linux-kernel - Re: [PATCH] mm: memcg: remove checking reclaim order in soft limit reclaim

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Date:	Wed, 18 Jan 2012 20:30:41 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: memcg: remove checking reclaim order in soft limit reclaim

On Tue, Jan 17, 2012 at 10:07 PM, Michal Hocko <mhocko@...e.cz> wrote:
> On Tue 17-01-12 21:29:52, Hillf Danton wrote:
>> On Tue, Jan 17, 2012 at 9:16 PM, Michal Hocko <mhocko@...e.cz> wrote:
>> > Hi,
>> >
>> > On Tue 17-01-12 20:47:59, Hillf Danton wrote:
>> >> If async order-O reclaim expected here, it is settled down when setting up scan
>> >> control, with scan priority hacked to be zero. Other than that, deny of reclaim
>> >> should be removed.
>> >
>> > Maybe I have misunderstood you but this is not right. The check is to
>> > protect from the _global_ reclaim with order > 0 when we prevent from
>> > memcg soft reclaim.
>> >
>> need to bear mm hog in this way?
>
> Could you be more specific? Are you trying to fix any particular
> problem?
>
My thought is simple, the outcome of softlimit reclaim depends little on the
value of reclaim order, zero or not, and only exceeding is reclaimed, so
selective response to swapd's request is incorrect.

> Global reclaim should take are of the global memory pressure. Soft
> reclaim is intended just to make its job easier. Btw. softlimit reclaim
> is on its way out of the kernel but this will not happen in 3.3.
>
I will check it in 3.3 if too late for 3.2.

Thanks
Hillf
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