Re: [PATCH] memcg: first step towards hierarchical controller

[Michal Hocko <mhocko@suse.cz>]

On Tue 26-06-12 22:22:04, Glauber Costa wrote:
> On 06/26/2012 10:12 PM, Tejun Heo wrote:
> >On Tue, Jun 26, 2012 at 05:30:28PM +0400, Glauber Costa wrote:
> >>Okay, so after recent discussions, I am proposing the following
> >>patch. It won't remove hierarchy, or anything like that. Just default
> >>to true in the root cgroup, and print a warning once if you try
> >>to set it back to 0.
> >>
> >>I am not adding it to feature-removal-schedule.txt because I don't
> >>view it as a consensus. Rather, changing the default would allow us
> >>to give it a time around in the open, and see if people complain
> >>and what we can learn about that.
> >>
> >>Signed-off-by: Glauber Costa <glommer@parallels.com>
> >>CC: Michal Hocko <mhocko@suse.cz>
> >>CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> >>CC: Johannes Weiner <hannes@cmpxchg.org>
> >>CC: Tejun Heo <tj@kernel.org>
> >
> >Just in case it wasn't clear in the other posting.
> >
> >  Nacked-by: Tejun Heo <tj@kernel.org>
> >
> >You can't change the default behavior silently.  Not in this scale.
> >
> >Thanks.
> >
> I certainly don't share your views of the matter here.
> 
> I would agree with you if we were changing a fundamental algorithm,
> with no way to resort back to a default setup. We are not removing any
> functionality whatsoever here.
> 
> I would agree with you if we were actually documenting explicitly
> that this is an expected default behavior.

Actually we did:
Documentation/cgroups/memory.txt
"
6.1 Enabling hierarchical accounting and reclaim

A memory cgroup by default disables the hierarchy feature. Support
can be enabled by writing 1 to memory.use_hierarchy file of the root
cgroup
"

But I do not think this is really that important. We are still
interested in making the thing sane. Flat_hierarchical trees just don't
seem right... Generic? Sure. Sane? Really?

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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