Commit 2bb921e5 authored by Christoph Lameter's avatar Christoph Lameter Committed by Linus Torvalds
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vmstat: create separate function to fold per cpu diffs into local counters

The main idea behind this patchset is to reduce the vmstat update overhead
by avoiding interrupt enable/disable and the use of per cpu atomics.

This patch (of 3):

It is better to have a separate folding function because
refresh_cpu_vm_stats() also does other things like expire pages in the
page allocator caches.

If we have a separate function then refresh_cpu_vm_stats() is only called
from the local cpu which allows additional optimizations.

The folding function is only called when a cpu is being downed and
therefore no other processor will be accessing the counters.  Also
simplifies synchronization.

[ fix UP build]
Signed-off-by: default avatarChristoph Lameter <>
Cc: KOSAKI Motohiro <>
CC: Tejun Heo <>
Cc: Joonsoo Kim <>
Cc: Alexey Dobriyan <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent d2cf5ad6
......@@ -198,7 +198,7 @@ extern void __inc_zone_state(struct zone *, enum zone_stat_item);
extern void dec_zone_state(struct zone *, enum zone_stat_item);
extern void __dec_zone_state(struct zone *, enum zone_stat_item);
void refresh_cpu_vm_stats(int);
void cpu_vm_stats_fold(int cpu);
void refresh_zone_stat_thresholds(void);
void drain_zonestat(struct zone *zone, struct per_cpu_pageset *);
......@@ -255,6 +255,7 @@ static inline void __dec_zone_page_state(struct page *page,
static inline void refresh_cpu_vm_stats(int cpu) { }
static inline void refresh_zone_stat_thresholds(void) { }
static inline void cpu_vm_stats_fold(int cpu) { }
static inline void drain_zonestat(struct zone *zone,
struct per_cpu_pageset *pset) { }
......@@ -5435,7 +5435,7 @@ static int page_alloc_cpu_notify(struct notifier_block *self,
* This is only okay since the processor is dead and cannot
* race with what we are doing.
return NOTIFY_OK;
......@@ -415,11 +415,7 @@ EXPORT_SYMBOL(dec_zone_page_state);
* Update the zone counters for one cpu.
* The cpu specified must be either the current cpu or a processor that
* is not online. If it is the current cpu then the execution thread must
* be pinned to the current cpu.
* Update the zone counters for the current cpu.
* Note that refresh_cpu_vm_stats strives to only access
* node local memory. The per cpu pagesets on remote zones are placed
......@@ -432,7 +428,7 @@ EXPORT_SYMBOL(dec_zone_page_state);
* with the global counters. These could cause remote node cache line
* bouncing and will have to be only done when necessary.
void refresh_cpu_vm_stats(int cpu)
static void refresh_cpu_vm_stats(int cpu)
struct zone *zone;
int i;
......@@ -493,6 +489,38 @@ void refresh_cpu_vm_stats(int cpu)
atomic_long_add(global_diff[i], &vm_stat[i]);
* Fold the data for an offline cpu into the global array.
* There cannot be any access by the offline cpu and therefore
* synchronization is simplified.
void cpu_vm_stats_fold(int cpu)
struct zone *zone;
int i;
int global_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
for_each_populated_zone(zone) {
struct per_cpu_pageset *p;
p = per_cpu_ptr(zone->pageset, cpu);
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
if (p->vm_stat_diff[i]) {
int v;
v = p->vm_stat_diff[i];
p->vm_stat_diff[i] = 0;
atomic_long_add(v, &zone->vm_stat[i]);
global_diff[i] += v;
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
if (global_diff[i])
atomic_long_add(global_diff[i], &vm_stat[i]);
* this is only called if !populated_zone(zone), which implies no other users of
* pset->vm_stat_diff[] exsist.
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