Why is the RAM space on the VDS constantly growing?

Question

Network administration

ISP Manager Panel
This screen shows some data:

When you switch to processes, it's different:

When the main page of RAM reaches almost the limit, the server reboots.
How to fix this or where to look for what it is connected with?

Answer 1

The memory is actively used for the file cache
There should not be a reboot, well, it's probably worth including the swap file

Answer 2

It will not work properly to control the load through the ISPmanager panel. Log in to the VDS via ssh and see the list of processes there using the top command. But already at first glance, the average load shows a 300 percent load on the processor - it is because of this that the VDSka is most likely rebooting, and not because of the RAM load. You need to think about either moving the project to a more powerful VDS / dedicated server, or getting serious about optimizing MySQL and PHP scripts. If this is an engine like Joomla, then where possible, you need to enable caching of queries to the database.
There is also a possibility that your site is under DDoS attack, see how many connections you have to the server with this command:

netstat -ntu | awk '{print $5}' | grep -vE "(Address|servers|127.0.0.1)" | cut -d: -f1 | sort | uniq -c | sort -n| sed 's/^[ \t]*//'