Re: [RFC PATCH 01/14] mm/rmap: add mm_find_pmd_raw helper

[Yang Shi <shy828301@gmail.com>]

On Tue, Mar 8, 2022 at 1:34 PM Zach O'Keefe <zokeefe@google.com> wrote:
>
> Later in the series, we want to find a pmd and take different actions,
> depending on if the pmd maps a thp or not.  Currently, mm_find_pmd()
> returns NULL if a valid pmd maps a thp, and so we can't use it directly.
>
> Split mm_find_pmd() into 2 parts: mm_find_pmd_raw(), which returns a
> raw pmd pointer, and the logic that filters out non-present none, or
> huge pmds.  mm_find_pmd_raw() can then be reused later in the series.
>
> Signed-off-by: Zach O'Keefe <zokeefe@google.com>
> ---
>  mm/internal.h |  1 +
>  mm/rmap.c     | 15 +++++++++++++--
>  2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 86277d90a5e2..aaea25bb9096 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -166,6 +166,7 @@ extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason
>  /*
>   * in mm/rmap.c:
>   */
> +pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address);
>  extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
>
>  /*
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 70375c331083..0ae99affcb27 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -758,13 +758,12 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
>         return vma_address(page, vma);
>  }
>
> -pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
> +pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address)

Typically we have the new helper and the users in the same patch. It
would make the review easier.


>  {
>         pgd_t *pgd;
>         p4d_t *p4d;
>         pud_t *pud;
>         pmd_t *pmd = NULL;
> -       pmd_t pmde;
>
>         pgd = pgd_offset(mm, address);
>         if (!pgd_present(*pgd))
> @@ -779,6 +778,18 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
>                 goto out;
>
>         pmd = pmd_offset(pud, address);
> +out:
> +       return pmd;
> +}
> +
> +pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
> +{
> +       pmd_t pmde;
> +       pmd_t *pmd;
> +
> +       pmd = mm_find_pmd_raw(mm, address);
> +       if (!pmd)
> +               goto out;
>         /*
>          * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
>          * without holding anon_vma lock for write.  So when looking for a
> --
> 2.35.1.616.g0bdcbb4464-goog
>