linux-kernel - Re: [PATCH 1/2] mm/memcontrol.c: remove meaningless while loop in mem_cgroup

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Message-ID: <20140422103420.GI29311@dhcp22.suse.cz>
Date:	Tue, 22 Apr 2014 12:34:21 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Jianyu Zhan <nasa4836@...il.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Balbir Singh <bsingharora@...il.com>,
	kamezawa.hiroyu@...fujitsu.com, Cgroups <cgroups@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/memcontrol.c: remove meaningless while loop in
 mem_cgroup_iter()

On Tue 22-04-14 18:17:09, Jianyu Zhan wrote:
> On Tue, Apr 22, 2014 at 5:47 PM, Michal Hocko <mhocko@...e.cz> wrote:
> > What about
> >   3. last_visited == last_node in the tree
> >
> > __mem_cgroup_iter_next returns NULL and the iterator would return
> > without visiting anything.
> 
> Hi,  Michal,
> 
> yep,  if 3 last_visited == last_node, then this means we have done a round-trip,
> thus __mem_cgroup_iter_next returns NULL, in turn mem_cgroup_iter() return NULL.

Sorry, I should have been more specific that I was talking about
mem_cgroup_reclaim_cookie path where the iteration for this particular
zone and priority ended at the last node without finishing the full
roundtrip last time. This new iteration (prev==NULL) wants to continue
and it should start a new roundtrip.

Makes sense?
-- 
Michal Hocko
SUSE Labs
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