linux-kernel - Re: [PATCH 2/5] memcg: use array and ID for quick look up

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Message-Id: <20100824164206.37595039.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 24 Aug 2010 16:42:06 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	linux-mm@...ck.org,
	"nishimura\@mxp.nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir\@linux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	m-ikeda@...jp.nec.com,
	"akpm\@linux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	kamezawa.hiroyuki@...il.com
Subject: Re: [PATCH 2/5] memcg: use array and ID for quick look up

On Tue, 24 Aug 2010 00:44:59 -0700
Greg Thelen <gthelen@...gle.com> wrote:

> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:
> 
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >
> > Now, memory cgroup has an ID per cgroup and make use of it at
> >  - hierarchy walk,
> >  - swap recording.
> >
> > This patch is for making more use of it. The final purpose is
> > to replace page_cgroup->mem_cgroup's pointer to an unsigned short.
> >
> > This patch caches a pointer of memcg in an array. By this, we
> > don't have to call css_lookup() which requires radix-hash walk.
> > This saves some amount of memory footprint at lookup memcg via id.
> >
> > Changelog: 20100811
> >  - adjusted onto mmotm-2010-08-11
> >  - fixed RCU related parts.
> >  - use attach_id() callback.
> >
> > Changelog: 20100804
> >  - fixed description in init/Kconfig
> >
> > Changelog: 20100730
> >  - fixed rcu_read_unlock() placement.
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> >  init/Kconfig    |   10 ++++++
> >  mm/memcontrol.c |   83 ++++++++++++++++++++++++++++++++++++++++++--------------
> >  2 files changed, 73 insertions(+), 20 deletions(-)
> >
> > Index: mmotm-0811/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-0811.orig/mm/memcontrol.c
> > +++ mmotm-0811/mm/memcontrol.c
> > @@ -195,6 +195,7 @@ static void mem_cgroup_oom_notify(struct
> >   */
> >  struct mem_cgroup {
> >  	struct cgroup_subsys_state css;
> > +	int	valid; /* for checking validness under RCU access.*/
> >  	/*
> >  	 * the counter to account for memory usage
> >  	 */
> > @@ -294,6 +295,29 @@ static bool move_file(void)
> >  					&mc.to->move_charge_at_immigrate);
> >  }
> >  
> > +/* 0 is unused */
> > +static atomic_t mem_cgroup_num;
> > +#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1)
> > +static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly;
> > +
> > +/* Must be called under rcu_read_lock */
> > +static struct mem_cgroup *id_to_memcg(unsigned short id)
> > +{
> > +	struct mem_cgroup *ret;
> > +	/* see mem_cgroup_free() */
> > +	ret = rcu_dereference_check(mem_cgroups[id], rch_read_lock_held());
> 
> I think this be rcu_read_lock_held() instead of rch_read_lock_held()?
> 
yes, mayb overwritten by following patch.. thank you for finding.


Thanks,
-Kame

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