From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759255Ab2IKRQI (ORCPT ); Tue, 11 Sep 2012 13:16:08 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:35466 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756652Ab2IKRQG (ORCPT ); Tue, 11 Sep 2012 13:16:06 -0400 Date: Tue, 11 Sep 2012 10:16:01 -0700 From: Tejun Heo To: Vivek Goyal Cc: linux-kernel@vger.kernel.org, Michal Hocko , Li Zefan , Glauber Costa , Peter Zijlstra , Paul Turner , Johannes Weiner , Thomas Graf , "Serge E. Hallyn" , Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , Neil Horman , "Aneesh Kumar K.V" Subject: Re: [PATCH RFC cgroup/for-3.7] cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them Message-ID: <20120911171601.GN7677@google.com> References: <20120910223125.GC7677@google.com> <20120911145106.GG12039@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120911145106.GG12039@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Vivek. On Tue, Sep 11, 2012 at 10:51:06AM -0400, Vivek Goyal wrote: > > * Move users away from using hierarchy on currently non-hierarchical > > subsystems, so that implementing proper hierarchy support on those > > doesn't surprise them. > > I know two current/potential users. systemd and libvirt. They are > anyway going to create hierarchy irrespective of the fact whether > controller supports it or not. systemd mounts all controllers by default but it only creates hierarchy for controllers other than cpu, so we're in the clear there. > So even if we start screaming, nothing is going to change there, I > suspect. Just that by default they expect every controller supports > hiearchies. As for libvirt, that's exactly the case where we want to be warning. The problem is that they're currently creating a hierarchy and expecting (or at least experiencing) flat behavior. We want them to be either switch to explicit flat cgroups or at least know very well that they're doing something unsupported and the behavior will change beneath them. > > * Keep track of which controllers are broken how and nudge the > > subsystems to implement proper hierarchy support. > > I thought we can easily keep track of this in a simple .txt file and > we really don't have to provide explicit warnings. > > I think for these controllers it is a known fact that they don't support > hiearchy yet. I am skeptical that providing explicit warnings is going > to help. We should change blkio to support full hierarchy and soon and the current users of the broken hierarchy should be warned loudly and clearly; otherwise, this whole excercise is pointless, so I don't think it makes sense to suppress warnings for known broken ones. In fact, my concern there is that it's too quiet and polite and I'm planning on promoting it to full-blown WARN in time. Thanks. -- tejun