From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933305Ab1JNPiz (ORCPT ); Fri, 14 Oct 2011 11:38:55 -0400 Received: from mail-wy0-f174.google.com ([74.125.82.174]:49898 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933252Ab1JNPix (ORCPT ); Fri, 14 Oct 2011 11:38:53 -0400 Date: Fri, 14 Oct 2011 17:38:47 +0200 From: Frederic Weisbecker To: Cyrill Gorcunov Cc: Tejun Heo , Andrew Morton , Kay Sievers , linux-kernel@vger.kernel.org, lennart@poettering.net, harald@redhat.com, david@fubar.dk, greg@kroah.com, "Kirill A. Shutemov" , Oleg Nesterov , Paul Menage , "Rafael J. Wysocki" , Pavel Emelyanov Subject: Re: A =?utf-8?Q?Plumber=E2=80=99?= =?utf-8?Q?s?= Wish List for Linux Message-ID: <20111014153844.GP14968@somewhere> References: <1317943022.1095.25.camel@mop> <20111011161600.6145aa6b.akpm@linux-foundation.org> <20111012005935.GD14968@somewhere> <20111012174014.GE6281@google.com> <20111012181641.GZ15413@moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111012181641.GZ15413@moon> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 12, 2011 at 10:16:41PM +0400, Cyrill Gorcunov wrote: > On Wed, Oct 12, 2011 at 10:40:14AM -0700, Tejun Heo wrote: > ... > > > > In general, I think making freezer work nicely with the rest of the > > system is a good idea and have been working towards that direction. > > Allowing a frozen task to be killed is not only handy for use cases > > like above but also makes solving freezer involved deadlocks much less > > likely and easier to solve. Another that I have in mind is allowing > > ptrace from unfrozen task to a frozen task. This can be helpful in > > general debugging (currently attaching to multi-threaded, violently > > cloning process is quite cumbersome) and userland checkpointing. > > Yeah, being able to ptrace a frozen cgroup would be great for us. > We stick with signals start/stop cycle at moment but the final target > is the cgroups and freezer of course. (btw while were poking freezer > code I noticed that there is no shortcut to move all tasks in cgroup > into the root cgroup, so I guess say "echo -1 > tasks" might be a good > addition to move all tasks from some particular cgroup to the root > by single action). 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?