linux-kernel - Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename sc.may_swap to may

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Date:	Tue, 31 Mar 2009 10:52:49 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	nishimura@....nes.nec.co.jp,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Rik van Riel <riel@...hat.com>,
	Balbir Singh <balbir@...ibm.com>
Subject: Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan:
 rename  sc.may_swap to may_unmap)

Hi,

> > ========
> > Subject: vmswan: reintroduce sc->may_swap
> >
> > vmscan-rename-scmay_swap-to-may_unmap.patch removed may_swap flag,
> > but memcg had used it as a flag for "we need to use swap?", as the
> > name indicate.
> >
> > And in current implementation, memcg cannot reclaim mapped file caches
> > when mem+swap hits the limit.
> >
> > re-introduce may_swap flag and handle it at get_scan_ratio().
> > This patch doesn't influence any scan_control users other than memcg.
> >
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > --
> >  mm/vmscan.c |   12 ++++++++++--
> >  1 files changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 3be6157..00ea4a1 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -63,6 +63,9 @@ struct scan_control {
> >        /* Can mapped pages be reclaimed? */
> >        int may_unmap;
> >
> > +       /* Can pages be swapped as part of reclaim? */
> > +       int may_swap;
> > +
> 
> Sorry for too late response.
> I don't know memcg well.
> 
> The memcg managed to use may_swap well with global page reclaim until now.
memcg had a bug that it cannot reclaim mapped file caches when it hit
the mem+swap limit :(


Thanks,
Daisuke Nishimura.
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