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From: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
Subject: Re: [RFD] Merge task counter into memcg
Date: Thu, 12 Apr 2012 22:50:23 -0300
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To: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
Cc: "Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, Daniel Walsh <dwalsh-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Hugh Dickins <hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>

On 04/12/2012 10:42 PM, KAMEZAWA Hiroyuki wrote:
> To be honest, I doubt that task counter is unnecessary...memcg can catch
> oom situation well. I often test 'make -j' under memcg.
>
> To the questions
> *   It sounds like a 'ulimit' cgroup. How about overwriting
>      ulimit values via cgroup ? (sounds joke?) Then, overhead will be small but
>      I'm not sure it can be hierarchical and doesn't break userland.
>
>      If people wants to limit the number of tasks, I think interface should provide it
>      in the unit of objects. Then, I'm ok to have other subsystem for counting something.
>      fork-bomb's memory overhead can be prevent by memcg. What memcg cannot handle
>      is ulimit. If forkbomb exhausts all ulimit/tasks, the user cannot login.
>      So, having task-limit cgroup subsys for a sandbox will make sense in some situation.
>
> In short, I don't think it's better to have task-counting and fd-counting in memcg.
> It's kmem, but it's more than that, I think.
> Please provide subsys like ulimit.
>
Kame,

You're talking about the memcg that is in the kernel today.
I think the discussion is orbiting around how it is going to be once we
start tracking kernel memory like the slab (for task_struct), or kernel 
stack pages.

In those scenarios, a fork bomb will be stopped anyway, because it will 
need kernel memory it can't grab.