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Subject: Re: [PATCH 15/16] mm/migration: fix possible do_pages_stat_array
 racing with memory offline
To:     "Huang, Ying" <ying.huang@intel.com>,
        Muchun Song <songmuchun@bytedance.com>
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From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <05c39882-0d61-92cb-9c63-479ea6dffb63@huawei.com>
Date:   Tue, 8 Mar 2022 19:33:42 +0800
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On 2022/3/7 15:42, Huang, Ying wrote:
> Muchun Song <songmuchun@bytedance.com> writes:
> 
>> On Mon, Mar 7, 2022 at 1:22 PM Huang, Ying <ying.huang@intel.com> wrote:
>>>
>>> Miaohe Lin <linmiaohe@huawei.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.
> .
>