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

From: Yang Shi <shy828301@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	hillf.zj@alibaba-inc.com,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	ak@linux.intel.com, yongjun_wei@trendmicro.com.cn,
	mhocko@suse.cz, Linux MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one
Date: Tue, 5 Jan 2021 10:04:13 -0800	[thread overview]
Message-ID: <CAHbLzko4BH6GOJsz33NEbwLTxJQJxVHH3qLzHzoM1LycT=ccbg@mail.gmail.com> (raw)
In-Reply-To: <d81664e1-bde0-4dcb-f602-6eb201ceada0@redhat.com>

On Tue, Jan 5, 2021 at 8:58 AM David Hildenbrand <david@redhat.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@bytedance.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
>
>