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

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Message-ID: <20091228035738.GH3601@balbir.in.ibm.com>
Date:	Mon, 28 Dec 2009 09:27:38 +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.

* Balbir Singh <balbir@...ux.vnet.ibm.com> [2009-12-28 09:26:39]:

> * 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? 
>

Sorry, I replied to wrong email, I should have been clearer that this
question is for Minchan Kim. 

-- 
	Balbir
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