From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH] fix bad behavior in use_hierarchy file Date: Tue, 26 Jun 2012 15:12:07 +0400 Message-ID: <4FE99907.1070305@parallels.com> References: <1340616061-1955-1-git-send-email-glommer@parallels.com> <20120625204908.GL3869@google.com> <20120626075653.GD6713@tiehlicka.suse.cz> <4FE98F97.6030406@parallels.com> <20120626111025.GE9566@tiehlicka.suse.cz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120626111025.GE9566-VqjxzfR4DlwKmadIfiO5sKVXKuFTiq87@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Michal Hocko Cc: Tejun Heo , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Andrew Morton , devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Dhaval Giani , Kamezawa Hiroyuki , Johannes Weiner , Ying Han On 06/26/2012 03:10 PM, Michal Hocko wrote: > On Tue 26-06-12 14:31:51, Glauber Costa wrote: >> On 06/26/2012 11:56 AM, Michal Hocko wrote: >>> [Adding Ying to CC - they are using hierarchies AFAIU in their workloads] >>> >>> On Mon 25-06-12 13:49:08, Tejun Heo wrote: >>> [...] >>>> A bit of delta but is there any chance we can either deprecate >>>> .use_hierarhcy or at least make it global toggle instead of subtree >>>> thing? >>> >>> So what you are proposing is to have all subtrees of the root either >>> hierarchical or not, right? >>> >>>> This seems needlessly complicated. :( >>> >>> Toggle wouldn't help much I am afraid. We would still have to >>> distinguish (non)hierarchical cases. And I am not sure we can make >>> everything hierarchical easily. >>> Most users (from my experience) ignored use_hierarchy for some reasons >>> and the end results might be really unexpected for them if they used >>> deeper subtrees (which might be needed due to combination with other >>> controller(s)). >>> >> Do we have any idea about who those users are, and how is their >> setup commonly done? > > Well, most of them use memory controller with combination of other > controller - usually cpuset or cpu - and memcg is used to cap the amount > of memory for each respective group. As I said most of those users > were not aware of use_hierarchy at all. > >> We can propose work arounds here, but not without first knowing work >> arounds to what =p > > No, please no workarounds. It will be even bigger mess. > Maybe a global switch is the first step in the right direction (on by > default). If somebody encounters any issue we can say it can be turned > off (something like one time switch) or advise on how to fix their > layout to fit hierarchy better. We can put WARN_ON_ONCE when the knob is > set to 0 in the second stage and finally remove the whole knob. > Sorry for the wording. I didn't mean work around in the sense of a kludge. I meant it as actually proposing solutions to the problem that would disrupt people as little as we can. Well, instead of a global switch, a much easier thing would be to set it to 1 by default. It would actually work as a global switch, because we always inherit the parent's value. You can set the root to 0 before you add other groups, but that generates a warning, as you suggested. But after it was first set to 0, he would be free to keep using mixed configurations if needed - this way we're likely to find out if there are actually users of that around.