[PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation
Barry Song
21cnbao at gmail.com
Wed Jun 25 14:03:23 PDT 2025
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);
Thanks
Barry
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