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

[Frederic Weisbecker <fweisbec@gmail.com>]

On Thu, Oct 06, 2011 at 12:23:48PM +0300, Kirill A. Shutemov wrote:
> 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@gmail.com>
> 
> Acked-by: Kirill A. Shutemov <kirill@shutemov.name>

Thanks a lot for your acks Kirill!