[PATCH] mm: vmscan : pgdemote vmstat is not getting updated when MGLRU is enabled.

[Donet Tom <donettom@linux.ibm.com>]

When MGLRU is enabled, the pgdemote_kswapd, pgdemote_direct, and
pgdemote_khugepaged stats in vmstat are not being updated.

'Commit f77f0c751478 ("mm,memcg: provide per-cgroup counters for
NUMA balancing operations")' moved the pgdemote vmstat update
from demote_folio_list() to shrink_inactive_list(), which is in
the normal LRU path. As a result, the pgdemote stats are updated
correctly for the normal LRU but not for MGLRU.

To address this, we have added the pgdemote stat update in the
evict_folios() function, which is in the MGLRU path. With this
patch, the pgdemote stats will now be updated correctly when MGLRU
is enabled.

Without this patch vmstat output when MGLRU is enabled
======================================================
pgdemote_kswapd 0
pgdemote_direct 0
pgdemote_khugepaged 0

With this patch vmstat output when MGLRU is enabled
===================================================
pgdemote_kswapd 43234
pgdemote_direct 4691
pgdemote_khugepaged 0

Fixes: f77f0c751478 ("mm,memcg: provide per-cgroup counters for NUMA balancing operations")
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
---
 mm/vmscan.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9a859b7d18d7..b1ec5ece067e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4642,6 +4642,9 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
 		reset_batch_size(walk);
 	}
 
+	__mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(),
+					stat.nr_demoted);
+
 	item = PGSTEAL_KSWAPD + reclaimer_offset();
 	if (!cgroup_reclaim(sc))
 		__count_vm_events(item, reclaimed);
-- 
2.43.5