netdev - Re: [PATCH v5 2/2] decrement static keys on real destroy time

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Message-Id: <20120516135755.cdcdf9ba.akpm@linux-foundation.org>
Date:	Wed, 16 May 2012 13:57:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Li Zefan <lizefan@...wei.com>, <cgroups@...r.kernel.org>,
	<linux-mm@...ck.org>, <devel@...nvz.org>,
	<kamezawa.hiroyu@...fujitsu.com>, <netdev@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH v5 2/2] decrement static keys on real destroy time

On Wed, 16 May 2012 11:03:47 +0400
Glauber Costa <glommer@...allels.com> wrote:

> On 05/14/2012 05:38 AM, Li Zefan wrote:
> >> +static void disarm_static_keys(struct mem_cgroup *memcg)
> > 
> >> +{
> >> +#ifdef CONFIG_INET
> >> +	if (memcg->tcp_mem.cg_proto.activated)
> >> +		static_key_slow_dec(&memcg_socket_limit_enabled);
> >> +#endif
> >> +}
> > 
> > 
> > Move this inside the ifdef/endif below ?
> > 
> > Otherwise I think you'll get compile error if !CONFIG_INET...
> 
> I don't fully get it.
> 
> We are supposed to provide a version of it for
> CONFIG_CGROUP_MEM_RES_CTLR_KMEM and an empty version for
> !CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> 
> Inside the first, we take an action for CONFIG_INET, and no action for
> !CONFIG_INET.
> 
> Bear in mind that the slab patches will add another test to that place,
> and that's why I am doing it this way from the beginning.
> 
> Well, that said, I not only can be wrong, I very frequently am.
> 
> But I just compiled this one with and without CONFIG_INET, and it seems
> to be going alright.
> 

Yes, the ifdeffings in that area are rather nasty.

I wonder if it would be simpler to do away with the ifdef nesting. 
At the top-level, just do

#if defined(CONFIG_CGROUP_MEM_RES_CTLR_KMEM) && defined(CONFIG_INET)
static void disarm_static_keys(struct mem_cgroup *memcg)
{
	if (memcg->tcp_mem.cg_proto.activated)
		static_key_slow_dec(&memcg_socket_limit_enabled);
}
#else
static inline void disarm_static_keys(struct mem_cgroup *memcg)
{
}
#endif


The tcp_proto_cgroup() definition could go inside that ifdef as well.
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