Re: [PATCH 2/2] mm: page_alloc: Add unlikely for MAX_ORDER check

[Dave Hansen <dave.hansen@linux.intel.com>]

On 07/28/2013 07:48 AM, SeungHun Lee wrote:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b8475ed..e644cf5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2408,7 +2408,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	 * be using allocators in order of preference for an area that is
>  	 * too large.
>  	 */
> -	if (order >= MAX_ORDER) {
> +	if (unlikely(order >= MAX_ORDER)) {
>  		WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));
>  		return NULL;
>  	}

What problem is this patch solving?  I can see doing this in hot paths,
or places where the compiler is known to be generating bad or suboptimal
code.  but, this costs me 512 bytes of text size:

 898384 Jul 29 15:40 mm/page_alloc.o.nothing
 898896 Jul 29 15:40 mm/page_alloc.o.unlikely

I really don't think we should be adding these without having _concrete_
reasons for it.

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