mm/vmstat: convert NUMA statistics to basic NUMA counters

NUMA statistics are maintained on the zone level for hits, misses, foreign
etc but nothing relies on them being perfectly accurate for functional
correctness.  The counters are used by userspace to get a general overview
of a workloads NUMA behaviour but the page allocator incurs a high cost to
maintain perfect accuracy similar to what is required for a vmstat like
NR_FREE_PAGES.  There even is a sysctl vm.numa_stat to allow userspace to
turn off the collection of NUMA statistics like NUMA_HIT.

This patch converts NUMA_HIT and friends to be NUMA events with similar
accuracy to VM events.  There is a possibility that slight errors will be
introduced but the overall trend as seen by userspace will be similar.
The counters are no longer updated from vmstat_refresh context as it is
unnecessary overhead for counters that may never be read by userspace.
Note that counters could be maintained at the node level to save space but
it would have a user-visible impact due to /proc/zoneinfo.

[lkp@intel.com: Fix misplaced closing brace for !CONFIG_NUMA]

Link: https://lkml.kernel.org/r/20210512095458.30632-4-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 29 insertions, 27 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0d6bb737e5a2..f86018d5e362 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -135,10 +135,10 @@ enum numa_stat_item {
 	NUMA_INTERLEAVE_HIT,	/* interleaver preferred this zone */
 	NUMA_LOCAL,		/* allocation from local node */
 	NUMA_OTHER,		/* allocation from other node */
-	NR_VM_NUMA_STAT_ITEMS
+	NR_VM_NUMA_EVENT_ITEMS
 };
 #else
-#define NR_VM_NUMA_STAT_ITEMS 0
+#define NR_VM_NUMA_EVENT_ITEMS 0
 #endif
 
 enum zone_stat_item {
@@ -357,7 +357,12 @@ struct per_cpu_zonestat {
 	s8 stat_threshold;
 #endif
 #ifdef CONFIG_NUMA
-	u16 vm_numa_stat_diff[NR_VM_NUMA_STAT_ITEMS];
+	/*
+	 * Low priority inaccurate counters that are only folded
+	 * on demand. Use a large type to avoid the overhead of
+	 * folding during refresh_cpu_vm_stats.
+	 */
+	unsigned long vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
 #endif
 };
 
@@ -623,7 +628,7 @@ struct zone {
 	ZONE_PADDING(_pad3_)
 	/* Zone statistics */
 	atomic_long_t		vm_stat[NR_VM_ZONE_STAT_ITEMS];
-	atomic_long_t		vm_numa_stat[NR_VM_NUMA_STAT_ITEMS];
+	atomic_long_t		vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
 } ____cacheline_internodealigned_in_smp;
 
 enum pgdat_flags {
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 0c5f36504613..59748bbbba4c 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -138,34 +138,27 @@ static inline void vm_events_fold_cpu(int cpu)
  * Zone and node-based page accounting with per cpu differentials.
  */
 extern atomic_long_t vm_zone_stat[NR_VM_ZONE_STAT_ITEMS];
-extern atomic_long_t vm_numa_stat[NR_VM_NUMA_STAT_ITEMS];
 extern atomic_long_t vm_node_stat[NR_VM_NODE_STAT_ITEMS];
+extern atomic_long_t vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
 
 #ifdef CONFIG_NUMA
-static inline void zone_numa_state_add(long x, struct zone *zone,
-				 enum numa_stat_item item)
+static inline void zone_numa_event_add(long x, struct zone *zone,
+				enum numa_stat_item item)
 {
-	atomic_long_add(x, &zone->vm_numa_stat[item]);
-	atomic_long_add(x, &vm_numa_stat[item]);
+	atomic_long_add(x, &zone->vm_numa_event[item]);
+	atomic_long_add(x, &vm_numa_event[item]);
 }
 
-static inline unsigned long global_numa_state(enum numa_stat_item item)
+static inline unsigned long zone_numa_event_state(struct zone *zone,
+					enum numa_stat_item item)
 {
-	long x = atomic_long_read(&vm_numa_stat[item]);
-
-	return x;
+	return atomic_long_read(&zone->vm_numa_event[item]);
 }
 
-static inline unsigned long zone_numa_state_snapshot(struct zone *zone,
-					enum numa_stat_item item)
+static inline unsigned long
+global_numa_event_state(enum numa_stat_item item)
 {
-	long x = atomic_long_read(&zone->vm_numa_stat[item]);
-	int cpu;
-
-	for_each_online_cpu(cpu)
-		x += per_cpu_ptr(zone->per_cpu_zonestats, cpu)->vm_numa_stat_diff[item];
-
-	return x;
+	return atomic_long_read(&vm_numa_event[item]);
 }
 #endif /* CONFIG_NUMA */
 
@@ -245,18 +238,22 @@ static inline unsigned long zone_page_state_snapshot(struct zone *zone,
 }
 
 #ifdef CONFIG_NUMA
-extern void __inc_numa_state(struct zone *zone, enum numa_stat_item item);
+extern void __count_numa_event(struct zone *zone, enum numa_stat_item item);
 extern unsigned long sum_zone_node_page_state(int node,
 					      enum zone_stat_item item);
-extern unsigned long sum_zone_numa_state(int node, enum numa_stat_item item);
+extern unsigned long sum_zone_numa_event_state(int node, enum numa_stat_item item);
 extern unsigned long node_page_state(struct pglist_data *pgdat,
 						enum node_stat_item item);
 extern unsigned long node_page_state_pages(struct pglist_data *pgdat,
 					   enum node_stat_item item);
+extern void fold_vm_numa_events(void);
 #else
 #define sum_zone_node_page_state(node, item) global_zone_page_state(item)
 #define node_page_state(node, item) global_node_page_state(item)
 #define node_page_state_pages(node, item) global_node_page_state_pages(item)
+static inline void fold_vm_numa_events(void)
+{
+}
 #endif /* CONFIG_NUMA */
 
 #ifdef CONFIG_SMP
@@ -428,7 +425,7 @@ static inline const char *numa_stat_name(enum numa_stat_item item)
 static inline const char *node_stat_name(enum node_stat_item item)
 {
 	return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
-			   NR_VM_NUMA_STAT_ITEMS +
+			   NR_VM_NUMA_EVENT_ITEMS +
 			   item];
 }
 
@@ -440,7 +437,7 @@ static inline const char *lru_list_name(enum lru_list lru)
 static inline const char *writeback_stat_name(enum writeback_stat_item item)
 {
 	return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
-			   NR_VM_NUMA_STAT_ITEMS +
+			   NR_VM_NUMA_EVENT_ITEMS +
 			   NR_VM_NODE_STAT_ITEMS +
 			   item];
 }
@@ -449,7 +446,7 @@ static inline const char *writeback_stat_name(enum writeback_stat_item item)
 static inline const char *vm_event_name(enum vm_event_item item)
 {
 	return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
-			   NR_VM_NUMA_STAT_ITEMS +
+			   NR_VM_NUMA_EVENT_ITEMS +
 			   NR_VM_NODE_STAT_ITEMS +
 			   NR_VM_WRITEBACK_STAT_ITEMS +
 			   item];