[PATCH RFC 3/4] mm/vmstat: rename pgdemote_* to pgdemote_dst_* and add pgdemote_src_*

[Li Zhijian <lizhijian@fujitsu.com>]

pgdemote_src_*: pages demoted from this node.
pgdemote_dst_*: pages demoted to this node.

So that we are able to know their demotion per-node stats by checking this.

In the environment, node0 and node1 are DRAM, node3 is PMEM.

Global stats:
$ grep -E 'demote' /proc/vmstat
pgdemote_src_kswapd 130155
pgdemote_src_direct 113497
pgdemote_src_khugepaged 0
pgdemote_dst_kswapd 130155
pgdemote_dst_direct 113497
pgdemote_dst_khugepaged 0

Per-node stats:
$ grep demote /sys/devices/system/node/node0/vmstat
pgdemote_src_kswapd 68454
pgdemote_src_direct 83431
pgdemote_src_khugepaged 0
pgdemote_dst_kswapd 0
pgdemote_dst_direct 0
pgdemote_dst_khugepaged 0

$ grep demote /sys/devices/system/node/node1/vmstat
pgdemote_src_kswapd 185834
pgdemote_src_direct 30066
pgdemote_src_khugepaged 0
pgdemote_dst_kswapd 0
pgdemote_dst_direct 0
pgdemote_dst_khugepaged 0

$ grep demote /sys/devices/system/node/node3/vmstat
pgdemote_src_kswapd 0
pgdemote_src_direct 0
pgdemote_src_khugepaged 0
pgdemote_dst_kswapd 254288
pgdemote_dst_direct 113497
pgdemote_dst_khugepaged 0

From above stats, we know node3 is the demotion destination which one
the node0 and node1 will demote to.

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---
RFC: their names are open to discussion, maybe pgdemote_from/to_*
Another defect of this patch is that, SUM(pgdemote_src_*) is always same
as SUM(pgdemote_dst_*) in the global stats, shall we hide one of them.
---
 include/linux/mmzone.h |  9 ++++++---
 mm/vmscan.c            | 13 ++++++++++---
 mm/vmstat.c            |  9 ++++++---
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ad0309eea850..a6140d894bec 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -207,9 +207,12 @@ enum node_stat_item {
 	PGPROMOTE_SUCCESS,	/* promote successfully */
 	PGPROMOTE_CANDIDATE,	/* candidate pages to promote */
 	/* PGDEMOTE_*: pages demoted */
-	PGDEMOTE_KSWAPD,
-	PGDEMOTE_DIRECT,
-	PGDEMOTE_KHUGEPAGED,
+	PGDEMOTE_SRC_KSWAPD,
+	PGDEMOTE_SRC_DIRECT,
+	PGDEMOTE_SRC_KHUGEPAGED,
+	PGDEMOTE_DST_KSWAPD,
+	PGDEMOTE_DST_DIRECT,
+	PGDEMOTE_DST_KHUGEPAGED,
 #endif
 	NR_VM_NODE_STAT_ITEMS
 };
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2f1fb4ec3235..55d2287d7150 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1111,13 +1111,18 @@ void drop_slab(void)
 static int reclaimer_offset(void)
 {
 	BUILD_BUG_ON(PGSTEAL_DIRECT - PGSTEAL_KSWAPD !=
-			PGDEMOTE_DIRECT - PGDEMOTE_KSWAPD);
+			PGDEMOTE_SRC_DIRECT - PGDEMOTE_SRC_KSWAPD);
 	BUILD_BUG_ON(PGSTEAL_DIRECT - PGSTEAL_KSWAPD !=
 			PGSCAN_DIRECT - PGSCAN_KSWAPD);
 	BUILD_BUG_ON(PGSTEAL_KHUGEPAGED - PGSTEAL_KSWAPD !=
-			PGDEMOTE_KHUGEPAGED - PGDEMOTE_KSWAPD);
+			PGDEMOTE_SRC_KHUGEPAGED - PGDEMOTE_SRC_KSWAPD);
 	BUILD_BUG_ON(PGSTEAL_KHUGEPAGED - PGSTEAL_KSWAPD !=
 			PGSCAN_KHUGEPAGED - PGSCAN_KSWAPD);
+	BUILD_BUG_ON(PGDEMOTE_SRC_DIRECT - PGDEMOTE_SRC_KSWAPD !=
+			PGDEMOTE_DST_DIRECT - PGDEMOTE_DST_KSWAPD);
+	BUILD_BUG_ON(PGDEMOTE_SRC_KHUGEPAGED - PGDEMOTE_SRC_KSWAPD !=
+			PGDEMOTE_DST_KHUGEPAGED - PGDEMOTE_DST_KSWAPD);
+
 
 	if (current_is_kswapd())
 		return 0;
@@ -1678,8 +1683,10 @@ static unsigned int demote_folio_list(struct list_head *demote_folios,
 		      (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION,
 		      &nr_succeeded);
 
+	mod_node_page_state(pgdat,
+		    PGDEMOTE_SRC_KSWAPD + reclaimer_offset(), nr_succeeded);
 	mod_node_page_state(NODE_DATA(target_nid),
-		    PGDEMOTE_KSWAPD + reclaimer_offset(), nr_succeeded);
+		    PGDEMOTE_DST_KSWAPD + reclaimer_offset(), nr_succeeded);
 
 	return nr_succeeded;
 }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index f141c48c39e4..63f106a5e008 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1244,9 +1244,12 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_NUMA_BALANCING
 	"pgpromote_success",
 	"pgpromote_candidate",
-	"pgdemote_kswapd",
-	"pgdemote_direct",
-	"pgdemote_khugepaged",
+	"pgdemote_src_kswapd",
+	"pgdemote_src_direct",
+	"pgdemote_src_khugepaged",
+	"pgdemote_dst_kswapd",
+	"pgdemote_dst_direct",
+	"pgdemote_dst_khugepaged",
 #endif
 
 	/* enum writeback_stat_item counters */
-- 
2.29.2