CPU hotplug, writeback: Don't call writeback_set_ratelimit() too often during hotplug

The CPU hotplug callback related to writeback calls writeback_set_ratelimit()
during every state change in the hotplug sequence. This is unnecessary
since num_online_cpus() changes only once during the entire hotplug operation.

So invoke the function only once per hotplug, thereby avoiding the
unnecessary repetition of those costly calculations.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 5ad5ce23c1e0..830893b2b3c7 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1602,10 +1602,18 @@ void writeback_set_ratelimit(void)
 }
 
 static int __cpuinit
-ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
+ratelimit_handler(struct notifier_block *self, unsigned long action,
+                  void *hcpu)
 {
-        writeback_set_ratelimit();
-        return NOTIFY_DONE;
+
+        switch (action & ~CPU_TASKS_FROZEN) {
+        case CPU_ONLINE:
+        case CPU_DEAD:
+                writeback_set_ratelimit();
+                return NOTIFY_OK;
+        default:
+                return NOTIFY_DONE;
+        }
 }
 
 static struct notifier_block __cpuinitdata ratelimit_nb = {