[RFC PATCH] mm: keep LRU order by move unisolated folios to tail

[zhaoyang.huang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

Unlike legacy LRU management, MGLRU will switch to other zones or types
when current lrugen[gen][type][zone] scanning failed, which means skipped
folios could become available in next scan. This commit would like to
suggest to keep the LRU's order by moving unisolated folios to the tail
of LRU during the first 2 round scan to avoid potential livelock on the
unisolated ones.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 mm/vmscan.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2e34de9cd0d4..cd1f38bb1d45 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4397,7 +4397,10 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
 		}
 
 		if (skipped_zone) {
-			list_splice(&moved, head);
+			if (sc->priority > DEF_PRIORITY - 2)
+				list_splice_tail(&moved, head);
+			else
+				list_splice(&moved, head);
 			__count_zid_vm_events(PGSCAN_SKIP, zone, skipped_zone);
 			skipped += skipped_zone;
 		}
-- 
2.25.1