[PATCH 1/2] mm/vmscan: Accumulate nr_demoted for accurate demotion statistics

[Li Zhijian <lizhijian@fujitsu.com>]

In the shrink_folio_list() function, demote_folio_list() can be called
multiple times, which can lead to inaccurate demotion statistics if the
number of demoted pages is not accumulated correctly.

Accumulate the nr_demoted count across multiple calls to
demote_folio_list(), ensuring accurate reporting of demotion statistics.

Fixes: f77f0c751478 ("mm,memcg: provide per-cgroup counters for NUMA balancing operations")
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9a859b7d18d7..430d580e37dd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1522,7 +1522,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 	/* 'folio_list' is always empty here */
 
 	/* Migrate folios selected for demotion */
-	stat->nr_demoted = demote_folio_list(&demote_folios, pgdat);
+	stat->nr_demoted += demote_folio_list(&demote_folios, pgdat);
 	nr_reclaimed += stat->nr_demoted;
 	/* Folios that could not be demoted are still in @demote_folios */
 	if (!list_empty(&demote_folios)) {
-- 
2.44.0