Re: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge when obsolete

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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

> * Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> [2009-01-14 17:51:21]:
> 
> > This is a new one. Please review.
> > 
> > ===
> > From: Daisuke Nishimura <nishimura@mxp.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 Check if the memcg is obsolete, and don't call res_counter_uncharge when obsole.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@mxp.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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