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SubjectRe: ZVC: Increase threshold for larger processor configurationss
On Thu, 29 Jun 2006, Christoph Lameter wrote:

> Thats one more memory reference. Hmmm... We could place the threshold in
> the same cacheline. That would also open up the possbiliity of dynamically
> calculating the threshold.
>

like this?

ZVC: Dynamic counter threshold configuration

We add a threshold before the first counter and calculate the
threshold based on the size of the zone assuming that larger machines have larger
zone sizes and therefore larger thresholds.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.17-mm4/mm/vmstat.c
===================================================================
--- linux-2.6.17-mm4.orig/mm/vmstat.c 2006-06-29 13:07:13.342483251 -0700
+++ linux-2.6.17-mm4/mm/vmstat.c 2006-06-29 13:17:52.978741713 -0700
@@ -112,37 +112,22 @@ atomic_long_t vm_stat[NR_VM_ZONE_STAT_IT
EXPORT_SYMBOL(vm_stat);

#ifdef CONFIG_SMP
-
-#define STAT_THRESHOLD 32
-
-/*
- * Determine pointer to currently valid differential byte given a zone and
- * the item number.
- *
- * Preemption must be off
- */
-static inline s8 *diff_pointer(struct zone *zone, enum zone_stat_item item)
-{
- return &zone_pcp(zone, smp_processor_id())->vm_stat_diff[item];
-}
-
/*
* For use when we know that interrupts are disabled.
*/
void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
int delta)
{
- s8 *p;
+ struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+ s8 *p = pcp->vm_stat_diff + item;
long x;

- p = diff_pointer(zone, item);
x = delta + *p;

- if (unlikely(x > STAT_THRESHOLD || x < -STAT_THRESHOLD)) {
+ if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
zone_page_state_add(x, zone, item);
x = 0;
}
-
*p = x;
}
EXPORT_SYMBOL(__mod_zone_page_state);
@@ -184,11 +169,12 @@ EXPORT_SYMBOL(mod_zone_page_state);
*/
static void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
{
- s8 *p = diff_pointer(zone, item);
+ struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+ s8 *p = pcp->vm_stat_diff + item;

(*p)++;

- if (unlikely(*p > STAT_THRESHOLD)) {
+ if (unlikely(*p > pcp->stat_threshold)) {
zone_page_state_add(*p, zone, item);
*p = 0;
}
@@ -203,11 +189,12 @@ EXPORT_SYMBOL(__inc_zone_page_state);
void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
{
struct zone *zone = page_zone(page);
- s8 *p = diff_pointer(zone, item);
+ struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+ s8 *p = pcp->vm_stat_diff + item;

(*p)--;

- if (unlikely(*p < -STAT_THRESHOLD)) {
+ if (unlikely(*p < -pcp->stat_threshold)) {
zone_page_state_add(*p, zone, item);
*p = 0;
}
@@ -238,16 +225,12 @@ EXPORT_SYMBOL(inc_zone_page_state);
void dec_zone_page_state(struct page *page, enum zone_stat_item item)
{
unsigned long flags;
- struct zone *zone;
- s8 *p;
+ struct zone *zone = page_zone(page);
+ struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
+ s8 *p = pcp->vm_stat_diff + item;

- zone = page_zone(page);
local_irq_save(flags);
- p = diff_pointer(zone, item);
-
- (*p)--;
-
- if (unlikely(*p < -STAT_THRESHOLD)) {
+ if (unlikely(*p < -pcp->stat_threshold)) {
zone_page_state_add(*p, zone, item);
*p = 0;
}
@@ -502,6 +485,7 @@ static int zoneinfo_show(struct seq_file
seq_printf(m,
")"
"\n pagesets");
+ seq_printf(m, "\n stat_threshold: %i", zone_pcp(zone, 0)->stat_threshold);
for_each_online_cpu(i) {
struct per_cpu_pageset *pageset;
int j;
Index: linux-2.6.17-mm4/include/linux/mmzone.h
===================================================================
--- linux-2.6.17-mm4.orig/include/linux/mmzone.h 2006-06-29 13:07:12.486090884 -0700
+++ linux-2.6.17-mm4/include/linux/mmzone.h 2006-06-29 13:07:26.486201908 -0700
@@ -77,6 +77,7 @@ struct per_cpu_pages {
struct per_cpu_pageset {
struct per_cpu_pages pcp[2]; /* 0: hot. 1: cold */
#ifdef CONFIG_SMP
+ s8 stat_threshold; /* maximum diff before update */
s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
#endif
} ____cacheline_aligned_in_smp;
Index: linux-2.6.17-mm4/mm/page_alloc.c
===================================================================
--- linux-2.6.17-mm4.orig/mm/page_alloc.c 2006-06-29 13:07:13.313188187 -0700
+++ linux-2.6.17-mm4/mm/page_alloc.c 2006-06-29 13:14:57.831351395 -0700
@@ -1918,6 +1918,8 @@ static int __cpuinit process_zones(int c
if (percpu_pagelist_fraction)
setup_pagelist_highmark(zone_pcp(zone, cpu),
(zone->present_pages / percpu_pagelist_fraction));
+
+ vm_stat_setup(zone, cpu);
}

return 0;
@@ -2039,6 +2041,7 @@ static __meminit void zone_pcp_init(stru
#else
setup_pageset(zone_pcp(zone,cpu), batch);
#endif
+ vm_stat_setup(zone, cpu);
}
if (zone->present_pages)
printk(KERN_DEBUG " %s zone: %lu pages, LIFO batch:%lu\n",
Index: linux-2.6.17-mm4/include/linux/vmstat.h
===================================================================
--- linux-2.6.17-mm4.orig/include/linux/vmstat.h 2006-06-29 13:07:12.916728323 -0700
+++ linux-2.6.17-mm4/include/linux/vmstat.h 2006-06-29 13:18:20.594224260 -0700
@@ -174,6 +175,27 @@ extern void inc_zone_state(struct zone *
void refresh_cpu_vm_stats(int);
void refresh_vm_stats(void);

+static inline void vm_stat_setup(struct zone *zone, int cpu)
+{
+ int threshold;
+
+ /*
+ * Increase the threshold for every 64 Megabyte of memory by one.
+ * The bigger the zone the more flexibility we can give us.
+ *
+ * The minimum threshold of 4 is equal to 256 MB of memory.
+ * The maximum of 125 reflects 8 Gigabytes.
+ */
+ threshold = zone->present_pages / (1024*1024*64 / PAGE_SIZE);
+
+ /*
+ * Threshold must be between 4 and 125
+ */
+ threshold = max(4, min(125, threshold));
+
+ zone_pcp(zone, cpu)->stat_threshold = threshold;
+}
+
#else /* CONFIG_SMP */

/*
@@ -210,6 +232,7 @@ static inline void __dec_zone_page_state

static inline void refresh_cpu_vm_stats(int cpu) { }
static inline void refresh_vm_stats(void) { }
+static inline void vm_stat_setup(struct zone *z, int cpu) { }
#endif

#endif /* _LINUX_VMSTAT_H */
-
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