md/raid6: move the spare page to a percpu allocation

In preparation for asynchronous handling of raid6 operations move the
spare page to a percpu allocation to allow multiple simultaneous
synchronous raid6 recovery operations.

Make this allocation cpu hotplug aware to maximize allocation
efficiency.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 52ba99954dec..07a7a4102f05 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -383,8 +383,13 @@ struct raid5_private_data {
                                             * (fresh device added).
                                             * Cleared when a sync completes.
                                             */
-
-        struct page             *spare_page; /* Used when checking P/Q in raid6 */
+        /* per cpu variables */
+        struct raid5_percpu {
+                struct page     *spare_page; /* Used when checking P/Q in raid6 */
+        } *percpu;
+#ifdef CONFIG_HOTPLUG_CPU
+        struct notifier_block   cpu_notify;
+#endif
 
         /*
          * Free stripes pool