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

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Message-ID: <CAHz2CGWrk3kuR=BLt2vT-8gxJVtJcj6h17ase9=1CoWXwK6a3w@mail.gmail.com>
Date:	Tue, 22 Apr 2014 18:17:09 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
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, 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.

This is what comments above mem_cgroup_iter() says:

>Returns references to children of the hierarchy below @root, or
>* @root itself, or %NULL after a full round-trip.

Actually, this condition could be reduced to conditon 2.1

Thanks,
Jianyu Zhan
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