[RFC PATCH 1/4] mm: mglru: only fall back when reclaim is running at high priority

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

Respect the type selected by positive_ctrl_err(), where swappiness
controls the relative weights of SP and PV. Falling back too readily
violates that bias.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 566c4e837c7d..f79402760776 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4855,9 +4855,12 @@ static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * If scanned > 0 and isolated == 0, avoid falling back to the
 		 * other type, as this type remains sufficient. Falling back
 		 * too readily can disrupt the positive_ctrl_err() bias.
+		 * Only fall back when reclaim is running at high priority.
 		 */
-		if (!scanned)
-			type = !type;
+		if (!scanned) {
+			if (!sc->priority)
+				type = !type;
+		}
 	}
 
 	return total_scanned;
-- 
2.39.3 (Apple Git-146)