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

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Date:	Thu, 6 Oct 2011 12:23:48 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Menage <paul@...lmenage.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Tim Hockin <thockin@...kin.org>, Tejun Heo <tj@...nel.org>,
	Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH 10/10] cgroups: Add a task counter subsystem

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@...il.com>

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

-- 
 Kirill A. Shutemov
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