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

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Message-ID: <20140422114838.GK29311@dhcp22.suse.cz>
Date:	Tue, 22 Apr 2014 13:48:39 +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 18:58:11, Jianyu Zhan wrote:
[...]
> This reminds me of my draft edition of this patch, I specifically handle
> this case as:
> 
> if (reclaim) {
>                if (!memcg ) {
>                               iter->generation++;
>                               if (!prev) {
>                                     memcg = root;
>                                     mem_cgroup_iter_update(iter, NULL, memcg, root,  seq);
>                                     goto out_unlock:
>                               }
>               }
>               mem_cgroup_iter_update(iter, last_visited, memcg, root,
>                                 seq);
>               if (!prev && memcg)
>                         reclaim->generation = iter->generation;
> }
> 
> This is literally manual unwinding the second while loop, and thus omit
> the while loop,
> to save a   mem_cgroup_iter_update() and a mem_cgroup_iter_update()
> 
> But it maybe a bit hard to read.

Dunno, this particular case is more explicit but it is also uglier so I
do not think this is an overall improvement. I would rather keep the
current state unless the change either simplifies the generated code
or it is much better to read.

Thanks!
-- 
Michal Hocko
SUSE Labs
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