linux-kernel - Re: [patch v2 4/6] memcg: simplify mem_cgroup

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Message-ID: <50B5D0C8.2010209@jp.fujitsu.com>
Date:	Wed, 28 Nov 2012 17:52:24 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	Ying Han <yinghan@...gle.com>, Tejun Heo <htejun@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [patch v2 4/6] memcg: simplify mem_cgroup_iter

(2012/11/27 3:47), Michal Hocko wrote:
> Current implementation of mem_cgroup_iter has to consider both css and
> memcg to find out whether no group has been found (css==NULL - aka the
> loop is completed) and that no memcg is associated with the found node
> (!memcg - aka css_tryget failed because the group is no longer alive).
> This leads to awkward tweaks like tests for css && !memcg to skip the
> current node.
> 
> It will be much easier if we got rid off css variable altogether and
> only rely on memcg. In order to do that the iteration part has to skip
> dead nodes. This sounds natural to me and as a nice side effect we will
> get a simple invariant that memcg is always alive when non-NULL and all
> nodes have been visited otherwise.
> 
> We could get rid of the surrounding while loop but keep it in for now to
> make review easier. It will go away in the following patch.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

seems nice clean up. I'll ack when I ack 3/6 and we make agreement on that
iterator will skip dead node.

Thanks,
-Kame

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