linux-kernel - Re: [PATCHv4 09/11] memcg: Use *_dec_not_zero instead of *_add

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Date:	Wed, 27 Jul 2011 13:58:15 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Sven Eckelmann <sven@...fation.org>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [PATCHv4 09/11] memcg: Use *_dec_not_zero instead of *_add_unless

On Wed 27-07-11 11:47:48, Sven Eckelmann wrote:
> atomic_dec_not_zero is defined for each architecture through
> <linux/atomic.h> to provide the functionality of
> atomic_add_unless(x, -1, 0).

yes, I like it because atomic_dec_* is more consistent (at least from
the code reading) with atomic_inc used by mem_cgroup_mark_under_oom
which.

> 
> Signed-off-by: Sven Eckelmann <sven@...fation.org>
> Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
> Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: linux-mm@...ck.org

Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/memcontrol.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5f84d23..00a7580 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1909,10 +1909,10 @@ static void mem_cgroup_unmark_under_oom(struct mem_cgroup *mem)
>  	/*
>  	 * When a new child is created while the hierarchy is under oom,
>  	 * mem_cgroup_oom_lock() may not be called. We have to use
> -	 * atomic_add_unless() here.
> +	 * atomic_dec_not_zero() here.
>  	 */
>  	for_each_mem_cgroup_tree(iter, mem)
> -		atomic_add_unless(&iter->under_oom, -1, 0);
> +		atomic_dec_not_zero(&iter->under_oom);
>  }
>  
>  static DEFINE_SPINLOCK(memcg_oom_lock);
> -- 
> 1.7.5.4
> 
> --
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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