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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.

[akpm@linux-foundation.org: fix UP build]
Signed-off-by: default avatarChristoph Lameter <cl@linux.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d2cf5ad6

include/linux/vmstat.h

+2 −1
Original line number Diff line number Diff line
@@ -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) { }

mm/page_alloc.c

+1 −1
Original line number Diff line number Diff line
@@ -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.

		 */

		refresh_cpu_vm_stats(cpu);

		cpu_vm_stats_fold(cpu);

	}

	return NOTIFY_OK;

}

mm/vmstat.c

+34 −6
Original line number Diff line number Diff line
@@ -415,11 +415,7 @@ EXPORT_SYMBOL(dec_zone_page_state); 
#endif



/*

 * 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.