Containers and /proc/sys/vm/drop_caches

Daniel Lezcano daniel.lezcano at free.fr
Wed Jan 5 01:49:55 PST 2011


On 01/05/2011 10:40 AM, Mike Hommey wrote:
> [Copy/pasted from a previous message to lkml, where it was suggested to
>   try containers@]
>
> Hi,
>
> I noticed that from within a lxc container, writing "3" to
> /proc/sys/vm/drop_caches would flush the host page cache. That sounds a
> little dangerous for VPS offerings that would be based on lxc, as in one
> VPS instance root user could impact the overall performance of the host.
> I don't know about other containers but I've been told openvz isn't
> subject to this problem.
> I only tested the current Debian Squeeze kernel, which is based on
> 2.6.32.27.

There is definitively a big work to do with /proc.

Some files should be not accessible (/proc/sys/vm/drop_caches, 
/proc/sys/kernel/sysrq, ...) and some other should be virtualized 
(/proc/meminfo, /proc/cpuinfo, ...).

Serge suggested to create something similar to the cgroup device 
whitelist but for /proc, maybe it is a good approach for denying access 
a specific proc's file.


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