linux-kernel - Re: [PATCH] mm: page_alloc: Avoid marking zones full prematurely after zone

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Message-ID: <20130321081902.GD6094@dhcp22.suse.cz>
Date:	Thu, 21 Mar 2013 09:19:02 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hedi Berriche <hedi@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: Avoid marking zones full prematurely
 after zone_reclaim()

On Thu 21-03-13 10:33:07, Simon Jeons wrote:
> Hi Mel,
> On 03/21/2013 02:19 AM, Mel Gorman wrote:
> >The following problem was reported against a distribution kernel when
> >zone_reclaim was enabled but the same problem applies to the mainline
> >kernel. The reproduction case was as follows
> >
> >1. Run numactl -m +0 dd if=largefile of=/dev/null
> >    This allocates a large number of clean pages in node 0
> 
> I confuse why this need allocate a large number of clean pages?

It reads from file and puts pages into the page cache. The pages are not
modified so they are clean. Output file is /dev/null so no pages are
written. dd doesn't call fadvise(POSIX_FADV_DONTNEED) on the input file
by default so pages from the file stay in the page cache
-- 
Michal Hocko
SUSE Labs
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