Le 02/09/2022 à 21:03, Mike Kravetz a écrit :
> During discussions of this series [1], it was suggested that hugetlb
> handling code in follow_page_mask could be simplified. At the beginning
> of follow_page_mask, there currently is a call to follow_huge_addr which
> 'may' handle hugetlb pages. ia64 is the only architecture which provides
> a follow_huge_addr routine that does not return error. Instead, at each
> level of the page table a check is made for a hugetlb entry. If a hugetlb
> entry is found, a call to a routine associated with that entry is made.
>
> Currently, there are two checks for hugetlb entries at each page table
> level. The first check is of the form:
> if (p?d_huge())
> page = follow_huge_p?d();
> the second check is of the form:
> if (is_hugepd())
> page = follow_huge_pd().
>
> We can replace these checks, as well as the special handling routines
> such as follow_huge_p?d() and follow_huge_pd() with a single routine to
> handle hugetlb vmas.
>
> A new routine hugetlb_follow_page_mask is called for hugetlb vmas at the
> beginning of follow_page_mask. hugetlb_follow_page_mask will use the
> existing routine huge_pte_offset to walk page tables looking for hugetlb
> entries. huge_pte_offset can be overwritten by architectures, and already
> handles special cases such as hugepd entries.
>
> [1]
> https://lore.kernel.org/linux-mm/cover.1661240170.git.baolin.w...@linux.alibaba.com/
>
> Suggested-by: David Hildenbrand <da...@redhat.com>
> Signed-off-by: Mike Kravetz <mike.krav...@oracle.com>
> ---
> v2 - Added WARN_ON_ONCE() and updated comment as suggested by David
> Fixed build issue found by kernel test robot
> Added vma (pmd sharing) locking to hugetlb_follow_page_mask
> ReBased on Baolin's patch to fix issues with CONT_* entries
>
> arch/ia64/mm/hugetlbpage.c | 15 ---
> arch/powerpc/mm/hugetlbpage.c | 37 -------
> include/linux/hugetlb.h | 51 ++--------
> mm/gup.c | 80 +++------------
> mm/hugetlb.c | 182 ++++++++++++----------------------
> 5 files changed, 87 insertions(+), 278 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index fe4944f89d34..275e554dd365 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -264,6 +255,13 @@ static inline void adjust_range_if_pmd_sharing_possible(
> {
> }
>
> +static inline struct page *hugetlb_follow_page_mask(struct vm_area_struct
> *vma,
> + unsigned long address, unsigned int flags)
> +{
> + WARN_ON_ONCE(1); /* should never be called if !CONFIG_HUGETLB_PAGE*/
> + return ERR_PTR(-EINVAL);
This function is called only when is_vm_hugetlb_page() is true.
When !CONFIG_HUGETLB_PAGE is_vm_hugetlb_page() always returns false, so
the call to hugetlb_follow_page_mask() should never be compiled in.
Use BUILD_BUG() to catch it at buildtime.
> +}
> +
> static inline long follow_hugetlb_page(struct mm_struct *mm,
> struct vm_area_struct *vma, struct page **pages,
> struct vm_area_struct **vmas, unsigned long *position,
> diff --git a/mm/gup.c b/mm/gup.c
> index 7691c65233c3..1515892a9d98 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -530,18 +530,6 @@ static struct page *follow_page_pte(struct
> vm_area_struct *vma,
> if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> (FOLL_PIN | FOLL_GET)))
> return ERR_PTR(-EINVAL);
> -
> - /*
> - * Considering PTE level hugetlb, like continuous-PTE hugetlb on
> - * ARM64 architecture.
> - */
> - if (is_vm_hugetlb_page(vma)) {
> - page = follow_huge_pmd_pte(vma, address, flags);
> - if (page)
> - return page;
> - return no_page_table(vma, flags);
> - }
> -
> retry:
> if (unlikely(pmd_bad(*pmd)))
> return no_page_table(vma, flags);
