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

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Message-ID: <4B38246C.3020209@redhat.com>
Date:	Sun, 27 Dec 2009 22:22:20 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	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.

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?

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