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Message-ID: <20200623093018.GA6069@L-31X9LVDL-1304.local>
Date: Tue, 23 Jun 2020 17:30:18 +0800
From: Wei Yang <richard.weiyang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.com>
Cc: Wei Yang <richard.weiyang@...il.com>,
Wei Yang <richard.weiyang@...ux.alibaba.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Michal Hocko <mhocko@...e.com>, stable@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Johannes Weiner <hannes@...xchg.org>,
Minchan Kim <minchan@...nel.org>,
Huang Ying <ying.huang@...el.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and
don't read garbage memmaps
On Tue, Jun 23, 2020 at 09:55:43AM +0200, David Hildenbrand wrote:
>On 23.06.20 09:39, David Hildenbrand wrote:
>>> Hmm.. I thought this is the behavior for early section, while it looks current
>>> code doesn't work like this:
>>>
>>> if (section_is_early && memmap)
>>> free_map_bootmem(memmap);
>>> else
>>> depopulate_section_memmap(pfn, nr_pages, altmap);
>>>
>>> section_is_early is always "true" for early section, while memmap is not-NULL
>>> only when sub-section map is empty.
>>>
>>> If my understanding is correct, when we remove a sub-section in early section,
>>> the code would call depopulate_section_memmap(), which in turn free related
>>> memmap. By removing the memmap, the return value from pfn_to_online_page() is
>>> not a valid one.
>>
>> I think you're right, and pfn_valid() would also return true, as it is
>> an early section. This looks broken.
>>
>>>
>>> Maybe we want to write the code like this:
>>>
>>> if (section_is_early)
>>> if (memmap)
>>> free_map_bootmem(memmap);
>>> else
>>> depopulate_section_memmap(pfn, nr_pages, altmap);
>>>
>>
>> I guess that should be the way to go
>>
>> @Dan, I think what Wei proposes here is correct, right? Or how does it
>> work in the VMEMMAP case with early sections?
>>
>
>Especially, if you would re-hot-add, section_activate() would assume
>there is a memmap, it must not be removed.
>
You are right here. I didn't notice it.
>@Wei, can you send a patch?
>
Sure, let me prepare for it.
>--
>Thanks,
>
>David / dhildenb
--
Wei Yang
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