mm/mglru: improve should_run_aging()

scan_control *sc does not need to be passed into should_run_aging(), as it
provides only the reclaim priority.  This can be moved to
get_nr_to_scan().

Refactor should_run_aging() and get_nr_to_scan() to improve code
readability.  No functional changes.

Link: https://lkml.kernel.org/r/20240214060538.3524462-3-kinseyho@google.comSigned-off-by: Kinsey Ho <kinseyho@google.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Donet Tom <donettom@linux.vnet.ibm.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -4584,14 +4584,13 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
 }
 
 static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
-			     struct scan_control *sc, bool can_swap, unsigned long *nr_to_scan)
+			     bool can_swap, unsigned long *nr_to_scan)
 {
 	int gen, type, zone;
 	unsigned long old = 0;
 	unsigned long young = 0;
 	unsigned long total = 0;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
-	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	DEFINE_MIN_SEQ(lruvec);
 
 	/* whether this lruvec is completely out of cold folios */
@@ -4619,13 +4618,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 		}
 	}
 
-	/* try to scrape all its memory if this memcg was deleted */
-	if (!mem_cgroup_online(memcg)) {
-		*nr_to_scan = total;
-		return false;
-	}
-
-	*nr_to_scan = total >> sc->priority;
+	*nr_to_scan = total;
 
 	/*
 	 * The aging tries to be lazy to reduce the overhead, while the eviction
@@ -4657,6 +4650,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
  */
 static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool can_swap)
 {
+	bool success;
 	unsigned long nr_to_scan;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	DEFINE_MAX_SEQ(lruvec);
@@ -4664,14 +4658,17 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, bool
 	if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg))
 		return -1;
 
-	if (!should_run_aging(lruvec, max_seq, sc, can_swap, &nr_to_scan))
-		return nr_to_scan;
+	success = should_run_aging(lruvec, max_seq, can_swap, &nr_to_scan);
 
-	/* skip the aging path at the default priority */
-	if (sc->priority == DEF_PRIORITY)
+	/* try to scrape all its memory if this memcg was deleted */
+	if (nr_to_scan && !mem_cgroup_online(memcg))
 		return nr_to_scan;
 
-	/* skip this lruvec as it's low on cold folios */
+	/* try to get away with not aging at the default priority */
+	if (!success || sc->priority == DEF_PRIORITY)
+		return nr_to_scan >> sc->priority;
+
+	/* stop scanning this lruvec as it's low on cold folios */
 	return try_to_inc_max_seq(lruvec, max_seq, can_swap, false) ? -1 : 0;
 }