linux-kernel - Re: [PATCH] mm: disallow direct reclaim page writeback

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Message-ID: <20100415062055.GQ2493@dastard>
Date:	Thu, 15 Apr 2010 16:20:55 +1000
From:	Dave Chinner <david@...morbit.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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
Subject: Re: [PATCH] mm: disallow direct reclaim page writeback

On Thu, Apr 15, 2010 at 01:09:01PM +0900, KOSAKI Motohiro wrote:
> 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

SO same as current.

> for low order allocation
> 	- kswapd:          always delegate io to flusher thread
> 	- direct reclaim:  delegate io to flusher thread only if vm pressure is low

IMO, this really doesn't fix either of the problems - the bad IO
patterns nor the stack usage. All it will take is a bit more memory
pressure to trigger stack and IO problems, and the user reporting the
problems is generating an awful lot of memory pressure...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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