linux-kernel - Re: [PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd

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Message-Id: <20100415172215.D19B.A69D9226@jp.fujitsu.com>
Date:	Thu, 15 Apr 2010 17:26:27 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Suleiman Souhlal <ssouhlal@...ebsd.org>,
	Dave Chinner <david@...morbit.com>, Mel Gorman <mel@....ul.ie>,
	Chris Mason <chris.mason@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, suleiman@...gle.com
Subject: Re: [PATCH 1/4] vmscan: delegate pageout io to flusher thread if current is kswapd

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@...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@...gle.com>
> 
> 
> 
> 



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