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From:   Yang Shi <shy828301@gmail.com>
Date:   Mon, 16 Sep 2019 10:22:18 -0700
Message-ID: <CAHbLzkq7JT=KE9R_W6YfXmBJBeESgXZvdReS30sH8no63YQE0Q@mail.gmail.com>
Subject: Re: [PATCH] mm, thp: Do not queue fully unmapped pages for deferred split
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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On Fri, Sep 13, 2019 at 2:18 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> Adding fully unmapped pages into deferred split queue is not productive:
> these pages are about to be freed or they are pinned and cannot be split
> anyway.

This change looks good to me. Reviewed-by: Yang Shi <yang.shi@linux.alibaba.com>

>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  mm/rmap.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 003377e24232..45388f1bf317 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
>         if (TestClearPageDoubleMap(page)) {
>                 /*
>                  * Subpages can be mapped with PTEs too. Check how many of
> -                * themi are still mapped.
> +                * them are still mapped.
>                  */
>                 for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
>                         if (atomic_add_negative(-1, &page[i]._mapcount))
>                                 nr++;
>                 }
> +
> +               /*
> +                * Queue the page for deferred split if at least one small
> +                * page of the compound page is unmapped, but at least one
> +                * small page is still mapped.
> +                */
> +               if (nr && nr < HPAGE_PMD_NR)
> +                       deferred_split_huge_page(page);
>         } else {
>                 nr = HPAGE_PMD_NR;
>         }
> @@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
>         if (unlikely(PageMlocked(page)))
>                 clear_page_mlock(page);
>
> -       if (nr) {
> +       if (nr)
>                 __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
> -               deferred_split_huge_page(page);
> -       }
>  }
>
>  /**
> --
> 2.21.0
>
>