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

[David Hildenbrand <david@redhat.com>]

On 02.10.25 05:31, Wei Yang wrote:
> Current code may skip some part of the range to
> pageblock_pfn_to_page() to check whether the range is in the same zone.
> 
> Function pageblock_pfn_to_page() is first introduced by commit 7d49d8868336
> ("mm, compaction: reduce zone checking frequency in the migration scanner"),
> in which it checks and isolates on the same range [pfn, block_end_pfn].
> 
> While after commit e1409c325fdc ("mm/compaction: pass only pageblock
> aligned range to pageblock_pfn_to_page"), we operate on two different
> ranges for check and isolation.
> 
>    * [block_start_pfn, block_end_pfn] to check it is in the same zone
>    * [pfn, block_end_pfn] to do isolation
> 
> It miss some range to check when start_pfn and zone->zone_start_pfn is
> in the same pageblock but (start_pfn < zone->zone_start_pfn). The range
> before zone_start_pfn is missed.
> 
>           start_pfn     zone_start_pfn
>      +----+-------------+-------------------+
>      block_start_pfn                        block_end_pfn
> 
> This leads to the range check is passed, but it will isolate a range in
> two different zones.

Can that actually happen? I recall that a zone always spans full pageblocks.

-- 
Cheers

David / dhildenb