[RFC PATCH v5 02/14] mm/mglru: extract lruvec_populated_min_seq() helper

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

From: Kairui Song <kasong@tencent.com>

The search for the oldest populated generation of a type, previously
embedded in try_to_inc_min_seq(), is extracted into the new
lruvec_populated_min_seq() helper. It returns the oldest populated seq
of a given type, bounded by the given max_seq so the search never goes
beyond it.

No functional change.

Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 43 +++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3be0d6c04a82..500ef23949fd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4131,30 +4131,45 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
 	return true;
 }
 
+/* Similar to lruvec_evictable_size, return the oldest populated seq of the type */
+static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
+					      unsigned long max_seq)
+{
+	int gen, zone;
+	unsigned long min_seq;
+	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+
+	lockdep_assert_held(&lruvec->lru_lock);
+
+	min_seq = READ_ONCE(lrugen->min_seq[type]);
+	while (min_seq <= max_seq) {
+		gen = lru_gen_from_seq(min_seq);
+		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+			if (!list_empty(&lrugen->folios[gen][type][zone]))
+				return min_seq;
+		}
+		min_seq++;
+	}
+
+	return max_seq;
+}
+
 static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
 {
-	int gen, type, zone;
+	int type;
 	bool seq_inc_flag = false;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	DEFINE_MIN_SEQ(lruvec);
+	unsigned long seq;
 
 	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
 
-	/* find the oldest populated generation */
+	/* Requires at least MIN_NR_GENS gens for basic functionality */
+	seq = lrugen->max_seq - MIN_NR_GENS;
 	for_each_evictable_type(type, swappiness) {
-		while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) {
-			gen = lru_gen_from_seq(min_seq[type]);
-
-			for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-				if (!list_empty(&lrugen->folios[gen][type][zone]))
-					goto next;
-			}
-
-			min_seq[type]++;
+		min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
+		if (min_seq[type] > lrugen->min_seq[type])
 			seq_inc_flag = true;
-		}
-next:
-		;
 	}
 
 	/*
-- 
2.34.1