http://linuxaria.com/howto/everything-you-need-to-know-about-apc-alternate-php-cache
http://gregrickaby.com/the-perfect-apc-configuration/
http://surniaulula.com/2012/11/22/save-memory-with-alternative-php-cache-apc/
http://serverfault.com/questions/403135/what-does-apc-mmap-file-mask-really-do