From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd
Cc: kosaki.motohiro@jp.fujitsu.com, Suleiman Souhlal <ssouhlal@freebsd.org>,
       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
In-Reply-To: <20100415171142.D192.A69D9226@jp.fujitsu.com>
References: <64BE60A8-EEF9-4AC6-AF0A-0ED3CB544726@freebsd.org> <20100415171142.D192.A69D9226@jp.fujitsu.com>
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Date: Thu, 15 Apr 2010 17:26:27 +0900 (JST)
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Cc to Johannes

> > 
> > 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? :)

Hannes, if my remember is correct, you tried similar swap-cluster IO
long time ago. now I can't remember why we didn't merged such patch.
Do you remember anything?


> 
> 
> > 
> >      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>
> 
> 
> 
> 


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