vmstat: use this_cpu() to avoid irqon/off sequence in refresh_cpu_vm_stats

Disabling interrupts repeatedly can be avoided in the inner loop if we use
a this_cpu operation.

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 158ca6494bc6488e134e208f1add00f47ea0dc6b..d57a09143bf9c9ba2358e8b6604fa08a32f7c622 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -437,33 +437,29 @@ static inline void fold_diff(int *diff)
  * with the global counters. These could cause remote node cache line
  * bouncing and will have to be only done when necessary.
  */
-static void refresh_cpu_vm_stats(int cpu)
+static void refresh_cpu_vm_stats(void)
 {
        struct zone *zone;
        int i;
        int global_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
 
        for_each_populated_zone(zone) {
-               struct per_cpu_pageset *p;
+               struct per_cpu_pageset __percpu *p = zone->pageset;
 
-               p = per_cpu_ptr(zone->pageset, cpu);
+               for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
+                       int v;
 
-               for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
-                       if (p->vm_stat_diff[i]) {
-                               unsigned long flags;
-                               int v;
+                       v = this_cpu_xchg(p->vm_stat_diff[i], 0);
+                       if (v) {
 
-                               local_irq_save(flags);
-                               v = p->vm_stat_diff[i];
-                               p->vm_stat_diff[i] = 0;
-                               local_irq_restore(flags);
                                atomic_long_add(v, &zone->vm_stat[i]);
                                global_diff[i] += v;
 #ifdef CONFIG_NUMA
                                /* 3 seconds idle till flush */
-                               p->expire = 3;
+                               __this_cpu_write(p->expire, 3);
 #endif
                        }
+               }
                cond_resched();
 #ifdef CONFIG_NUMA
                /*
@@ -473,23 +469,24 @@ static void refresh_cpu_vm_stats(int cpu)
                 * Check if there are pages remaining in this pageset
                 * if not then there is nothing to expire.
                 */
-               if (!p->expire || !p->pcp.count)
+               if (!__this_cpu_read(p->expire) ||
+                              !__this_cpu_read(p->pcp.count))
                        continue;
 
                /*
                 * We never drain zones local to this processor.
                 */
                if (zone_to_nid(zone) == numa_node_id()) {
-                       p->expire = 0;
+                       __this_cpu_write(p->expire, 0);
                        continue;
                }
 
-               p->expire--;
-               if (p->expire)
+
+               if (__this_cpu_dec_return(p->expire))
                        continue;
 
-               if (p->pcp.count)
-                       drain_zone_pages(zone, &p->pcp);
+               if (__this_cpu_read(p->pcp.count))
+                       drain_zone_pages(zone, __this_cpu_ptr(&p->pcp));
 #endif
        }
        fold_diff(global_diff);
@@ -1216,7 +1213,7 @@ int sysctl_stat_interval __read_mostly = HZ;
 
 static void vmstat_update(struct work_struct *w)
 {
-       refresh_cpu_vm_stats(smp_processor_id());
+       refresh_cpu_vm_stats();
        schedule_delayed_work(&__get_cpu_var(vmstat_work),
                round_jiffies_relative(sysctl_stat_interval));
 }