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

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

Commit f77f0c7 ("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

Link: https://lkml.kernel.org/r/20250109060540.451261-1-donettom@linux.ibm.com
Fixes: f77f0c7 ("mm,memcg: provide per-cgroup counters for NUMA balancing operations")
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Acked-by: Yu Zhao <yuzhao@google.com>
Tested-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Cc: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kaiyang Zhao <kaiyang2@cs.cmu.edu>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: donettom-1

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);