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

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Date:	Tue, 20 Sep 2011 11:17:38 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <jweiner@...hat.com>
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 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:
[...]
> > > @@ -1853,13 +1865,13 @@ static int vmscan_swappiness(struct scan_control *sc)
> > >   *
> > >   * nr[0] = anon pages to scan; nr[1] = file pages to scan
> > >   */
> > > -static void get_scan_count(struct zone *zone, struct scan_control *sc,
> > > -					unsigned long *nr, int priority)
> > > +static void get_scan_count(struct mem_cgroup_zone *mz, struct scan_control *sc,
> > > +			   unsigned long *nr, int priority)
> > >  {
> > >  	unsigned long anon, file, free;
> > >  	unsigned long anon_prio, file_prio;
> > >  	unsigned long ap, fp;
> > > -	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
> > > +	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
> > >  	u64 fraction[2], denominator;
> > >  	enum lru_list l;
> > >  	int noswap = 0;
> > 
> > You can save some patch lines by:
> > 	struct zone *zone = mz->zone;
> > and not doing zone => mz->zone changes that follow.
> 
> Actually, I really hate that I had to do that local zone variable in
> other places.  I only did it where it's used so often that it would
> have changed every other line.  If you insist, I'll change it, but I
> would prefer to avoid it when possible.

Just a suggestion feel free to ignore it. I have no preference.

> 
> > > @@ -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);
 }
 
 /*

Thanks
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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