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: Christoph 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 8a8da1f..aaee663 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -415,11 +415,7 @@
#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 @@
* 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;
@@ -494,6 +490,38 @@
}
/*
+ * 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.
*/