mm: update NUMA counter threshold size (1d90ca89) · Commits · 戴 / test

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 Link: http://lkml.kernel.org/r/1503568801-21305-3-git-send-email-kemi.wang@intel.com Signed-off-by:

Kemi Wang <kemi.wang@intel.com> Reported-by:

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

Dave Hansen <dave.hansen@intel.com> Suggested-by:

Ying Huang <ying.huang@intel.com> Acked-by:

Mel Gorman <mgorman@techsingularity.net> Cc: Aaron Lu <aaron.lu@intel.com> Cc: Andi Kleen <andi.kleen@intel.com> Cc: Christopher Lameter <cl@linux.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Tim Chen <tim.c.chen@intel.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -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;

mm/vmstat.c

+10 −18

Original line number	Diff line number	Diff line
		@@ -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
		}
		}
		}

		@@ -874,16 +868,14 @@ 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);
		}
		}

		@@ -1798,7 +1790,7 @@ 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.

Admin message