linux-kernel - Re: [PATCH 1/3] mm/slub: Only define kmalloc_large_node

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Date:   Tue, 23 May 2017 09:56:08 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH 1/3] mm/slub: Only define kmalloc_large_node_hook() for
 NUMA systems

Hi David,

El Mon, May 22, 2017 at 06:35:23PM -0700 David Rientjes ha dit:

> On Mon, 22 May 2017, Andrew Morton wrote:
> 
> > > > Is clang not inlining kmalloc_large_node_hook() for some reason?  I don't 
> > > > think this should ever warn on gcc.
> > > 
> > > clang warns about unused static inline functions outside of header
> > > files, in difference to gcc.
> > 
> > I wish it wouldn't.  These patches just add clutter.
> > 
> 
> Matthias, what breaks if you do this?
> 
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index de179993e039..e1895ce6fa1b 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -15,3 +15,8 @@
>   * with any version that can compile the kernel
>   */
>  #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
> +
> +#ifdef inline
> +#undef inline
> +#define inline __attribute__((unused))
> +#endif

Thanks for the suggestion!

Nothing breaks and the warnings are silenced. It seems we could use
this if there is a stong opposition against having warnings on unused
static inline functions in .c files.

Still I am not convinced that gcc's behavior is preferable in this
case. True, it saves us from adding a bunch of __maybe_unused or
#ifdefs, on the other hand the warning is a useful tool to spot truly
unused code. So far about 50% of the warnings I looked into fall into
this category.