+ mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all.patch added to mm-new branch

+ mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/gup: local lru_add_drain() to avoid lru_add_drain_all()
has been added to the -mm mm-new branch.  Its filename is
     mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm/gup: local lru_add_drain() to avoid lru_add_drain_all()
Date: Sun, 31 Aug 2025 02:08:26 -0700 (PDT)

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 a03db236aebf ("gup: optimize longterm
pin_user_pages() for large folio") first.

Link: https://lkml.kernel.org/r/165ccfdb-16b5-ac11-0d66-2984293590c8@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
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: David Hildenbrand <david@redhat.com>
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: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/gup.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/gup.c~mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all
+++ a/mm/gup.c
@@ -2291,6 +2291,8 @@ static unsigned long collect_longterm_un
 	struct folio *folio;
 	long i = 0;
 
+	lru_add_drain();
+
 	for (folio = pofs_get_folio(pofs, i); folio;
 	     folio = pofs_next_folio(folio, pofs, &i)) {
 
_

Patches currently in -mm which might be from hughd@google.com are

mm-fix-folio_expected_ref_count-when-pg_private_2.patch
mm-gup-check-ref_count-instead-of-lru-before-migration.patch
mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all.patch
mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch.patch
mm-revert-mm-vmscanc-fix-oom-on-swap-stress-test.patch
mm-folio_may_be_cached-unless-folio_test_large.patch
mm-lru_add_drain_all-do-local-lru_add_drain-first.patch