From: Hugh Dickins <hughd@google.com>
Date: Mon, 8 Sep 2025 22:16:53 +0000 (-0700)
Subject: mm/gup: local lru_add_drain() to avoid lru_add_drain_all()
X-Git-Tag: v6.1.155~54
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9557ba5fd368b98329cf1882d538a670abaaacec;p=thirdparty%2Fkernel%2Fstable.git

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

[ Upstream commit a09a8a1fbb374e0053b97306da9dbc05bd384685 ]

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/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>
[ Resolved minor conflicts ]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/mm/gup.c b/mm/gup.c
index 44e5fe2535d0e..e1f125af9c844 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1968,7 +1968,7 @@ static unsigned long collect_longterm_unpinnable_pages(
 {
 	unsigned long i, collected = 0;
 	struct folio *prev_folio = NULL;
-	bool drain_allow = true;
+	int drained = 0;
 
 	for (i = 0; i < nr_pages; i++) {
 		struct folio *folio = page_folio(pages[i]);
@@ -1990,10 +1990,17 @@ static unsigned long collect_longterm_unpinnable_pages(
 			continue;
 		}
 
-		if (drain_allow && folio_ref_count(folio) !=
-				   folio_expected_ref_count(folio) + 1) {
+		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))