On Mon 08-03-21 18:28:07, Muchun Song wrote:
> When the "struct page size" crosses page boundaries we cannot
> make use of this feature. Let free_vmemmap_pages_per_hpage()
> return zero if that is the case, most of the functions can be
> optimized away.
I am confused. Don't you check for this in early_hugetlb_free_vmemmap_param already?
Why do we need any runtime checks?
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> Tested-by: Chen Huang <chenhuang5@xxxxxxxxxx>
> Tested-by: Bodeddula Balasubramaniam <bodeddub@xxxxxxxxxx>
> ---
> include/linux/hugetlb.h | 3 ++-
> mm/hugetlb_vmemmap.c | 7 +++++++
> mm/hugetlb_vmemmap.h | 6 ++++++
> 3 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index c70421e26189..333dd0479fc2 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -880,7 +880,8 @@ extern bool hugetlb_free_vmemmap_enabled;
>
> static inline bool is_hugetlb_free_vmemmap_enabled(void)
> {
> - return hugetlb_free_vmemmap_enabled;
> + return hugetlb_free_vmemmap_enabled &&
> + is_power_of_2(sizeof(struct page));
> }
> #else
> static inline bool is_hugetlb_free_vmemmap_enabled(void)
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 33e42678abe3..1ba1ef45c48c 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -265,6 +265,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> BUILD_BUG_ON(__NR_USED_SUBPAGE >=
> RESERVE_VMEMMAP_SIZE / sizeof(struct page));
>
> + /*
> + * The compiler can help us to optimize this function to null
> + * when the size of the struct page is not power of 2.
> + */
> + if (!is_power_of_2(sizeof(struct page)))
> + return;
> +
> if (!hugetlb_free_vmemmap_enabled)
> return;
>
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index cb2bef8f9e73..29aaaf7b741e 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -21,6 +21,12 @@ void hugetlb_vmemmap_init(struct hstate *h);
> */
> static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> {
> + /*
> + * This check aims to let the compiler help us optimize the code as
> + * much as possible.
> + */
> + if (!is_power_of_2(sizeof(struct page)))
> + return 0;
> return h->nr_free_vmemmap_pages;
> }
> #else
> --
> 2.11.0
>
--
Michal Hocko
SUSE Labs
