为什么要用内存池
为什么要用内存池?首先,在7 * 24h的服务器中如果不使用内存池,而使用malloc和free,那么就非常容易产生内存碎片,早晚都会申请内存失败;并且在比较复杂的代码或者继承的屎山中,非常容易出现内存泄漏导致mmo的问题。
为了解决这两个问题,内存池就应运而生了。内存池预先分配一大块内存来做一个内存池,业务中的内存分配和释放都由这个内存池来管理,内存池内的内存不足时其内部会自己申请。所以内存碎片的问题就交由内存池的算法来优化,而内存泄漏的问题只需要遵守内存池提供的api,就非常容易避免内存泄漏了。
即使出现了内存泄漏,排查的思路也很清晰。1.检查是不是内存池的问题;2.如果不是内存池的问题,就检查是不是第三方库的内存泄漏。
内存池的使用场景
- 全局内存池
- 一个连接一个内存池(本文实现这个场景的内存池)
设计一个内存池
总体介绍
由于本文是一个连接一个内存池,所以后续介绍和代码都是以4k为分界线,大于4k的我们认为是大块内存;小于4k的我们认为是小块内存。并且注意这里的4k,并不是严格遵照4096,而是在描述上,用4k比较好描述。
在真正使用内存之前,内存池提前分配一定数量且大小相等的内存块以作备用,当真正被用户调用api分配内存的时候,直接从内存块中获取内存(指小块内存),当内存块不够用了,再有内存池取申请新的内存块。而如果是需要大块内存,则内存池直接申请大块内存再返回给用户。
内存池:就是将这些提前申请的内存块组织管理起来的数据结构,内存池实现原理主要分为分配,回收,扩容三部分。
内存池原理之小块内存:分配=> 内存池预申请一块4k的内存块,这里称为block,即block=4k内存块。当用户向内存池申请内存size小于4k时,内存池从block的空间中划分出去size空间,当再有新申请时,再划分出去。扩容=> 直到block中的剩余空间不足以分配size大小,那么此时内存池会再次申请一块block,再从新的block中划分size空间给用户。回收=> 每一次申请小内存,都会在对应的block中引用计数加1,每一次释放小内存时,都会在block中引用计数减1,只有当引用计数为零的时候,才会回收block使他重新成为空闲空间,以便重复利用空间。这样,内存池避免频繁向内核申请/释放内存,从而提高系统性能。
内存池原理之大块内存:分配=> 因为大块内存是大于4k的,所以内存池不预先申请内存,也就是用户申请的时候,内存池再申请内存,然后返回给用户。扩容=> 大块内存不存在扩容。回收=> 对于大块内存来说,回收就直接free掉即可。
上面理论讲完了,下面来介绍如何管理小块内存和大块内存。
小块内存的分配与管理
在创建内存池的时候,会预先申请一块4k的内存,并且在起始处将pool的结构体和node的结构体放进去,从last开始一直到end都是空闲内存,中间的区域就用来存储小块内存。每一次mp_malloc,就将last指针后移,直到 e n d − l a s t < s i z e end - last < size end−last
初始状态
分配内存
扩容
大块内存的分配与管理
对于大块内存,前面已经说了,用户申请的时候,内存池才申请
申请一块大内存
再申请一块大内存
内存池代码实现
向外提供的api
- mp_create_pool:创建一个线程池,其核心是创建struct mp_pool_s这个结构体,并申请4k内存,将各个指针指向上文初始状态的图一样。
- mp_destroy_pool:销毁内存池,遍历小块结构体和大块结构体,进行free释放内存
- mp_malloc:提供给用户申请内存的api
- mp_calloc:通过mp_malloc申请内存后置零,相当于calloc
- mp_free:释放由mp_malloc返回的内存
- mp_reset_pool:将block的last置为初始状态,销毁所有大块内存
- monitor_mp_poll:监控内存池状态
struct mp_pool_s *mp_create_pool(size_t size);
void mp_destroy_pool(struct mp_pool_s *pool);
void *mp_malloc(struct mp_pool_s *pool, size_t size);
void *mp_calloc(struct mp_pool_s *pool, size_t size);
void mp_free(struct mp_pool_s *pool, void *p);
void mp_reset_pool(struct mp_pool_s *pool);
void monitor_mp_poll(struct mp_pool_s *pool, char *tk);
相关结构体的定义
mp_pool_s 就是整个内存池的管理结构,我们做的内存池是一个连接一个内存池,所以对于整个程序而言,内存池对象是有很多个的。
可能读者会有疑问,有了head,为什么还有current,是因为如果一个block剩余空间小于size超过一定次数后,将current指向下一个block,这样就加快内存分配效率,减少遍历次数。
//每4k一block结点
struct mp_node_s {
unsigned char *end;//块的结尾
unsigned char *last;//使用到哪了
struct mp_node_s *next;//链表
int quote;//引用计数
int failed;//失效次数
};
struct mp_large_s {
struct mp_large_s *next;//链表
int size;//alloc的大小
void *alloc;//大块内存的起始地址
};
struct mp_pool_s {
struct mp_large_s *large;
struct mp_node_s *head;
struct mp_node_s *current;
};
内存对齐
访问速度是内存对齐的原因之一,另外一个原因是某些平台(arm)不支持未内存对齐的访问
在4k里面划分内存,那么必然有很多地方是不对齐的,所以这里提供两个内存对齐的函数。那么为什么要内存对齐呢?其一:提高访问速度;其二:某些平台arm不支持未对其的内存访问,会出错。
#define mp_align(n, alignment) (((n)+(alignment-1)) & ~(alignment-1))
#define mp_align_ptr(p, alignment) (void *)((((size_t)p)+(alignment-1)) & ~(alignment-1))
创建与销毁内存池
创建一个线程池,其核心是创建struct mp_pool_s这个结构体,并申请4k内存,将各个指针指向上文初始状态的图一样。
销毁内存池,遍历小块结构体和大块结构体,进行free释放内存。
//创建内存池
struct mp_pool_s *mp_create_pool(size_t size) {
struct mp_pool_s *pool;
if (size < PAGE_SIZE || size % PAGE_SIZE != 0) {
size = PAGE_SIZE;
}
//分配4k以上不用malloc,用posix_memalign
/*
int posix_memalign (void **memptr, size_t alignment, size_t size);
*/
int ret = posix_memalign((void **) &pool, MP_ALIGNMENT, size); //4K + mp_pool_s
if (ret) {
return NULL;
}
pool- >large = NULL;
pool- >current = pool- >head = (unsigned char *) pool + sizeof(struct mp_pool_s);
pool- >head- >last = (unsigned char *) pool + sizeof(struct mp_pool_s) + sizeof(struct mp_node_s);
pool- >head- >end = (unsigned char *) pool + PAGE_SIZE;
pool- >head- >failed = 0;
return pool;
}
//销毁内存池
void mp_destroy_pool(struct mp_pool_s *pool) {
struct mp_large_s *large;
for (large = pool- >large; large; large = large- >next) {
if (large- >alloc) {
free(large- >alloc);
}
}
struct mp_node_s *cur, *next;
cur = pool- >head- >next;
while (cur) {
next = cur- >next;
free(cur);
cur = next;
}
free(pool);
}
提供给用户的内存申请api
申请的内存以size做区分,如果大于4k就分配大块内存,小于4k就去block里面划分。
//分配内存
void *mp_malloc(struct mp_pool_s *pool, size_t size) {
if (size <= 0) {
return NULL;
}
if (size > PAGE_SIZE - sizeof(struct mp_node_s)) {
//large
return mp_malloc_large(pool, size);
}
else {
//small
unsigned char *mem_addr = NULL;
struct mp_node_s *cur = NULL;
cur = pool- >current;
while (cur) {
mem_addr = mp_align_ptr(cur- >last, MP_ALIGNMENT);
if (cur- >end - mem_addr >= size) {
cur- >quote++;//引用+1
cur- >last = mem_addr + size;
return mem_addr;
}
else {
cur = cur- >next;
}
}
return mp_malloc_block(pool, size);// open new space
}
}
void *mp_calloc(struct mp_pool_s *pool, size_t size) {
void *mem_addr = mp_malloc(pool, size);
if (mem_addr) {
memset(mem_addr, 0, size);
}
return mem_addr;
}
小块内存block扩容
所有的block都 e n d − l a s t < s i z e end - last < size end−last
//new block 4k
void *mp_malloc_block(struct mp_pool_s *pool, size_t size) {
unsigned char *block;
int ret = posix_memalign((void **) &block, MP_ALIGNMENT, PAGE_SIZE); //4K
if (ret) {
return NULL;
}
struct mp_node_s *new_node = (struct mp_node_s *) block;
new_node- >end = block + PAGE_SIZE;
new_node- >next = NULL;
unsigned char *ret_addr = mp_align_ptr(block + sizeof(struct mp_node_s), MP_ALIGNMENT);
new_node- >last = ret_addr + size;
new_node- >quote++;
struct mp_node_s *current = pool- >current;
struct mp_node_s *cur = NULL;
for (cur = current; cur- >next; cur = cur- >next) {
if (cur- >failed++ > 4) {
current = cur- >next;
}
}
//now cur = last node
cur- >next = new_node;
pool- >current = current;
return ret_addr;
}
分配大块内存
//size >4k
void *mp_malloc_large(struct mp_pool_s *pool, size_t size) {
unsigned char *big_addr;
int ret = posix_memalign((void **) &big_addr, MP_ALIGNMENT, size); //size
if (ret) {
return NULL;
}
struct mp_large_s *large;
//released struct large resume
int n = 0;
for (large = pool- >large; large; large = large- >next) {
if (large- >alloc == NULL) {
large- >size = size;
large- >alloc = big_addr;
return big_addr;
}
if (n++ > 3) {
break;// 为了避免过多的遍历,限制次数
}
}
large = mp_malloc(pool, sizeof(struct mp_large_s));
if (large == NULL) {
free(big_addr);
return NULL;
}
large- >size = size;
large- >alloc = big_addr;
large- >next = pool- >large;
pool- >large = large;
return big_addr;
}
释放内存
如果是大块内存,找到之后直接释放;如果是小块内存,将引用计数减1,如果引用计数为0则重置last。
//释放内存
void mp_free(struct mp_pool_s *pool, void *p) {
struct mp_large_s *large;
for (large = pool- >large; large; large = large- >next) {//大块
if (p == large- >alloc) {
free(large- >alloc);
large- >size = 0;
large- >alloc = NULL;
return;
}
}
//小块 引用-1
struct mp_node_s *cur = NULL;
for (cur = pool- >head; cur; cur = cur- >next) {
// printf("cur:%p p:%p end:%pn", (unsigned char *) cur, (unsigned char *) p, (unsigned char *) cur- >end);
if ((unsigned char *) cur <= (unsigned char *) p && (unsigned char *) p <= (unsigned char *) cur- >end) {
cur- >quote--;
if (cur- >quote == 0) {
if (cur == pool- >head) {
pool- >head- >last = (unsigned char *) pool + sizeof(struct mp_pool_s) + sizeof(struct mp_node_s);
}
else {
cur- >last = (unsigned char *) cur + sizeof(struct mp_node_s);
}
cur- >failed = 0;
pool- >current = pool- >head;
}
return;
}
}
}
内存池测试
//
// Created by 68725 on 2022/7/26.
//
#include < stdlib.h >
#include < stdio.h >
#include < string.h >
#define PAGE_SIZE 4096
#define MP_ALIGNMENT 16
#define mp_align(n, alignment) (((n)+(alignment-1)) & ~(alignment-1))
#define mp_align_ptr(p, alignment) (void *)((((size_t)p)+(alignment-1)) & ~(alignment-1))
//每4k一block结点
struct mp_node_s {
unsigned char *end;//块的结尾
unsigned char *last;//使用到哪了
struct mp_node_s *next;//链表
int quote;//引用计数
int failed;//失效次数
};
struct mp_large_s {
struct mp_large_s *next;//链表
int size;//alloc的大小
void *alloc;//大块内存的起始地址
};
struct mp_pool_s {
struct mp_large_s *large;
struct mp_node_s *head;
struct mp_node_s *current;
};
struct mp_pool_s *mp_create_pool(size_t size);
void mp_destroy_pool(struct mp_pool_s *pool);
void *mp_malloc(struct mp_pool_s *pool, size_t size);
void *mp_calloc(struct mp_pool_s *pool, size_t size);
void mp_free(struct mp_pool_s *pool, void *p);
void mp_reset_pool(struct mp_pool_s *pool);
void monitor_mp_poll(struct mp_pool_s *pool, char *tk);
void mp_reset_pool(struct mp_pool_s *pool) {
struct mp_node_s *cur;
struct mp_large_s *large;
for (large = pool- >large; large; large = large- >next) {
if (large- >alloc) {
free(large- >alloc);
}
}
pool- >large = NULL;
pool- >current = pool- >head;
for (cur = pool- >head; cur; cur = cur- >next) {
cur- >last = (unsigned char *) cur + sizeof(struct mp_node_s);
cur- >failed = 0;
cur- >quote = 0;
}
}
//创建内存池
struct mp_pool_s *mp_create_pool(size_t size) {
struct mp_pool_s *pool;
if (size < PAGE_SIZE || size % PAGE_SIZE != 0) {
size = PAGE_SIZE;
}
//分配4k以上不用malloc,用posix_memalign
/*
int posix_memalign (void **memptr, size_t alignment, size_t size);
*/
int ret = posix_memalign((void **) &pool, MP_ALIGNMENT, size); //4K + mp_pool_s
if (ret) {
return NULL;
}
pool- >large = NULL;
pool- >current = pool- >head = (unsigned char *) pool + sizeof(struct mp_pool_s);
pool- >head- >last = (unsigned char *) pool + sizeof(struct mp_pool_s) + sizeof(struct mp_node_s);
pool- >head- >end = (unsigned char *) pool + PAGE_SIZE;
pool- >head- >failed = 0;
return pool;
}
//销毁内存池
void mp_destroy_pool(struct mp_pool_s *pool) {
struct mp_large_s *large;
for (large = pool- >large; large; large = large- >next) {
if (large- >alloc) {
free(large- >alloc);
}
}
struct mp_node_s *cur, *next;
cur = pool- >head- >next;
while (cur) {
next = cur- >next;
free(cur);
cur = next;
}
free(pool);
}
//size >4k
void *mp_malloc_large(struct mp_pool_s *pool, size_t size) {
unsigned char *big_addr;
int ret = posix_memalign((void **) &big_addr, MP_ALIGNMENT, size); //size
if (ret) {
return NULL;
}
struct mp_large_s *large;
//released struct large resume
int n = 0;
for (large = pool- >large; large; large = large- >next) {
if (large- >alloc == NULL) {
large- >size = size;
large- >alloc = big_addr;
return big_addr;
}
if (n++ > 3) {
break;// 为了避免过多的遍历,限制次数
}
}
large = mp_malloc(pool, sizeof(struct mp_large_s));
if (large == NULL) {
free(big_addr);
return NULL;
}
large- >size = size;
large- >alloc = big_addr;
large- >next = pool- >large;
pool- >large = large;
return big_addr;
}
//new block 4k
void *mp_malloc_block(struct mp_pool_s *pool, size_t size) {
unsigned char *block;
int ret = posix_memalign((void **) &block, MP_ALIGNMENT, PAGE_SIZE); //4K
if (ret) {
return NULL;
}
struct mp_node_s *new_node = (struct mp_node_s *) block;
new_node- >end = block + PAGE_SIZE;
new_node- >next = NULL;
unsigned char *ret_addr = mp_align_ptr(block + sizeof(struct mp_node_s), MP_ALIGNMENT);
new_node- >last = ret_addr + size;
new_node- >quote++;
struct mp_node_s *current = pool- >current;
struct mp_node_s *cur = NULL;
for (cur = current; cur- >next; cur = cur- >next) {
if (cur- >failed++ > 4) {
current = cur- >next;
}
}
//now cur = last node
cur- >next = new_node;
pool- >current = current;
return ret_addr;
}
//分配内存
void *mp_malloc(struct mp_pool_s *pool, size_t size) {
if (size <= 0) {
return NULL;
}
if (size > PAGE_SIZE - sizeof(struct mp_node_s)) {
//large
return mp_malloc_large(pool, size);
}
else {
//small
unsigned char *mem_addr = NULL;
struct mp_node_s *cur = NULL;
cur = pool- >current;
while (cur) {
mem_addr = mp_align_ptr(cur- >last, MP_ALIGNMENT);
if (cur- >end - mem_addr >= size) {
cur- >quote++;//引用+1
cur- >last = mem_addr + size;
return mem_addr;
}
else {
cur = cur- >next;
}
}
return mp_malloc_block(pool, size);// open new space
}
}
void *mp_calloc(struct mp_pool_s *pool, size_t size) {
void *mem_addr = mp_malloc(pool, size);
if (mem_addr) {
memset(mem_addr, 0, size);
}
return mem_addr;
}
//释放内存
void mp_free(struct mp_pool_s *pool, void *p) {
struct mp_large_s *large;
for (large = pool- >large; large; large = large- >next) {//大块
if (p == large- >alloc) {
free(large- >alloc);
large- >size = 0;
large- >alloc = NULL;
return;
}
}
//小块 引用-1
struct mp_node_s *cur = NULL;
for (cur = pool- >head; cur; cur = cur- >next) {
// printf("cur:%p p:%p end:%pn", (unsigned char *) cur, (unsigned char *) p, (unsigned char *) cur- >end);
if ((unsigned char *) cur <= (unsigned char *) p && (unsigned char *) p <= (unsigned char *) cur- >end) {
cur- >quote--;
if (cur- >quote == 0) {
if (cur == pool- >head) {
pool- >head- >last = (unsigned char *) pool + sizeof(struct mp_pool_s) + sizeof(struct mp_node_s);
}
else {
cur- >last = (unsigned char *) cur + sizeof(struct mp_node_s);
}
cur- >failed = 0;
pool- >current = pool- >head;
}
return;
}
}
}
void monitor_mp_poll(struct mp_pool_s *pool, char *tk) {
printf("rnrn------start monitor poll------%srnrn", tk);
struct mp_node_s *head = NULL;
int i = 0;
for (head = pool- >head; head; head = head- >next) {
i++;
if (pool- >current == head) {
printf("current== >第%d块n", i);
}
if (i == 1) {
printf("第%02d块small block 已使用:%4ld 剩余空间:%4ld 引用:%4d failed:%4dn", i,
(unsigned char *) head- >last - (unsigned char *) pool,
head- >end - head- >last, head- >quote, head- >failed);
}
else {
printf("第%02d块small block 已使用:%4ld 剩余空间:%4ld 引用:%4d failed:%4dn", i,
(unsigned char *) head- >last - (unsigned char *) head,
head- >end - head- >last, head- >quote, head- >failed);
}
}
struct mp_large_s *large;
i = 0;
for (large = pool- >large; large; large = large- >next) {
i++;
if (large- >alloc != NULL) {
printf("第%d块large block size=%dn", i, large- >size);
}
}
printf("rnrn------stop monitor poll------rnrn");
}
int main() {
struct mp_pool_s *p = mp_create_pool(PAGE_SIZE);
monitor_mp_poll(p, "create memory pool");
#if 0
printf("mp_align(5, %d): %d, mp_align(17, %d): %dn", MP_ALIGNMENT, mp_align(5, MP_ALIGNMENT), MP_ALIGNMENT,
mp_align(17, MP_ALIGNMENT));
printf("mp_align_ptr(p- >current, %d): %p, p- >current: %pn", MP_ALIGNMENT, mp_align_ptr(p- >current, MP_ALIGNMENT),
p- >current);
#endif
void *mp[30];
int i;
for (i = 0; i < 30; i++) {
mp[i] = mp_malloc(p, 512);
}
monitor_mp_poll(p, "申请512字节30个");
for (i = 0; i < 30; i++) {
mp_free(p, mp[i]);
}
monitor_mp_poll(p, "销毁512字节30个");
int j;
for (i = 0; i < 50; i++) {
char *pp = mp_calloc(p, 32);
for (j = 0; j < 32; j++) {
if (pp[j]) {
printf("calloc wrongn");
exit(-1);
}
}
}
monitor_mp_poll(p, "申请32字节50个");
for (i = 0; i < 50; i++) {
char *pp = mp_malloc(p, 3);
}
monitor_mp_poll(p, "申请3字节50个");
void *pp[10];
for (i = 0; i < 10; i++) {
pp[i] = mp_malloc(p, 5120);
}
monitor_mp_poll(p, "申请大内存5120字节10个");
for (i = 0; i < 10; i++) {
mp_free(p, pp[i]);
}
monitor_mp_poll(p, "销毁大内存5120字节10个");
mp_reset_pool(p);
monitor_mp_poll(p, "reset pool");
for (i = 0; i < 100; i++) {
void *s = mp_malloc(p, 256);
}
monitor_mp_poll(p, "申请256字节100个");
mp_destroy_pool(p);
return 0;
}
nginx内存池对比分析
相关结构体定义对比
创建内存池对比
内存申请对比
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