Date: Thu, 4 Dec 2008 18:34:28 +0900
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>,
       "kosaki.motohiro@jp.fujitsu.com" <kosaki.motohiro@jp.fujitsu.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "lizf@cn.fujitsu.com" <lizf@cn.fujitsu.com>,
       Paul Menage <menage@google.com>, nishimura@mxp.nes.nec.co.jp
Subject: Re: [Experimental][PATCH 19/21] memcg-fix-pre-destroy.patch
Message-Id: <20081204183428.19cbd22d.nishimura@mxp.nes.nec.co.jp>
In-Reply-To: <20081203141117.d3685413.kamezawa.hiroyu@jp.fujitsu.com>
References: <20081203134718.6b60986f.kamezawa.hiroyu@jp.fujitsu.com>
	<20081203141117.d3685413.kamezawa.hiroyu@jp.fujitsu.com>
Organization: NEC Soft, Ltd.
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1136
Lines: 31

Added CC: Paul Menage <menage@google.com>

> @@ -2096,7 +2112,7 @@ static void mem_cgroup_get(struct mem_cg
>  static void mem_cgroup_put(struct mem_cgroup *mem)
>  {
>  	if (atomic_dec_and_test(&mem->refcnt)) {
> -		if (!mem->obsolete)
> +		if (!css_under_removal(&mem->css))
>  			return;
>  		mem_cgroup_free(mem);
>  	}
I don't think it's safe to check css_under_removal here w/o cgroup_lock.
(It's safe *NOW* just because memcg is the only user of css->refcnt.)

As Li said before, css_under_removal doesn't necessarily mean
this this group has been destroyed, but mem_cgroup will be freed.

But adding cgroup_lock/unlock here causes another dead lock,
because mem_cgroup_get_next_node calls mem_cgroup_put.

hmm.. hierarchical reclaim code will be re-written completely by [21/21],
so would it be better to change patch order or to take another approach ?


Thanks,
Daisuke Nishimura.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/