[RFC PATCH 1/3] mm: avoid unnecessary lru drain for wp_can_reuse_anon_folio()

["Barry Song (Xiaomi)" <baohua@kernel.org>]

We always unconditionally drain the LRU before retrying anon folio
reuse in wp_can_reuse_anon_folio(). Instead, assume !LRU anon folios
are in lru_cache, and use the refcount to avoid many unnecessary LRU
drains.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/memory.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 56be920c56d7..487a34377a7b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4193,12 +4193,18 @@ static bool wp_can_reuse_anon_folio(struct folio *folio,
 	 */
 	if (folio_test_ksm(folio) || folio_ref_count(folio) > 3)
 		return false;
-	if (!folio_test_lru(folio))
+	if (!folio_test_lru(folio)) {
+		/*
+		 * Assume folio is on lru_cache and holds a cache reference.
+		 */
+		if (folio_ref_count(folio) > 2 + folio_test_swapcache(folio))
+			return false;
 		/*
 		 * We cannot easily detect+handle references from
 		 * remote LRU caches or references to LRU folios.
 		 */
 		lru_add_drain();
+	}
 	if (folio_ref_count(folio) > 1 + folio_test_swapcache(folio))
 		return false;
 	if (!folio_trylock(folio))
-- 
2.39.3 (Apple Git-146)