linux-kernel - Re: [patch v3 -mm 3/3] vmscan, memcg: Do softlimit reclaim also for targeted reclaim

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Message-ID: <20130516231238.GA15025@mtj.dyndns.org>
Date:	Thu, 16 May 2013 16:12:38 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ying Han <yinghan@...gle.com>, Hugh Dickins <hughd@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	Michel Lespinasse <walken@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [patch v3 -mm 3/3] vmscan, memcg: Do softlimit reclaim also for
 targeted reclaim

On Mon, May 13, 2013 at 09:46:12AM +0200, Michal Hocko wrote:
> Soft reclaim has been done only for the global reclaim (both background
> and direct). Since "memcg: integrate soft reclaim tighter with zone
> shrinking code" there is no reason for this limitation anymore as the
> soft limit reclaim doesn't use any special code paths and it is a
> part of the zone shrinking code which is used by both global and
> targeted reclaims.
...
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

 Reviewed-by: Tejun Heo <tj@...nel.org>

Some nitpicks follow.

>  /*
> - * A group is eligible for the soft limit reclaim if it is
> - * 	a) is over its soft limit
> + * A group is eligible for the soft limit reclaim under the given root
> + * hierarchy if
> + * 	a) it is over its soft limit
>   * 	b) any parent up the hierarchy is over its soft limit

This was added before but in general I think the use of parent for
ancestor is a bit confusing.  Not a big deal but no reason to continue
it.

>  	/*
> -	 * If any parent up the hierarchy is over its soft limit then we
> -	 * have to obey and reclaim from this group as well.
> +	 * If any parent up to the root in the hierarchy is over its soft limit
> +	 * then we have to obey and reclaim from this group as well.

Prolly using terms ancestors and subtree would make the explanation
clearer?

>  static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
>  {
> -	return global_reclaim(sc);
> +	return true;

Kinda silly after this change, maybe just modify shrink_zone() like
the following?

        if (IS_ENABLED(CONFIG_MEMCG)) {
		__shrink_zone(zone, sc, true);
		if (sc->nr_scanned == nr_scanned)
			__shrink_zone(zone, sc, false);
	} else {
		__shrink_zone(zone, sc, false);
        }

> @@ -1974,7 +1974,7 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
>  			struct lruvec *lruvec;
>  
>  			if (soft_reclaim &&
> -					!mem_cgroup_soft_reclaim_eligible(memcg)) {
> +					!mem_cgroup_soft_reclaim_eligible(memcg, root)) {

Weird indentation which breaks line and goes over 80 col, why not do
the following?

		if (soft_reclaim &&
		    !mem_cgroup_soft_reclaim_eligible(memcg, root)) {
			memcg = mem_cgroup_iter(root, memcg, &reclaim);
			continue;
		}

Thanks.

-- 
tejun
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