[RFC PATCH v4 10/16] mm/mglru: batch move folios to the second-oldest gen's LRU

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

Detect folios that need to move from the oldest generation to
the second-oldest generation, and batch-move them together.
This can significantly reduce the sys time of inc_min_seq(),
especially when the other type is significantly behind the
preferred type.

Assisted-by: gemini:gemini-3.6-flash
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 17357b16d1a7..b6c17ece3b3f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3922,6 +3922,19 @@ static void clear_mm_walk(void)
 		kfree(walk);
 }
 
+static inline void flush_lru_batch(struct list_head *head, struct list_head **batch_end,
+				   struct list_head *dst)
+{
+	LIST_HEAD(movable);
+
+	if (!*batch_end)
+		return;
+
+	list_cut_position(&movable, head, *batch_end);
+	list_splice_tail_init(&movable, dst);
+	*batch_end = NULL;
+}
+
 static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 {
 	int zone;
@@ -3941,9 +3954,11 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 
 	/* prevent cold/hot inversion if the type is evictable */
 	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+		struct list_head *target_list = &lrugen->folios[target_gen][type][zone];
 		struct list_head *head = &lrugen->folios[old_gen][type][zone];
 		unsigned long protected[MAX_NR_TIERS] = {}, delta = 0;
 		struct list_head *pos = head->next;
+		struct list_head *batch_end = NULL;
 
 		while (pos != head) {
 			struct folio *folio = list_entry(pos, struct folio, lru);
@@ -3962,7 +3977,8 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 			new_gen = __folio_inc_gen(folio, old_gen, &gen_increased);
 			if (gen_increased) {
 				delta += nr_pages;
-				list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
+				batch_end = &folio->lru;
+
 				/* don't count the workingset being lazily promoted */
 				if (refs + workingset != BIT(LRU_REFS_WIDTH) + 1) {
 					int tier = lru_tier_from_refs(refs, workingset);
@@ -3970,11 +3986,14 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 					protected[tier] += nr_pages;
 				}
 			} else {
+				flush_lru_batch(head, &batch_end, target_list);
 				list_move(&folio->lru, &lrugen->folios[new_gen][type][zone]);
 			}
 			if (!--remaining)
 				break;
 		}
+		flush_lru_batch(head, &batch_end, target_list);
+
 		WRITE_ONCE(lrugen->nr_pages[old_gen][type][zone],
 			   lrugen->nr_pages[old_gen][type][zone] - delta);
 		WRITE_ONCE(lrugen->nr_pages[target_gen][type][zone],
-- 
2.34.1