Re: [PATCH v5] mm, sysctl: make NUMA stats configurable

[Michal Hocko]

On Wed 18-10-17 09:42:07, Kemi Wang wrote:
> This is the second step which introduces a tunable interface that allow
> numa stats configurable for optimizing zone_statistics(), as suggested by
> Dave Hansen and Ying Huang.
> 
> =========================================================================
> 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:
>   V4->V5
>   a) Scope vm_numa_stat_lock into the sysctl handler function, as suggested
>   by Michal Hocko;
>   b) Only allow 0/1 value when setting a value to numa_stat at userspace,
>   that would keep the possibility for add auto mode in future (e.g. 2 for
>   auto mode), as suggested by Michal Hocko.
> 
>   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@xxxxxxxxxx>
> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
> Suggested-by: Ying Huang <ying.huang@xxxxxxxxx>
> Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks!

> ---
>  Documentation/sysctl/vm.txt | 16 +++++++++++
>  include/linux/vmstat.h      | 10 +++++++
>  kernel/sysctl.c             |  9 ++++++
>  mm/mempolicy.c              |  3 ++
>  mm/page_alloc.c             |  6 ++++
>  mm/vmstat.c                 | 70 +++++++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 114 insertions(+)
> 
> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> index 9baf66a..f65c5c7 100644
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -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
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index ade7cb5..c605c94 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -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.
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index d9c31bc..8f272db 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1371,6 +1371,15 @@ 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,
> +		.extra1			= &zero,
> +		.extra2			= &one,
> +	},
>  #endif
>  	 {
>  		.procname	= "hugetlb_shm_group",
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index a2af6d5..78344cf 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -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);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 77e4d3c..7bdb4f7 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
>  
> +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;
>  
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 4bb13e7..1faf30d 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -32,6 +32,76 @@
>  
>  #define NUMA_STATS_THRESHOLD (U16_MAX - 2)
>  
> +#ifdef CONFIG_NUMA
> +int sysctl_vm_numa_stat = ENABLE_NUMA_STAT;
> +
> +/* 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;
> +	DEFINE_MUTEX(vm_numa_stat_lock);
> +
> +	mutex_lock(&vm_numa_stat_lock);
> +	if (write)
> +		oldval = sysctl_vm_numa_stat;
> +	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
> +	if (ret || !write)
> +		goto out;
> +
> +	if (oldval == sysctl_vm_numa_stat)
> +		goto out;
> +	else if (sysctl_vm_numa_stat == ENABLE_NUMA_STAT) {
> +		static_branch_enable(&vm_numa_stat_key);
> +		pr_info("enable numa statistics\n");
> +	} else {
> +		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);
> -- 
> 2.7.4
> 

-- 
Michal Hocko
SUSE Labs