[PATCH v2 0/3] Separate NUMA statistics from zone statistics

[PATCH v2 0/3] Separate NUMA statistics from zone statistics

[Kemi Wang]

Each page allocation updates a set of per-zone statistics with a call to
zone_statistics(). As discussed in 2017 MM summit, these are a substantial
source of overhead in the page allocator and are very rarely consumed. This
significant overhead in cache bouncing caused by zone counters (NUMA
associated counters) update in parallel in multi-threaded page allocation
(pointed out by Dave Hansen).

A link to the MM summit slides:
http://people.netfilter.org/hawk/presentations/MM-summit2017/MM-summit2017
-JesperBrouer.pdf

To mitigate this overhead, this patchset separates NUMA statistics from
zone statistics framework, and update NUMA counter threshold to a fixed
size of MAX_U16 - 2, as a small threshold greatly increases the update
frequency of the global counter from local per cpu counter (suggested by
Ying Huang). The rationality is that these statistics counters don't need
to be read often, unlike other VM counters, so it's not a problem to use a
large threshold and make readers more expensive.

With this patchset, we see 31.3% drop of CPU cycles(537-->369, see below)
for per single page allocation and reclaim on Jesper's page_bench03
benchmark. Meanwhile, this patchset keeps the same style of virtual memory
statistics with little end-user-visible effects (only move the numa stats
to show behind zone page stats, see the first patch for details).

I did an experiment of single page allocation and reclaim concurrently
using Jesper's page_bench03 benchmark on a 2-Socket Broadwell-based server
(88 processors with 126G memory) with different size of threshold of pcp
counter.

Benchmark provided by Jesper D Brouer(increase loop times to 10000000):
https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/mm/
bench

   Threshold   CPU cycles    Throughput(88 threads)
      32        799         241760478
      64        640         301628829
      125       537         358906028 <==> system by default
      256       468         412397590
      512       428         450550704
      4096      399         482520943
      20000     394         489009617
      30000     395         488017817
      65533     369(-31.3%) 521661345(+45.3%) <==> with this patchset
      N/A       342(-36.3%) 562900157(+56.8%) <==> disable zone_statistics

Kemi Wang (3):
  mm: Change the call sites of numa statistics items
  mm: Update NUMA counter threshold size
  mm: Consider the number in local CPUs when *reads* NUMA stats

 drivers/base/node.c    |  22 ++++---
 include/linux/mmzone.h |  24 +++++---
 include/linux/vmstat.h |  33 +++++++++++
 mm/page_alloc.c        |  10 ++--
 mm/vmstat.c            | 152 +++++++++++++++++++++++++++++++++++++++++++++++--
 5 files changed, 217 insertions(+), 24 deletions(-)

-- 
2.7.4

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[PATCH v2 1/3] mm: Change the call sites of numa statistics items

[Kemi Wang]

In this patch,  NUMA statistics is separated from zone statistics
framework, all the call sites of NUMA stats are changed to use
numa-stats-specific functions, it does not have any functionality change
except that the number of NUMA stats is shown behind zone page stats when
users *read* the zone info.

E.g. cat /proc/zoneinfo
    ***Base***                           ***With this patch***
nr_free_pages 3976                         nr_free_pages 3976
nr_zone_inactive_anon 0                    nr_zone_inactive_anon 0
nr_zone_active_anon 0                      nr_zone_active_anon 0
nr_zone_inactive_file 0                    nr_zone_inactive_file 0
nr_zone_active_file 0                      nr_zone_active_file 0
nr_zone_unevictable 0                      nr_zone_unevictable 0
nr_zone_write_pending 0                    nr_zone_write_pending 0
nr_mlock     0                             nr_mlock     0
nr_page_table_pages 0                      nr_page_table_pages 0
nr_kernel_stack 0                          nr_kernel_stack 0
nr_bounce    0                             nr_bounce    0
nr_zspages   0                             nr_zspages   0
numa_hit 0                                *nr_free_cma  0*
numa_miss 0                                numa_hit     0
numa_foreign 0                             numa_miss    0
numa_interleave 0                          numa_foreign 0
numa_local   0                             numa_interleave 0
numa_other   0                             numa_local   0
*nr_free_cma 0*                            numa_other 0
    ...                                        ...
vm stats threshold: 10                     vm stats threshold: 10
    ...                                        ...

The next patch updates the numa stats counter size and threshold.

Changelog:

v2:
a) Modify the name of numa-stats-specific functions and params to avoid
confusion with those for zone/node page stats.
b) Get rid of showing the number of numa stat threshold in /proc/zoneinfo
since the value of this item is a constant.

Signed-off-by: Kemi Wang <kemi.wang@intel.com>
---
 drivers/base/node.c    |  22 ++++---
 include/linux/mmzone.h |  25 +++++---
 include/linux/vmstat.h |  29 +++++++++
 mm/page_alloc.c        |  10 ++--
 mm/vmstat.c            | 159 +++++++++++++++++++++++++++++++++++++++++++++++--
 5 files changed, 219 insertions(+), 26 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index d8dc830..3855902 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -160,12 +160,12 @@ static ssize_t node_read_numastat(struct device *dev,
 		       "interleave_hit %lu\n"
 		       "local_node %lu\n"
 		       "other_node %lu\n",
-		       sum_zone_node_page_state(dev->id, NUMA_HIT),
-		       sum_zone_node_page_state(dev->id, NUMA_MISS),
-		       sum_zone_node_page_state(dev->id, NUMA_FOREIGN),
-		       sum_zone_node_page_state(dev->id, NUMA_INTERLEAVE_HIT),
-		       sum_zone_node_page_state(dev->id, NUMA_LOCAL),
-		       sum_zone_node_page_state(dev->id, NUMA_OTHER));
+		       sum_zone_numa_state(dev->id, NUMA_HIT),
+		       sum_zone_numa_state(dev->id, NUMA_MISS),
+		       sum_zone_numa_state(dev->id, NUMA_FOREIGN),
+		       sum_zone_numa_state(dev->id, NUMA_INTERLEAVE_HIT),
+		       sum_zone_numa_state(dev->id, NUMA_LOCAL),
+		       sum_zone_numa_state(dev->id, NUMA_OTHER));
 }
 static DEVICE_ATTR(numastat, S_IRUGO, node_read_numastat, NULL);
 
@@ -181,9 +181,17 @@ static ssize_t node_read_vmstat(struct device *dev,
 		n += sprintf(buf+n, "%s %lu\n", vmstat_text[i],
 			     sum_zone_node_page_state(nid, i));
 
-	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
+#ifdef CONFIG_NUMA
+	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
 		n += sprintf(buf+n, "%s %lu\n",
 			     vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
+			     sum_zone_numa_state(nid, i));
+#endif
+
+	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
+		n += sprintf(buf+n, "%s %lu\n",
+			     vmstat_text[i + NR_VM_ZONE_STAT_ITEMS +
+			     NR_VM_NUMA_STAT_ITEMS],
 			     node_page_state(pgdat, i));
 
 	return n;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fda9afb..582f6d9 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -114,6 +114,20 @@ struct zone_padding {
 #define ZONE_PADDING(name)
 #endif
 
+#ifdef CONFIG_NUMA
+enum numa_stat_item {
+	NUMA_HIT,		/* allocated in intended node */
+	NUMA_MISS,		/* allocated in non intended node */
+	NUMA_FOREIGN,		/* was intended here, hit elsewhere */
+	NUMA_INTERLEAVE_HIT,	/* interleaver preferred this zone */
+	NUMA_LOCAL,		/* allocation from local node */
+	NUMA_OTHER,		/* allocation from other node */
+	NR_VM_NUMA_STAT_ITEMS
+};
+#else
+#define NR_VM_NUMA_STAT_ITEMS 0
+#endif
+
 enum zone_stat_item {
 	/* First 128 byte cacheline (assuming 64 bit words) */
 	NR_FREE_PAGES,
@@ -132,14 +146,6 @@ enum zone_stat_item {
 #if IS_ENABLED(CONFIG_ZSMALLOC)
 	NR_ZSPAGES,		/* allocated in zsmalloc */
 #endif
-#ifdef CONFIG_NUMA
-	NUMA_HIT,		/* allocated in intended node */
-	NUMA_MISS,		/* allocated in non intended node */
-	NUMA_FOREIGN,		/* was intended here, hit elsewhere */
-	NUMA_INTERLEAVE_HIT,	/* interleaver preferred this zone */
-	NUMA_LOCAL,		/* allocation from local node */
-	NUMA_OTHER,		/* allocation from other node */
-#endif
 	NR_FREE_CMA_PAGES,
 	NR_VM_ZONE_STAT_ITEMS };
 
@@ -276,6 +282,8 @@ struct per_cpu_pageset {
 	struct per_cpu_pages pcp;
 #ifdef CONFIG_NUMA
 	s8 expire;
+	s8 numa_stat_threshold;
+	s8 vm_numa_stat_diff[NR_VM_NUMA_STAT_ITEMS];
 #endif
 #ifdef CONFIG_SMP
 	s8 stat_threshold;
@@ -496,6 +504,7 @@ 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];
 } ____cacheline_internodealigned_in_smp;
 
 enum pgdat_flags {
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 97e11ab..a29bd98 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -107,8 +107,33 @@ 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];
 
+#ifdef CONFIG_NUMA
+static inline void zone_numa_state_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]);
+}
+
+static inline unsigned long global_numa_state(enum numa_stat_item item)
+{
+	long x = atomic_long_read(&vm_numa_stat[item]);
+
+	return x;
+}
+
+static inline unsigned long zone_numa_state(struct zone *zone,
+					enum numa_stat_item item)
+{
+	long x = atomic_long_read(&zone->vm_numa_stat[item]);
+
+	return x;
+}
+#endif /* CONFIG_NUMA */
+
 static inline void zone_page_state_add(long x, struct zone *zone,
 				 enum zone_stat_item item)
 {
@@ -194,8 +219,12 @@ static inline unsigned long node_page_state_snapshot(pg_data_t *pgdat,
 
 
 #ifdef CONFIG_NUMA
+extern void __inc_numa_state(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 node_page_state(struct pglist_data *pgdat,
 						enum node_stat_item item);
 #else
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 67b696e..f7b6f98 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2721,18 +2721,18 @@ int __isolate_free_page(struct page *page, unsigned int order)
 static inline void zone_statistics(struct zone *preferred_zone, struct zone *z)
 {
 #ifdef CONFIG_NUMA
-	enum zone_stat_item local_stat = NUMA_LOCAL;
+	enum numa_stat_item local_stat = NUMA_LOCAL;
 
 	if (z->node != numa_node_id())
 		local_stat = NUMA_OTHER;
 
 	if (z->node == preferred_zone->node)
-		__inc_zone_state(z, NUMA_HIT);
+		__inc_numa_state(z, NUMA_HIT);
 	else {
-		__inc_zone_state(z, NUMA_MISS);
-		__inc_zone_state(preferred_zone, NUMA_FOREIGN);
+		__inc_numa_state(z, NUMA_MISS);
+		__inc_numa_state(preferred_zone, NUMA_FOREIGN);
 	}
-	__inc_zone_state(z, local_stat);
+	__inc_numa_state(z, local_stat);
 #endif
 }
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index c7e4b84..0c3b54b 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -87,8 +87,10 @@ void vm_events_fold_cpu(int cpu)
  * vm_stat contains the global counters
  */
 atomic_long_t vm_zone_stat[NR_VM_ZONE_STAT_ITEMS] __cacheline_aligned_in_smp;
+atomic_long_t vm_numa_stat[NR_VM_NUMA_STAT_ITEMS] __cacheline_aligned_in_smp;
 atomic_long_t vm_node_stat[NR_VM_NODE_STAT_ITEMS] __cacheline_aligned_in_smp;
 EXPORT_SYMBOL(vm_zone_stat);
+EXPORT_SYMBOL(vm_numa_stat);
 EXPORT_SYMBOL(vm_node_stat);
 
 #ifdef CONFIG_SMP
@@ -192,7 +194,10 @@ void refresh_zone_stat_thresholds(void)
 
 			per_cpu_ptr(zone->pageset, cpu)->stat_threshold
 							= threshold;
-
+#ifdef CONFIG_NUMA
+			per_cpu_ptr(zone->pageset, cpu)->numa_stat_threshold
+							= threshold;
+#endif
 			/* Base nodestat threshold on the largest populated zone. */
 			pgdat_threshold = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold;
 			per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold
@@ -226,9 +231,14 @@ void set_pgdat_percpu_threshold(pg_data_t *pgdat,
 			continue;
 
 		threshold = (*calculate_pressure)(zone);
-		for_each_online_cpu(cpu)
+		for_each_online_cpu(cpu) {
 			per_cpu_ptr(zone->pageset, cpu)->stat_threshold
 							= threshold;
+#ifdef CONFIG_NUMA
+			per_cpu_ptr(zone->pageset, cpu)->numa_stat_threshold
+							= threshold;
+#endif
+		}
 	}
 }
 
@@ -604,6 +614,32 @@ EXPORT_SYMBOL(dec_node_page_state);
  * Fold a differential into the global counters.
  * Returns the number of counters updated.
  */
+#ifdef CONFIG_NUMA
+static int fold_diff(int *zone_diff, int *numa_diff, int *node_diff)
+{
+	int i;
+	int changes = 0;
+
+	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
+		if (zone_diff[i]) {
+			atomic_long_add(zone_diff[i], &vm_zone_stat[i]);
+			changes++;
+	}
+
+	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
+		if (numa_diff[i]) {
+			atomic_long_add(numa_diff[i], &vm_numa_stat[i]);
+			changes++;
+	}
+
+	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
+		if (node_diff[i]) {
+			atomic_long_add(node_diff[i], &vm_node_stat[i]);
+			changes++;
+	}
+	return changes;
+}
+#else
 static int fold_diff(int *zone_diff, int *node_diff)
 {
 	int i;
@@ -622,6 +658,7 @@ static int fold_diff(int *zone_diff, int *node_diff)
 	}
 	return changes;
 }
+#endif /* CONFIG_NUMA */
 
 /*
  * Update the zone counters for the current cpu.
@@ -645,6 +682,9 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
 	struct zone *zone;
 	int i;
 	int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
+#ifdef CONFIG_NUMA
+	int global_numa_diff[NR_VM_NUMA_STAT_ITEMS] = { 0, };
+#endif
 	int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };
 	int changes = 0;
 
@@ -666,6 +706,18 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
 			}
 		}
 #ifdef CONFIG_NUMA
+		for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++) {
+			int v;
+
+			v = this_cpu_xchg(p->vm_numa_stat_diff[i], 0);
+			if (v) {
+
+				atomic_long_add(v, &zone->vm_numa_stat[i]);
+				global_numa_diff[i] += v;
+				__this_cpu_write(p->expire, 3);
+			}
+		}
+
 		if (do_pagesets) {
 			cond_resched();
 			/*
@@ -712,7 +764,11 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
 		}
 	}
 
+#ifdef CONFIG_NUMA
+	changes += fold_diff(global_zone_diff, global_numa_diff, global_node_diff);
+#else
 	changes += fold_diff(global_zone_diff, global_node_diff);
+#endif
 	return changes;
 }
 
@@ -727,6 +783,9 @@ void cpu_vm_stats_fold(int cpu)
 	struct zone *zone;
 	int i;
 	int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
+#ifdef CONFIG_NUMA
+	int global_numa_diff[NR_VM_NUMA_STAT_ITEMS] = { 0, };
+#endif
 	int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };
 
 	for_each_populated_zone(zone) {
@@ -743,6 +802,18 @@ void cpu_vm_stats_fold(int cpu)
 				atomic_long_add(v, &zone->vm_stat[i]);
 				global_zone_diff[i] += v;
 			}
+
+#ifdef CONFIG_NUMA
+		for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
+			if (p->vm_numa_stat_diff[i]) {
+				int v;
+
+				v = p->vm_numa_stat_diff[i];
+				p->vm_numa_stat_diff[i] = 0;
+				atomic_long_add(v, &zone->vm_numa_stat[i]);
+				global_numa_diff[i] += v;
+			}
+#endif
 	}
 
 	for_each_online_pgdat(pgdat) {
@@ -761,7 +832,11 @@ void cpu_vm_stats_fold(int cpu)
 			}
 	}
 
+#ifdef CONFIG_NUMA
+	fold_diff(global_zone_diff, global_numa_diff, global_node_diff);
+#else
 	fold_diff(global_zone_diff, global_node_diff);
+#endif
 }
 
 /*
@@ -779,10 +854,37 @@ void drain_zonestat(struct zone *zone, struct per_cpu_pageset *pset)
 			atomic_long_add(v, &zone->vm_stat[i]);
 			atomic_long_add(v, &vm_zone_stat[i]);
 		}
+
+#ifdef CONFIG_NUMA
+	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
+		if (pset->vm_numa_stat_diff[i]) {
+			int v = pset->vm_numa_stat_diff[i];
+			pset->vm_numa_stat_diff[i] = 0;
+			atomic_long_add(v, &zone->vm_numa_stat[i]);
+			atomic_long_add(v, &vm_numa_stat[i]);
+		}
+#endif
 }
 #endif
 
 #ifdef CONFIG_NUMA
+void __inc_numa_state(struct zone *zone,
+				 enum numa_stat_item item)
+{
+	struct per_cpu_pageset __percpu *pcp = zone->pageset;
+	s8 __percpu *p = pcp->vm_numa_stat_diff + item;
+	s8 v, t;
+
+	v = __this_cpu_inc_return(*p);
+	t = __this_cpu_read(pcp->numa_stat_threshold);
+	if (unlikely(v > t)) {
+		s8 overstep = t >> 1;
+
+		zone_numa_state_add(v + overstep, zone, item);
+		__this_cpu_write(*p, -overstep);
+	}
+}
+
 /*
  * Determine the per node value of a stat item. This function
  * is called frequently in a NUMA machine, so try to be as
@@ -801,6 +903,19 @@ unsigned long sum_zone_node_page_state(int node,
 	return count;
 }
 
+unsigned long sum_zone_numa_state(int node,
+				 enum numa_stat_item item)
+{
+	struct zone *zones = NODE_DATA(node)->node_zones;
+	int i;
+	unsigned long count = 0;
+
+	for (i = 0; i < MAX_NR_ZONES; i++)
+		count += zone_numa_state(zones + i, item);
+
+	return count;
+}
+
 /*
  * Determine the per node value of a stat item.
  */
@@ -937,6 +1052,9 @@ const char * const vmstat_text[] = {
 #if IS_ENABLED(CONFIG_ZSMALLOC)
 	"nr_zspages",
 #endif
+	"nr_free_cma",
+
+	/* enum numa_stat_item counters */
 #ifdef CONFIG_NUMA
 	"numa_hit",
 	"numa_miss",
@@ -945,7 +1063,6 @@ const char * const vmstat_text[] = {
 	"numa_local",
 	"numa_other",
 #endif
-	"nr_free_cma",
 
 	/* Node-based counters */
 	"nr_inactive_anon",
@@ -1106,7 +1223,6 @@ const char * const vmstat_text[] = {
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA */
 
-
 #if (defined(CONFIG_DEBUG_FS) && defined(CONFIG_COMPACTION)) || \
      defined(CONFIG_PROC_FS)
 static void *frag_start(struct seq_file *m, loff_t *pos)
@@ -1384,7 +1500,8 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		seq_printf(m, "\n  per-node stats");
 		for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) {
 			seq_printf(m, "\n      %-12s %lu",
-				vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
+				vmstat_text[i + NR_VM_ZONE_STAT_ITEMS +
+				NR_VM_NUMA_STAT_ITEMS],
 				node_page_state(pgdat, i));
 		}
 	}
@@ -1421,6 +1538,13 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		seq_printf(m, "\n      %-12s %lu", vmstat_text[i],
 				zone_page_state(zone, i));
 
+#ifdef CONFIG_NUMA
+	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
+		seq_printf(m, "\n      %-12s %lu",
+				vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
+				zone_numa_state(zone, i));
+#endif
+
 	seq_printf(m, "\n  pagesets");
 	for_each_online_cpu(i) {
 		struct per_cpu_pageset *pageset;
@@ -1497,6 +1621,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 	if (*pos >= ARRAY_SIZE(vmstat_text))
 		return NULL;
 	stat_items_size = NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long) +
+			  NR_VM_NUMA_STAT_ITEMS * sizeof(unsigned long) +
 			  NR_VM_NODE_STAT_ITEMS * sizeof(unsigned long) +
 			  NR_VM_WRITEBACK_STAT_ITEMS * sizeof(unsigned long);
 
@@ -1512,6 +1637,12 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 		v[i] = global_zone_page_state(i);
 	v += NR_VM_ZONE_STAT_ITEMS;
 
+#ifdef CONFIG_NUMA
+	for(i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
+		v[i] = global_numa_state(i);
+	v += NR_VM_NUMA_STAT_ITEMS;
+#endif
+
 	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
 		v[i] = global_node_page_state(i);
 	v += NR_VM_NODE_STAT_ITEMS;
@@ -1613,6 +1744,16 @@ int vmstat_refresh(struct ctl_table *table, int write,
 			err = -EINVAL;
 		}
 	}
+#ifdef CONFIG_NUMA
+	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++) {
+		val = atomic_long_read(&vm_numa_stat[i]);
+		if (val < 0) {
+			pr_warn("%s: %s %ld\n",
+				__func__, vmstat_text[i + NR_VM_ZONE_STAT_ITEMS], val);
+			err = -EINVAL;
+		}
+	}
+#endif
 	if (err)
 		return err;
 	if (write)
@@ -1654,13 +1795,19 @@ static bool need_update(int cpu)
 		struct per_cpu_pageset *p = per_cpu_ptr(zone->pageset, cpu);
 
 		BUILD_BUG_ON(sizeof(p->vm_stat_diff[0]) != 1);
+#ifdef CONFIG_NUMA
+		BUILD_BUG_ON(sizeof(p->vm_numa_stat_diff[0]) != 1);
+#endif
 		/*
 		 * The fast way of checking if there are any vmstat diffs.
 		 * This works because the diffs are byte sized items.
 		 */
 		if (memchr_inv(p->vm_stat_diff, 0, NR_VM_ZONE_STAT_ITEMS))
 			return true;
-
+#ifdef CONFIG_NUMA
+		if (memchr_inv(p->vm_numa_stat_diff, 0, NR_VM_NUMA_STAT_ITEMS))
+			return true;
+#endif
 	}
 	return false;
 }
-- 
2.7.4

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[PATCH v2 2/3] mm: Update NUMA counter threshold size

[Kemi Wang]

There is significant overhead in cache bouncing caused by zone counters
(NUMA associated counters) update in parallel in multi-threaded page
allocation (suggested by Dave Hansen).

This patch updates NUMA counter threshold to a fixed size of MAX_U16 - 2,
as a small threshold greatly increases the update frequency of the global
counter from local per cpu counter(suggested by Ying Huang).

The rationality is that these statistics counters don't affect the kernel's
decision, unlike other VM counters, so it's not a problem to use a large
threshold.

With this patchset, we see 31.3% drop of CPU cycles(537-->369) for per
single page allocation and reclaim on Jesper's page_bench03 benchmark.

Benchmark provided by Jesper D Brouer(increase loop times to 10000000):
https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/mm/
bench

 Threshold   CPU cycles    Throughput(88 threads)
     32          799         241760478
     64          640         301628829
     125         537         358906028 <==> system by default (base)
     256         468         412397590
     512         428         450550704
     4096        399         482520943
     20000       394         489009617
     30000       395         488017817
     65533       369(-31.3%) 521661345(+45.3%) <==> with this patchset
     N/A         342(-36.3%) 562900157(+56.8%) <==> disable zone_statistics

Changelog:
v2:
    a) Change the type of vm_numa_stat_diff[] from s16 to u16, since numa
    stats counter is always a incremental field.
    b) Remove numa_stat_threshold field in struct per_cpu_pageset, since it
    is a constant value and rarely be changed.
    c) Cut down instructions in __inc_numa_state() due to the incremental
    numa counter and the consistant numa threshold.
    d) Move zone_numa_state_snapshot() to an individual patch, since it
    does not appear to be related to this patch.

Signed-off-by: Kemi Wang <kemi.wang@intel.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Suggested-by: Ying Huang <ying.huang@intel.com>
---
 include/linux/mmzone.h |  3 +--
 mm/vmstat.c            | 28 ++++++++++------------------
 2 files changed, 11 insertions(+), 20 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 582f6d9..c386ec4 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -282,8 +282,7 @@ struct per_cpu_pageset {
 	struct per_cpu_pages pcp;
 #ifdef CONFIG_NUMA
 	s8 expire;
-	s8 numa_stat_threshold;
-	s8 vm_numa_stat_diff[NR_VM_NUMA_STAT_ITEMS];
+	u16 vm_numa_stat_diff[NR_VM_NUMA_STAT_ITEMS];
 #endif
 #ifdef CONFIG_SMP
 	s8 stat_threshold;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 0c3b54b..b015f39 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -30,6 +30,8 @@
 
 #include "internal.h"
 
+#define NUMA_STATS_THRESHOLD (U16_MAX - 2)
+
 #ifdef CONFIG_VM_EVENT_COUNTERS
 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
 EXPORT_PER_CPU_SYMBOL(vm_event_states);
@@ -194,10 +196,7 @@ void refresh_zone_stat_thresholds(void)
 
 			per_cpu_ptr(zone->pageset, cpu)->stat_threshold
 							= threshold;
-#ifdef CONFIG_NUMA
-			per_cpu_ptr(zone->pageset, cpu)->numa_stat_threshold
-							= threshold;
-#endif
+
 			/* Base nodestat threshold on the largest populated zone. */
 			pgdat_threshold = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold;
 			per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold
@@ -231,14 +230,9 @@ void set_pgdat_percpu_threshold(pg_data_t *pgdat,
 			continue;
 
 		threshold = (*calculate_pressure)(zone);
-		for_each_online_cpu(cpu) {
+		for_each_online_cpu(cpu)
 			per_cpu_ptr(zone->pageset, cpu)->stat_threshold
 							= threshold;
-#ifdef CONFIG_NUMA
-			per_cpu_ptr(zone->pageset, cpu)->numa_stat_threshold
-							= threshold;
-#endif
-		}
 	}
 }
 
@@ -872,16 +866,14 @@ void __inc_numa_state(struct zone *zone,
 				 enum numa_stat_item item)
 {
 	struct per_cpu_pageset __percpu *pcp = zone->pageset;
-	s8 __percpu *p = pcp->vm_numa_stat_diff + item;
-	s8 v, t;
+	u16 __percpu *p = pcp->vm_numa_stat_diff + item;
+	u16 v;
 
 	v = __this_cpu_inc_return(*p);
-	t = __this_cpu_read(pcp->numa_stat_threshold);
-	if (unlikely(v > t)) {
-		s8 overstep = t >> 1;
 
-		zone_numa_state_add(v + overstep, zone, item);
-		__this_cpu_write(*p, -overstep);
+	if (unlikely(v > NUMA_STATS_THRESHOLD)) {
+		zone_numa_state_add(v, zone, item);
+		__this_cpu_write(*p, 0);
 	}
 }
 
@@ -1796,7 +1788,7 @@ static bool need_update(int cpu)
 
 		BUILD_BUG_ON(sizeof(p->vm_stat_diff[0]) != 1);
 #ifdef CONFIG_NUMA
-		BUILD_BUG_ON(sizeof(p->vm_numa_stat_diff[0]) != 1);
+		BUILD_BUG_ON(sizeof(p->vm_numa_stat_diff[0]) != 2);
 #endif
 		/*
 		 * The fast way of checking if there are any vmstat diffs.
-- 
2.7.4

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[PATCH v2 3/3] mm: Consider the number in local CPUs when *reads* NUMA stats

[Kemi Wang]

To avoid deviation, the per cpu number of NUMA stats in vm_numa_stat_diff[]
is included when a user *reads* the NUMA stats.

Since NUMA stats does not be read by users frequently, and kernel does not
need it to make a decision, it will not be a problem to make the readers
more expensive.

Changelog:
v2:
    a) new creation.

Signed-off-by: Kemi Wang <kemi.wang@intel.com>
---
 include/linux/vmstat.h | 6 +++++-
 mm/vmstat.c            | 9 +++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index a29bd98..72e9ca6 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -125,10 +125,14 @@ static inline unsigned long global_numa_state(enum numa_stat_item item)
 	return x;
 }
 
-static inline unsigned long zone_numa_state(struct zone *zone,
+static inline unsigned long zone_numa_state_snapshot(struct zone *zone,
 					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->pageset, cpu)->vm_numa_stat_diff[item];
 
 	return x;
 }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index b015f39..abeab81 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -895,6 +895,10 @@ unsigned long sum_zone_node_page_state(int node,
 	return count;
 }
 
+/*
+ * Determine the per node value of a numa stat item. To avoid deviation,
+ * the per cpu stat number in vm_numa_stat_diff[] is also included.
+ */
 unsigned long sum_zone_numa_state(int node,
 				 enum numa_stat_item item)
 {
@@ -903,7 +907,7 @@ unsigned long sum_zone_numa_state(int node,
 	unsigned long count = 0;
 
 	for (i = 0; i < MAX_NR_ZONES; i++)
-		count += zone_numa_state(zones + i, item);
+		count += zone_numa_state_snapshot(zones + i, item);
 
 	return count;
 }
@@ -1534,7 +1538,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 	for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
 		seq_printf(m, "\n      %-12s %lu",
 				vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
-				zone_numa_state(zone, i));
+				zone_numa_state_snapshot(zone, i));
 #endif
 
 	seq_printf(m, "\n  pagesets");
@@ -1790,6 +1794,7 @@ static bool need_update(int cpu)
 #ifdef CONFIG_NUMA
 		BUILD_BUG_ON(sizeof(p->vm_numa_stat_diff[0]) != 2);
 #endif
+
 		/*
 		 * The fast way of checking if there are any vmstat diffs.
 		 * This works because the diffs are byte sized items.
-- 
2.7.4

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Re: [PATCH v2 0/3] Separate NUMA statistics from zone statistics

[Mel Gorman]

On Thu, Aug 24, 2017 at 05:59:58PM +0800, Kemi Wang wrote:
> Each page allocation updates a set of per-zone statistics with a call to
> zone_statistics(). As discussed in 2017 MM summit, these are a substantial
> source of overhead in the page allocator and are very rarely consumed. This
> significant overhead in cache bouncing caused by zone counters (NUMA
> associated counters) update in parallel in multi-threaded page allocation
> (pointed out by Dave Hansen).
> 

For the series;

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

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Re: [PATCH v2 0/3] Separate NUMA statistics from zone statistics

[Jesper Dangaard Brouer]

On Fri, 25 Aug 2017 09:04:37 +0100
Mel Gorman <mgorman@techsingularity.net> wrote:

> On Thu, Aug 24, 2017 at 05:59:58PM +0800, Kemi Wang wrote:
> > Each page allocation updates a set of per-zone statistics with a call to
> > zone_statistics(). As discussed in 2017 MM summit, these are a substantial
> > source of overhead in the page allocator and are very rarely consumed. This
> > significant overhead in cache bouncing caused by zone counters (NUMA
> > associated counters) update in parallel in multi-threaded page allocation
> > (pointed out by Dave Hansen).
> >   
> 
> For the series;
> 
> Acked-by: Mel Gorman <mgorman@techsingularity.net>
> 

I'm very happy to see these issues being worked on, from our MM-summit
interactions. I would like to provide/have a:

Reported-by: Jesper Dangaard Brouer <brouer@redhat.com>

As I'm not sure an acked-by from me have any value/merit here ;-)
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

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