netdev - Re: [PATCH 4/5] page allocator: Pre-emptively wake kswapd when high-order watermarks are hit

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Date:	Fri, 23 Oct 2009 13:31:10 +0200 (CEST)
From:	Tobias Oetiker <tobi@...iker.ch>
To:	Mel Gorman <mel@....ul.ie>
cc:	David Rientjes <rientjes@...gle.com>,
	Frans Pop <elendil@...net.nl>, Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	David Miller <davem@...emloft.net>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Kalle Valo <kalle.valo@....fi>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mohamed Abbas <mohamed.abbas@...el.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	"John W. Linville" <linville@...driver.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Stephan von Krawczynski <skraw@...net.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 4/5] page allocator: Pre-emptively wake kswapd when
 high-order watermarks are hit

Mel,

Today Mel Gorman wrote:

> On Fri, Oct 23, 2009 at 02:36:53AM -0700, David Rientjes wrote:
> > On Fri, 23 Oct 2009, Mel Gorman wrote:
> >
> > > > Hmm, is this really supposed to be added to __alloc_pages_high_priority()?
> > > > By the patch description I was expecting kswapd to be woken up
> > > > preemptively whenever the preferred zone is below ALLOC_WMARK_LOW and
> > > > we're known to have just allocated at a higher order, not just when
> > > > current was oom killed (when we should already be freeing a _lot_ of
> > > > memory soon) or is doing a higher order allocation during direct reclaim.
> > > >
> > >
> > > It was a somewhat arbitrary choice to have it trigger in the event high
> > > priority allocations were happening frequently.
> > >
> >
> > I don't quite understand, users of PF_MEMALLOC shouldn't be doing these
> > higher order allocations and if ALLOC_NO_WATERMARKS is by way of the oom
> > killer, we should be freeing a substantial amount of memory imminently
> > when it exits that waking up kswapd would be irrelevant.
> >
>
> I agree. I think it's highly unlikely this patch will make any
> difference but I wanted to eliminate it as a possibility. Patch 3 and 4
> were previously one patch that were tested together.

hi hi ... I have tested '3 only' this morning, and the allocation
problems started again ... so for me 3 alone does not work while
3+4 does.

cheers
tobi

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi@...iker.ch ++41 62 775 9902 / sb: -9900
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