Merge: [FJ10.0 Bug]: Demotion doesn't occurs when the DRAM is exhausted. [rhel-10.0]

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/321

JIRA: https://issues.redhat.com/browse/RHEL-71335

- mm/vmscan: accumulate nr_demoted for accurate demotion statistics (Herton R. Krzesinski) [[RHEL-71335](https://issues.redhat.com/browse/RHEL-71335)]
- mm: vmscan : pgdemote vmstat is not getting updated when MGLRU is enabled. (Herton R. Krzesinski) [[RHEL-71335](https://issues.redhat.com/browse/RHEL-71335)]

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>

Approved-by: Rafael Aquini <raquini@redhat.com>
Approved-by: John W. Linville <linville@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Jan Stancek <jstancek@redhat.com>

Author: jstancek

mm/vmscan.c

@@ -1053,7 +1053,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 	struct folio_batch free_folios;
 	LIST_HEAD(ret_folios);
 	LIST_HEAD(demote_folios);
-	unsigned int nr_reclaimed = 0;
+	unsigned int nr_reclaimed = 0, nr_demoted = 0;
 	unsigned int pgactivate = 0;
 	bool do_demote_pass;
 	struct swap_iocb *plug = NULL;
@@ -1522,8 +1522,9 @@ 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);
-	nr_reclaimed += stat->nr_demoted;
+	nr_demoted = demote_folio_list(&demote_folios, pgdat);
+	nr_reclaimed += nr_demoted;
+	stat->nr_demoted += nr_demoted;
 	/* Folios that could not be demoted are still in @demote_folios */
 	if (!list_empty(&demote_folios)) {
 		/* Folios which weren't demoted go back on @folio_list */
@@ -4637,6 +4638,9 @@ 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);