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 16:14:31 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"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

On Wed, 13 May 2009, KOSAKI Motohiro wrote:

> > All these expiration modifications do not take into account that a desktop
> > may sit idle for hours while some other things run in the background (like
> > backups at night or updatedb and other maintenance things). This still
> > means that the desktop will be usuable in the morning.
>
> Have you seen this phenomenom?
> I always use linux desktop for development. but I haven't seen it.
> perhaps I have no luck. I really want to know reproduce way.
>
> Please let me know reproduce way.

Run a backup (or rsync) over a few hundred GB.

> > 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.

> key point is access-once vs access-many.

Nothing against it if it works.

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