Re: [PATCH 0/2] mm/compaction: some fix for the range passed to pageblock_pfn_to_page()

[Wei Yang <richard.weiyang@gmail.com>]

On Tue, Oct 07, 2025 at 06:29:22PM -0700, Andrew Morton wrote:
>On Thu,  2 Oct 2025 03:31:38 +0000 Wei Yang <richard.weiyang@gmail.com> wrote:
>
>> During the code reading of isolate_migratepages_range(), first spot the range
>> passed to pageblock_pfn_to_page() is different from that to
>> isolate_migratepages_block().
>> 
>> This implies there is a chance that pageblock_pfn_to_page() thinks the range
>> is in the same zone, but isolate_migratepages_block() will isolate range in
>> two different zones. This is not what we expect.
>> 
>> Then I found pageblock_pfn_to_page() has an optimization if zone->contiguous,
>> this means even the range is across two different zones, it will think the
>> range is within the same zone.
>> 
>> So introduce two patches to fix it:
>
>What do you think might be the worst-case userspace-visible effects
>of the bug?

I don't see userspace-visible effect yet.

Since I lack the knowledge of the consequence of isolating cross zone range,
currently I can't tell the effect accurately.

The worst case in my mind is we put some page on a different zone's freelist.
But I don't totally understand the behavior now.

>
>Thanks.

-- 
Wei Yang
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