linux-kernel - Re: [RFC][PATCH 5/4] memcg: don't call res_counter

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Message-Id: <20090115114846.388781a7.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 15 Jan 2009 11:48:46 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Li Zefan <lizf@...fujitsu.com>, Paul Menage <menage@...gle.com>
Subject: Re: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge when
 obsolete

On Wed, 14 Jan 2009 19:25:39 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * Daisuke Nishimura <nishimura@....nes.nec.co.jp> [2009-01-14 17:51:21]:
> 
> > This is a new one. Please review.
> > 
> > ===
> > From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > 
> > mem_cgroup_get ensures that the memcg that has been got can be accessed
> > even after the directory has been removed, but it doesn't ensure that parents
> > of it can be accessed: parents might have been freed already by rmdir.
> > 
> > This causes a bug in case of use_hierarchy==1, because res_counter_uncharge
> > climb up the tree.
> > 
> > Check if the memcg is obsolete, and don't call res_counter_uncharge when obsole.
> > 
> > Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> 
> I liked the earlier, EBUSY approach that ensured that parents could
> not go away if children exist. IMHO, the code has gotten too complex
> and has too many corner cases. Time to revisit it.
> 
It's on my plan. 
I'll fix this by CSS-ID patch.

When I recored memcg's CSS-ID to swap_cgroup (not pointer to memcg), 
we never need memcg's refcnt.

Thanks,
-Kame

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