linux-kernel - Re: [PATCH 12/19] mm: migrate: Introduce migrate_misplaced

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Date:	Tue, 13 Nov 2012 11:56:24 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 12/19] mm: migrate: Introduce migrate_misplaced_page()

On Tue, Nov 13, 2012 at 12:43:44PM +0100, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > * Mel Gorman <mgorman@...e.de> wrote:
> > 
> > > From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > 
> > > Note: This was originally based on Peter's patch "mm/migrate: Introduce
> > > 	migrate_misplaced_page()" but borrows extremely heavily from Andrea's
> > > 	"autonuma: memory follows CPU algorithm and task/mm_autonuma stats
> > > 	collection". The end result is barely recognisable so signed-offs
> > > 	had to be dropped. If original authors are ok with it, I'll
> > > 	re-add the signed-off-bys.
> > > 
> > > Add migrate_misplaced_page() which deals with migrating pages from
> > > faults.
> > > 
> > > Based-on-work-by: Lee Schermerhorn <Lee.Schermerhorn@...com>
> > > Based-on-work-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > Based-on-work-by: Andrea Arcangeli <aarcange@...hat.com>
> > > Signed-off-by: Mel Gorman <mgorman@...e.de>
> > > ---
> > >  include/linux/migrate.h |    8 ++++
> > >  mm/migrate.c            |  104 ++++++++++++++++++++++++++++++++++++++++++++++-
> > >  2 files changed, 110 insertions(+), 2 deletions(-)
> > 
> > That's a nice patch - the TASK_NUMA_FAULT approach in the 
> > original patch was not very elegant.
> > 
> > I've started testing it to see how well your version works.
> 
> Hm, I'm seeing some instability - see the boot crash below. If I 
> undo your patch it goes away.
> 

Hah, I would not describe a "boot crash" as some instability. That's
just outright broken :)

I've not built at tree with the latest of Peter's code yet so I don't
know at this time which line it is BUG()ing on. However, it is *very*
likely that this patch is not a drop-in replacement for your tree
because IIRC, there are differences in how and when we call get_page().
That is the likely source of the snag.

-- 
Mel Gorman
SUSE Labs
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