linux-kernel - Re: [PATCH -mm] vmscan: protect a fraction of file backed mapped pages from reclaim

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Date:	Thu, 14 May 2009 19:42:48 -0400
From:	Rik van Riel <riel@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>
Subject: Re: [PATCH -mm] vmscan: protect a fraction of file backed mapped
 pages from reclaim

KOSAKI Motohiro wrote:

>>>> The percentage of file backed pages protected is set via
>>>> /proc/sys/vm/file_mapped_ratio. This defaults to 20%.
>>> Why do you think typical mapped ratio is less than 20% on desktop machine?
>> Observation of the typical mapped size of Firefox under KDE.
> 
> My point is, desktop people have very various mapped ratio.
> Do you oppose this?

I suspect that the mapped ratio could be much higher
on my system.  I have only 2GB of RAM dedicated to my
dom0 (which is also my desktop) and the amount of page
cache often goes down to about 150MB.

At the moment nr_mapped is 26400 and the amount of
memory taken up by buffer and page cache together is
a little over 300MB.  That's close to 50%.

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