linux-kernel - Re: [PATCH 15/16] mm/migration: fix possible do_pages_stat

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Date:   Tue, 8 Mar 2022 19:33:42 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Muchun Song <songmuchun@...edance.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Matthew Wilcox <willy@...radead.org>, Zi Yan <ziy@...dia.com>,
        Minchan Kim <minchan@...nel.org>,
        Alistair Popple <apopple@...dia.com>,
        <ave.hansen@...ux.intel.com>, <o451686892@...il.com>,
        Mina Almasry <almasrymina@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Peter Xu <peterx@...hat.com>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Michal Hocko <mhocko@...e.com>,
        <riel@...hat.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 15/16] mm/migration: fix possible do_pages_stat_array
 racing with memory offline

On 2022/3/7 15:42, Huang, Ying wrote:
> Muchun Song <songmuchun@...edance.com> writes:
> 
>> On Mon, Mar 7, 2022 at 1:22 PM Huang, Ying <ying.huang@...el.com> wrote:
>>>
>>> Miaohe Lin <linmiaohe@...wei.com> writes:
>>>
>>>> When follow_page peeks a page, the page could be reclaimed under heavy
>>>> memory pressure
>>>
>>> I don't think that memory pressure and reclaiming will be an issue.
>>
>> I think he means a page first to be reclaimed then to be offline
>> could encounter this issue and reclaiming is a precondition.
> 
> I don't think reclaiming is a precondition.  It seems possible that the
> virtual page is migrated, then the physical page is offlined.
> 

What I indeed mean is a page could first be reclaimed, migrated and so on.
And then be offlined. Sorry for confusing.

Thanks both of you.

> Best Regards,
> Huang, Ying
> 
>> Thanks.
>>
>>>
>>>> and thus be offlined while it's still being used by the
>>>> do_pages_stat_array().
>>>
>>> "offline" seems a possible problem.
> .
>