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Date: Wed, 29 Sep 2010 23:02:52 +0900
From: Daisuke Nishimura <d-nishimura@mtf.biglobe.ne.jp>
To: "Kirill A. Shutsemov" <kirill@shutemov.name>
Cc: linux-mm@kvack.org, Balbir Singh <balbir@linux.vnet.ibm.com>,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [BUGFIX][PATCH] memcg: fix thresholds with use_hierarchy == 1
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On Wed, 29 Sep 2010 15:27:25 +0300
"Kirill A. Shutsemov" <kirill@shutemov.name> wrote:

> From: Kirill A. Shutemov <kirill@shutemov.name>
> 
> We need to check parent's thresholds if parent has use_hierarchy == 1 to
> be sure that parent's threshold events will be triggered even if parent
> itself is not active (no MEM_CGROUP_EVENTS).
> 
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> ---
>  mm/memcontrol.c |   17 ++++++++++++++---
>  1 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3eed583..196f710 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3587,9 +3587,20 @@ unlock:
>  
>  static void mem_cgroup_threshold(struct mem_cgroup *memcg)
>  {
> -	__mem_cgroup_threshold(memcg, false);
> -	if (do_swap_account)
> -		__mem_cgroup_threshold(memcg, true);
> +	struct cgroup *parent;
> +
> +	while (1) {
> +		__mem_cgroup_threshold(memcg, false);
> +		if (do_swap_account)
> +			__mem_cgroup_threshold(memcg, true);
> +
> +		parent = memcg->css.cgroup->parent;
> +		if (!parent)
> +			break;
> +		memcg = mem_cgroup_from_cont(parent);
> +		if (!memcg->use_hierarchy)
> +			break;
> +	}
I think you can simplify this part by using parent_mem_cgroup() like:

	parent = parent_mem_cgroup(memcg);
	if (!memcg)
		break;

Thanks,
Daisuke Nishimura.