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SubjectRe: [PATCH 3/3] mm: sparse: remove __section_nr() function
On Fri 02-07-21 18:41:32, Ohhoon Kwon wrote:
> __section_nr() was used to convert struct mem_section * to section_nr.
>
> With CONFIG_SPARSEMEM_EXTREME enabled, however, __section_nr() can be
> costly since it iterates all section roots to check if the given
> mem_section is in its range.
>
> On the other hand, __nr_to_section() which converts section_nr to
> mem_section can be done in O(1).
>
> The only users of __section_nr() was section_mark_present() and
> find_memory_block().
>
> Since I changed both functions to use section_nr directly in the
> preceeding patches, let's remove __section_nr() which has no users.
>
> Signed-off-by: Ohhoon Kwon <ohoono.kwon@samsung.com>

I would go with a much shorter changelog. The function is not used
anymore so it can be simply dropped.
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> include/linux/mmzone.h | 1 -
> mm/sparse.c | 26 --------------------------
> 2 files changed, 27 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 0d53eba1c383..8931f95cf885 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1321,7 +1321,6 @@ static inline struct mem_section *__nr_to_section(unsigned long nr)
> return NULL;
> return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
> }
> -extern unsigned long __section_nr(struct mem_section *ms);
> extern size_t mem_section_usage_size(void);
>
> /*
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 4a2700e9a65f..1b32d15593e4 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -108,32 +108,6 @@ static inline int sparse_index_init(unsigned long section_nr, int nid)
> }
> #endif
>
> -#ifdef CONFIG_SPARSEMEM_EXTREME
> -unsigned long __section_nr(struct mem_section *ms)
> -{
> - unsigned long root_nr;
> - struct mem_section *root = NULL;
> -
> - for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
> - root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
> - if (!root)
> - continue;
> -
> - if ((ms >= root) && (ms < (root + SECTIONS_PER_ROOT)))
> - break;
> - }
> -
> - VM_BUG_ON(!root);
> -
> - return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
> -}
> -#else
> -unsigned long __section_nr(struct mem_section *ms)
> -{
> - return (unsigned long)(ms - mem_section[0]);
> -}
> -#endif
> -
> /*
> * During early boot, before section_mem_map is used for an actual
> * mem_map, we use section_mem_map to store the section's NUMA
> --
> 2.17.1

--
Michal Hocko
SUSE Labs

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