Re: [PATCH 1/3] mm/sparse: add likely to mem_section[root] check in sparse_index_init()

[Dave Hansen <dave.hansen@xxxxxxxxx>]

On 08/23/2018 06:07 AM, Wei Yang wrote:
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -78,7 +78,7 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
>  	unsigned long root = SECTION_NR_TO_ROOT(section_nr);
>  	struct mem_section *section;
>  
> -	if (mem_section[root])
> +	if (likely(mem_section[root]))
>  		return -EEXIST;

We could add likely()/unlikely() to approximately a billion if()s around
the kernel if we felt like it.  We don't because it's messy and it
actually takes away choices from the compiler.

Please don't send patches like this unless you have some *actual*
analysis that shows the benefit of the patch.  Performance numbers are best.