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Message-ID: <165ccfdb-16b5-ac11-0d66-2984293590c8@google.com>
Date: Sun, 31 Aug 2025 02:08:26 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Will Deacon <will@...nel.org>, David Hildenbrand <david@...hat.com>,
Shivank Garg <shivankg@....com>, Matthew Wilcox <willy@...radead.org>,
Christoph Hellwig <hch@...radead.org>, Keir Fraser <keirf@...gle.com>,
Jason Gunthorpe <jgg@...pe.ca>, John Hubbard <jhubbard@...dia.com>,
Frederick Mayle <fmayle@...gle.com>, Peter Xu <peterx@...hat.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Vlastimil Babka <vbabka@...e.cz>,
Alexander Krabler <Alexander.Krabler@...a.com>,
Ge Yang <yangge1116@....com>, Li Zhe <lizhe.67@...edance.com>,
Chris Li <chrisl@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Yuanchu Xie <yuanchu@...gle.com>, Wei Xu <weixugc@...gle.com>,
Konstantin Khlebnikov <koct9i@...il.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: [PATCH 3/7] 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 a03db236aebf ("gup:
optimize longterm pin_user_pages() for large folio") first.
Signed-off-by: Hugh Dickins <hughd@...gle.com>
Cc: <stable@...r.kernel.org>
---
mm/gup.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c
index 82aec6443c0a..9f7c87f504a9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2291,6 +2291,8 @@ static unsigned long collect_longterm_unpinnable_folios(
struct folio *folio;
long i = 0;
+ lru_add_drain();
+
for (folio = pofs_get_folio(pofs, i); folio;
folio = pofs_next_folio(folio, pofs, &i)) {
--
2.51.0
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