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 10:04:13 -0800
From:   Yang Shi <shy828301@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        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 Tue, Jan 5, 2021 at 8:58 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 04.01.21 07:58, Muchun Song 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;
> > +     }
> > +
> >       new_hpage = get_new_page(hpage, private);
> >       if (!new_hpage)
> >               return -ENOMEM;
> >
>
> This series seems to fix quite some important cases (thanks). Do we want
> to cc stable some/all?

For this particular one, I don't think so IMHO. It is an optimization
rather than a bug fix.

>
> --
> Thanks,
>
> David / dhildenb
>
>