Re: [PATCH] mm/memory: avoid unnecessary #PF on mTHP allocation race

[Wandun <chenwandun1@gmail.com>]

On 5/12/26 18:35, David Hildenbrand (Arm) wrote:
> On 5/12/26 11:50, Wandun Chen wrote:
>> When an mTHP folio is allocated in do_anonymous_page() and the target
>> pte range is not fully empty, current code would release the folio
>> and return.
>>
>> This results an illusion that a page fault has already been processed
>> even if the fact is vmf->address itself is still pte_none(). Another
>> page fault will be triggered again.
> Yes. Why is that a problem?
Honestly, the only data I have is the reproducer; I haven't been able to 
show a measurable impact on a real workload. The motivation was "we did 
the work of allocatingan mTHP folio and then throw it away just to redo 
it from #PF, and this #PF can be avoided by adding a small check + 
retry". But as you point out, the second fault path can handle this case 
properly, the behaviour is already correct.Please drop the patch. I'll 
come back with numbers if I run into a workload where this race is 
actually hot.Thanks for taking a look. Best regards, Wandun
>