Cc a few people who have looked at huge_pte_offset() recently.
On 4/23/20 5:49 AM, Li Xinhai wrote:
> When huge_pte_offset() is called, the parameter sz can only be PUD_SIZE
> or PMD_SIZE.
> If sz is PUD_SIZE and code can reach pud, then *pud must be none, or
> normal hugetlb entry, or non-present (migration or hwpoisoned) hugetlb
> entry, and we can directly return pud.
> When sz is PMD_SIZE, pud must be none or present, and if code can reach
> pmd, we can directly return pmd.
>
> So, after this patch, the code is simplified by first check on the
> parameter sz, and avoid unnecessary checks in current code.
>
> Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> mm/hugetlb.c | 24 +++++++++---------------
> 1 file changed, 9 insertions(+), 15 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bcabbe0..e1424f5 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5365,8 +5365,8 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
> {
> pgd_t *pgd;
> p4d_t *p4d;
> - pud_t *pud, pud_entry;
> - pmd_t *pmd, pmd_entry;
> + pud_t *pud;
> + pmd_t *pmd;
>
> pgd = pgd_offset(mm, addr);
> if (!pgd_present(*pgd))
> @@ -5376,22 +5376,16 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
> return NULL;
>
> pud = pud_offset(p4d, addr);
> - pud_entry = READ_ONCE(*pud);
> - if (sz != PUD_SIZE && pud_none(pud_entry))
> - return NULL;
> - /* hugepage or swap? */
> - if (pud_huge(pud_entry) || !pud_present(pud_entry))
> + if (sz == PUD_SIZE)
> + /* must be pud_huge or pud_none */
> return (pte_t *)pud;
> -
> - pmd = pmd_offset(pud, addr);
> - pmd_entry = READ_ONCE(*pmd);
> - if (sz != PMD_SIZE && pmd_none(pmd_entry))
> + if (!pud_present(*pud))
> return NULL;
> - /* hugepage or swap? */
> - if (pmd_huge(pmd_entry) || !pmd_present(pmd_entry))
> - return (pte_t *)pmd;
> + /* must have a valid entry and size to go further */
>
> - return NULL;
> + pmd = pmd_offset(pud, addr);
Can we get here with sz = PMD_SIZE and pud_none(*pud)? Would that be
an issue for the pmd_offset() call?
--
Mike Kravetz
> + /* must be pmd_huge or pmd_none */
> + return (pte_t *)pmd;
> }
>
> #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
>
