From 1d90ca897cb05cf38bd62f36756d219e02913b7d Mon Sep 17 00:00:00 2001 From: Kemi Wang Date: Fri, 8 Sep 2017 16:12:52 -0700 Subject: [PATCH] mm: update NUMA counter threshold size 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 Reported-by: Jesper Dangaard Brouer Suggested-by: Dave Hansen Suggested-by: Ying Huang Acked-by: Mel Gorman Cc: Aaron Lu Cc: Andi Kleen Cc: Christopher Lameter Cc: Johannes Weiner Cc: Michal Hocko Cc: Tim Chen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 e65d91c02e30..356a814e7c8e 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 daea02833e2e..153d8129c155 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 - } } } @@ -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. -- 2.20.1