linux-kernel - Re: [RFC 6/8] In order putback lru core

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Date:	Thu, 28 Apr 2011 08:43:08 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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>,
	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 6/8] In order putback lru core

On Wed, Apr 27, 2011 at 5:34 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 27 Apr 2011 01:25:23 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> This patch defines new APIs to putback the page into previous position of LRU.
>> The idea is simple.
>>
>> When we try to putback the page into lru list and if friends(prev, next) of the pages
>> still is nearest neighbor, we can insert isolated page into prev's next instead of
>> head of LRU list. So it keeps LRU history without losing the LRU information.
>>
>> Before :
>>       LRU POV : H - P1 - P2 - P3 - P4 -T
>>
>> Isolate P3 :
>>       LRU POV : H - P1 - P2 - P4 - T
>>
>> Putback P3 :
>>       if (P2->next == P4)
>>               putback(P3, P2);
>>       So,
>>       LRU POV : H - P1 - P2 - P3 - P4 -T
>>
>> For implement, we defines new structure pages_lru which remebers
>> both lru friend pages of isolated one and handling functions.
>>
>> But this approach has a problem on contiguous pages.
>> In this case, my idea can not work since friend pages are isolated, too.
>> It means prev_page->next == next_page always is false and both pages are not
>> LRU any more at that time. It's pointed out by Rik at LSF/MM summit.
>> So for solving the problem, I can change the idea.
>> I think we don't need both friend(prev, next) pages relation but
>> just consider either prev or next page that it is still same LRU.
>> Worset case in this approach, prev or next page is free and allocate new
>> so it's in head of LRU and our isolated page is located on next of head.
>> But it's almost same situation with current problem. So it doesn't make worse
>> than now and it would be rare. But in this version, I implement based on idea
>> discussed at LSF/MM. If my new idea makes sense, I will change it.
>>
>
> I think using only 'next'(prev?) pointer will be enough.

I think so but let's wait other's opinion. :)
-- 
Kind regards,
Minchan Kim
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