linux-kernel - Re: [rfc patch 2/6] vmscan: make distinction between memcg reclaim and LRU list selection

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Message-ID: <20110513065854.GB18610@cmpxchg.org>
Date:	Fri, 13 May 2011 08:58:54 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ying Han <yinghan@...gle.com>, Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc patch 2/6] vmscan: make distinction between memcg reclaim
 and LRU list selection

On Fri, May 13, 2011 at 08:50:27AM +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 12 May 2011 16:53:54 +0200
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > The reclaim code has a single predicate for whether it currently
> > reclaims on behalf of a memory cgroup, as well as whether it is
> > reclaiming from the global LRU list or a memory cgroup LRU list.
> > 
> > Up to now, both cases always coincide, but subsequent patches will
> > change things such that global reclaim will scan memory cgroup lists.
> > 
> > This patch adds a new predicate that tells global reclaim from memory
> > cgroup reclaim, and then changes all callsites that are actually about
> > global reclaim heuristics rather than strict LRU list selection.
> > 
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> 
> 
> Hmm, isn't it better to merge this to patches where the meaning of
> new variable gets clearer ?

I apologize for the confusing order.  I am going to merge them.

> >  mm/vmscan.c |   96 ++++++++++++++++++++++++++++++++++------------------------
> >  1 files changed, 56 insertions(+), 40 deletions(-)
> > 
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index f6b435c..ceeb2a5 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -104,8 +104,12 @@ struct scan_control {
> >  	 */
> >  	reclaim_mode_t reclaim_mode;
> >  
> > -	/* Which cgroup do we reclaim from */
> > -	struct mem_cgroup *mem_cgroup;
> > +	/*
> > +	 * The memory cgroup we reclaim on behalf of, and the one we
> > +	 * are currently reclaiming from.
> > +	 */
> > +	struct mem_cgroup *memcg;
> > +	struct mem_cgroup *current_memcg;
> >  
> 
> I wonder if you avoid renaming exisiting one, the patch will
> be clearer...

I renamed it mostly because I thought current_mem_cgroup too long.
It's probably best if both get more descriptive names.

> > @@ -154,16 +158,24 @@ static LIST_HEAD(shrinker_list);
> >  static DECLARE_RWSEM(shrinker_rwsem);
> >  
> >  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > -#define scanning_global_lru(sc)	(!(sc)->mem_cgroup)
> > +static bool global_reclaim(struct scan_control *sc)
> > +{
> > +	return !sc->memcg;
> > +}
> > +static bool scanning_global_lru(struct scan_control *sc)
> > +{
> > +	return !sc->current_memcg;
> > +}
> 
> 
> Could you add comments ?

Yes, I will.

Thanks for your input!
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