Re: [PATCH 6.12.y] mm: folio_may_be_lru_cached() unless folio_test_large()

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Sep 21, 2025 at 11:41:34AM -0400, Sasha Levin wrote:
> From: Hugh Dickins <hughd@google.com>
> 
> [ Upstream commit 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 ]
> 
> 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".
> 
> Link: https://lkml.kernel.org/r/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com
> Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region")
> Signed-off-by: Hugh Dickins <hughd@google.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
> Cc: Axel Rasmussen <axelrasmussen@google.com>
> Cc: Chris Li <chrisl@kernel.org>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Keir Fraser <keirf@google.com>
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>
> Cc: Li Zhe <lizhe.67@bytedance.com>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Shivank Garg <shivankg@amd.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Xu <weixugc@google.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: yangge <yangge1116@126.com>
> Cc: Yuanchu Xie <yuanchu@google.com>
> Cc: Yu Zhao <yuzhao@google.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> [ adapted to drain_allow instead of drained ]
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---

Does not apply as it conflicts with the other mm changes you sent right
before this one :(