Nginx memory management-PHP Tutorial-php.cn

1. Source code location

Header file: http://trac.nginx.org/nginx/browser/nginx/src/core/ngx_palloc.h

Source file: http://trac.nginx.org/ nginx/browser/nginx/src/core/ngx_palloc.c

2. Data structure definition

Let’s first learn about several main data structures of nginx memory pool:

ngx_pool_data_t (memory pool data block structure)

1:typedef struct {<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 2: u_char *last; <precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 3: u_char *end;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 4: ngx_pool_t *next;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 5: ngx_uint_t failed;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 6: } ngx_pool_data_t;<ul> <li>last: It is an unsigned char type pointer, which saves the last address allocated to the current memory pool, that is, the next allocation starts here. </li> <li>end: The end position of the memory pool; </li> <li>next: There are many blocks of memory in the memory pool. These memory blocks are connected into a linked list through this pointer, and next points to the next block of memory. </li> <li>failed: The number of memory pool allocation failures. </li> </ul><blockquote>ngx_pool_s (memory pool header structure) </blockquote><divcourier new width:950px color:black padding:0px direction:ltr line-height:12pt background-color:rgb><precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1:struct ngx_pool_s {<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 2: ngx_pool_data_t d;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 3: size_t max;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 4: ngx_pool_t *current;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 5: ngx_chain_t *chain;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 6: ngx_pool_large_t *large;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 7: ngx_pool_cleanup_t *cleanup;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 8: ngx_log_t *log;<precourier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 9: };<ul> <li>d: the data block of the memory pool; </li> <li>max: the maximum value of the memory pool data block; </li> <li>current: points to the current memory pool; </li> <li> chain: This pointer is attached to an ngx_chain_t structure; </li> <li>large: a large memory linked list, which is used when the allocated space exceeds max; </li> <li>cleanup: callback to release the memory pool </li> <li>log: log information </li> </ul> is composed of ngx_pool_data_t and ngx_pool_t The composed nginx memory pool structure is shown in the figure below: <img src="http://image.codes51.com/Article/image/20150814/20150814194335_5243.jpg" style="max-width:90%" style="max-width:90%" alt="Nginx memory management" > 3. Introduction to related functions <blockquote> Before analyzing the memory pool method, we need to introduce several main memory-related functions: ngx_alloc: (just对malloc进行了简单的封装） <divcourier new width:870px color:black padding:0px direction:ltr line-height:12pt background-color:rgb><precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1:void *<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 2: ngx_alloc(size_t size, ngx_log_t *log)<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 3: {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 4: void *p;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 5: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 6: p = malloc(size);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 7: if (p == NULL) {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 8: ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 9: "malloc(%uz) failed", size);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 10: }<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 11: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 12: ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, log, 0, "malloc: %p:%uz", p, size);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 13: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 14: return p;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 15: }</precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></divcourier> </blockquote><blockquote>ngx_calloc：（调用malloc并初始化为0）</blockquote><blockquote><divcourier new width:870px color:black padding:0px direction:ltr line-height:12pt background-color:rgb><precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1:void *<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 2: ngx_calloc(size_t size, ngx_log_t *log)<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 3: {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 4: void *p;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 5: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 6: p = ngx_alloc(size, log);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 7: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 8: if (p) {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 9: ngx_memzero(p, size);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 10: }<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 11: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 12: return p;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 13: }</precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></divcourier></blockquote><blockquote> ngx_memzero： <divcourier new width:870px color:black padding:0px direction:ltr line-height:12pt background-color:rgb><precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1: #define ngx_memzero(buf, n) (void) memset(buf, 0, n)</precourier></divcourier> </blockquote><blockquote> ngx_free : <divcourier new width:870px color:black padding:0px direction:ltr line-height:12pt background-color:rgb><precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1: #define ngx_free free</precourier></divcourier> </blockquote><blockquote> ngx_memalign: <divcourier new width:870px color:black padding:0px direction:ltr line-height:12pt background-color:rgb></divcourier> <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1:void *<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 2: ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 3: {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 4: void *p;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 5: int err;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 6: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 7: err = posix_memalign(&p, alignment, size);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 8: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 9: if (err) {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 10: ngx_log_error(NGX_LOG_EMERG, log, err,<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 11: "posix_memalign(%uz, %uz) failed", alignment, size);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 12: p = NULL;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 13: }<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 14: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 15: ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, 0,<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 16: "posix_memalign: %p:%uz @%uz", p, size, alignment);rrree</precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier></precourier> </blockquote> <limicrosoft yahei font-size:15px line-height:35px><blockquote> The alignment here is mainly for some unix platforms that require dynamic alignment. It encapsulates posix_memalign() provided by POSIX 1003.1d. In most cases, In this case, the compiler and C library transparently handle the alignment problem for you. nginx is controlled through the macro NGX_HAVE_POSIX_MEMALIGN; calling posix_memalign( ) successfully will return sizebytes of dynamic memory, and the address of this memory is a multiple of alignment. The parameter alignment must be a power of 2, or a multiple of the size of the void pointer. The address of the returned memory block is placed in memptr, and the function return value is 0</blockquote>.<limicrosoft yahei font-size:15px line-height:35px><blockquote></blockquote> 4. Basic operations of the memory pool🎜<ul><li>The main external methods of the memory pool are: </li></ul> <limicrosoft yahei font-size:15px line-height:35px><table cellspacing="0" cellpadding="2" border="1"><tbody> <tr> <td valign="top" width="118">Create a memory pool</td> <td valign="top" width="768">ngx_pool_t * ngx_create_pool(size_t size, ngx_log_t *log);</td> </tr> <tr> <td valign="top" width="118">Destroy the memory pool</td> <td valign="top" width="768">vo id ngx_destroy_pool(ngx_pool_t *pool ; ( Not aligned)</td> </tr>void * ngx_pnalloc(ngx_pool_t *pool, size_t size);<tr> <td valign="top" width="118"></td> <td valign="top" width="768">Memory clearing</td> </tr>ngx_int_t ngx_pfree(ngx_pool_t *pool, void *p);<tr> <td valign="top" width="118"></td> <td valign="top" width="768"><limicrosoft yahei font-size:15px line-height:35px><limicrosoft yahei font-size:15px line-height:35px>4.1 创建内存池ngx_create_pool <blockquote>ngx_create_pool用于创建一个内存池，我们创建时，传入我们的需要的初始大小：</blockquote> <limicrosoft yahei font-size:15px line-height:35px><blockquote><divcourier new width:870px color:black padding:0px direction:ltr line-height:12pt background-color:rgb><precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 1: ngx_pool_t *<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 2: ngx_create_pool(size_t size, ngx_log_t *log)<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 3: {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 4: ngx_pool_t *p;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 5: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 6: //以16（NGX_POOL_ALIGNMENT）字节对齐分配size内存<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 7: p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 8: if (p == NULL) {<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 9: return NULL;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 10: }<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 11: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 12: //初始状态：last指向ngx_pool_t结构体之后数据取起始位置<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 13: p->d.last = (u_char *) p + sizeof(ngx_pool_t);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 14: //end指向分配的整个size大小的内存的末尾<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 15: p->d.end = (u_char *) p + size;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 16: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 17: p->d.next = NULL;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 18: p->d.failed = 0;<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 19: <precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 20: size = size - sizeof(ngx_pool_t);<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 21: //#define NGX_MAX_ALLOC_FROM_POOL (ngx_pagesize - 1)，内存池最大不超过4095，x86中页的大小为4K<precourier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb> 22: p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;

Copy after login

23:

Copy after login

24: p->current = p; 25: p->chain = NULL; 26: p->large = NULL; 27: p->cleanup = NULL; 28: p->log = log; 29: 30: return p; 31: }

nginx对内存的管理分为大内存与小内存，当某一个申请的内存大于某一个值时，就需要从大内存中分配空间，否则从小内存中分配空间。

nginx中的内存池是在创建的时候就设定好了大小，在以后分配小块内存的时候，如果内存不够，则是重新创建一块内存串到内存池中，而不是将原有的内存池进行扩张。当要分配大块内存是，则是在内存池外面再分配空间进行管理的，称为大块内存池。

4.2 内存申请 ngx_palloc

1:void * 2: ngx_palloc(ngx_pool_t *pool, size_t size) 3: { 4: u_char *m; 5: ngx_pool_t *p; 6: 7: //如果申请的内存大小小于内存池的max值 8: if (size <= pool->max) { 9: 10: p = pool->current; 11: 12: do { 13: //对内存地址进行对齐处理 14: m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT); 15: 16: //如果当前内存块够分配内存，则直接分配 17: if ((size_t) (p->d.end - m) >= size) 18: { 19: p->d.last = m + size; 20: 21: return m; 22: } 23: 24: //如果当前内存块有效容量不够分配，则移动到下一个内存块进行分配 25: p = p->d.next; 26: 27: } while (p); 28: 29: //当前所有内存块都没有空闲了，开辟一块新的内存，如下2详细解释 30: return ngx_palloc_block(pool, size); 31: } 32: 33: //分配大块内存 34: return ngx_palloc_large(pool, size); 35: }

需要说明的几点：

1、ngx_align_ptr，这是一个用来内存地址取整的宏，非常精巧，一句话就搞定了。作用不言而喻，取整可以降低CPU读取内存的次数，提高性能。因为这里并没有真正意义调用malloc等函数申请内存，而是移动指针标记而已，所以内存对齐的活，C编译器帮不了你了，得自己动手。

1: #define ngx_align_ptr(p, a) \ 2: (u_char *) (((uintptr_t) (p) + ((uintptr_t) a - 1)) & ~((uintptr_t) a - 1))

2、开辟一个新的内存块 ngx_palloc_block(ngx_pool_t *pool, size_t size)

这个函数是用来分配新的内存块，为pool内存池开辟一个新的内存块，并申请使用size大小的内存；

1:static void * 2: ngx_palloc_block(ngx_pool_t *pool, size_t size) 3: { 4: u_char *m; 5: size_t psize; 6: ngx_pool_t *p, *new; 7: 8: //计算内存池第一个内存块的大小 9: psize = (size_t) (pool->d.end - (u_char *) pool); 10: 11: //分配和第一个内存块同样大小的内存块 12: m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log); 13: if (m == NULL) { 14: return NULL; 15: } 16: 17: new = (ngx_pool_t *) m; 18: 19: //设置新内存块的end 20: new->d.end = m + psize; 21: new->d.next = NULL; 22: new->d.failed = 0; 23: 24: //将指针m移动到d后面的一个位置，作为起始位置 25: m += sizeof(ngx_pool_data_t); 26: //对m指针按4字节对齐处理 27: m = ngx_align_ptr(m, NGX_ALIGNMENT); 28: //设置新内存块的last，即申请使用size大小的内存 29: new->d.last = m + size; 30: 31: //这里的循环用来找最后一个链表节点，这里failed用来控制循环的长度，如果分配失败次数达到5次，就忽略，不需要每次都从头找起 32: for (p = pool->current; p->d.next; p = p->d.next) { 33: if (p->d.failed++ > 4) { 34: pool->current = p->d.next; 35: } 36: } 37: 38: p->d.next = new; 39: 40: return m; 41: }

3、分配大块内存 ngx_palloc_large(ngx_pool_t *pool, size_t size)

在ngx_palloc中首先会判断申请的内存大小是否超过内存块的最大限值，如果超过，则直接调用ngx_palloc_large，进入大内存块的分配流程；

1:static void * 2: ngx_palloc_large(ngx_pool_t *pool, size_t size) 3: { 4: void *p; 5: ngx_uint_t n; 6: ngx_pool_large_t *large; 7: 8: // 直接在系统堆中分配一块大小为size的空间 9: p = ngx_alloc(size, pool->log); 10: if (p == NULL) { 11: return NULL; 12: } 13: 14: n = 0; 15: 16: // 查找到一个空的large区，如果有，则将刚才分配的空间交由它管理 17: for (large = pool->large; large; large = large->next) { 18: if (large->alloc == NULL) { 19: large->alloc = p; 20: return p; 21: } 22: //为了提高效率，如果在三次内没有找到空的large结构体，则创建一个 23: if (n++ > 3) { 24: break; 25: } 26: } 27: 28: 29: large = ngx_palloc(pool, sizeof(ngx_pool_large_t)); 30: if (large == NULL) { 31: ngx_free(p); 32: return NULL; 33: } 34: 35: //将large链接到内存池 36: large->alloc = p; 37: large->next = pool->large; 38: pool->large = large; 39: 40: return p; 41: }

整个内存池分配如下图：

4.3 内存池重置 ngx_reset_pool

1:void 2: ngx_reset_pool(ngx_pool_t *pool) 3: { 4: ngx_pool_t *p; 5: ngx_pool_large_t *l; 6: 7: //释放大块内存 8: for (l = pool->large; l; l = l->next) { 9: if (l->alloc) { 10: ngx_free(l->alloc); 11: } 12: } 13: 14: // 重置所有小块内存区 15: for (p = pool; p; p = p->d.next) { 16: p->d.last = (u_char *) p + sizeof(ngx_pool_t); 17: p->d.failed = 0; 18: } 19: 20: pool->current = pool; 21: pool->chain = NULL; 22: pool->large = NULL; 23: }

4.4 内存池释放 ngx_pfree

1: ngx_int_t 2: ngx_pfree(ngx_pool_t *pool, void *p) 3: { 4: ngx_pool_large_t *l; 5: 6: //只检查是否是大内存块，如果是大内存块则释放 7: for (l = pool->large; l; l = l->next) { 8: if (p == l->alloc) { 9: ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0, 10: "free: %p", l->alloc); 11: ngx_free(l->alloc); 12: l->alloc = NULL; 13: 14: return NGX_OK; 15: } 16: } 17: