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

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Message-ID: <e6eb5ffa-403a-7012-db7e-f2e5a015f6de@redhat.com>
Date:   Tue, 5 Jan 2021 19:05:12 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Yang Shi <shy828301@...il.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 05.01.21 19:04, Yang Shi wrote:
> 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.

I'm rather referring to the actual fixes (I received no cover letter so
I picked the first patch in the series)


-- 
Thanks,

David / dhildenb