[PATCH 3/7] mm/gup: local lru_add_drain() to avoid lru_add_drain_all()

[Hugh Dickins <hughd@google.com>]

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@google.com>
Cc: <stable@vger.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