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Subject[PATCH 2/3] mm: Handle numa statistics distinctively based-on different VM stats modes
Date
Each page allocation updates a set of per-zone statistics with a call to
zone_statistics(). As discussed at the 2017 MM Summit, these are a
substantial source of overhead in the page allocator and are very rarely
consumed.

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

Therefore, with different VM stats mode, numa counters update can operate
differently so that everybody can benefit:
If vmstat_mode = auto, automatic detection of numa statistics, numa counter
update is skipped unless it has been read by users at least once,
e.g. cat /proc/zoneinfo.

If vmstat_mode = strict, numa counter is updated for each page allocation.

If vmstat_mode = coarse, numa counter update is ignored. We can see about
*4.8%*(185->176) drop of cpu cycles per single page allocation and reclaim
on Jesper's page_bench01 (single thread) and *8.1%*(343->315) drop of cpu
cycles per single page allocation and reclaim on Jesper's page_bench03 (88
threads) running on a 2-Socket Broadwell-based server (88 threads, 126G
memory).

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

Reported-by: Jesper Dangaard Brouer <brouer@redhat.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Suggested-by: Ying Huang <ying.huang@intel.com>
Signed-off-by: Kemi Wang <kemi.wang@intel.com>
---
drivers/base/node.c | 2 ++
include/linux/vmstat.h | 6 +++++
mm/page_alloc.c | 13 +++++++++++
mm/vmstat.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++---
4 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 3855902..033c0c3 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -153,6 +153,7 @@ static DEVICE_ATTR(meminfo, S_IRUGO, node_read_meminfo, NULL);
static ssize_t node_read_numastat(struct device *dev,
struct device_attribute *attr, char *buf)
{
+ disable_zone_statistics = false;
return sprintf(buf,
"numa_hit %lu\n"
"numa_miss %lu\n"
@@ -194,6 +195,7 @@ static ssize_t node_read_vmstat(struct device *dev,
NR_VM_NUMA_STAT_ITEMS],
node_page_state(pgdat, i));

+ disable_zone_statistics = false;
return n;
}
static DEVICE_ATTR(vmstat, S_IRUGO, node_read_vmstat, NULL);
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index c3634c7..ca9854c 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -9,6 +9,7 @@

extern int sysctl_stat_interval;

+extern bool disable_zone_statistics;
/*
* vmstat_mode:
* 0 = auto mode of vmstat, automatic detection of VM statistics.
@@ -19,6 +20,7 @@ extern int sysctl_stat_interval;
#define VMSTAT_STRICT_MODE 1
#define VMSTAT_COARSE_MODE 2
#define VMSTAT_MODE_LEN 16
+extern int vmstat_mode;
extern char sysctl_vmstat_mode[];
extern int sysctl_vmstat_mode_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos);
@@ -243,6 +245,10 @@ extern unsigned long sum_zone_node_page_state(int node,
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);
+extern void zero_zone_numa_counters(struct zone *zone);
+extern void zero_zones_numa_counters(void);
+extern void zero_global_numa_counters(void);
+extern void invalid_numa_statistics(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)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c841af8..010a620 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -83,6 +83,8 @@ DEFINE_PER_CPU(int, numa_node);
EXPORT_PER_CPU_SYMBOL(numa_node);
#endif

+bool disable_zone_statistics = true;
+
#ifdef CONFIG_HAVE_MEMORYLESS_NODES
/*
* N.B., Do NOT reference the '_numa_mem_' per cpu variable directly.
@@ -2743,6 +2745,17 @@ static inline void zone_statistics(struct zone *preferred_zone, struct zone *z)
#ifdef CONFIG_NUMA
enum numa_stat_item local_stat = NUMA_LOCAL;

+ /*
+ * skip zone_statistics() if vmstat is a coarse mode or zone statistics
+ * is inactive in auto vmstat mode
+ */
+
+ if (vmstat_mode) {
+ if (vmstat_mode == VMSTAT_COARSE_MODE)
+ return;
+ } else if (disable_zone_statistics)
+ return;
+
if (z->node != numa_node_id())
local_stat = NUMA_OTHER;

diff --git a/mm/vmstat.c b/mm/vmstat.c
index e675ad2..bcaef62 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -85,15 +85,31 @@ int sysctl_vmstat_mode_handler(struct ctl_table *table, int write,
/* no change */
mutex_unlock(&vmstat_mode_lock);
return 0;
- } else if (vmstat_mode == VMSTAT_AUTO_MODE)
+ } else if (vmstat_mode == VMSTAT_AUTO_MODE) {
pr_info("vmstat mode changes from %s to auto mode\n",
vmstat_mode_name[oldval]);
- else if (vmstat_mode == VMSTAT_STRICT_MODE)
+ /*
+ * Set default numa stats action when vmstat mode changes
+ * from coarse to auto
+ */
+ if (oldval == VMSTAT_COARSE_MODE)
+ disable_zone_statistics = true;
+ } else if (vmstat_mode == VMSTAT_STRICT_MODE)
pr_info("vmstat mode changes from %s to strict mode\n",
vmstat_mode_name[oldval]);
- else if (vmstat_mode == VMSTAT_COARSE_MODE)
+ else if (vmstat_mode == VMSTAT_COARSE_MODE) {
pr_info("vmstat mode changes from %s to coarse mode\n",
vmstat_mode_name[oldval]);
+#ifdef CONFIG_NUMA
+ /*
+ * Invalidate numa counters when vmstat mode is set to coarse
+ * mode, because users can't tell the difference between the
+ * dead state and when allocator activity is quiet once
+ * zone_statistics() is turned off.
+ */
+ invalid_numa_statistics();
+#endif
+ }
else
pr_warn("invalid vmstat_mode:%d\n", vmstat_mode);
}
@@ -984,6 +1000,42 @@ unsigned long sum_zone_numa_state(int node,
return count;
}

+/* zero numa counters within a zone */
+void zero_zone_numa_counters(struct zone *zone)
+{
+ int item, cpu;
+
+ for (item = 0; item < NR_VM_NUMA_STAT_ITEMS; item++) {
+ atomic_long_set(&zone->vm_numa_stat[item], 0);
+ for_each_online_cpu(cpu)
+ per_cpu_ptr(zone->pageset, cpu)->vm_numa_stat_diff[item] = 0;
+ }
+}
+
+/* zero numa counters of all the populated zones */
+void zero_zones_numa_counters(void)
+{
+ struct zone *zone;
+
+ for_each_populated_zone(zone)
+ zero_zone_numa_counters(zone);
+}
+
+/* zero global numa counters */
+void zero_global_numa_counters(void)
+{
+ int item;
+
+ for (item = 0; item < NR_VM_NUMA_STAT_ITEMS; item++)
+ atomic_long_set(&vm_numa_stat[item], 0);
+}
+
+void invalid_numa_statistics(void)
+{
+ zero_zones_numa_counters();
+ zero_global_numa_counters();
+}
+
/*
* Determine the per node value of a stat item.
*/
@@ -1652,6 +1704,7 @@ static int zoneinfo_show(struct seq_file *m, void *arg)
{
pg_data_t *pgdat = (pg_data_t *)arg;
walk_zones_in_node(m, pgdat, false, false, zoneinfo_show_print);
+ disable_zone_statistics = false;
return 0;
}

@@ -1748,6 +1801,7 @@ static int vmstat_show(struct seq_file *m, void *arg)

static void vmstat_stop(struct seq_file *m, void *arg)
{
+ disable_zone_statistics = false;
kfree(m->private);
m->private = NULL;
}
--
2.7.4
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