Nginx – Installed php53 but still displaying php 5.1.6 in phpinfo()

I think your max_children is too low

<value name="max_children">3</value>

Also you can try switching from TCP port to unix socket for php-fpm:

php-fpm.conf

<value name="listen_address">/tmp/php.sock</value>

nginx.conf

fastcgi_pass unix:/tmp/php.sock;

Elaborated:

1. Unix sockets are ~20% faster
2. You don't use time-wait sockets for each connect

You can compile and install manually only the mcrypt extension. This is what I did in my CentOS 5.6 VPS:

First install some required packages:

yum install php53-devel libmcrypt-devel gcc gcc-c++

Then download the php 5.3.6 source code from php.net and unpack it:

wget http://mx2.php.net/get/php-5.3.6.tar.bz2/from/us3.php.net/mirror
tar xvjf php-5.3.6.tar.bz2

(Please note that the download link will change with every subsequent PHP release.)

Go to the directory with the mcrypt extension source code and compile:

cd php-5.3.6/ext/mcrypt/
phpize
aclocal
./configure
make

Then install:

make install

Create the configuration file for PHP /etc/php.d/mcrypt.ini containing:

extension=mcrypt.so

Restart apache:

/etc/init.d/httpd restart

Create a file with phpinfo just to check if the extension was loaded:

<?php
phpinfo();
?>