Commit a09a8a1f authored Sep 08, 2025 by Hugh Dickins Committed by Andrew Morton Sep 13, 2025

mm/gup: local lru_add_drain() to avoid lru_add_drain_all()

In many cases, if collect_longterm_unpinnable_folios() does need to drain
the LRU cache to release a reference, the cache in question is on this
same CPU, and much more efficiently drained by a preliminary local
lru_add_drain(), than the later cross-CPU lru_add_drain_all().

Marked for stable, to counter the increase in lru_add_drain_all()s from
"mm/gup: check ref_count instead of lru before migration".  Note for clean
backports: can take 6.16 commit a03db236 ("gup: optimize longterm
pin_user_pages() for large folio") first.

Link: https://lkml.kernel.org/r/66f2751f-283e-816d-9530-765db7edc465@google.com


Signed-off-by: Hugh Dickins <hughd@google.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>

parent 98c6d259

mm/gup.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -2287,8 +2287,8 @@ static unsigned long collect_longterm_unpinnable_folios(
		struct pages_or_folios *pofs)
		{
		unsigned long collected = 0;
		bool drain_allow = true;
		struct folio *folio;
		int drained = 0;
		long i = 0;

		for (folio = pofs_get_folio(pofs, i); folio;
		@@ -2307,10 +2307,17 @@ static unsigned long collect_longterm_unpinnable_folios(
		continue;
		}

		if (drain_allow && folio_ref_count(folio) !=
		if (drained == 0 &&
		folio_ref_count(folio) !=
		folio_expected_ref_count(folio) + 1) {
		lru_add_drain();
		drained = 1;
		}
		if (drained == 1 &&
		folio_ref_count(folio) !=
		folio_expected_ref_count(folio) + 1) {
		lru_add_drain_all();
		drain_allow = false;
		drained = 2;
		}

		if (!folio_isolate_lru(folio))