Re: [PATCH v9] mm/memory hotplug: Fix zone->contiguous always false when hotplug

[David Hildenbrand (Arm)]

On 1/30/26 17:06, Tianyou Li wrote:
> From: Yuan Liu <yuan1.liu@xxxxxxxxx>
>
> set_zone_contiguous() uses __pageblock_pfn_to_page() to detect
> pageblocks that either do not exist (hole) or that do not belong
> to the same zone.
>
> __pageblock_pfn_to_page(), however, relies on pfn_to_online_page(),
> effectively always returning NULL for memory ranges that were not
> onlined yet. So when called on a range-to-be-onlined, it indicates
> a memory hole to set_zone_contiguous().
>
> Consequently, the set_zone_contiguous() call in move_pfn_range_to_zone(),
> which happens early during memory onlining, will never detect a
> zone as being contiguous. Bad: the fast path relies on the zone
> contiguous state may skipped.
>
> To fix the issue, move the set_zone_contiguous() call to a later
> stage in memory onlining, where pfn_to_online_page() will succeed:
> after we mark the memory sections to be online.
>
> Fixes: 2d070eab2e82 ("mm: consider zone which is not fully populated to have holes")
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Nanhai Zou <nanhai.zou@xxxxxxxxx>
> Signed-off-by: Yuan Liu <yuan1.liu@xxxxxxxxx>
> Signed-off-by: Tianyou Li <tianyou.li@xxxxxxxxx>


I assume this one is to be ignored :)

--
Cheers,

David