[PATCH 07/10] mm: vmscan: add page demotion counter

[Yang Shi]

Demoted pages are counted into reclaim_state->nr_demoted instead of
nr_reclaimed since they are not reclaimed actually.  They are still in
memory, but just migrated to PMEM.

Add pgdemote_kswapd and pgdemote_direct VM counters showed in
/proc/vmstat.

Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
---
 include/linux/vm_event_item.h |  2 ++
 include/linux/vmstat.h        |  1 +
 mm/vmscan.c                   | 14 ++++++++++++++
 mm/vmstat.c                   |  2 ++
 4 files changed, 19 insertions(+)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 47a3441..499a3aa 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -32,6 +32,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		PGREFILL,
 		PGSTEAL_KSWAPD,
 		PGSTEAL_DIRECT,
+		PGDEMOTE_KSWAPD,
+		PGDEMOTE_DIRECT,
 		PGSCAN_KSWAPD,
 		PGSCAN_DIRECT,
 		PGSCAN_DIRECT_THROTTLE,
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 2db8d60..eb5d21c 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -29,6 +29,7 @@ struct reclaim_stat {
 	unsigned nr_activate;
 	unsigned nr_ref_keep;
 	unsigned nr_unmap_fail;
+	unsigned nr_demoted;
 };
 
 #ifdef CONFIG_VM_EVENT_COUNTERS
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bdcab6b..3c7ba7e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1286,6 +1286,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 
 			if (has_nonram_online()) {
 				list_add(&page->lru, &demote_pages);
+				if (PageTransHuge(page))
+					stat->nr_demoted += HPAGE_PMD_NR;
+				else
+					stat->nr_demoted++;
 				unlock_page(page);
 				continue;
 			}
@@ -1523,7 +1527,17 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			putback_movable_pages(&demote_pages);
 
 			list_splice(&ret_pages, &demote_pages);
+
+			if (err > 0)
+				stat->nr_demoted -= err;
+			else
+				stat->nr_demoted = 0;
 		}
+
+		if (current_is_kswapd())
+			__count_vm_events(PGDEMOTE_KSWAPD, stat->nr_demoted);
+		else
+			__count_vm_events(PGDEMOTE_DIRECT, stat->nr_demoted);
 	}
 
 	mem_cgroup_uncharge_list(&free_pages);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 36b56f8..0e863e7 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1192,6 +1192,8 @@ int fragmentation_index(struct zone *zone, unsigned int order)
 	"pgrefill",
 	"pgsteal_kswapd",
 	"pgsteal_direct",
+	"pgdemote_kswapd",
+	"pgdemote_direct",
 	"pgscan_kswapd",
 	"pgscan_direct",
 	"pgscan_direct_throttle",
-- 
1.8.3.1