linux-kernel - Re: [PATCH] memcg: stop warning on memcg_propagate

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Date:	Mon, 4 Feb 2013 09:36:58 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Lord Glauber Costa of Sealand <glommer@...allels.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] memcg: stop warning on memcg_propagate_kmem

On Mon 04-02-13 12:04:06, Glauber Costa wrote:
> On 02/04/2013 11:57 AM, Michal Hocko wrote:
> > On Sun 03-02-13 20:29:01, Hugh Dickins wrote:
> >> Whilst I run the risk of a flogging for disloyalty to the Lord of Sealand,
> >> I do have CONFIG_MEMCG=y CONFIG_MEMCG_KMEM not set, and grow tired of the
> >> "mm/memcontrol.c:4972:12: warning: `memcg_propagate_kmem' defined but not
> >> used [-Wunused-function]" seen in 3.8-rc: move the #ifdef outwards.
> >>
> >> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> > 
> > Acked-by: Michal Hocko <mhocko@...e.cz>
> > 
> > Hmm, if you are not too tired then moving the function downwards to
> > where it is called (memcg_init_kmem) will reduce the number of ifdefs.
> > But this can wait for a bigger clean up which is getting due:
> > git grep "def.*CONFIG_MEMCG_KMEM" mm/memcontrol.c | wc -l
> > 12
> > 
> 
> The problem is that I was usually keeping things in clearly separated
> blocks, like this :
> 
> #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_INET)
>         struct tcp_memcontrol tcp_mem;
> #endif
> #if defined(CONFIG_MEMCG_KMEM)
>         /* analogous to slab_common's slab_caches list. per-memcg */
>         struct list_head memcg_slab_caches;
>         /* Not a spinlock, we can take a lot of time walking the list */
>         struct mutex slab_caches_mutex;
>         /* Index in the kmem_cache->memcg_params->memcg_caches array */
>         int kmemcg_id;
> #endif
> 
> If it would be preferable to everybody, this could be easily rewritten as:
> 
> #if defined(CONFIG_MEMCG_KMEM)
> #if defined(CONFIG_INET)
>         struct tcp_memcontrol tcp_mem;
> #endif
>         /* analogous to slab_common's slab_caches list. per-memcg */
>         struct list_head memcg_slab_caches;
>         /* Not a spinlock, we can take a lot of time walking the list */
>         struct mutex slab_caches_mutex;
>         /* Index in the kmem_cache->memcg_params->memcg_caches array */
>         int kmemcg_id;
> #endif

I was rather interested in reducing CONFIG_KMEM block, the above example
doesn't bother me that much.
 
> This would allow us to collapse some blocks a bit down as well.
> 
> It doesn't bother me *that* much, though.

Yes and a quick attempt shows that a clean up would bring a lot of
churn.
-- 
Michal Hocko
SUSE Labs
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