[RFC PATCH 2/3] mm/vmscan: handle racing max_seq advancement

[Ehab Ababneh]

When kswapd support is expanded to multiple threads per node, concurrent
aging becomes more likely and try_to_inc_max_seq() can lose a race to
another aging pass that has already advanced max_seq.

Treat that case as success instead of warning, since the desired state has
already been reached by a concurrent updater.

Signed-off-by: Ehab Ababneh <ehab.ababneh@xxxxxxxxx>
---
 mm/vmscan.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index fbb04848f59b..ad2b398a68f9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3942,15 +3942,18 @@ static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 restart:
 	if (seq < READ_ONCE(lrugen->max_seq))
-		return false;
+		return true;
 
 	lruvec_lock_irq(lruvec);
 
 	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
 
 	success = seq == lrugen->max_seq;
-	if (!success)
+	if (!success) {
+		/* Concurrent aging advanced max_seq first; goal achieved. */
+		success = true;
 		goto unlock;
+	}
 
 	for (type = 0; type < ANON_AND_FILE; type++) {
 		if (get_nr_gens(lruvec, type) != MAX_NR_GENS)
@@ -4045,10 +4048,8 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long seq,
 			walk_mm(mm, walk);
 	} while (mm);
 done:
-	if (success) {
+	if (success)
 		success = inc_max_seq(lruvec, seq, swappiness);
-		WARN_ON_ONCE(!success);
-	}
 
 	return success;
 }
-- 
2.43.0