linux-kernel - Re: [PATCH] mm/mempolicy: clean up the code logic in queue_pages_pte

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Date:   Wed, 20 Apr 2022 17:44:27 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/mempolicy: clean up the code logic in queue_pages_pte_range

On Tue, Apr 19, 2022 at 5:22 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> Since commit e5947d23edd8 ("mm: mempolicy: don't have to split pmd for
> huge zero page"), THP is never splited in queue_pages_pmd. Thus 2 is
> never returned now. We can remove such unnecessary ret != 2 check and
> clean up the relevant comment. Minor improvements in readability.

Nice catch. Yeah, it was missed when I worked on that commit.

Reviewed-by: Yang Shi <shy828301@...il.com>

>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/mempolicy.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 75a8b247f631..3934476fb708 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -441,12 +441,11 @@ static inline bool queue_pages_required(struct page *page,
>  }
>
>  /*
> - * queue_pages_pmd() has four possible return values:
> + * queue_pages_pmd() has three possible return values:
>   * 0 - pages are placed on the right node or queued successfully, or
>   *     special page is met, i.e. huge zero page.
>   * 1 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
>   *     specified.
> - * 2 - THP was split.
>   * -EIO - is migration entry or only MPOL_MF_STRICT was specified and an
>   *        existing page was already on a node that does not follow the
>   *        policy.
> @@ -508,18 +507,13 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
>         struct page *page;
>         struct queue_pages *qp = walk->private;
>         unsigned long flags = qp->flags;
> -       int ret;
>         bool has_unmovable = false;
>         pte_t *pte, *mapped_pte;
>         spinlock_t *ptl;
>
>         ptl = pmd_trans_huge_lock(pmd, vma);
> -       if (ptl) {
> -               ret = queue_pages_pmd(pmd, ptl, addr, end, walk);
> -               if (ret != 2)
> -                       return ret;
> -       }
> -       /* THP was split, fall through to pte walk */
> +       if (ptl)
> +               return queue_pages_pmd(pmd, ptl, addr, end, walk);
>
>         if (pmd_trans_unstable(pmd))
>                 return 0;
> --
> 2.23.0
>
>