On 08/23/2018 06:21 AM, Michal Hocko wrote: > --- 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]; > } This patch has no practical effect and only adds unnecessary churn. #ifdef CONFIG_SPARSEMEM_EXTREME ... #else struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]; #endif The compiler knows that NR_SECTION_ROOTS==1 and that !mem_section[SECTION_NR_TO_ROOT(nr) is always false. It doesn't need our help. My goal with the sparsemem code, and code in general is t avoid #ifdefs whenever possible and limit their scope to the smallest possible area whenever possible.
