linux-kernel - Re: [PATCH mmotm] vmscan move pgdeactivate modification to shrink_active

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Date:	Sat, 29 Aug 2009 14:22:18 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH mmotm] vmscan move pgdeactivate modification to shrink_active_list fix

On Sat, Aug 29, 2009 at 07:00:47PM +0900, KOSAKI Motohiro wrote:
> Hi Hugh
> 
> 2009/8/29 Hugh Dickins <hugh.dickins@...cali.co.uk>:
> > mmotm 2009-08-27-16-51 lets the OOM killer loose on my loads even
> > quicker than last time: one bug fixed but another bug introduced.
> > vmscan-move-pgdeactivate-modification-to-shrink_active_list.patch
> > forgot to add NR_LRU_BASE to lru index to make zone_page_state index.
> >
> > Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
> 
> Can I use your test case?
> Currently LRU_BASE is 0. it mean
> 
> LRU_BASE == NR_INACTIVE_ANON == 0
> LRU_ACTIVE == NR_ACTIVE_ANON == 1

The zone counters are

	NR_FREE_PAGES = 0
	NR_INACTIVE_ANON = NR_LRU_BASE = 1
	NR_ACTIVE_ANON = 2
	...,

and NR_LRU_BASE is the offset of the LRU items within the zone stat
items.  You missed this offset, so accounting to LRU_BASE + 0 *
LRU_FILE actually accounts to NR_FREE_PAGES, not to NR_INACTIVE_ANON.

I get the feeling we should make this thing more robust...

	Hannes

> Therefore, I doubt there are another issue in current mmotm.
> Can I join your strange oom fixing works?
> 
> 
> > ---
> >
> >  mm/vmscan.c |    6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > --- mmotm/mm/vmscan.c   2009-08-28 10:07:57.000000000 +0100
> > +++ linux/mm/vmscan.c   2009-08-28 18:30:33.000000000 +0100
> > @@ -1381,8 +1381,10 @@ static void shrink_active_list(unsigned
> >        reclaim_stat->recent_rotated[file] += nr_rotated;
> >        __count_vm_events(PGDEACTIVATE, nr_deactivated);
> >        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
> > -       __mod_zone_page_state(zone, LRU_ACTIVE + file * LRU_FILE, nr_rotated);
> > -       __mod_zone_page_state(zone, LRU_BASE + file * LRU_FILE, nr_deactivated);
> > +       __mod_zone_page_state(zone, NR_ACTIVE_ANON + file * LRU_FILE,
> > +                                                       nr_rotated);
> > +       __mod_zone_page_state(zone, NR_INACTIVE_ANON + file * LRU_FILE,
> > +                                                       nr_deactivated);
> >        spin_unlock_irq(&zone->lru_lock);
> >  }
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