On 07/04/16 15:37, Anshuman Khandual wrote:
> Currently the config ARCH_WANT_GENERAL_HUGETLB enabled functions like
> 'huge_pte_alloc' and 'huge_pte_offset' dont take into account HugeTLB
> page implementation at the PGD level. This is also true for functions
> like 'follow_page_mask' which is called from move_pages() system call.
> This lack of PGD level huge page support prohibits some architectures
> to use these generic HugeTLB functions.
>
>From what I know of move_pages(), it will always call follow_page_mask()
with FOLL_GET (I could be wrong here) and the implementation below
returns NULL for follow_huge_pgd().
> This change adds the required PGD based implementation awareness and
> with that, more architectures like POWER which implements 16GB pages
> at the PGD level along with the 16MB pages at the PMD level can now
> use ARCH_WANT_GENERAL_HUGETLB config option.
>
> Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> ---
> include/linux/hugetlb.h | 3 +++
> mm/gup.c | 6 ++++++
> mm/hugetlb.c | 20 ++++++++++++++++++++
> 3 files changed, 29 insertions(+)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 7d953c2..71832e1 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -115,6 +115,8 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmd, int flags);
> struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
> pud_t *pud, int flags);
> +struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
> + pgd_t *pgd, int flags);
> int pmd_huge(pmd_t pmd);
> int pud_huge(pud_t pmd);
> unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
> @@ -143,6 +145,7 @@ static inline void hugetlb_show_meminfo(void)
> }
> #define follow_huge_pmd(mm, addr, pmd, flags) NULL
> #define follow_huge_pud(mm, addr, pud, flags) NULL
> +#define follow_huge_pgd(mm, addr, pgd, flags) NULL
> #define prepare_hugepage_range(file, addr, len) (-EINVAL)
> #define pmd_huge(x) 0
> #define pud_huge(x) 0
> diff --git a/mm/gup.c b/mm/gup.c
> index fb87aea..9bac78c 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -234,6 +234,12 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
> pgd = pgd_offset(mm, address);
> if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
> return no_page_table(vma, flags);
> + if (pgd_huge(*pgd) && vma->vm_flags & VM_HUGETLB) {
> + page = follow_huge_pgd(mm, address, pgd, flags);
> + if (page)
> + return page;
> + return no_page_table(vma, flags);
This will return NULL as well?
> + }
>
> pud = pud_offset(pgd, address);
> if (pud_none(*pud))
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 19d0d08..5ea3158 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4250,6 +4250,11 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
> pte_t *pte = NULL;
>
> pgd = pgd_offset(mm, addr);
> + if (sz == PGDIR_SIZE) {
> + pte = (pte_t *)pgd;
> + goto huge_pgd;
> + }
> +
No allocation for a pgd slot - right?
> pud = pud_alloc(mm, pgd, addr);
> if (pud) {
> if (sz == PUD_SIZE) {
> @@ -4262,6 +4267,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
> pte = (pte_t *)pmd_alloc(mm, pud, addr);
> }
> }
> +
> +huge_pgd:
> BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte));
>
> return pte;
> @@ -4275,6 +4282,8 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
>
> pgd = pgd_offset(mm, addr);
> if (pgd_present(*pgd)) {
> + if (pgd_huge(*pgd))
> + return (pte_t *)pgd;
> pud = pud_offset(pgd, addr);
> if (pud_present(*pud)) {
> if (pud_huge(*pud))
> @@ -4343,6 +4352,17 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address,
> return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
> }
>
> +struct page * __weak
> +follow_huge_pgd(struct mm_struct *mm, unsigned long address,
> + pgd_t *pgd, int flags)
> +{
> + if (flags & FOLL_GET)
> + return NULL;
> +
> + return pte_page(*(pte_t *)pgd) +
> + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);
> +}
> +
> #ifdef CONFIG_MEMORY_FAILURE
>
> /*
>
--
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