I Use Odoo 8 Run in My VPS

Spec :

4 Core

8GB Memory

Ubuntu 16.04

With Config Like This :

workers = 9
max_cron_threads = 3
limit_time_cpu = 60
limit_time_real = 170
limit_memory_soft = 572662306
limit_memory_hard = 6870269952

But why odoo non use all memory that i provide

20 multiple user use apps at same time, odoo just use 30% of my RAM

100 multiple user use apps at same time, odoo just use 30% of my RAM too

it causes odoo apps to respond slowly if there are multiple users