linux-kernel - Re: [RFC 2/5] memcg: rework mem_cgroup

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Message-ID: <20121115095103.GB11990@dhcp22.suse.cz>
Date:	Thu, 15 Nov 2012 10:51:03 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <htejun@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Ying Han <yinghan@...gle.com>,
	Glauber Costa <glommer@...allels.com>
Subject: Re: [RFC 2/5] memcg: rework mem_cgroup_iter to use cgroup iterators

On Wed 14-11-12 10:52:45, Tejun Heo wrote:
> Hello, Michal.
> 
> On Wed, Nov 14, 2012 at 09:51:29AM +0100, Michal Hocko wrote:
> > > 	reclaim(root);
> > > 	for_each_descendent_pre()
> > > 		reclaim(descendant);
> > 
> > We cannot do for_each_descendent_pre here because we do not iterate
> > through the whole hierarchy all the time. Check shrink_zone.
> 
> I'm a bit confused.  Why would that make any difference?  Shouldn't it
> be just able to test the condition and continue?

Ohh, I misunderstood your proposal. So what you are suggesting is
to put all the logic we have in mem_cgroup_iter inside what you call
reclaim here + mem_cgroup_iter_break inside the loop, right?

I do not see how this would help us much. mem_cgroup_iter is not the
nicest piece of code but it handles quite a complex requirements that we
have currently (css reference count, multiple reclaimers racing). So I
would rather keep it this way. Further simplifications are welcome of
course.

Is there any reason why you are not happy about direct using of
cgroup_next_descendant_pre?
-- 
Michal Hocko
SUSE Labs
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