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

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Date:	Wed, 27 Apr 2011 17:34:50 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.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, 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.

Thanks,
-Kame

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