linux-kernel - Re: mmap vs fs cache

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Message-ID: <513DD0BD.8000400@symas.com>
Date:	Mon, 11 Mar 2013 05:40:29 -0700
From:	Howard Chu <hyc@...as.com>
To:	Jan Kara <jack@...e.cz>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Chris Friesen <chris.friesen@...band.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: mmap vs fs cache

Jan Kara wrote:
> On Fri 08-03-13 12:04:46, Howard Chu wrote:
>> The test clearly is accessing only 30GB of data. Once slapd reaches
>> this process size, the test can be stopped and restarted any number
>> of times, run for any number of hours continuously, and memory use
>> on the system is unchanged, and no pageins occur.
>    Interesting. It might be worth trying what happens if you do
> madvise(..., MADV_DONTNEED) on the data file instead of dropping caches
> with /proc/sys/vm/drop_caches. That way we can establish whether the extra
> cached data is in the data file (things will look the same way as with
> drop_caches) or somewhere else (there will be still unmapped page cache).

I screwed up. My madvise(RANDOM) call used the wrong address/len so it didn't 
cover the whole region. After fixing this, the test now runs as expected - the 
slapd process size grows to 30GB without any problem. Sorry for the noise.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/
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