From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755216Ab2ITNYM (ORCPT ); Thu, 20 Sep 2012 09:24:12 -0400 Received: from cantor2.suse.de ([195.135.220.15]:60449 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753501Ab2ITNYK (ORCPT ); Thu, 20 Sep 2012 09:24:10 -0400 Date: Thu, 20 Sep 2012 15:24:00 +0200 From: Michal Hocko To: David Rientjes Cc: Tejun Heo , containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, 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" , Dave Jones , Ben Hutchings Subject: Re: [PATCH 2.6.32] memcg: warn on deeper hierarchies with use_hierarchy==0 Message-ID: <20120920132400.GC23872@dhcp22.suse.cz> References: <20120913205827.GO7677@google.com> <20120914150306.GQ28039@dhcp22.suse.cz> <20120919140203.GA5398@dhcp22.suse.cz> <20120919140308.GB5398@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 19-09-12 12:38:18, David Rientjes wrote: > On Wed, 19 Sep 2012, Michal Hocko wrote: > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index f99f599..b61c34b 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -3106,6 +3106,11 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont) > > } else { > > parent = mem_cgroup_from_cont(cont->parent); > > mem->use_hierarchy = parent->use_hierarchy; > > + WARN_ONCE(!mem->use_hierarchy && parent != root_mem_cgroup, > > + "Creating hierarchies with use_hierarchy==0 " > > + "(flat hierarchy) is considered deprecated. " > > + "If you believe that your setup is correct, " > > + "we kindly ask you to contact linux-mm@kvack.org and let us know"); > > When I deprecated /proc/pid/oom_adj (now removed), we did a WARN_ONCE() > and others complained that this unnecessarily alters userspace scripts > that a serious issue has occurred and Linus agreed that we shouldn't do > deprecation in this way. The alternative is to use printk_once() instead. Yes printk_once is an alternative but I really wanted to have this as much visible as possible. People tend to react to stack traceces more and this one will trigger only if somebody is either doing something wrong or the configuration is the one we are looking for. Comparing to oom_adj, that one was used much more often so the WARN_ONCE was too verbose especially when you usually had to wait for an userspace update which is not the case here. -- Michal Hocko SUSE Labs