linux-kernel - Re: [PATCH -mmotm-2009-12-10-17-19] Prevent churning of zero page in LRU list.

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Message-ID: <20091228035639.GG3601@balbir.in.ibm.com>
Date:	Mon, 28 Dec 2009 09:26:39 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mmotm-2009-12-10-17-19] Prevent churning of zero page in
 LRU list.

* Rik van Riel <riel@...hat.com> [2009-12-27 22:22:20]:

> On 12/27/2009 09:53 PM, Minchan Kim wrote:
> >
> >VM doesn't add zero page to LRU list.
> >It means zero page's churning in LRU list is pointless.
> >
> >As a matter of fact, zero page can't be promoted by mark_page_accessed
> >since it doesn't have PG_lru.
> >
> >This patch prevent unecessary mark_page_accessed call of zero page
> >alghouth caller want FOLL_TOUCH.
> >
> >Signed-off-by: Minchan Kim<minchan.kim@...il.com>
> 
> The code looks correct, but I wonder how frequently we run into
> the zero page in this code, vs. how much the added cost is of
> having this extra code in follow_page.
> 
> What kind of problem were you running into that motivated you
> to write this patch?
>

Frequent moving of zero page should ideally put it to the head of the
LRU list, leaving it untouched is likely to cause it to be scanned 
often - no? Should this be moved to the unevictable list? 

-- 
	Balbir
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