Re: [PATCH 10/10] cgroups: Add a task counter subsystem

From: Kirill A. Shutemov
Date: Thu Oct 06 2011 - 05:23:52 EST

On Mon, Oct 03, 2011 at 09:07:12PM +0200, Frederic Weisbecker wrote:
> Add a new subsystem to limit the number of running tasks,
> similar to the NR_PROC rlimit but in the scope of a cgroup.
> The user can set an upper bound limit that is checked every
> time a task forks in a cgroup or is moved into a cgroup
> with that subsystem binded.
> The primary goal is to protect against forkbombs that explode
> inside a container. The traditional NR_PROC rlimit is not
> efficient in that case because if we run containers in parallel
> under the same user, one of these could starve all the others
> by spawning a high number of tasks close to the user wide limit.
> This is a prevention against forkbombs, so it's not deemed to
> cure the effects of a forkbomb when the system is in a state
> where it's not responsive. It's aimed at preventing from ever
> reaching that state and stop the spreading of tasks early.
> While defining the limit on the allowed number of tasks, it's
> up to the user to find the right balance between the resource
> its containers may need and what it can afford to provide.
> As it's totally dissociated from the rlimit NR_PROC, both
> can be complementary: the cgroup task counter can set an upper
> bound per container and the rlmit can be an upper bound on the
> overall set of containers.
> Also this subsystem can be used to kill all the tasks in a cgroup
> without races against concurrent forks, by setting the limit of
> tasks to 0, any further forks can be rejected. This is a good
> way to kill a forkbomb in a container, or simply kill any container
> without the need to retry an unbound number of times.
> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>

Acked-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>

Kirill A. Shutemov
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