linux-kernel - Re: [PATCH] mm: memcontrol: avoid unused function warning

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Date:   Wed, 24 Aug 2016 10:41:21 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Vladimir Davydov <vdavydov@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcontrol: avoid unused function warning

On Wed 24-08-16 10:22:43, Arnd Bergmann wrote:
> A bugfix in v4.8-rc2 introduced a harmless warning when CONFIG_MEMCG_SWAP
> is disabled but CONFIG_MEMCG is enabled:
> 
> mm/memcontrol.c:4085:27: error: 'mem_cgroup_id_get_online' defined but not used [-Werror=unused-function]
>  static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
> 
> This adds an extra #ifdef that matches the one around the caller to
> avoid the warning.

Thanks for fixing that! Could you please move the function to the same
ifdef section as its users please.

> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 1f47b61fb407 ("mm: memcontrol: fix swap counter leak on swapout from offline cgroup")

Anyway
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/memcontrol.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2ff0289ad061..e8d787163b65 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4082,6 +4082,7 @@ static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
>  	atomic_add(n, &memcg->id.ref);
>  }
>  
> +#ifdef CONFIG_MEMCG_SWAP
>  static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
>  {
>  	while (!atomic_inc_not_zero(&memcg->id.ref)) {
> @@ -4099,6 +4100,7 @@ static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
>  	}
>  	return memcg;
>  }
> +#endif
>  
>  static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
>  {
> -- 
> 2.9.0
> 
> --
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-- 
Michal Hocko
SUSE Labs