linux-kernel - Re: [RFC 2/8] compaction: make isolate_lru

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Date:	Sat, 30 Apr 2011 00:15:01 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC 2/8] compaction: make isolate_lru_page with filter aware

Hi Hannes,

On Thu, Apr 28, 2011 at 5:48 PM, Johannes Weiner <hannes@...xchg.org> wrote:
> On Wed, Apr 27, 2011 at 01:25:19AM +0900, Minchan Kim wrote:
>> In async mode, compaction doesn't migrate dirty or writeback pages.
>> So, it's meaningless to pick the page and re-add it to lru list.
>>
>> Of course, when we isolate the page in compaction, the page might
>> be dirty or writeback but when we try to migrate the page, the page
>> would be not dirty, writeback. So it could be migrated. But it's
>> very unlikely as isolate and migration cycle is much faster than
>> writeout.
>>
>> So, this patch helps cpu and prevent unnecessary LRU churning.
>>
>> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Rik van Riel <riel@...hat.com>
>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
>> ---
>>  mm/compaction.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index dea32e3..9f80b5a 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -335,7 +335,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
>>               }
>>
>>               /* Try isolate the page */
>> -             if (__isolate_lru_page(page, ISOLATE_BOTH, 0, 0, 0) != 0)
>> +             if (__isolate_lru_page(page, ISOLATE_BOTH, 0, !cc->sync, 0) != 0)
>>                       continue;
>
> With the suggested flags argument from 1/8, this would look like:
>
>        flags = ISOLATE_BOTH;
>        if (!cc->sync)
>                flags |= ISOLATE_CLEAN;
>
> ?

Yes. I will change it.

>
> Anyway, nice change indeed!

Thanks!


-- 
Kind regards,
Minchan Kim
--
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