[RFC PATCH 6/8] memcg: add stats for offline memcgs recharging

[Yosry Ahmed <yosryahmed@xxxxxxxxxx>]

Add vm events for scanning pages for recharge, successfully recharging
pages, and cancelling a recharge due to failure to charge the target
memcg.

Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
 include/linux/vm_event_item.h | 5 +++++
 mm/memcontrol.c               | 6 ++++++
 mm/vmstat.c                   | 6 +++++-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 8abfa1240040..cd80c00c50c2 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -60,6 +60,11 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		PAGEOUTRUN, PGROTATED,
 		DROP_PAGECACHE, DROP_SLAB,
 		OOM_KILL,
+#ifdef CONFIG_MEMCG
+		RECHARGE_PGSCANNED,
+		RECHARGE_PGMOVED,
+		RECHARGE_PGCANCELLED,
+#endif
 #ifdef CONFIG_NUMA_BALANCING
 		NUMA_PTE_UPDATES,
 		NUMA_HUGE_PTE_UPDATES,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cf9fb51ecfcc..2fe9c6f1be80 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6394,6 +6394,8 @@ static bool mem_cgroup_recharge_folio(struct folio *folio,
 				      old_memcg, new_memcg);
 	cancel_charge(err ? new_memcg : old_memcg, nr_pages);
 out:
+	count_vm_events(err ? RECHARGE_PGCANCELLED : RECHARGE_PGMOVED,
+			nr_pages);
 	return err == 0;
 }
 
@@ -6469,6 +6471,7 @@ static bool memcg_recharge_lruvec_list(struct lruvec *lruvec,
 	int isolated_idx = NR_ISOLATED_ANON + is_file_lru(lru);
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	unsigned long *nr_recharged = arg;
+	unsigned long nr_scanned = 0;
 	unsigned long nr_staged = 0;
 	LIST_HEAD(folios_skipped);
 	LIST_HEAD(folios_staged);
@@ -6505,6 +6508,7 @@ static bool memcg_recharge_lruvec_list(struct lruvec *lruvec,
 			continue;
 		}
 
+		nr_scanned += folio_nr_pages(folio);
 		if (unlikely(!folio_try_get(folio))) {
 			list_move(&folio->lru, &folios_skipped);
 			continue;
@@ -6543,6 +6547,7 @@ static bool memcg_recharge_lruvec_list(struct lruvec *lruvec,
 	}
 	mem_cgroup_end_move_charge(memcg);
 	mod_lruvec_state(lruvec, isolated_idx, -nr_staged);
+	count_vm_events(RECHARGE_PGSCANNED, nr_scanned);
 	return false;
 }
 
@@ -6679,6 +6684,7 @@ void folio_memcg_deferred_recharge(struct folio *folio)
 	if (unlikely(!memcg_recharge_wq))
 		return;
 
+	count_vm_events(RECHARGE_PGSCANNED, folio_nr_pages(folio));
 	if (unlikely(!folio_try_get(folio)))
 		return;
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index b731d57996c5..e425a1aa7890 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1303,7 +1303,11 @@ const char * const vmstat_text[] = {
 	"drop_pagecache",
 	"drop_slab",
 	"oom_kill",
-
+#ifdef CONFIG_MEMCG
+	"recharge_pgs_scanned",
+	"recharge_pgs_moved",
+	"recharge_pgs_cancelled",
+#endif
 #ifdef CONFIG_NUMA_BALANCING
 	"numa_pte_updates",
 	"numa_huge_pte_updates",
-- 
2.41.0.255.g8b1d071c50-goog