Re: [PATCH] mm/huge_memory: avoid transient none PMDs during lazyfree reclaim

[David Hildenbrand (Arm)]

On 10/9/26 22:27, Zi Yan wrote:
> On 9 Oct 2026, at 16:23, David Hildenbrand (Arm) wrote:
> 
>> On 10/9/26 20:17, Zi Yan wrote:
>>>
>>> There are some gaps we need to close before getting this fix in:
>>>
>>> 1. GUP-fast cannot follow the invalidated PMD: riscv and LoongArch need
>>> pmd_access_permitted() that requires _PAGE_PRESENT; s390's
>>> pmdp_invalidate() needs a change.
>>
>> Ugh. We really need pmdp_invalidate() to have reasonable semantics. This whole
>> PMD locking is a mess :(
>>
>>>
>>> 2. sparc64's thp_pte_count can be imbalanced with this change (based on
>>> Lance's offlist feedback).
>>
>> Ack.
>>
>>>
>>> In addition, powerpc has a page table check issue similr to riscv, where riscv
>>> fixed it with commit 9f4a88b8d01a6. This is not related to this issue
>>> but discovered along with the investigation.
>>
>> Zi, do you have the capacity to take over this patch?
> 
> Yes, I can take over it. My plan is to send a series including
> patches for 1 and this patch as is. powerpc fix can be a separate one.
> 
> Best Regards,
> Yan, Zi

If we need a quick stable fix we could temporarily disable the whole thing until
it is fixed, just a thought.

-- 
Cheers,

David