Re: [PATCH v2 5/6] mm: folio_may_be_lru_cached() unless folio_test_large()

[David Hildenbrand]

On 09.09.25 00:23, Hugh Dickins wrote:
> mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as
> a large folio is added: so collect_longterm_unpinnable_folios() just
> wastes effort when calling lru_add_drain[_all]() on a large folio.
>
> But although there is good reason not to batch up PMD-sized folios,
> we might well benefit from batching a small number of low-order mTHPs
> (though unclear how that "small number" limitation will be implemented).
>
> So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to
> insulate those particular checks from future change.  Name preferred
> to "folio_is_batchable" because large folios can well be put on a batch:
> it's just the per-CPU LRU caches, drained much later, which need care.
>
> Marked for stable, to counter the increase in lru_add_drain_all()s
> from "mm/gup: check ref_count instead of lru before migration".
>
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers

David / dhildenb