Re: [PATCH 2/3] page allocator: Do not allow interrupts to use ALLOC_HARDER

[Mel Gorman <mel@csn.ul.ie>]

On Tue, Oct 27, 2009 at 01:09:24PM -0700, Andrew Morton wrote:
> On Tue, 27 Oct 2009 13:40:32 +0000
> Mel Gorman <mel@csn.ul.ie> wrote:
> 
> > Commit 341ce06f69abfafa31b9468410a13dbd60e2b237 altered watermark logic
> > slightly by allowing rt_tasks that are handling an interrupt to set
> > ALLOC_HARDER. This patch brings the watermark logic more in line with
> > 2.6.30.
> > 
> > [rientjes@google.com: Spotted the problem]
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
> > Reviewed-by: Rik van Riel <riel@redhat.com>
> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > ---
> >  mm/page_alloc.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index dfa4362..7f2aa3e 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1769,7 +1769,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
> >  		 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
> >  		 */
> >  		alloc_flags &= ~ALLOC_CPUSET;
> > -	} else if (unlikely(rt_task(p)))
> > +	} else if (unlikely(rt_task(p)) && !in_interrupt())
> >  		alloc_flags |= ALLOC_HARDER;
> >  
> >  	if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
> 
> What are the runtime-observeable effects of this change?
> 

A reduction of high-order GFP_ATOMIC allocation failures reported 

http://www.gossamer-threads.com/lists/linux/kernel/1144153

> The description is a bit waffly-sounding for a -stable backportable
> thing, IMO.  What reason do the -stable maintainers and users have to
> believe that this patch is needed, and an improvement?
> 

Allocation failure reports are occuring against 2.6.31.4 that did not
occur in 2.6.30. The bug reporter observes no such allocation failures
with this and the previous patch applied. The data is fuzzier than I'd
like but both patches do appear to be required.

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

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