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

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Message-ID: <514AC583.2090909@gmail.com>
Date:	Thu, 21 Mar 2013 16:32:03 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
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()

Hi Michal,
On 03/21/2013 04:19 PM, Michal Hocko wrote:
> 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

Thanks for your clarify Michal.
dd will use page cache instead of direct IO? Where can I got dd source 
codes?
One offline question, when should use page cache and when should use 
direct IO?


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