Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps

Wei Yang
2020-07-24T05:45:57Z

On Thu, Jul 23, 2020 at 08:08:46PM -0700, Andrew Morton wrote:
>On Tue, 23 Jun 2020 17:30:18 +0800 Wei Yang <richard.weiyang@linux.alibaba.com> wrote:
>
>> 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.
>
>Still awaiting this, and the v3 patch was identical to this v2 patch.
>
>It's tagged for -stable, so there's some urgency. Should we just go
>ahead with the decently-tested v2?

This message is to me right?

I thought the fix patch is merged, the patch link may be
https://lkml.org/lkml/2020/6/23/380.

If I missed something, just let me know.

--
Wei Yang
Help you, Help me