Re: [PATCH] mm/slab: make calculate_alignment() function static

[Michal Hocko]

On Sun 10-12-17 17:01:32, Byongho Lee wrote:
> calculate_alignment() function is only used inside 'slab_common.c'.
> So make it static and let compiler do more optimizations.
> 
> After this patch there's small improvements in 'text' and 'data' size.
> 
> $ gcc --version
>   gcc (GCC) 7.2.1 20171128
> 
> Before:
>   text	   data	    bss	    dec	     hex	filename
>   9890457  3828702  1212364 14931523 e3d643	vmlinux
> 
> After:
>   text	   data	    bss	    dec	     hex	filename
>   9890437  3828670  1212364 14931471 e3d60f	vmlinux
> 
> Also I fixed a 'style problem' reported by 'scripts/checkpatch.pl'.
> 
>   WARNING: Missing a blank line after declarations
>   #53: FILE: mm/slab_common.c:286:
>   +		unsigned long ralign = cache_line_size();
>   +		while (size <= ralign / 2)
> 
> Signed-off-by: Byongho Lee <bhlee.kernel@xxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  mm/slab.h        |  3 ---
>  mm/slab_common.c | 56 +++++++++++++++++++++++++++++---------------------------
>  2 files changed, 29 insertions(+), 30 deletions(-)
> 
> diff --git a/mm/slab.h b/mm/slab.h
> index 028cdc7df67e..e894889dc24a 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -79,9 +79,6 @@ extern const struct kmalloc_info_struct {
>  	unsigned long size;
>  } kmalloc_info[];
>  
> -unsigned long calculate_alignment(unsigned long flags,
> -		unsigned long align, unsigned long size);
> -
>  #ifndef CONFIG_SLOB
>  /* Kmalloc array related functions */
>  void setup_kmalloc_cache_index_table(void);
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 0d7fe71ff5e4..d25e7b56e20b 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -267,6 +267,35 @@ static inline void memcg_unlink_cache(struct kmem_cache *s)
>  }
>  #endif /* CONFIG_MEMCG && !CONFIG_SLOB */
>  
> +/*
> + * Figure out what the alignment of the objects will be given a set of
> + * flags, a user specified alignment and the size of the objects.
> + */
> +static unsigned long calculate_alignment(unsigned long flags,
> +		unsigned long align, unsigned long size)
> +{
> +	/*
> +	 * If the user wants hardware cache aligned objects then follow that
> +	 * suggestion if the object is sufficiently large.
> +	 *
> +	 * The hardware cache alignment cannot override the specified
> +	 * alignment though. If that is greater then use it.
> +	 */
> +	if (flags & SLAB_HWCACHE_ALIGN) {
> +		unsigned long ralign;
> +
> +		ralign = cache_line_size();
> +		while (size <= ralign / 2)
> +			ralign /= 2;
> +		align = max(align, ralign);
> +	}
> +
> +	if (align < ARCH_SLAB_MINALIGN)
> +		align = ARCH_SLAB_MINALIGN;
> +
> +	return ALIGN(align, sizeof(void *));
> +}
> +
>  /*
>   * Find a mergeable slab cache
>   */
> @@ -337,33 +366,6 @@ struct kmem_cache *find_mergeable(size_t size, size_t align,
>  	return NULL;
>  }
>  
> -/*
> - * Figure out what the alignment of the objects will be given a set of
> - * flags, a user specified alignment and the size of the objects.
> - */
> -unsigned long calculate_alignment(unsigned long flags,
> -		unsigned long align, unsigned long size)
> -{
> -	/*
> -	 * If the user wants hardware cache aligned objects then follow that
> -	 * suggestion if the object is sufficiently large.
> -	 *
> -	 * The hardware cache alignment cannot override the specified
> -	 * alignment though. If that is greater then use it.
> -	 */
> -	if (flags & SLAB_HWCACHE_ALIGN) {
> -		unsigned long ralign = cache_line_size();
> -		while (size <= ralign / 2)
> -			ralign /= 2;
> -		align = max(align, ralign);
> -	}
> -
> -	if (align < ARCH_SLAB_MINALIGN)
> -		align = ARCH_SLAB_MINALIGN;
> -
> -	return ALIGN(align, sizeof(void *));
> -}
> -
>  static struct kmem_cache *create_cache(const char *name,
>  		size_t object_size, size_t size, size_t align,
>  		unsigned long flags, void (*ctor)(void *),
> -- 
> 2.15.1
> 
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-- 
Michal Hocko
SUSE Labs