[PATCH v6 6/7] mm/mglru: add lruvec_gen_size() helper

[Ridong Chen <ridong.chen@linux.dev>]

From: Ridong Chen <chenridong@xiaomi.com>

The number of pages of a given type in a generation is computed by
summing lrugen->nr_pages[gen][type][] over all zones and clamping each
per-zone counter to >= 0, since the counters are updated locklessly and
can transiently go negative. This loop is open-coded in
lruvec_evictable_size() and in the debugfs lru_gen output.

Add lruvec_gen_size() to compute it from a seq, and convert both users.
Put it in mm/vmscan.h so that the vmscan tracepoints, which include that
header, can use it as well.
An upcoming tracepoint and the MGLRU swappiness rework will also use it.

No functional change.

Suggested-by: Barry Song <baohua@kernel.org>
Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
---
 mm/vmscan.c | 18 ++++++------------
 mm/vmscan.h | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3054175717ab..1581b73aec56 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4207,18 +4207,15 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
 
 static unsigned long lruvec_evictable_size(struct lruvec *lruvec, int swappiness)
 {
-	int gen, type, zone;
+	int type;
 	unsigned long seq, total = 0;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	DEFINE_MAX_SEQ(lruvec);
 	DEFINE_MIN_SEQ(lruvec);
 
 	for_each_evictable_type(type, swappiness) {
-		for (seq = min_seq[type]; seq <= max_seq; seq++) {
-			gen = lru_gen_from_seq(seq);
-			for (zone = 0; zone < MAX_NR_ZONES; zone++)
-				total += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
-		}
+		for (seq = min_seq[type]; seq <= max_seq; seq++)
+			total += lruvec_gen_size(lrugen, type, seq);
 	}
 
 	return total;
@@ -5723,20 +5720,17 @@ static int lru_gen_seq_show(struct seq_file *m, void *v)
 		seq = 0;
 
 	for (; seq <= max_seq; seq++) {
-		int type, zone;
+		int type;
 		int gen = lru_gen_from_seq(seq);
 		unsigned long birth = READ_ONCE(lruvec->lrugen.timestamps[gen]);
 
 		seq_printf(m, " %10lu %10u", seq, jiffies_to_msecs(jiffies - birth));
 
 		for (type = 0; type < ANON_AND_FILE; type++) {
-			unsigned long size = 0;
 			char mark = full && seq < min_seq[type] ? 'x' : ' ';
 
-			for (zone = 0; zone < MAX_NR_ZONES; zone++)
-				size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
-
-			seq_printf(m, " %10lu%c", size, mark);
+			seq_printf(m, " %10lu%c",
+				   lruvec_gen_size(lrugen, type, seq), mark);
 		}
 
 		seq_putc(m, '\n');
diff --git a/mm/vmscan.h b/mm/vmscan.h
index adb22e80d760..c6b583fc7493 100644
--- a/mm/vmscan.h
+++ b/mm/vmscan.h
@@ -3,6 +3,7 @@
 #define _MM_VMSCAN_H
 
 #include <linux/gfp_types.h>
+#include <linux/mm_inline.h>
 #include <linux/nodemask.h>
 #include <linux/swap.h>
 #include <linux/types.h>
@@ -115,4 +116,19 @@ struct scan_control {
 	struct reclaim_state reclaim_state;
 };
 
+#ifdef CONFIG_LRU_GEN
+/* The number of pages of @type in the generation @seq, summed over all zones */
+static inline unsigned long lruvec_gen_size(struct lru_gen_folio *lrugen,
+					    int type, unsigned long seq)
+{
+	int gen = lru_gen_from_seq(seq);
+	unsigned long size = 0;
+
+	for (int zone = 0; zone < MAX_NR_ZONES; zone++)
+		size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
+
+	return size;
+}
+#endif /* CONFIG_LRU_GEN */
+
 #endif /* _MM_VMSCAN_H */
-- 
2.34.1