Re: [PATCH v12 11/22] mm: pagewalk: Add p4d_entry() and pgd_entry()

[Zong Li <zongbox@gmail.com>]

Steven Price <steven.price@arm.com> 於 2019年10月19日 週六 下午4:14寫道：
>
> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410
> ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were
> no users. We're about to add users so reintroduce them, along with
> p4d_entry() as we now have 5 levels of tables.
>
> Note that commit a00cc7d9dd93d66a ("mm, x86: add support for
> PUD-sized transparent hugepages") already re-added pud_entry() but with
> different semantics to the other callbacks. Since there have never
> been upstream users of this, revert the semantics back to match the
> other callbacks. This means pud_entry() is called for all entries, not
> just transparent huge pages.
>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
>  include/linux/pagewalk.h | 19 +++++++++++++------
>  mm/pagewalk.c            | 27 ++++++++++++++++-----------
>  2 files changed, 29 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
> index bddd9759bab9..12004b097eae 100644
> --- a/include/linux/pagewalk.h
> +++ b/include/linux/pagewalk.h
> @@ -8,15 +8,15 @@ struct mm_walk;
>
>  /**
>   * mm_walk_ops - callbacks for walk_page_range
> - * @pud_entry:         if set, called for each non-empty PUD (2nd-level) entry
> - *                     this handler should only handle pud_trans_huge() puds.
> - *                     the pmd_entry or pte_entry callbacks will be used for
> - *                     regular PUDs.
> - * @pmd_entry:         if set, called for each non-empty PMD (3rd-level) entry
> + * @pgd_entry:         if set, called for each non-empty PGD (top-level) entry
> + * @p4d_entry:         if set, called for each non-empty P4D entry
> + * @pud_entry:         if set, called for each non-empty PUD entry
> + * @pmd_entry:         if set, called for each non-empty PMD entry
>   *                     this handler is required to be able to handle
>   *                     pmd_trans_huge() pmds.  They may simply choose to
>   *                     split_huge_page() instead of handling it explicitly.
> - * @pte_entry:         if set, called for each non-empty PTE (4th-level) entry
> + * @pte_entry:         if set, called for each non-empty PTE (lowest-level)
> + *                     entry
>   * @pte_hole:          if set, called for each hole at all levels
>   * @hugetlb_entry:     if set, called for each hugetlb entry
>   * @test_walk:         caller specific callback function to determine whether
> @@ -24,8 +24,15 @@ struct mm_walk;
>   *                     "do page table walk over the current vma", returning
>   *                     a negative value means "abort current page table walk
>   *                     right now" and returning 1 means "skip the current vma"
> + *
> + * p?d_entry callbacks are called even if those levels are folded on a
> + * particular architecture/configuration.
>   */
>  struct mm_walk_ops {
> +       int (*pgd_entry)(pgd_t *pgd, unsigned long addr,
> +                        unsigned long next, struct mm_walk *walk);
> +       int (*p4d_entry)(p4d_t *p4d, unsigned long addr,
> +                        unsigned long next, struct mm_walk *walk);
>         int (*pud_entry)(pud_t *pud, unsigned long addr,
>                          unsigned long next, struct mm_walk *walk);
>         int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index d48c2a986ea3..fc4d98a3a5a0 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -93,15 +93,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>                 }
>
>                 if (ops->pud_entry) {
> -                       spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
> -
> -                       if (ptl) {
> -                               err = ops->pud_entry(pud, addr, next, walk);
> -                               spin_unlock(ptl);
> -                               if (err)
> -                                       break;
> -                               continue;
> -                       }
> +                       err = ops->pud_entry(pud, addr, next, walk);
> +                       if (err)
> +                               break;
>                 }
>
>                 split_huge_pud(walk->vma, pud, addr);
> @@ -135,7 +129,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
>                                 break;
>                         continue;
>                 }
> -               if (ops->pmd_entry || ops->pte_entry)
> +               if (ops->p4d_entry) {
> +                       err = ops->p4d_entry(p4d, addr, next, walk);
> +                       if (err)
> +                               break;
> +               }
> +               if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)
>                         err = walk_pud_range(p4d, addr, next, walk);
>                 if (err)
>                         break;
> @@ -162,7 +161,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
>                                 break;
>                         continue;
>                 }
> -               if (ops->pmd_entry || ops->pte_entry)
> +               if (ops->pgd_entry) {
> +                       err = ops->pgd_entry(pgd, addr, next, walk);
> +                       if (err)
> +                               break;
> +               }
> +               if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry ||
> +                   ops->pte_entry)
>                         err = walk_p4d_range(pgd, addr, next, walk);
>                 if (err)
>                         break;
> --
> 2.20.1
>

It's good to me.

Tested-by: Zong Li <zong.li@sifive.com>