linux-kernel - Re: [patch 03/11] mm: vmscan: distinguish between memcg triggering reclaim and memcg being scanned

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Date:	Thu, 29 Sep 2011 09:55:54 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <bsingharora@...il.com>,
	Ying Han <yinghan@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 03/11] mm: vmscan: distinguish between memcg triggering
 reclaim and memcg being scanned

On Tue, Sep 20, 2011 at 11:17:38AM +0200, Michal Hocko wrote:
> On Tue 20-09-11 10:58:11, Johannes Weiner wrote:
> > On Mon, Sep 19, 2011 at 04:29:55PM +0200, Michal Hocko wrote:
> > > On Mon 12-09-11 12:57:20, Johannes Weiner wrote:
> > > > @@ -2390,6 +2413,18 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
> > > >  }
> > > >  #endif
> > > >  
> > > > +static void age_active_anon(struct zone *zone, struct scan_control *sc,
> > > > +			    int priority)
> > > > +{
> > > > +	struct mem_cgroup_zone mz = {
> > > > +		.mem_cgroup = NULL,
> > > > +		.zone = zone,
> > > > +	};
> > > > +
> > > > +	if (inactive_anon_is_low(&mz))
> > > > +		shrink_active_list(SWAP_CLUSTER_MAX, &mz, sc, priority, 0);
> > > > +}
> > > > +
> > > 
> > > I do not like this very much because we are using a similar construct in
> > > shrink_mem_cgroup_zone so we are duplicating that code. 
> > > What about adding age_mem_cgroup_active_anon (something like shrink_zone).
> > 
> > I am not sure I follow and I don't see what could be shared between
> > the zone shrinking and this as there are different exit conditions to
> > the hierarchy walk.  Can you elaborate?
> 
> Sorry for not being clear enough. Maybe it is not very much important
> but what about something like:
> 
> Index: linus_tree/mm/vmscan.c
> ===================================================================
> --- linus_tree.orig/mm/vmscan.c	2011-09-20 11:07:57.000000000 +0200
> +++ linus_tree/mm/vmscan.c	2011-09-20 11:12:53.000000000 +0200
> @@ -2041,6 +2041,13 @@ static inline bool should_continue_recla
>  	}
>  }
>  
> +static void age_mem_cgroup_active_anon(struct mem_cgroup_zone *mz,
> +		struct scan_control *sc, int priority)
> +{
> +	if (inactive_anon_is_low(mz))
> +		shrink_active_list(SWAP_CLUSTER_MAX, mz, sc, priority, 0);
> +}
> +
>  /*
>   * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
>   */
> @@ -2090,8 +2097,7 @@ restart:
>  	 * Even if we did not try to evict anon pages at all, we want to
>  	 * rebalance the anon lru active/inactive ratio.
>  	 */
> -	if (inactive_anon_is_low(mz))
> -		shrink_active_list(SWAP_CLUSTER_MAX, mz, sc, priority, 0);
> +	age_mem_cgroup_active_anon(mz, sc, priority);
>  
>  	/* reclaim/compaction might need reclaim to continue */
>  	if (should_continue_reclaim(mz, nr_reclaimed,
> @@ -2421,8 +2427,7 @@ static void age_active_anon(struct zone
>  		.zone = zone,
>  	};
>  
> -	if (inactive_anon_is_low(&mz))
> -		shrink_active_list(SWAP_CLUSTER_MAX, &mz, sc, priority, 0);
> +	age_mem_cgroup_active_anon(&mz, sc, priority);
>  }

Ahh, understood.

I think it would be an unrelated change, though.  There already are
two of those constructs, I just move one of them.
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