=========================================================================
When page allocation performance becomes a bottleneck and you can tolerate
some possible tool breakage and decreased numa counter precision, you can
do:
echo 0 > /proc/sys/vm/numa_stat
In this case, 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
=========================================================================
When page allocation performance is not a bottleneck and you want all
tooling to work, you can do:
echo 1 > /proc/sys/vm/numa_stat
This is system default setting.
Many thanks to Michal Hocko, Dave Hansen, Ying Huang and Vlastimil Babka
for comments to help improve the original patch.
ChangeLog:
V3->V4
a) Get rid of auto mode of numa stats, and may add it back if necessary,
as alignment before;
b) Skip NUMA_INTERLEAVE_HIT counter update when numa stats is disabled,
as reported by Andrey Ryabinin. See commit "de55c8b2519" for details
c) Remove extern declaration for those clear_numa_ function, and make
them static in vmstat.c, as suggested by Vlastimil Babka.
V2->V3:
a) Propose a better way to use jump label to eliminate the overhead of
branch selection in zone_statistics(), as inspired by Ying Huang;
b) Add a paragraph in commit log to describe the way for branch target
selection;
c) Use a more descriptive name numa_stats_mode instead of vmstat_mode,
and change the description accordingly, as suggested by Michal Hocko;
d) Make this functionality NUMA-specific via ifdef
V1->V2:
a) Merge to one patch;
b) Use jump label to eliminate the overhead of branch selection;
c) Add a single-time log message at boot time to help tell users what
happened.
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>
---
Documentation/sysctl/vm.txt | 16 +++++++++++
include/linux/vmstat.h | 10 +++++++
kernel/sysctl.c | 7 +++++
mm/mempolicy.c | 3 ++
mm/page_alloc.c | 6 ++++
mm/vmstat.c | 70 +++++++++++++++++++++++++++++++++++++++++++++
6 files changed, 112 insertions(+)
@@ -58,6 +58,7 @@ Currently, these files are in /proc/sys/vm:
- percpu_pagelist_fraction
- stat_interval
- stat_refresh
+- numa_stat
- swappiness
- user_reserve_kbytes
- vfs_cache_pressure
@@ -792,6 +793,21 @@ with no ill effects: errors and warnings on these stats are suppressed.)
==============================================================
+numa_stat
+
+This interface allows runtime configuration of numa statistics.
+
+When page allocation performance becomes a bottleneck and you can tolerate
+some possible tool breakage and decreased numa counter precision, you can
+do:
+ echo 0 > /proc/sys/vm/numa_stat
+
+When page allocation performance is not a bottleneck and you want all
+tooling to work, you can do:
+ echo 1 > /proc/sys/vm/numa_stat
+
+==============================================================
+
swappiness
This control is used to define how aggressive the kernel will swap
@@ -6,9 +6,19 @@
#include <linux/mmzone.h>
#include <linux/vm_event_item.h>
#include <linux/atomic.h>
+#include <linux/static_key.h>
extern int sysctl_stat_interval;
+#ifdef CONFIG_NUMA
+#define ENABLE_NUMA_STAT 1
+#define DISABLE_NUMA_STAT 0
+extern int sysctl_vm_numa_stat;
+DECLARE_STATIC_KEY_TRUE(vm_numa_stat_key);
+extern int sysctl_vm_numa_stat_handler(struct ctl_table *table,
+ int write, void __user *buffer, size_t *length, loff_t *ppos);
+#endif
+
#ifdef CONFIG_VM_EVENT_COUNTERS
/*
* Light weight per cpu counter implementation.
@@ -1371,6 +1371,13 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = &hugetlb_mempolicy_sysctl_handler,
},
+ {
+ .procname = "numa_stat",
+ .data = &sysctl_vm_numa_stat,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = sysctl_vm_numa_stat_handler,
+ },
#endif
{
.procname = "hugetlb_shm_group",
@@ -1920,6 +1920,9 @@ static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
struct page *page;
page = __alloc_pages(gfp, order, nid);
+ /* skip NUMA_INTERLEAVE_HIT counter update if numa stats is disabled */
+ if (!static_branch_likely(&vm_numa_stat_key))
+ return page;
if (page && page_to_nid(page) == nid) {
preempt_disable();
__inc_numa_state(page_zone(page), NUMA_INTERLEAVE_HIT);
@@ -83,6 +83,8 @@ DEFINE_PER_CPU(int, numa_node);
EXPORT_PER_CPU_SYMBOL(numa_node);
#endif
+DEFINE_STATIC_KEY_TRUE(vm_numa_stat_key);
+
#ifdef CONFIG_HAVE_MEMORYLESS_NODES
/*
* N.B., Do NOT reference the '_numa_mem_' per cpu variable directly.
@@ -2743,6 +2745,10 @@ static inline void zone_statistics(struct zone *preferred_zone, struct zone *z)
#ifdef CONFIG_NUMA
enum numa_stat_item local_stat = NUMA_LOCAL;
+ /* skip numa counters update if numa stats is disabled */
+ if (!static_branch_likely(&vm_numa_stat_key))
+ return;
+
if (z->node != numa_node_id())
local_stat = NUMA_OTHER;
@@ -32,6 +32,76 @@
#define NUMA_STATS_THRESHOLD (U16_MAX - 2)
+#ifdef CONFIG_NUMA
+int sysctl_vm_numa_stat = ENABLE_NUMA_STAT;
+static DEFINE_MUTEX(vm_numa_stat_lock);
+
+/* zero numa counters within a zone */
+static 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 */
+static void zero_zones_numa_counters(void)
+{
+ struct zone *zone;
+
+ for_each_populated_zone(zone)
+ zero_zone_numa_counters(zone);
+}
+
+/* zero global numa counters */
+static 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);
+}
+
+static void invalid_numa_statistics(void)
+{
+ zero_zones_numa_counters();
+ zero_global_numa_counters();
+}
+
+int sysctl_vm_numa_stat_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *length, loff_t *ppos)
+{
+ int ret, oldval;
+
+ mutex_lock(&vm_numa_stat_lock);
+ if (write)
+ oldval = sysctl_vm_numa_stat;
+ ret = proc_dointvec(table, write, buffer, length, ppos);
+ if (ret || !write)
+ goto out;
+
+ if (oldval == sysctl_vm_numa_stat)
+ goto out;
+ else if (oldval == DISABLE_NUMA_STAT) {
+ static_branch_enable(&vm_numa_stat_key);
+ pr_info("enable numa statistics\n");
+ } else if (sysctl_vm_numa_stat == DISABLE_NUMA_STAT) {
+ static_branch_disable(&vm_numa_stat_key);
+ invalid_numa_statistics();
+ pr_info("disable numa statistics, and clear numa counters\n");
+ }
+
+out:
+ mutex_unlock(&vm_numa_stat_lock);
+ return ret;
+}
+#endif
+
#ifdef CONFIG_VM_EVENT_COUNTERS
DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
EXPORT_PER_CPU_SYMBOL(vm_event_states);