If you are not using any PHP opcache accelerator, you should. If you are using APC, you should move to OPCache. If you are already using it, you should use opcache-dashboard also.
Set up properly and monitor your Zend OPCache with this dashboard that will help you checking memory, hits and status, configuring for optimal performance (warning you when cache full, validation, etc.) and reseting one or all scripts with one click.
Made with Bootstrap 3, it’s easy to install (one file), easy to read and very useful for detecting issues. Check it on GitHub.