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

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Date:	Thu, 15 Apr 2010 15:35:14 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	kosaki.motohiro@...fujitsu.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
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.

Yes. as same as you propsed.

> 
> > 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...

This patch doesn't care stack usage. because
  - again, I think all stack eater shold be diet.
  - under allowing lumpy reclaim world, only deny low order reclaim
    doesn't solve anything.

Please don't forget priority=0 recliam failure incvoke OOM-killer.
I don't imagine anyone want it.

And, Which IO workload trigger <6 priority vmscan?



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