Re: [PATCH] mm: memcontrol.c: move mem_cgroup_id_get_many under CONFIG_MMU

[Chris Down]

Hi Kuninori,

Michal Hocko writes:
> On Tue 17-12-19 15:47:40, Kuninori Morimoto wrote:
> > From: Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx>
> >
> > mem_cgroup_id_get_many() is used under CONFIG_MMU.
>
> Not really. It is used when SWAP is enabled currently. But it is not
> really bound to the swap functionality by any means. It just happens
> that we do not have other users currently. We might put it under
> CONFIG_SWAP but I do not really think it is a big improvement.

Agreed, I think we shouldn't wrap this in preprocessor conditionals it since 
it's entirely possible it will end up used elsewhere and we'll end up with a 
mess of #ifdefs.

> > This patch moves it to under CONFIG_MMU.
> > We will get below warning without this patch
> > if .config doesn't have CONFIG_MMU.
> >
> > 	LINUX/mm/memcontrol.c:4814:13: warning: 'mem_cgroup_id_get_many'\
> > 		defined but not used [-Wunused-function]
> > 	static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
> > 	^~~~~~~~~~~~~~~~~~~~~~
>
> Is this warning really a big deal? The function is not used, alright,
> and the compiler will likely just drop it.

Let's just add __maybe_unused, since it seems like what we want in this 
scenario -- it avoids new users having to enter preprocessor madness, while 
also not polluting the build output.

Once you've done that, I'll send over my ack. :-)

Thanks.