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

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Date:   Mon, 07 Mar 2022 15:42:43 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Miaohe Lin <linmiaohe@...wei.com>,
        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

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.

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.