先释放外部资源，调用外部资源清楚函数回调，再释放大块，最后小块。因为小块里面会有前面的头信息