Re: [PATCH v3 6/6] arm64: mm: implement the architecture-specific test_and_clear_young_ptes()

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 3/9/26 10:39 PM, David Hildenbrand (Arm) wrote:
>>>
>>> (b) The first pte is !pte_cont(), but some others in there are?
>>
>> IMO they can’t be handled in a single batch. Since the folio_pte_batch()
>> will group consecutive !cont PTEs into one batch and consecutive cont
>> PTEs into another (assume all PTEs belong to a single large folio),
>> because their PTE entries have different CONT bits.
> Interesting, thanks. I thought that folio_pte_batch() would be able to
> batch that.
> 
> But yes, pte_batch_hint() relies on the CONT bit still being set after a
> ptep_get(). I wonder whether we should document somewhere that the arm
> implementation depends on that.
> 
> This might be something to look into in the future. (make
> folio_pte_batch() ignore cont information when comparing and make the
> arm implementation be able to deal with that).
> 
> Assume we unmapped the last page of a large folio. Ideally, we'd be able
> to process the remaining THP pieces (all ptes) in a single operation. I
> guess right now it would be two.

Right. Let me investigate this further and see if I can figure out how 
to optimize this case.

Thanks for reviewing.