linux-kernel - Re: [mmotm][PATCH 2/2] memcg: reduce calls for soft limit excess

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Date:	Wed, 2 Sep 2009 14:20:01 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [mmotm][PATCH 2/2] memcg: reduce calls for soft limit excess

On Wed, 2 Sep 2009 14:16:39 +0900
Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:

> On Wed, 2 Sep 2009 09:35:51 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > In charge path, usage_in_excess is calculated repeatedly and
> > it takes res_counter's spin_lock every time.
> > 
> Hmm, mem_cgroup_update_tree() is called in both charge and uncharge path.
> So, this patch have effect on both path, doesn't it ?
> 
> > This patch removes unnecessary calls for res_count_soft_limit_excess.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> >  mm/memcontrol.c |   31 +++++++++++++++----------------
> >  1 file changed, 15 insertions(+), 16 deletions(-)
> > 
> > Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
> > +++ mmotm-2.6.31-Aug27/mm/memcontrol.c
> > @@ -313,7 +313,8 @@ soft_limit_tree_from_page(struct page *p
> >  static void
> >  __mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
> >  				struct mem_cgroup_per_zone *mz,
> > -				struct mem_cgroup_tree_per_zone *mctz)
> > +				struct mem_cgroup_tree_per_zone *mctz,
> > +				unsigned long new_usage_in_excess)
> It might be a nitpick, shouldn't it be unsigned long long ?
> 
Ouch, yes. I'll post fixed one, today.
Thank you for pointing out.

-Kame

> Otherwise, it looks good to me.
> 
> 	Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> 
> Thanks,
> Daisuke Nishimura.
> 
> >  {
> >  	struct rb_node **p = &mctz->rb_root.rb_node;
> >  	struct rb_node *parent = NULL;
> > @@ -322,7 +323,9 @@ __mem_cgroup_insert_exceeded(struct mem_
> >  	if (mz->on_tree)
> >  		return;
> >  
> > -	mz->usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> > +	mz->usage_in_excess = new_usage_in_excess;
> > +	if (!mz->usage_in_excess)
> > +		return;
> >  	while (*p) {
> >  		parent = *p;
> >  		mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
> > @@ -382,7 +385,7 @@ static bool mem_cgroup_soft_limit_check(
> >  
> >  static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
> >  {
> > -	unsigned long long new_usage_in_excess;
> > +	unsigned long long excess;
> >  	struct mem_cgroup_per_zone *mz;
> >  	struct mem_cgroup_tree_per_zone *mctz;
> >  	int nid = page_to_nid(page);
> > @@ -395,25 +398,21 @@ static void mem_cgroup_update_tree(struc
> >  	 */
> >  	for (; mem; mem = parent_mem_cgroup(mem)) {
> >  		mz = mem_cgroup_zoneinfo(mem, nid, zid);
> > -		new_usage_in_excess =
> > -			res_counter_soft_limit_excess(&mem->res);
> > +		excess = res_counter_soft_limit_excess(&mem->res);
> >  		/*
> >  		 * We have to update the tree if mz is on RB-tree or
> >  		 * mem is over its softlimit.
> >  		 */
> > -		if (new_usage_in_excess || mz->on_tree) {
> > +		if (excess || mz->on_tree) {
> >  			spin_lock(&mctz->lock);
> >  			/* if on-tree, remove it */
> >  			if (mz->on_tree)
> >  				__mem_cgroup_remove_exceeded(mem, mz, mctz);
> >  			/*
> > -			 * if over soft limit, insert again. mz->usage_in_excess
> > -			 * will be updated properly.
> > +			 * Insert again. mz->usage_in_excess will be updated.
> > +			 * If excess is 0, no tree ops.
> >  			 */
> > -			if (new_usage_in_excess)
> > -				__mem_cgroup_insert_exceeded(mem, mz, mctz);
> > -			else
> > -				mz->usage_in_excess = 0;
> > +			__mem_cgroup_insert_exceeded(mem, mz, mctz, excess);
> >  			spin_unlock(&mctz->lock);
> >  		}
> >  	}
> > @@ -2216,6 +2215,7 @@ unsigned long mem_cgroup_soft_limit_recl
> >  	unsigned long reclaimed;
> >  	int loop = 0;
> >  	struct mem_cgroup_tree_per_zone *mctz;
> > +	unsigned long long excess;
> >  
> >  	if (order > 0)
> >  		return 0;
> > @@ -2260,9 +2260,8 @@ unsigned long mem_cgroup_soft_limit_recl
> >  				__mem_cgroup_largest_soft_limit_node(mctz);
> >  			} while (next_mz == mz);
> >  		}
> > -		mz->usage_in_excess =
> > -			res_counter_soft_limit_excess(&mz->mem->res);
> >  		__mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
> > +		excess = res_counter_soft_limit_excess(&mz->mem->res);
> >  		/*
> >  		 * One school of thought says that we should not add
> >  		 * back the node to the tree if reclaim returns 0.
> > @@ -2271,8 +2270,8 @@ unsigned long mem_cgroup_soft_limit_recl
> >  		 * memory to reclaim from. Consider this as a longer
> >  		 * term TODO.
> >  		 */
> > -		if (mz->usage_in_excess)
> > -			__mem_cgroup_insert_exceeded(mz->mem, mz, mctz);
> > +		/* If excess == 0, no tree ops */
> > +		__mem_cgroup_insert_exceeded(mz->mem, mz, mctz, excess);
> >  		spin_unlock(&mctz->lock);
> >  		css_put(&mz->mem->css);
> >  		loop++;
> > 
> 

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