This is a performance monkey-patch using runkit for base64_decode and unserialize for PHP 5.x series.
Context is https://id-rsa.pub/post/shimming-php-for-fun-and-profit/.
I suggest that you have CloudLinux, CageFS and PHP Selector setup.
You will need to build runkit from source and follow http://docs.cloudlinux.com/compiling_your_own_extensions.html .
You will need to ensure that runkit.internal_override = on s set - follow http://docs.cloudlinux.com/individual_php_ini_files.html .