Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable sysctl"

David Hildenbrand
2025-10-08T19:52:29Z

On 08.10.25 21:44, Gregory Price wrote:
> On Wed, Oct 08, 2025 at 09:01:09PM +0200, David Hildenbrand wrote:
>>>
>>> fwiw this works cleanly. Just dropping this here, but should continue
>>> the zone conversation. I need to check, but does this actually allow
>>> pinnable allocations? I thought pinning kicked off migration.
>>
>> Yes, it should because longterm pinning -> unmovable.
>>
>
> You know i just realized, my test here only works before I allocated 1GB
> pages on both node0 and node1. If I only allocate 1gb hugetlb on node1,
> then the migrate pages call fails - because there are no 1gb pages
> available there.
>
> I imagine this would cause hot-unplug/offline to fail since it uses the
> same migration mechanisms.
>
> Worse I would imagine this would fail for 2MB.
>
> Seems like the 1GB limitation is arbitrary if 2MB causes the same issue.

Yeah, with hugetlb allocations there are no guarantees either. It's just
that page compaction / defragmentation makes it much less likely to fail
in many scenarios.

--
Cheers

David / dhildenb