linux-kernel - Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

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Message-Id: <20080905105137.5A47.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Fri, 05 Sep 2008 10:52:10 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

> > Hi Andy,
> > 
> > I like almost part of your patch.
> > (at least, I can ack patch 1/4 - 3/4)
> > 
> > So, I worry about OOM risk.
> > Can you remember desired page size to capture list (or any other location)?
> > if possible, __capture_on_page can avoid to capture unnecessary pages.
> > 
> > So, if __capture_on_page() can make desired size page by buddy merging, 
> > it can free other pages on capture_list.
> > 
> > In worst case, shrink_zone() is called by very much process at the same time.
> > Then, if each process doesn't back few pages, very many pages doesn't be backed.
> 
> The testing we have done pushes the system pretty damn hard, about as
> hard as you can.  Without the zone watermark checks in capture we would
> periodically lose a test to an OOM.  Since adding that I have never seen
> an OOM, so I am confident we are safe.  That said, clearly some wider
> testing in -mm would be very desirable to confirm that this does not
> tickle OOM for some unexpected workload.
>
> I think the idea of trying to short-circuit capture once it has a page
> of the requisit order or greater is eminently sensible.  I suspect we
> are going to have trouble getting the information to the right place,
> but it is clearly worth investigating.  It feels like a logical step on
> top of this, so I would propose to do it as a patch on top of this set.
> 
> Thanks for your feedback.

Ok. makes sense.
Thanks for good patch.

Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>



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