Re: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation

[David Hildenbrand <david@redhat.com>]

>>> +			/* Nuke the page table entry. */
>>> +			pteval = get_and_clear_full_ptes(mm, address, pvmw.pte, nr_pages, 0);
>>> +			/*
>>> +			 * We clear the PTE but do not flush so potentially
>>> +			 * a remote CPU could still be writing to the folio.
>>> +			 * If the entry was previously clean then the
>>> +			 * architecture must guarantee that a clear->dirty
>>> +			 * transition on a cached TLB entry is written through
>>> +			 * and traps if the PTE is unmapped.
>>> +			 */
>>> +			if (should_defer_flush(mm, flags))
>>> +				set_tlb_ubc_flush_pending(mm, pteval, address, end_addr);
>>
>> When the first pte of a PTE-mapped THP has _PAGE_PROTNONE bit set
>> (by NUMA balancing), can set_tlb_ubc_flush_pending() mistakenly think that
>> it doesn't need to flush the whole range, although some ptes in the range
>> doesn't have _PAGE_PROTNONE bit set?
> 
> No, then folio_pte_batch() should have returned nr < folio_nr_pages(folio).

Right, folio_pte_batch() does currently not batch across PTEs that 
differ in pte_protnone().

-- 
Cheers,

David / dhildenb