linux-kernel - Re: [PATCH 13/14] Do not compact within a preferred zone after a compaction failure

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Date:	Wed, 7 Apr 2010 02:55:47 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 13/14] Do not compact within a preferred zone after a
 compaction failure

On Tue, Apr 06, 2010 at 05:06:16PM -0700, Andrew Morton wrote:
> > ---
> >  include/linux/compaction.h |   35 +++++++++++++++++++++++++++++++++++
> >  include/linux/mmzone.h     |    7 +++++++
> >  mm/page_alloc.c            |    5 ++++-
> >  3 files changed, 46 insertions(+), 1 deletions(-)
> > 
> > diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> > index ae98afc..2a02719 100644
> > --- a/include/linux/compaction.h
> > +++ b/include/linux/compaction.h
> > @@ -18,6 +18,32 @@ extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
> >  extern int fragmentation_index(struct zone *zone, unsigned int order);
> >  extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
> >  			int order, gfp_t gfp_mask, nodemask_t *mask);
> > +
> > +/* defer_compaction - Do not compact within a zone until a given time */
> > +static inline void defer_compaction(struct zone *zone, unsigned long resume)
> > +{
> > +	/*
> > +	 * This function is called when compaction fails to result in a page
> > +	 * allocation success. This is somewhat unsatisfactory as the failure
> > +	 * to compact has nothing to do with time and everything to do with
> > +	 * the requested order, the number of free pages and watermarks. How
> > +	 * to wait on that is more unclear, but the answer would apply to
> > +	 * other areas where the VM waits based on time.
> > +	 */
> 
> c'mon, let's not make this rod for our backs.

Actually I skipped this one in the unified tree (I'm running both
patchsets at the same time as I write this and I should have tweaked
it so that the defrag sysfs control in transparent hugepage turns
memory compaction on and off, plus I embedded the
set_recommended_min_free_kbytes() code inside huge_memory.c
initialization). I merged the whole V7 except the above. It also
didn't pass my threshold, also because this only checks 1 jiffy that
is random and too short to matter.
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