Re: [PATCH 2/3] mm/sparse: expand the CONFIG_SPARSEMEM_EXTREME range in __nr_to_section()

[Michal Hocko <mhocko@suse.com>]

[Cc Dave]

On Thu 23-08-18 21:07:31, Wei Yang wrote:
> When CONFIG_SPARSEMEM_EXTREME is not defined, mem_section is a static
> two dimension array. This means !mem_section[SECTION_NR_TO_ROOT(nr)] is
> always true.
> 
> This patch expand the CONFIG_SPARSEMEM_EXTREME range to return a proper
> mem_section when CONFIG_SPARSEMEM_EXTREME is not defined.

As long as all callers provide a valid section number then yes. I am not
really sure this is the case though.

> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> ---
>  include/linux/mmzone.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 32699b2dc52a..33086f86d1a7 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1155,9 +1155,9 @@ static inline struct mem_section *__nr_to_section(unsigned long nr)
>  #ifdef CONFIG_SPARSEMEM_EXTREME
>  	if (!mem_section)
>  		return NULL;
> -#endif
>  	if (!mem_section[SECTION_NR_TO_ROOT(nr)])
>  		return NULL;
> +#endif
>  	return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
>  }
>  extern int __section_nr(struct mem_section* ms);
> -- 
> 2.15.1
> 

-- 
Michal Hocko
SUSE Labs