Re: [PATCH mm-unstable v18 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse

[David Hildenbrand (Arm)]

On 6/1/26 12:47, Lance Yang wrote:
> 
> 
> On 2026/6/1 18:23, David Hildenbrand (Arm) wrote:
>> On 6/1/26 11:08, Lance Yang wrote:
>>>
>>>
>>>
>>> One small thing, I think we should probably keep the smp_wmb(), and just
>>> move it before the earlier pmd_populate().
>>>
>>> IIUC, the ordering we want is still:
>>>
>>>    clear old PTEs
>>>    smp_wmb()
>>>    pmd_populate()
>>>
>>> so another CPU cannot walk through the re-installed PMD and still observe
>>> the old PTEs, right?
>>
>> There is a smp_wmb() in __folio_mark_uptodate(), that should be sufficient?
> 
> Ah, cool! __folio_mark_uptodate() already does the job :P
> 
> So yeah, no extra smp_wmb() needed here!

Yeah. BTW, I think we'd need a spin_lock_nested(), so @Nico, treat my code as a
draft.

-- 
Cheers,

David