linux-kernel - Re: [PATCH] mm: only define hashdist variable when needed

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Date:	Wed, 6 May 2015 13:12:45 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: only define hashdist variable when needed

On Mon 04-05-15 17:27:29, Rasmus Villemoes wrote:
> For !CONFIG_NUMA, hashdist will always be 0, since it's setter is
> otherwise compiled out. So we can save 4 bytes of data and some .text
> (although mostly in __init functions) by only defining it for
> CONFIG_NUMA.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Reviewed-by: Michal Hocko <mhocko@...e.cz>

> ---
>  include/linux/bootmem.h | 8 ++++----
>  mm/page_alloc.c         | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
> index 0995c2de8162..f589222bfa87 100644
> --- a/include/linux/bootmem.h
> +++ b/include/linux/bootmem.h
> @@ -357,12 +357,12 @@ extern void *alloc_large_system_hash(const char *tablename,
>  /* Only NUMA needs hash distribution. 64bit NUMA architectures have
>   * sufficient vmalloc space.
>   */
> -#if defined(CONFIG_NUMA) && defined(CONFIG_64BIT)
> -#define HASHDIST_DEFAULT 1
> +#ifdef CONFIG_NUMA
> +#define HASHDIST_DEFAULT IS_ENABLED(CONFIG_64BIT)
> +extern int hashdist;		/* Distribute hashes across NUMA nodes? */
>  #else
> -#define HASHDIST_DEFAULT 0
> +#define hashdist (0)
>  #endif
> -extern int hashdist;		/* Distribute hashes across NUMA nodes? */
>  
>  
>  #endif /* _LINUX_BOOTMEM_H */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ebffa0e4a9c0..159dbbc3375d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6013,9 +6013,9 @@ out:
>  	return ret;
>  }
>  
> +#ifdef CONFIG_NUMA
>  int hashdist = HASHDIST_DEFAULT;
>  
> -#ifdef CONFIG_NUMA
>  static int __init set_hashdist(char *str)
>  {
>  	if (!str)
> -- 
> 2.1.3
> 

-- 
Michal Hocko
SUSE Labs
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