VM statistics: Make timer deferrable

VM statistics updates do not matter if the kernel is in idle powersaving
mode.  So allow the timer to be deferred.

It would be better though if we could switch the timer between deferrable
and nondeferrable based on differentials present.  The timer would start
out nondeferrable and if we find that there were no updates in the last
statistics interval then we would switch the timer to deferrable.  If the
timer later finds again that there are differentials then go to
nondeferrable again.

And yet another way would be to run the timer shortly before going to idle?

The solution here means that the VM counters may be slightly off during
idle since differentials may be still pending while the timer is deferred.

Signed-off-by: Christoph Lameter <clameter@sgi.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 9832d9a41d8c721129a29f6b235b248b22de05dd..8faf27e5aa98b8fdaee347963e220febef2f45e9 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -698,7 +698,7 @@ static void __devinit start_cpu_timer(int cpu)
 {
        struct delayed_work *vmstat_work = &per_cpu(vmstat_work, cpu);
 
-       INIT_DELAYED_WORK(vmstat_work, vmstat_update);
+       INIT_DELAYED_WORK_DEFERRABLE(vmstat_work, vmstat_update);
        schedule_delayed_work_on(cpu, vmstat_work, HZ + cpu);
 }