High caсhed memory load

Steps to reproduce

  1. A large load of RAM and cached mem. Is it possible to clean cached memory and how to do it correctly?

Expected behaviour

Fast work owncloud web interface. Quick photo preview

Actual behaviour

Server configuration

Operating system:
"user_ldap" 0.9.1
Operating system: Ubuntu Server 15.10
Web server:Apache/2.4.12
Database:mariaDB 10.0.25
PHP version:PHP 5.6.11
ownCloud version (see ownCloud admin page): ownCloud 10.0.3 (stable)
Updated from an older ownCloud or fresh install:
Special configuration (external storage - nas, external authentication- ldap, reverse proxy - no, server-side-encryption-no):

The content of config/config.php:
config.txt (1.3 KB)

I this happening when viewing images for the first time or on consecutive views as well?

After rebooting the server, everything is fine. But as soon as users start working, it starts to grow and remains at this level. Can I need to do a job in cron for cleansing the cache? Or increase memory?

Maybe the following page helps you to understand the memory handling and the cached memory topic on linux: https://www.linuxatemyram.com/