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Message-ID: <ba72d967-aa4e-47e5-5f99-df3dd0bf21d2@suse.cz>
Date: Thu, 22 Apr 2021 17:18:38 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Mel Gorman <mgorman@...hsingularity.net>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Chuck Lever <chuck.lever@...cle.com>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Michal Hocko <mhocko@...nel.org>,
Linux-MM <linux-mm@...ck.org>,
Linux-RT-Users <linux-rt-users@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/9] mm/vmstat: Convert NUMA statistics to basic NUMA
counters
On 4/22/21 1:14 PM, Mel Gorman wrote:
> NUMA statistics are maintained on the zone level for hits, misses, foreign
> etc but nothing relies on them being perfectly accurate for functional
> correctness. The counters are used by userspace to get a general overview
> of a workloads NUMA behaviour but the page allocator incurs a high cost to
> maintain perfect accuracy similar to what is required for a vmstat like
> NR_FREE_PAGES. There even is a sysctl vm.numa_stat to allow userspace to
> turn off the collection of NUMA statistics like NUMA_HIT.
>
> This patch converts NUMA_HIT and friends to be NUMA events with similar
> accuracy to VM events. There is a possibility that slight errors will be
> introduced but the overall trend as seen by userspace will be similar.
> The counters are no longer updated from vmstat_refresh context as it is
> unnecessary overhead for counters that may never be read by userspace.
> Note that counters could be maintained at the node level to save space
> but it would have a user-visible impact due to /proc/zoneinfo.
>
> [lkp@...el.com: Fix misplaced closing brace for !CONFIG_NUMA]
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
...
> @@ -731,26 +722,34 @@ static int fold_diff(int *zone_diff, int *numa_diff, int *node_diff)
> }
> return changes;
> }
> -#else
> -static int fold_diff(int *zone_diff, int *node_diff)
> +
> +#ifdef CONFIG_NUMA
> +static void fold_vm_zone_numa_events(struct zone *zone)
> {
> - int i;
> - int changes = 0;
> + int zone_numa_events[NR_VM_NUMA_EVENT_ITEMS] = { 0, };
Should this be long? pzstats are, the global counters too, so seems weird to use
int as intermediate sum counter.
> + int cpu;
> + enum numa_stat_item item;
>
> - for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
> - if (zone_diff[i]) {
> - atomic_long_add(zone_diff[i], &vm_zone_stat[i]);
> - changes++;
> - }
> + for_each_online_cpu(cpu) {
> + struct per_cpu_zonestat *pzstats;
>
> - for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
> - if (node_diff[i]) {
> - atomic_long_add(node_diff[i], &vm_node_stat[i]);
> - changes++;
> + pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
> + for (item = 0; item < NR_VM_NUMA_EVENT_ITEMS; item++)
> + zone_numa_events[item] += xchg(&pzstats->vm_numa_event[item], 0);
> }
> - return changes;
> +
> + for (item = 0; item < NR_VM_NUMA_EVENT_ITEMS; item++)
> + zone_numa_event_add(zone_numa_events[item], zone, item);
> }
> -#endif /* CONFIG_NUMA */
> +
> +void fold_vm_numa_events(void)
> +{
> + struct zone *zone;
> +
> + for_each_populated_zone(zone)
> + fold_vm_zone_numa_events(zone);
> +}
> +#endif
>
> /*
> * Update the zone counters for the current cpu.
> @@ -774,15 +773,14 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
> struct zone *zone;
> int i;
> int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
> -#ifdef CONFIG_NUMA
> - int global_numa_diff[NR_VM_NUMA_STAT_ITEMS] = { 0, };
> -#endif
> int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };
> int changes = 0;
>
> for_each_populated_zone(zone) {
> struct per_cpu_zonestat __percpu *pzstats = zone->per_cpu_zonestats;
> +#ifdef CONFIG_NUMA
> struct per_cpu_pages __percpu *pcp = zone->per_cpu_pageset;
> +#endif
>
> for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
> int v;
> @@ -799,17 +797,6 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
> }
> }
> #ifdef CONFIG_NUMA
> - for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++) {
> - int v;
> -
> - v = this_cpu_xchg(pzstats->vm_numa_stat_diff[i], 0);
> - if (v) {
> -
> - atomic_long_add(v, &zone->vm_numa_stat[i]);
> - global_numa_diff[i] += v;
> - __this_cpu_write(pcp->expire, 3);
> - }
> - }
>
> if (do_pagesets) {
> cond_resched();
> @@ -857,12 +844,7 @@ static int refresh_cpu_vm_stats(bool do_pagesets)
> }
> }
>
> -#ifdef CONFIG_NUMA
> - changes += fold_diff(global_zone_diff, global_numa_diff,
> - global_node_diff);
> -#else
> changes += fold_diff(global_zone_diff, global_node_diff);
> -#endif
> return changes;
> }
>
> @@ -877,9 +859,6 @@ void cpu_vm_stats_fold(int cpu)
> struct zone *zone;
> int i;
> int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
> -#ifdef CONFIG_NUMA
> - int global_numa_diff[NR_VM_NUMA_STAT_ITEMS] = { 0, };
> -#endif
> int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };
>
> for_each_populated_zone(zone) {
> @@ -887,7 +866,7 @@ void cpu_vm_stats_fold(int cpu)
>
> pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
>
> - for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
> + for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
> if (pzstats->vm_stat_diff[i]) {
> int v;
>
> @@ -896,17 +875,17 @@ void cpu_vm_stats_fold(int cpu)
> atomic_long_add(v, &zone->vm_stat[i]);
> global_zone_diff[i] += v;
> }
> -
> + }
> #ifdef CONFIG_NUMA
> - for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
> - if (pzstats->vm_numa_stat_diff[i]) {
> + for (i = 0; i < NR_VM_NUMA_EVENT_ITEMS; i++) {
> + if (pzstats->vm_numa_event[i]) {
> int v;
Also long?
>
> - v = pzstats->vm_numa_stat_diff[i];
> - pzstats->vm_numa_stat_diff[i] = 0;
> - atomic_long_add(v, &zone->vm_numa_stat[i]);
> - global_numa_diff[i] += v;
> + v = pzstats->vm_numa_event[i];
> + pzstats->vm_numa_event[i] = 0;
> + zone_numa_event_add(v, zone, i);
> }
> + }
> #endif
> }
>
> @@ -926,11 +905,7 @@ void cpu_vm_stats_fold(int cpu)
> }
> }
>
> -#ifdef CONFIG_NUMA
> - fold_diff(global_zone_diff, global_numa_diff, global_node_diff);
> -#else
> fold_diff(global_zone_diff, global_node_diff);
> -#endif
> }
>
> /*
> @@ -939,43 +914,36 @@ void cpu_vm_stats_fold(int cpu)
> */
> void drain_zonestat(struct zone *zone, struct per_cpu_zonestat *pzstats)
> {
> - int i;
> + int i, v;
And the 'v' here. Maybe keep using local to each loop below and make it long for
the NUMA one?
> - for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
> + for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
> if (pzstats->vm_stat_diff[i]) {
> - int v = pzstats->vm_stat_diff[i];
> + v = pzstats->vm_stat_diff[i];
> pzstats->vm_stat_diff[i] = 0;
> - atomic_long_add(v, &zone->vm_stat[i]);
> - atomic_long_add(v, &vm_zone_stat[i]);
> + zone_page_state_add(v, zone, i);
> }
> + }
>
> #ifdef CONFIG_NUMA
> - for (i = 0; i < NR_VM_NUMA_STAT_ITEMS; i++)
> - if (pzstats->vm_numa_stat_diff[i]) {
> - int v = pzstats->vm_numa_stat_diff[i];
> -
> - pzstats->vm_numa_stat_diff[i] = 0;
> - atomic_long_add(v, &zone->vm_numa_stat[i]);
> - atomic_long_add(v, &vm_numa_stat[i]);
> + for (i = 0; i < NR_VM_NUMA_EVENT_ITEMS; i++) {
> + if (pzstats->vm_numa_event[i]) {
> + v = pzstats->vm_numa_event[i];
> + pzstats->vm_numa_event[i] = 0;
> + zone_numa_event_add(v, zone, i);
> }
> + }
> #endif
> }
> #endif
>
> #ifdef CONFIG_NUMA
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