netdev - Re: [PATCH 2/2] page allocator: Direct reclaim should always obey watermarks

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Message-ID: <20091016223237.GE32397@csn.ul.ie>
Date:	Fri, 16 Oct 2009 23:32:37 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	stable <stable@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	David Miller <davem@...emloft.net>,
	Frans Pop <elendil@...net.nl>,
	reinette chatre <reinette.chatre@...el.com>,
	Kalle Valo <kalle.valo@....fi>,
	"John W. Linville" <linville@...driver.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 2/2] page allocator: Direct reclaim should always obey
	watermarks

On Fri, Oct 16, 2009 at 12:07:07PM -0700, David Rientjes wrote:
> On Fri, 16 Oct 2009, Mel Gorman wrote:
> 
> > ALLOC_NO_WATERMARKS should be cleared when trying to allocate from the
> > free-lists after a direct reclaim. If it's not, __GFP_NOFAIL allocations
> > from a process that is exiting can ignore watermarks. __GFP_NOFAIL is not
> > often used but the journal layer is one of those places. This is suspected of
> > causing an increase in the number of GFP_ATOMIC allocation failures reported.
> > 
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > ---
> >  mm/page_alloc.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index dfa4362..a3e5fed 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1860,7 +1860,8 @@ rebalance:
> >  	page = __alloc_pages_direct_reclaim(gfp_mask, order,
> >  					zonelist, high_zoneidx,
> >  					nodemask,
> > -					alloc_flags, preferred_zone,
> > +					alloc_flags & ~ALLOC_NO_WATERMARKS,
> > +					preferred_zone,
> >  					migratetype, &did_some_progress);
> >  	if (page)
> >  		goto got_pg;
> 
> I don't get it.  __alloc_pages_high_priority() will already loop 
> indefinitely if ALLOC_NO_WATERMARKS is set and its a __GFP_NOFAIL 
> allocation.  How do we even reach this code in such a condition?
> 

Frans, you reported that both patches in combination reduced the number
of failures. Was it in fact just the kswapd change that made the
difference?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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