On Wed, 1 Sep 2010, Christoph Lameter wrote:
> The effect needs to be the same as retrieving a global or
> zone ZVC counter. Which is currently implemented in the following way:
>
> static inline unsigned long zone_page_state(struct zone *zone,
> enum zone_stat_item item)
> {
> long x = atomic_long_read(&zone->vm_stat[item]);
> #ifdef CONFIG_SMP
> if (x < 0)
> x = 0;
> #endif
> return x;
> }
>
Here is a patch that defined a snapshot function that works in the same
way:
Subject: Add a snapshot function for vm statistics
Add a snapshot function that can more accurately determine
the current value of a zone counter.
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
Index: linux-2.6/include/linux/vmstat.h
===================================================================
--- linux-2.6.orig/include/linux/vmstat.h 2010-09-01 19:45:23.506071189 -0500
+++ linux-2.6/include/linux/vmstat.h 2010-09-01 19:53:02.978979081 -0500
@@ -170,6 +170,28 @@
return x;
}
+/*
+ * More accurate version that also considers the currently pending
+ * deltas. For that we need to loop over all cpus to find the current
+ * deltas. There is no synchronization so the result cannot be
+ * exactly accurate either.
+ */
+static inline unsigned long zone_page_state_snapshot(struct zone *zone,
+ enum zone_stat_item item)
+{
+ int cpu;
+ long x = atomic_long_read(&zone->vm_stat[item]);
+
+#ifdef CONFIG_SMP
+ for_each_online_cpu(cpu)
+ x += per_cpu_ptr(zone->pageset, cpu)->vm_stat_diff[item];
+
+ if (x < 0)
+ x = 0;
+#endif
+ return x;
+}
+
extern unsigned long global_reclaimable_pages(void);
extern unsigned long zone_reclaimable_pages(struct zone *zone);
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