On Thu 23-08-18 21:07:32, Wei Yang wrote:
> And it is known, __highest_present_section_nr is a more strict boundary
> than NR_MEM_SECTIONS.
>
> This patch uses a __highest_present_section_nr to check a valid pfn.
But why is this an improvement? Sure when you loop over all sections
than __highest_present_section_nr makes a lot of sense. But all the
updated function perform a trivial comparision.
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> ---
> include/linux/mmzone.h | 4 ++--
> mm/sparse.c | 1 +
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 33086f86d1a7..5138efde11ae 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1237,7 +1237,7 @@ extern int __highest_present_section_nr;
> #ifndef CONFIG_HAVE_ARCH_PFN_VALID
> static inline int pfn_valid(unsigned long pfn)
> {
> - if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> + if (pfn_to_section_nr(pfn) > __highest_present_section_nr)
> return 0;
> return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
> }
> @@ -1245,7 +1245,7 @@ static inline int pfn_valid(unsigned long pfn)
>
> static inline int pfn_present(unsigned long pfn)
> {
> - if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> + if (pfn_to_section_nr(pfn) > __highest_present_section_nr)
> return 0;
> return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
> }
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 90bab7f03757..a9c55c8da11f 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -174,6 +174,7 @@ void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
> * those loops early.
> */
> int __highest_present_section_nr;
> +EXPORT_SYMBOL(__highest_present_section_nr);
> static void section_mark_present(struct mem_section *ms)
> {
> int section_nr = __section_nr(ms);
> --
> 2.15.1
>
--
Michal Hocko
SUSE Labs
