linux-kernel - Re: [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one

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Date:   Tue, 5 Jan 2021 10:04:44 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        hillf.zj@...baba-inc.com,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        ak@...ux.intel.com, yongjun_wei@...ndmicro.com.cn, mhocko@...e.cz,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose
 refcount is one

On Sun, Jan 3, 2021 at 11:01 PM Muchun Song <songmuchun@...edance.com> wrote:
>
> If the refcount is one when it is migrated, it means that the page
> was freed from under us. So we are done and do not need to migrate.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  mm/migrate.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4385f2fb5d18..a6631c4eb6a6 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
>                 return -ENOSYS;
>         }
>
> +       if (page_count(hpage) == 1) {
> +               /* page was freed from under us. So we are done. */
> +               putback_active_hugepage(hpage);
> +               return MIGRATEPAGE_SUCCESS;
> +       }
> +

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

>         new_hpage = get_new_page(hpage, private);
>         if (!new_hpage)
>                 return -ENOMEM;
> --
> 2.11.0
>
>