Flush SLRU counters in checkpointer process

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index de0bbbfa79..1e2eea0d69 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -504,7 +504,6 @@ CheckpointerMain(void)
 
 		/* Report pending statistics to the cumulative stats system */
 		pgstat_report_checkpointer();
-		pgstat_report_wal(true);
 
 		/*
 		 * If any checkpoint flags have been set, redo the loop to handle the
@@ -582,7 +581,6 @@ HandleCheckpointerInterrupts(void)
 		PendingCheckpointerStats.requested_checkpoints++;
 		ShutdownXLOG(0, 0);
 		pgstat_report_checkpointer();
-		pgstat_report_wal(true);
 
 		/* Normal exit from the checkpointer is here */
 		proc_exit(0);			/* done */
diff --git a/src/backend/utils/activity/pgstat_checkpointer.c b/src/backend/utils/activity/pgstat_checkpointer.c
index 3e9ab45103..d9ff536404 100644
--- a/src/backend/utils/activity/pgstat_checkpointer.c
+++ b/src/backend/utils/activity/pgstat_checkpointer.c
@@ -24,10 +24,22 @@ PgStat_CheckpointerStats PendingCheckpointerStats = {0};
 
 
 /*
- * Report checkpointer statistics
+ * Report checkpointer statistics along with
+ * wal and slru statistics
  */
 void
 pgstat_report_checkpointer(void)
+{
+	pgstat_flush_checkpointer();
+	pgstat_report_wal(true);
+	pgstat_report_slru();
+}
+
+/*
+ * Flush out locally pending checkpointer stats
+ */
+void
+pgstat_flush_checkpointer(void)
 {
 	/* We assume this initializes to zeroes */
 	static const PgStat_CheckpointerStats all_zeroes;
diff --git a/src/backend/utils/activity/pgstat_slru.c b/src/backend/utils/activity/pgstat_slru.c
index 1b16740f39..8da5b2b3e2 100644
--- a/src/backend/utils/activity/pgstat_slru.c
+++ b/src/backend/utils/activity/pgstat_slru.c
@@ -35,6 +35,19 @@ static PgStat_SLRUStats pending_SLRUStats[SLRU_NUM_ELEMENTS];
 bool		have_slrustats = false;
 
 
+/*
+ * Calculate how much SLRU usage counters have increased and update
+ * shared statistics.
+ *
+ * Must be called by processes that interact with SLRU caches, that
+ * do not call pgstat_report_stat(), like checkpointer.
+ */
+void
+pgstat_report_slru(void)
+{
+	pgstat_slru_flush(true);
+}
+
 /*
  * Reset counters for a single SLRU.
  *
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index d3e965d744..d2dbc5dcb1 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -592,6 +592,7 @@ extern PgStat_StatReplSlotEntry *pgstat_fetch_replslot(NameData slotname);
  * Functions in pgstat_slru.c
  */
 
+extern void pgstat_report_slru(void);
 extern void pgstat_reset_slru(const char *);
 extern void pgstat_count_slru_page_zeroed(int slru_idx);
 extern void pgstat_count_slru_page_hit(int slru_idx);
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 08412d6404..6e688e5ace 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -526,6 +526,7 @@ extern void pgstat_bgwriter_snapshot_cb(void);
 
 extern void pgstat_checkpointer_reset_all_cb(TimestampTz ts);
 extern void pgstat_checkpointer_snapshot_cb(void);
+extern void pgstat_flush_checkpointer(void);
 
 
 /*
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 1d84407a03..a7c009383f 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -783,11 +783,14 @@ SELECT sessions > :db_stat_sessions FROM pg_stat_database WHERE datname = (SELEC
 (1 row)
 
 -- Test pg_stat_bgwriter checkpointer-related stats, together with pg_stat_wal
+-- and pg_stat_slru
 SELECT checkpoints_req AS rqst_ckpts_before FROM pg_stat_bgwriter \gset
 -- Test pg_stat_wal (and make a temp table so our temp schema exists)
 SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
 CREATE TEMP TABLE test_stats_temp AS SELECT 17;
 DROP TABLE test_stats_temp;
+-- Test pg_stat_slru, checkpoint should generate SLRU flushes
+SELECT SUM(flushes) AS slru_flushes_before from pg_stat_slru \gset
 -- Checkpoint twice: The checkpointer reports stats after reporting completion
 -- of the checkpoint. But after a second checkpoint we'll see at least the
 -- results of the first.
@@ -805,6 +808,12 @@ SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
  t
 (1 row)
 
+SELECT SUM(flushes) > :slru_flushes_before FROM pg_stat_slru;
+ ?column? 
+----------
+ t
+(1 row)
+
 -- Test pg_stat_get_backend_idset() and some allied functions.
 -- In particular, verify that their notion of backend ID matches
 -- our temp schema index.
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index b4d6753c71..cb1173f7ae 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -388,6 +388,7 @@ SELECT pg_stat_force_next_flush();
 SELECT sessions > :db_stat_sessions FROM pg_stat_database WHERE datname = (SELECT current_database());
 
 -- Test pg_stat_bgwriter checkpointer-related stats, together with pg_stat_wal
+-- and pg_stat_slru
 SELECT checkpoints_req AS rqst_ckpts_before FROM pg_stat_bgwriter \gset
 
 -- Test pg_stat_wal (and make a temp table so our temp schema exists)
@@ -396,6 +397,9 @@ SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
 CREATE TEMP TABLE test_stats_temp AS SELECT 17;
 DROP TABLE test_stats_temp;
 
+-- Test pg_stat_slru, checkpoint should generate SLRU flushes
+SELECT SUM(flushes) AS slru_flushes_before from pg_stat_slru \gset
+
 -- Checkpoint twice: The checkpointer reports stats after reporting completion
 -- of the checkpoint. But after a second checkpoint we'll see at least the
 -- results of the first.
@@ -404,6 +408,7 @@ CHECKPOINT;
 
 SELECT checkpoints_req > :rqst_ckpts_before FROM pg_stat_bgwriter;
 SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
+SELECT SUM(flushes) > :slru_flushes_before FROM pg_stat_slru;
 
 -- Test pg_stat_get_backend_idset() and some allied functions.
 -- In particular, verify that their notion of backend ID matches

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index aaad5c5228..5eac4aa8e3 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -504,7 +504,6 @@ CheckpointerMain(void)
 
 		/* Report pending statistics to the cumulative stats system */
 		pgstat_report_checkpointer();
-		pgstat_report_wal(true);
 
 		/*
 		 * If any checkpoint flags have been set, redo the loop to handle the
@@ -582,7 +581,6 @@ HandleCheckpointerInterrupts(void)
 		PendingCheckpointerStats.requested_checkpoints++;
 		ShutdownXLOG(0, 0);
 		pgstat_report_checkpointer();
-		pgstat_report_wal(true);
 
 		/* Normal exit from the checkpointer is here */
 		proc_exit(0);			/* done */
diff --git a/src/backend/utils/activity/pgstat_checkpointer.c b/src/backend/utils/activity/pgstat_checkpointer.c
index 26dec112f6..fd4a1c1adc 100644
--- a/src/backend/utils/activity/pgstat_checkpointer.c
+++ b/src/backend/utils/activity/pgstat_checkpointer.c
@@ -24,10 +24,22 @@ PgStat_CheckpointerStats PendingCheckpointerStats = {0};
 
 
 /*
- * Report checkpointer and IO statistics
+ * Report checkpointer, IO, WAL and SLRU statistics
  */
 void
 pgstat_report_checkpointer(void)
+{
+	pgstat_flush_checkpointer();
+	pgstat_flush_wal(true);
+	pgstat_flush_io(true);
+	pgstat_slru_flush(true);
+}
+
+/*
+ * Flush out locally pending checkpointer stats
+ */
+void
+pgstat_flush_checkpointer(void)
 {
 	/* We assume this initializes to zeroes */
 	static const PgStat_CheckpointerStats all_zeroes;
@@ -62,11 +74,6 @@ pgstat_report_checkpointer(void)
 	 * Clear out the statistics buffer, so it can be re-used.
 	 */
 	MemSet(&PendingCheckpointerStats, 0, sizeof(PendingCheckpointerStats));
-
-	/*
-	 * Report IO statistics
-	 */
-	pgstat_flush_io(false);
 }
 
 /*
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 6badb2fde4..00851c9474 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -540,6 +540,7 @@ extern void pgstat_bgwriter_snapshot_cb(void);
 
 extern void pgstat_checkpointer_reset_all_cb(TimestampTz ts);
 extern void pgstat_checkpointer_snapshot_cb(void);
+extern void pgstat_flush_checkpointer(void);
 
 
 /*
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 937b2101b3..bae1b54b31 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -783,11 +783,14 @@ SELECT sessions > :db_stat_sessions FROM pg_stat_database WHERE datname = (SELEC
 (1 row)
 
 -- Test pg_stat_bgwriter checkpointer-related stats, together with pg_stat_wal
+-- and pg_stat_slru
 SELECT checkpoints_req AS rqst_ckpts_before FROM pg_stat_bgwriter \gset
 -- Test pg_stat_wal (and make a temp table so our temp schema exists)
 SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
 CREATE TEMP TABLE test_stats_temp AS SELECT 17;
 DROP TABLE test_stats_temp;
+-- Test pg_stat_slru, checkpoint should generate SLRU flushes
+SELECT SUM(flushes) AS slru_flushes_before from pg_stat_slru \gset
 -- Checkpoint twice: The checkpointer reports stats after reporting completion
 -- of the checkpoint. But after a second checkpoint we'll see at least the
 -- results of the first.
@@ -805,6 +808,12 @@ SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
  t
 (1 row)
 
+SELECT SUM(flushes) > :slru_flushes_before FROM pg_stat_slru;
+ ?column? 
+----------
+ t
+(1 row)
+
 -- Test pg_stat_get_backend_idset() and some allied functions.
 -- In particular, verify that their notion of backend ID matches
 -- our temp schema index.
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 74e592aa8a..dada15835f 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -388,6 +388,7 @@ SELECT pg_stat_force_next_flush();
 SELECT sessions > :db_stat_sessions FROM pg_stat_database WHERE datname = (SELECT current_database());
 
 -- Test pg_stat_bgwriter checkpointer-related stats, together with pg_stat_wal
+-- and pg_stat_slru
 SELECT checkpoints_req AS rqst_ckpts_before FROM pg_stat_bgwriter \gset
 
 -- Test pg_stat_wal (and make a temp table so our temp schema exists)
@@ -396,6 +397,9 @@ SELECT wal_bytes AS wal_bytes_before FROM pg_stat_wal \gset
 CREATE TEMP TABLE test_stats_temp AS SELECT 17;
 DROP TABLE test_stats_temp;
 
+-- Test pg_stat_slru, checkpoint should generate SLRU flushes
+SELECT SUM(flushes) AS slru_flushes_before from pg_stat_slru \gset
+
 -- Checkpoint twice: The checkpointer reports stats after reporting completion
 -- of the checkpoint. But after a second checkpoint we'll see at least the
 -- results of the first.
@@ -404,6 +408,7 @@ CHECKPOINT;
 
 SELECT checkpoints_req > :rqst_ckpts_before FROM pg_stat_bgwriter;
 SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
+SELECT SUM(flushes) > :slru_flushes_before FROM pg_stat_slru;
 
 -- Test pg_stat_get_backend_idset() and some allied functions.
 -- In particular, verify that their notion of backend ID matches