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Date: Tue, 12 May 2009 13:39:57 -0400
From: Rik van Riel <riel@redhat.com>
Organization: Red Hat, Inc
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To: Christoph Lameter <cl@linux-foundation.org>
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Wu Fengguang <fengguang.wu@intel.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
       "peterz@infradead.org" <peterz@infradead.org>,
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       "elladan@eskimo.com" <elladan@eskimo.com>,
       "npiggin@suse.de" <npiggin@suse.de>,
       "minchan.kim@gmail.com" <minchan.kim@gmail.com>
Subject: Re: [PATCH -mm] vmscan: protect a fraction of file backed mapped
 pages from reclaim
References: <20090508125859.210a2a25.akpm@linux-foundation.org> <20090512025246.GC7518@localhost> <20090512120002.D616.A69D9226@jp.fujitsu.com> <alpine.DEB.1.10.0905121650090.14226@qirst.com> <4A09AC91.4060506@redhat.com> <alpine.DEB.1.10.0905121718040.24066@qirst.com>
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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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