From mboxrd@z Thu Jan  1 00:00:00 1970
From: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [RFD] Merge task counter into memcg
Date: Wed, 18 Apr 2012 08:54:33 +0200
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To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Hugh Dickins <hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>, Daniel Walsh <dwalsh-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>

On Tue, Apr 17, 2012 at 08:17:53AM -0700, Tejun Heo wrote:
> Hello, Frederic.
> 
> On Thu, Apr 12, 2012 at 06:59:27PM +0200, Frederic Weisbecker wrote:
> > I want:
> > 
> > a) to prevent the forkbomb from going far enough to DDOS the machine
> > b) to be able to kill that forkbomb once detected, in one go without race
> > against concurrent forks.
> > 
> > I think a) can work just fine with kernel stack limiting. I also need
> > to be notified about the fact we reached the limit. And b) should
> > be feasible with the help of the cgroup freezer. 
> 
> kmem allocation fail after reaching the limit which in turn should
> fail task creation.  Isn't that the same effect as the task_counter as
> implemented?

That's it.

> 
> > > Is there anything for which you need to know exactly the number of
> > > processes?
> > 
> > No that's really about prevent/kill forkbomb as far as I'm concerned.
> 
> Hmm... so, accounting overhead aside, if the only purpose is
> preventing the whole machine being brought down by a fork bomb, kmem
> limiting is enough, right?

I think so yeah.