linux-kernel - Re: [PATCH 2/2] memcg: clean up force_empty

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Message-Id: <20120619165815.5ce24be7.akpm@linux-foundation.org>
Date:	Tue, 19 Jun 2012 16:58:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	cgroups@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/2] memcg: clean up force_empty_list() return value
 check

On Mon, 18 Jun 2012 20:59:44 +0900
Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> 
> By commit "memcg: move charges to root cgroup if use_hierarchy=0"
> mem_cgroup_move_parent() only returns -EBUSY, -EINVAL.
> So, we can remove -ENOMEM and -EINTR checks.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  mm/memcontrol.c |    5 -----
>  1 files changed, 0 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index cf8a0f6..726b7c6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3847,8 +3847,6 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
>  		pc = lookup_page_cgroup(page);
>  
>  		ret = mem_cgroup_move_parent(page, pc, memcg, GFP_KERNEL);
> -		if (ret == -ENOMEM || ret == -EINTR)
> -			break;
>  
>  		if (ret == -EBUSY || ret == -EINVAL) {

This looks a bit fragile - if mem_cgroup_move_parent() is later changed
(intentionally or otherwise!) to return -Esomethingelse then
mem_cgroup_force_empty_list() will subtly break.  Why not just do

		if (ret < 0)

here?


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