[PATCH v7 11/16] mm/mglru: Run aging when one type has no populatable folios

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

We may have scan budget remaining for anon or file
but no folios in populatable generations to scan.
In this case, `scan_folios()` may waste time scanning
that type while the other type still has populatable
folios.

Run aging in this case to make more folios
populatable. This also helps respect the scan budget
distribution determined by swappiness.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index bf30c5b95478..27c1547012bf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5104,7 +5104,8 @@ static bool lru_gen_imbalanced(struct lruvec *lruvec, struct scan_control *sc,
 }
 
 static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
-			     struct scan_control *sc, int swappiness)
+			     struct scan_control *sc, int swappiness,
+			     bool no_populatable)
 {
 	DEFINE_MIN_SEQ(lruvec);
 
@@ -5116,6 +5117,13 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 	if (sc->priority == DEF_PRIORITY)
 		return false;
 
+	/*
+	 * Run aging if scan budget remains but no folios
+	 * in populatable generations are available to scan.
+	 */
+	if (no_populatable)
+		return true;
+
 	/* better to run aging even though eviction is still possible */
 	if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq)
 		return true;
@@ -5220,20 +5228,17 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 	lru_gen_prepare_scan(lruvec, sc, memcg, swappiness, nr);
 
 	while (nr[LRU_GEN_ANON] > 0 || nr[LRU_GEN_FILE] > 0) {
+		unsigned long orig_file, orig_anon;
 		DEFINE_MAX_SEQ(lruvec);
+		bool no_populatable;
 
 		if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) {
 			need_rotate = true;
 			break;
 		}
 
-		if (should_run_aging(lruvec, max_seq, sc, swappiness)) {
-			trace_mm_mglru_aging(lruvec, sc, swappiness);
-			if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
-				need_rotate = true;
-			should_age = true;
-		}
-
+		orig_anon = nr[LRU_GEN_ANON];
+		orig_file = nr[LRU_GEN_FILE];
 		if (!evict_folio_lists(nr, lruvec, sc, swappiness, MIN_LRU_BATCH))
 			break;
 
@@ -5247,6 +5252,15 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 		if (root_reclaim(sc) && should_age)
 			break;
 
+		no_populatable = (nr[LRU_GEN_ANON] && nr[LRU_GEN_ANON] == orig_anon) ||
+				 (nr[LRU_GEN_FILE] && nr[LRU_GEN_FILE] == orig_file);
+		if (should_run_aging(lruvec, max_seq, sc, swappiness, no_populatable)) {
+			trace_mm_mglru_aging(lruvec, sc, swappiness);
+			if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false))
+				need_rotate = true;
+			should_age = true;
+		}
+
 		cond_resched();
 	}
 
-- 
2.34.1