linux-kernel - Re: [PATCH v3 3/4] memcg: optimize memcg_get_hierarchical

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Message-ID: <20120625094649.GF19805@tiehlicka.suse.cz>
Date:	Mon, 25 Jun 2012 11:46:50 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Wanpeng Li <liwp.linux@...il.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Arun Sharma <asharma@...com>, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: Re: [PATCH v3 3/4] memcg: optimize memcg_get_hierarchical_limit

On Mon 25-06-12 16:44:32, Wanpeng Li wrote:
> From: Wanpeng Li <liwp@...ux.vnet.ibm.com>
> 
> Optimize memcg_get_hierarchical_limit to save cpu cycle.

How did you check that this actually saves some cycles?
There are no (compiler) barriers here so it should reordered.

> Signed-off-by: Wanpeng Li <liwp.linux@...il.com>
> ---
>  mm/memcontrol.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2e81328..4520b57 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3917,9 +3917,9 @@ static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
>  
>  	min_limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
>  	min_memsw_limit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> -	cgroup = memcg->css.cgroup;
>  	if (!memcg->use_hierarchy)
>  		goto out;
> +	cgroup = memcg->css.cgroup;
>  
>  	while (cgroup->parent) {
>  		cgroup = cgroup->parent;
> -- 
> 1.7.9.5
> 

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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