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

[Li, Tianyou]

On 2/6/2026 9:03 PM, David Hildenbrand (Arm) wrote
> On 1/30/26 17:09, Tianyou Li wrote:
> > From: Yuan Liu <yuan1.liu@xxxxxxxxx>
>
> Nit: subject should start with "mm/memory_hotplug:"

Got it. My bad, will pay attention next time. Thanks David.


> > 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>
>
> How was Yuan Liu involved? If he is a co-author there is a
>
>     Co-developed-by: Yuan Liu <yuan1.liu@xxxxxxxxx>
>
> missing.

Yes, Yuan Liu co-author the patch. Thanks and I will pay attention next 
time. Appreciated.


> Likely there is no resend required if you tell Andrew what to do, so 
> he can just fixup when applying.
>
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

+ Andrew Morton for awareness.

Hi Andrew,

Please kindly let me know if resend required or you are willing to 
kindly fixup the titile and Co-developed-by tag for me. Appreciated in 
advance for any additional burden that costs.

Regards,

Tianyou