Introducing solutions to reduce PHP-FPM memory usage

Abstract:PHP-FPM is a FastCGI process manager for PHP. In Unix-like operating systems (including Linux and BSD systems), PHP-FPM is used by installing php5-fpm (Linux) or php56-fpm (FreeBSD 10.1). But the biggest problem with PHP-FPM installed by default and installed according to the recommendations of many blogs is...

PHP-FPMis the ## ofPHP#FastCGIProcess Manager. InUnix-like operating systems (includingLinuxandBSDsystems),PHP-FPMis installed byphp5-fpm(Linux) orphp56-fpm(FreeBSD 10.1) to use.

But the biggest problem with the default installation andPHP-FPMinstalled as recommended by a large number of blogs is that it consumes a lot of resources, including memory andCPU. The server used by this blog suffered a similar fate. Because I also installed according to those tutorials, and the description of the configuration options ofPHP-FPMin the tutorials is not effective enough.

You can find these inefficient configuration options in the/etc/php5/fpm/pool.ddirectory. For example, here are the inefficient options on my server (not the current site, of course):

; Choose how the process manager will control the number of child processes. pm = dynamic pm.max_children = 75pm.start_servers = 10pm.min_spare_servers = 5pm.max_spare_servers = 20pm.max_requests = 500

That server is aDigitalOcean Droplet, configured512MMemory. A new website was running on it, and even when it was completely idle, it had to swap memory to avoid freezing. Executing thetopcommand displays the processes that occupy the most memory on the server.

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 13891 cont 20 396944 56596 33416 S 0.0 11.3 :14.05 php5-fpm 13889 cont 20 396480 56316 32916 S 0.0 11.2 :17.67 php5-fpm 13887 cont 20 624212 55088 32008 S 0.0 11.0 :14.02 php5-fpm 13890 cont 20 396384 55032 32312 S 0.0 11.0 :13.39 php5-fpm 13888 cont 20 397056 54972 31988 S 0.0 11.0 :14.16 php5-fpm 14464 cont 20 397020 54696 31832 S 0.0 10.9 :09.44 php5-fpm 13892 cont 20 396640 54704 31936 S 0.0 10.9 :12.84 php5-fpm 13883 cont 20 396864 54692 31940 S 0.0 10.9 :15.64 php5-fpm 13893 cont 20 396860 54628 32004 S 0.0 10.9 :15.13 php5-fpm 13885 cont 20 396852 54412 32116 S 0.0 10.8 :13.94 php5-fpm 13884 cont 20 395164 53916 32364 S 0.0 10.7 :13.51 php5-fpm 13989 cont 20 394960 53548 32108 S 3.7 10.7 :14.37 php5-fpm 2778 mysql 20 1359152 31704 1728 S 0.7 6.3 1:38.80 mysqld 13849 root 20 373832 1180 188 S 0.0 0.2 :03.27 php5-fpm

输出结果显示有12个php5-fpm子进程（用户名是cont）和一个主进程（用户名是root）。而这12个子进程只是呆坐在那里，什么事也不做，每个子进程白白消耗超过10%的内存。这些子进程主要是由pm=dynamic这个配置选项产生的。

老实说，绝大部分的云主机拥有者也不知道所有这些配置选项是干什么用的，只是简单地复制粘贴而已。我也不准备假装我了解每个PHP配置文件里的每一个选项的目的和意义。我在很大程度上也是复制粘贴的受害者。

但是我经常检查服务器的资源占用情况，困惑于为什么我的服务器占用这么多的内存和CPU。举另外一个例子，是这台服务器上的free -mt命令的结果：

total used free shared buffers cached Mem: 490 480 9 31 6 79 -/+ buffers/cache: 393 96 Swap: 2047 491 1556 Total: 2538 971 1566

在没有任何访问量的情况下，也几乎有整整1G的内存（实际内存加上交换内存）被占用。当然，通过调整配置pm的数量可以有所改变，但只是轻微的。只要设置pm=dynamic，就会有空闲的子进程等在那里等待被使用。

直到读了一篇文章《A better way to run PHP-FPM》(更好地运行PHP-FPM)之后，我开始意识到应该如何修改我的配置文件。那篇文章是大约一年前写的，令人失望的是我从昨天晚上搜索相关主题时才看到它。如果你也有服务器并且使用PHP-FPM的话，我建议你好好读一下那篇文章。

读完文章之后，我修改了我的pm选项，如下：

; Choose how the process manager will control the number of child processes.pm = ondemand pm.max_children = 75pm.process_idle_timeout = 10s pm.max_requests = 500

最主要的改动就是用pm=ondemand替换了pm=dynamic。这一改动对资源占用的影响是巨大的。下面是改动并重新加载php5-fpm之后运行free -mt的结果：

total used free shared buffers cached Mem: 490 196 293 28 9 70 -/+ buffers/cache: 116 373 Swap: 2047 452 1595 Total: 2538 649 1888

和之前的结果对比，内存使用量下降了50%。产生这一下降的原因通过执行top命令一目了然：

2778 mysql 20 1359152 56708 3384 S 0.0 11.3 2:11.06 mysqld 26896 root 20 373828 19000 13532 S 0.0 3.8 :02.42 php5-fpm 25818 root 20 64208 4148 1492 S 0.0 0.8 :01.88 php5-fpm 25818 root 20 64208 4148 1492 S 0.0 0.8 :01.88 php5-fpm 17385 root 20 64208 4068 1416 S 0.0 0.8 :02.23 php5-fpm 1465 ossec 20 15592 2960 480 S 0.0 0.6 :08.60 ossec-analysisd 1500 root 20 6312 2072 328 S 0.0 0.4 :45.55 ossec-syscheckd 1 root 20 33444 1940 812 S 0.0 0.4 :03.29 init

你注意到这里已经没有子进程了吗？它们去哪里了？这就是设置pm=ondemand的作用。这样设置之后，只有当有需要的时候，子进程才会被产生。事情做完之后，子进程会留在内存中10秒钟时间（pm.process_idle_timeout = 10s），然后自己退出。

我只是对PHP-FPM的配置做了一点小小的修改，就节省了50%的内存。当然，这台服务器没有承受大并发的压力，但我相信它能顶得住合理的高负载，考虑到它只有512M内存。再加上Nginx微缓存的配置，我想它会做的更好。当然还有另外一些PHP-FPM和Percona MySQL的配置优化我还没有做。这里只是给大家分享一个我觉得非常有用的小窍门。

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