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

[Michal Hocko <mhocko@suse.com>]

On Thu 23-08-18 21:07:30, Wei Yang wrote:
> Each time SECTIONS_PER_ROOT number of mem_section is allocated when
> mem_section[root] is null. This means only (1 / SECTIONS_PER_ROOT) chance
> of the mem_section[root] check is false.
> 
> This patch adds likely to the if check to optimize this a little.

Could you evaluate how much does this help if any? Does this have any
impact on the initialization path at all?

> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> ---
>  mm/sparse.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 10b07eea9a6e..90bab7f03757 100644
> --- 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;
>  
>  	section = sparse_index_alloc(nid);
> -- 
> 2.15.1
> 

-- 
Michal Hocko
SUSE Labs