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

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Date:	Tue, 12 May 2009 13:39:57 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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

Christoph Lameter wrote:
> On Tue, 12 May 2009, Rik van Riel wrote:
> 
>> The patch that only allows active file pages to be deactivated
>> if the active file LRU is larger than the inactive file LRU should
>> protect the working set from being evicted due to streaming IO.
> 
> Streaming I/O means access once? 

Yeah, "used-once pages" would be a better criteria, since
you could go through a gigantic set of used-once pages without
doing linear IO.

I expect that some databases might do that.

> What exactly are the criteria for a page
> to be part of streaming I/O? AFAICT the definition is more dependent on
> the software running than on a certain usage pattern discernible to the
> VM. Software may after all perform multiple scans over a stream of data or
> go back to prior locations in the file.


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