[PATCH 8/8] cgroups: Add a task counter subsystem

[Kirill A. Shutemov]

On Fri, Jan 13, 2012 at 07:14:00PM +0100, 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 at gmail.com>
> Cc: Paul Menage <paul at paulmenage.org>
> Cc: Li Zefan <lizf at cn.fujitsu.com>
> Cc: Johannes Weiner <hannes at cmpxchg.org>
> Cc: Aditya Kali <adityakali at google.com>
> Cc: Oleg Nesterov <oleg at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Kay Sievers <kay.sievers at vrfy.org>
> Cc: Tim Hockin <thockin at hockin.org>
> Cc: Tejun Heo <tj at kernel.org>
> Cc: Kirill A. Shutemov <kirill at shutemov.name>
> Cc: Containers <containers at lists.linux-foundation.org>

Acked-by: Kirill A. Shutemov <kirill at shutemov.name>

-- 
 Kirill A. Shutemov