linux-kernel - Re: [PATCH] mm/memcg: remove redundant checking on root memcg

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Message-ID: <20120717105640.GB25435@tiehlicka.suse.cz>
Date:	Tue, 17 Jul 2012 12:56:40 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>
Subject: Re: [PATCH] mm/memcg: remove redundant checking on root memcg

On Tue 17-07-12 17:42:27, Wanpeng Li wrote:
> Function __mem_cgroup_cancel_local_charge is only called by
> mem_cgroup_move_parent. For this case, root memcg has been
> checked by mem_cgroup_move_parent. So we needn't check that
> again in function __mem_cgroup_cancel_local_charge and just
> remove the check in function __mem_cgroup_cancel_local_charge.

It's true that the check is not necessary but on the other hand
__mem_cgroup_cancel_charge does check it and it would be unfortunate to
have two very similar functions with different expectations (one can be
called for the root cgroup while other one cannot).

> Signed-off-by: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> ---
>  mm/memcontrol.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6392c0a..d346347 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2404,9 +2404,6 @@ static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg,
>  {
>  	unsigned long bytes = nr_pages * PAGE_SIZE;
>  
> -	if (mem_cgroup_is_root(memcg))
> -		return;
> -
>  	res_counter_uncharge_until(&memcg->res, memcg->res.parent, bytes);
>  	if (do_swap_account)
>  		res_counter_uncharge_until(&memcg->memsw,
> -- 
> 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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