linux-kernel - Re: A Plumber’s Wish List for Linux

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Message-ID: <20111014161946.GR14968@somewhere>
Date:	Fri, 14 Oct 2011 18:19:50 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, lennart@...ttering.net,
	harald@...hat.com, david@...ar.dk, greg@...ah.com,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul Menage <paul@...lmenage.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: A Plumber’s Wish List for Linux

On Fri, Oct 14, 2011 at 08:08:09PM +0400, Cyrill Gorcunov wrote:
> On Fri, Oct 14, 2011 at 08:01:10PM +0400, Cyrill Gorcunov wrote:
> ...
> > > Well, wouldn't it be better to pull that complexity to userspace?
> > > After all, moving tasks from a cgroup to another is not a performance
> > > critical operation so that probably doesn't need to be all handled by
> > > the kernel.
> > > 
> > > If one worries about concurrent clone/fork while moving tasks, then
> > > freezing the cgroup and moving its tasks away from userspace could
> > > be enough?
> > 
> > Well, it's not that problem to make it task-by-task, still I think
> > it's just a convenient shortcut :)
> > 
> 
> Frederic, don't get me wrong, but when I've tried cgroups and freezer for
> first time (and I did it not by any script but by hands rather) it makes
> me scream out that once I've moved a number of tasks to some freezer cgroup
> now I need to move them back again. Of course there is a way to write some
> script of whatever but I thought we had some echo -1 shortcut. Anyway,
> I can live with it ;)

Using a script would be a much better shortcut.
The script may be a few dozen lines. Push that in the kernel and it may
be much more.

Have a close overall look at kernel/cgroup.c and ask yourself if you would
like to add 100 more lines to it, to avoid to make it in userspace ;)
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