[RFC PATCH v2 2/5] 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
undermines that bias. Only fall back after making a sufficient effort
to reclaim from the preferred type.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index babbce4bbfe8..4a387cc4145a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4857,10 +4857,14 @@ static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		 * type is still reclaimable; otherwise, it would have
 		 * already run out of reclaimable generations. Falling
 		 * back too readily can disrupt the positive_ctrl_err()
-		 * bias.
+		 * bias. Also, only fall back when reclaim is running at
+		 * a high priority.
 		 */
-		if (scanned < nr_to_scan && *isolated < MIN_LRU_BATCH)
+		if (scanned < nr_to_scan && *isolated < MIN_LRU_BATCH) {
+			if (sc->priority > 2)
+				break;
 			type = !type;
+		}
 	}
 
 	return total_scanned;
-- 
2.39.3 (Apple Git-146)