Re: [PATCH v2 02/10] mm/hugetlb: Don't wait for migration entry during follow page

John Hubbard
2022-12-07T22:05:38Z

On 12/7/22 12:30, Peter Xu wrote:
> That's what the code does with !hugetlb pages, so we should logically do
> the same for hugetlb, so migration entry will also be treated as no page.

This reasoning make good sense to me. I looked again at the follow_page*()
paths and just double-checked that this is accurate, and it is.

>
> This is probably also the last piece in follow_page code that may sleep,
> the last one should be removed in cf994dd8af27 ("mm/gup: remove
> FOLL_MIGRATION", 2022-11-16).
>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/hugetlb.c | 11 -----------
> 1 file changed, 11 deletions(-)

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
--
John Hubbard
NVIDIA

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1088f2f41c88..c8a6673fe5b4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6232,7 +6232,6 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> if (WARN_ON_ONCE(flags & FOLL_PIN))
> return NULL;
>
> -retry:
> pte = huge_pte_offset(mm, haddr, huge_page_size(h));
> if (!pte)
> return NULL;
> @@ -6255,16 +6254,6 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> page = NULL;
> goto out;
> }
> - } else {
> - if (is_hugetlb_entry_migration(entry)) {
> - spin_unlock(ptl);
> - __migration_entry_wait_huge(pte, ptl);
> - goto retry;
> - }
> - /*
> - * hwpoisoned entry is treated as no_page_table in
> - * follow_page_mask().
> - */
> }
> out:
> spin_unlock(ptl);