How to clear cache in OpenVZ?

Question

I have OpenVZ VPS and have problem with clearing the cache:

In OpenVZ not work echo 3 > /proc/sys/vm/drop_caches

How may be this cache clear?

Answer 1

This was reported on the OpenVZ bug tracker. It has been resolved as RESOLVED WONTFIX

From Kir Kolyshkin in the bug report (project leader of OpenVZ):

All containers share the same page cache (although there is per-container accounting), so to drop caches of one single container we have to check each page:

1 Whether it belongs to the container or not -- supposing we do have that information, which I am not sure of

2 Whether this page is used by other containers.

So, while this is trivial on the host system, it is much less trivial for a container. And this is not a critical piece of functionality -- drop_caches is only useful for running various sorts of benchmarks.

Since your don't get your own kernel instance with OpenVZ you are prevented from running the command.

Answer 2

As a result, in order to clear the cache -> must restart VPS.