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

[David Hildenbrand]

On 26.06.25 03:17, Lance Yang wrote:
> 
> 
> On 2025/6/26 05:03, Barry Song wrote:
>> On Thu, Jun 26, 2025 at 12:25 AM David Hildenbrand <david at redhat.com> wrote:
>>>
>>> On 25.06.25 14:20, Lance Yang wrote:
>> [...]
>>>> Hmm... I have a question about the reference counting here ...
>>>>
>>>>                 if (vma->vm_flags & VM_LOCKED)
>>>>                         mlock_drain_local();
>>>>                 folio_put(folio);
>>>>                 /* We have already batched the entire folio */
>>>>
>>>> Does anyone else still hold a reference to this folio after folio_put()?
>>>
>>> The caller of the unmap operation should better hold a reference :)
>>>
>>> Also, I am not sure why we don't perform a
>>>
>>> folio_put_refs(folio, nr_pages);
>>
>> Because we've already called folio_ref_sub(folio, nr_pages - 1);
>> Looking back, it’s kind of ugly, huh.
>>
>> discard:
>>                   if (unlikely(folio_test_hugetlb(folio))) {
>>                           hugetlb_remove_rmap(folio);
>>                   } else {
>>                           folio_remove_rmap_ptes(folio, subpage, nr_pages, vma);
>>                           folio_ref_sub(folio, nr_pages - 1);
>>                   }
>>
>> I assume Lance will send a patch? If so, remember to remove this
>> when switching to folio_put_refs(folio, nr_pages);
> 
> Ah, got it. Thanks for pointing that out!

Obviously I was hinting that the split refcount update can be merged 
into a single refcount update :)

-- 
Cheers,

David / dhildenb