[lxc-devel] Memory Resources

Krzysztof Taraszka krzysztof.taraszka at gnuhosting.net
Sun Aug 23 09:59:22 PDT 2009

2009/8/23 Daniel Lezcano <daniel.lezcano at free.fr>

> Krzysztof Taraszka wrote:
>> Hello,
>> I am running lxc on my debian unstable sandbox and I have a few question
>> about memory managament inside linux containers based on lxc project.
>> I have got linux kernel with enabled :
>> +Resource counter
>> ++ Memory Resource Controller for Control Groups
>>  +++ Memory Resource Controller Swap Extension(EXPERIMENTAL)
>> lxc-checkconfig pass all checks.
>> I read about cgroups memory managament (Documentation/cgroups/memory.txt)
>> and I tried to pass those value to my debian sandbox.
>> And...
>> 'free -m' and 'top/htop' still show all available memory inside container
>> (also If I set 32M for lxc.cgroup.memory.limit_in_bytes and
>> lxc.cgroup.memory.usage_in_bytes; and 64M for
>> lxc.cgroup.memory.memsw.usage_in_bytes and
>> lxc.cgroup.memory.memsw.limit_in_bytes free and top show all resources).
>> What I did wrong? Does the container always show all available memory
>> resources  without cgroup limitations?
> At the first glance I would say the configuration is correct.
> But AFAIR, the memory cgroup is not isolated, if you specify 32MB you will
> see all the memory available on the system either if you are not allowed to
> use more than 32MB. If you create a program which allocates 64MB within a
> container configured with 32MB, and you "touch" the pages (may be that can
> be done with one mmap call with the MAP_POPULATE option), you should see the
> application swapping and the "memory.failcnt" increasing.
> IMHO, showing all the memory available for the system instead of showing
> the allowed memory with the cgroup is weird but maybe there is a good reason
> to do that.

Thank you Daniel for your reply.
I think that LXC should isolate memory available for containers like Vserver
or FreeVPS do (memory + swap) if .cgroup.memory.* and
lxc.cgroup.memory.memsw.* is set.
Is there any possibility to make a patch for linux kernel / lxc-tools to
show the limitations inside cointainers propertly? I think is a good idea
and it should be apply as soon as possible.

Krzysztof Taraszka

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