linux-kernel - Re: [PATCH] mm/memcg: wrap mem_cgroup_from

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Date:	Thu, 19 Jul 2012 09:31:29 +0800
From:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/memcg: wrap mem_cgroup_from_css function

On Wed, Jul 18, 2012 at 02:36:12PM -0700, Andrew Morton wrote:
>On Wed, 18 Jul 2012 11:05:30 +0800
>Wanpeng Li <liwanp@...ux.vnet.ibm.com> wrote:
>
>> wrap mem_cgroup_from_css function to clarify get mem cgroup
>> from cgroup_subsys_state.
>
>This certainly adds clarity.
>
>But it also adds a little more type-safety - these container_of() calls
>can be invoked against *any* struct which has a field called "css". 
>With your patch, we add a check that the code is indeed using a
>cgroup_subsys_state*.  A small thing, but it's all good.
>
>
>I changed the patch title to the more idiomatic "memcg: add
>mem_cgroup_from_css() helper" and rewrote the changelog to
>
>: Add a mem_cgroup_from_css() helper to replace open-coded invokations of
>: container_of().  To clarify the code and to add a little more type safety.
>
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -396,6 +396,12 @@ static void mem_cgroup_put(struct mem_cgroup *memcg);
>>  #include <net/sock.h>
>>  #include <net/ip.h>
>>  
>> +static inline
>> +struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
>> +{
>> +	return container_of(s, struct mem_cgroup, css);
>> +}
>
>And with great self-control, I avoided renaming this to
>memcg_from_css().  Sigh.  I guess all that extra typing has cardio
>benefits.

Thank you for your time, Andrew. :-)

Thanks & Best Regards,
Wanpeng Li

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