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

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Date:   Fri, 24 Jul 2020 13:45:48 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Wei Yang <richard.weiyang@...ux.alibaba.com>,
        David Hildenbrand <david@...hat.com>,
        Wei Yang <richard.weiyang@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Michal Hocko <mhocko@...e.com>, stable@...r.kernel.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 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@...ux.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