linux-kernel - Re: [PATCH] mm: Make mem_cgroup_id_get_many dependent on MMU and MEMCG

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Message-ID: <20200304165336.GO16139@dhcp22.suse.cz>
Date:   Wed, 4 Mar 2020 17:53:36 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: Make mem_cgroup_id_get_many dependent on MMU and
 MEMCG_SWAP

On Wed 04-03-20 14:23:48, Vincenzo Frascino wrote:
> mem_cgroup_id_get_many() is currently used only when MMU or MEMCG_SWAP
> configuration options are enabled. Having them disabled triggers the
> following warning at compile time:
> 
> linux/mm/memcontrol.c:4797:13: 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)
> 
> Make mem_cgroup_id_get_many() dependent on MMU and MEMCG_SWAP to address
> the issue.

A similar patch has been proposed recently
http://lkml.kernel.org/r/87fthjh2ib.wl-kuninori.morimoto.gx@renesas.com.
The conclusion was that the warning is not really worth adding code.

> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> ---
>  mm/memcontrol.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d09776cd6e10..628cebeb4bdd 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4794,10 +4794,12 @@ static void mem_cgroup_id_remove(struct mem_cgroup *memcg)
>  	}
>  }
>  
> +#if defined(CONFIG_MEMCG_SWAP) || defined(CONFIG_MMU)
>  static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
>  {
>  	refcount_add(n, &memcg->id.ref);
>  }
> +#endif
>  
>  static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
>  {
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs