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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Suleiman Souhlal <ssouhlal@freebsd.org>
Subject: Re: [PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd
Cc: kosaki.motohiro@jp.fujitsu.com, Dave Chinner <david@fromorbit.com>,
       Mel Gorman <mel@csn.ul.ie>, Chris Mason <chris.mason@oracle.com>,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       linux-fsdevel@vger.kernel.org, suleiman@google.com
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Date: Thu, 15 Apr 2010 17:17:33 +0900 (JST)
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> 
> On Apr 14, 2010, at 9:11 PM, KOSAKI Motohiro wrote:
> 
> > Now, vmscan pageout() is one of IO throuput degression source.
> > Some IO workload makes very much order-0 allocation and reclaim
> > and pageout's 4K IOs are making annoying lots seeks.
> >
> > At least, kswapd can avoid such pageout() because kswapd don't
> > need to consider OOM-Killer situation. that's no risk.
> >
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> 
> What's your opinion on trying to cluster the writes done by pageout,  
> instead of not doing any paging out in kswapd?
> Something along these lines:

Interesting. 
So, I'd like to review your patch carefully. can you please give me one
day? :)


> 
>      Cluster writes to disk due to memory pressure.
> 
>      Write out logically adjacent pages to the one we're paging out
>      so that we may get better IOs in these situations:
>      These pages are likely to be contiguous on disk to the one we're
>      writing out, so they should get merged into a single disk IO.
> 
>      Signed-off-by: Suleiman Souhlal <suleiman@google.com>