linux-ext4 - Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep

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Message-ID: <BANLkTin6HJSrxcJYB3Y6XYgs8xuDWaQ15Q@mail.gmail.com>
Date:	Thu, 19 May 2011 07:55:35 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	James.Bottomley@...senpartnership.com, akpm@...ux-foundation.org,
	colin.king@...onical.com, raghu.prabhu13@...il.com, jack@...e.cz,
	chris.mason@...cle.com, cl@...ux.com, penberg@...nel.org,
	riel@...hat.com, hannes@...xchg.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long,
 allow it to sleep

On Wed, May 18, 2011 at 6:58 PM, Mel Gorman <mgorman@...e.de> wrote:
> On Wed, May 18, 2011 at 02:44:48PM +0900, Minchan Kim wrote:
>> On Wed, May 18, 2011 at 10:05 AM, KOSAKI Motohiro
>> <kosaki.motohiro@...fujitsu.com> wrote:
>> >> It would be better to put cond_resched after balance_pgdat?
>> >>
>> >> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> >> index 292582c..61c45d0 100644
>> >> --- a/mm/vmscan.c
>> >> +++ b/mm/vmscan.c
>> >> @@ -2753,6 +2753,7 @@ static int kswapd(void *p)
>> >>                 if (!ret) {
>> >>                         trace_mm_vmscan_kswapd_wake(pgdat->node_id,
>> >> order);
>> >>                         order = balance_pgdat(pgdat,
>> >> order,&classzone_idx);
>> >> +                       cond_resched();
>> >>                 }
>> >>         }
>> >>         return 0;
>> >>
>> >>>>> While it appears unlikely, there are bad conditions which can result
>> >>>
>> >>> in cond_resched() being avoided.
>> >
>> > Every reclaim priority decreasing or every shrink_zone() calling makes more
>> > fine grained preemption. I think.
>>
>> It could be.
>> But in direct reclaim case, I have a concern about losing pages
>> reclaimed to other tasks by preemption.
>>
>> Hmm,, anyway, we also needs test.
>> Hmm,, how long should we bother them(Colins and James)?
>> First of all, Let's fix one just between us and ask test to them and
>> send the last patch to akpm.
>>
>> 1. shrink_slab
>> 2. right after balance_pgdat
>> 3. shrink_zone
>> 4. reclaim priority decreasing routine.
>>
>> Now, I vote 1) and 2).
>>
>
> I've already submitted a pair of patches for option 1. I don't think
> option 2 gains us anything. I think it's more likely we should worry
> about all_unreclaimable being set when shrink_slab is returning 0 and we
> are encountering so many dirty pages that pages_scanned is high enough.

Okay.

Colin reported he had no problem with patch 1 in this series and
mine(ie, just cond_resched right after balance_pgdat call without no
patch of shrink_slab).

If Colin's test is successful, I don't insist on mine.
(I don't want to drag on for days :( )
If KOSAKI agree, let's ask the test to Colin and confirm our last test.

KOSAKI. Could you post a your opinion?

-- 
Kind regards,
Minchan Kim
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