linux-kernel - Re: [patch v2 3/6] memcg: rework mem_cgroup

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Date:	Fri, 14 Dec 2012 13:07:07 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Ying Han <yinghan@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <htejun@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [patch v2 3/6] memcg: rework mem_cgroup_iter to use cgroup
 iterators

On Thu 13-12-12 17:14:13, Ying Han wrote:
[...]
> I haven't tried this patch set yet. Before I am doing that, I am
> curious whether changing the target reclaim to be consistent with
> global reclaim something worthy to consider based my last reply:
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 53dcde9..3f158c5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1911,20 +1911,6 @@ static void shrink_zone(struct zone *zone,
> struct scan_control *sc)
> 
>                 shrink_lruvec(lruvec, sc);
> 
> -               /*
> -                * Limit reclaim has historically picked one memcg and
> -                * scanned it with decreasing priority levels until
> -                * nr_to_reclaim had been reclaimed.  This priority
> -                * cycle is thus over after a single memcg.
> -                *
> -                * Direct reclaim and kswapd, on the other hand, have
> -                * to scan all memory cgroups to fulfill the overall
> -                * scan target for the zone.
> -                */
> -               if (!global_reclaim(sc)) {
> -                       mem_cgroup_iter_break(root, memcg);
> -                       break;
> -               }
>                 memcg = mem_cgroup_iter(root, memcg, &reclaim);

This wouldn't work because you would over-reclaim proportionally to the
number of groups in the hierarchy.

>         } while (memcg);
>  }
> 
> --Ying

-- 
Michal Hocko
SUSE Labs
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