[libvirt-users] LXC + passthrough mount and host filesystem-cache

[Daniel P. Berrange]

On Wed, Mar 26, 2014 at 02:52:58PM -0500, James R. Leu wrote:
> Hello,
> 
> I'm using libvirt to build/run LXC instances.  My LXC instances use
> passthrough filesystem mounts.  When I try to do large file systems
> operations (ex tar or rsync) the file systems cache on the host
> spikes and causes the OOM handler to run and kills processes
> in the LXC.

So it is specifically targetting processes inside the container
and not the host ?

If you run the same tar/rsync operations outside the container
on the same filesystem, presumably you don't see the OOM killer
behaviour ?

> Has anyone else seen this? Is there a way around this?
> At this point I'm resorting to running a cron job that dumps
> the filesystem cache every 5 minutes.  The result is the filesystem
> cache on the host never grows too large and OOM never runs against
> LXC processes.  The obvious down fall is that I'm killing my filesystem
> performance by duming the cache.

This is the first I've heard of this problem and it certainly
seems odd/bad.  I wonder if there's some cgroup tunables that
are being set badly, or that need to be set ? Or some global
proc/sysfs settings

Regards,
Daniel
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