On Mon, 18 Oct 2010, KOSAKI Motohiro wrote:
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 39c24eb..699cdea 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -185,6 +185,7 @@ struct per_cpu_pageset {
> #ifdef CONFIG_SMP
> s8 stat_threshold;
> s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
> + s8 vm_stat_drifted[NR_VM_ZONE_STAT_ITEMS];
> #endif
> };
Significantly increases cache footprint for per_cpu_pagesets.
> @@ -168,10 +175,14 @@ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
> int delta)
> {
> struct per_cpu_pageset *pcp = this_cpu_ptr(zone->pageset);
> -
> s8 *p = pcp->vm_stat_diff + item;
> long x;
>
> + if (unlikely(!vm_stat_drift_take(zone, item))) {
> + zone_page_state_add(delta, zone, item);
> + return;
> + }
> +
> x = delta + *p;
>
> if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
> @@ -224,6 +235,11 @@ void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
> struct per_cpu_pageset *pcp = this_cpu_ptr(zone->pageset);
> s8 *p = pcp->vm_stat_diff + item;
>
> + if (unlikely(!vm_stat_drift_take(zone, item))) {
> + zone_page_state_add(1, zone, item);
> + return;
> + }
> +
> (*p)++;
>
> if (unlikely(*p > pcp->stat_threshold)) {
> @@ -245,6 +261,11 @@ void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
> struct per_cpu_pageset *pcp = this_cpu_ptr(zone->pageset);
> s8 *p = pcp->vm_stat_diff + item;
>
> + if (unlikely(!vm_stat_drift_take(zone, item))) {
> + zone_page_state_add(-1, zone, item);
> + return;
> + }
> +
> (*p)--;
>
> if (unlikely(*p < - pcp->stat_threshold)) {
Increased overhead for basic VM counter management.
Instead of all of this why not simply set the stat_threshold to 0 for
select cpus?
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