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

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Date:	Fri, 14 Dec 2012 15:08:40 -0800
From:	Ying Han <yinghan@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
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 Fri, Dec 14, 2012 at 4:07 AM, Michal Hocko <mhocko@...e.cz> wrote:
> 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.

Don't get it and especially of why it is different from global
reclaim? I view the global reclaim should be viewed as target reclaim,
just a matter of the root cgroup is under memory pressure.

Anyway, don't want to distract you from working on the next post. So
feel free to not follow up on this.

--Ying

>
>>         } while (memcg);
>>  }
>>
>> --Ying
>
> --
> Michal Hocko
> SUSE Labs
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