From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH] mm: disallow direct reclaim page writeback
Cc: kosaki.motohiro@jp.fujitsu.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
In-Reply-To: <20100415130212.D16E.A69D9226@jp.fujitsu.com>
References: <20100415013436.GO2493@dastard> <20100415130212.D16E.A69D9226@jp.fujitsu.com>
Message-Id: <20100415133332.D183.A69D9226@jp.fujitsu.com>
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Date: Thu, 15 Apr 2010 13:35:17 +0900 (JST)
Sender: linux-kernel-owner@vger.kernel.org
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> Hi
> 
> > How about this? For now, we stop direct reclaim from doing writeback
> > only on order zero allocations, but allow it for higher order
> > allocations. That will prevent the majority of situations where
> > direct reclaim blows the stack and interferes with background
> > writeout, but won't cause lumpy reclaim to change behaviour.
> > This reduces the scope of impact and hence testing and validation
> > the needs to be done.
> 
> Tend to agree. but I would proposed slightly different algorithm for
> avoind incorrect oom.
> 
> for high order allocation
> 	allow to use lumpy reclaim and pageout() for both kswapd and direct reclaim
> 
> for low order allocation
> 	- kswapd:          always delegate io to flusher thread
> 	- direct reclaim:  delegate io to flusher thread only if vm pressure is low
> 
> This seems more safely. I mean Who want see incorrect oom regression?
> I've made some pathes for this. I'll post it as another mail.

Now, kernel compile and/or backup operation seems keep nr_vmscan_write==0.
Dave, can you please try to run your pageout annoying workload?


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