md: use new plugging interface for RAID IO.

md/raid submits a lot of IO from the various raid threads.
So adding start/finish plug calls to those so that some
plugging happens.

Signed-off-by: NeilBrown <[e-mail]>

drivers/md/raid1.c

···
 	conf_t *conf = mddev->private;
 	struct list_head *head = &conf->retry_list;
 	mdk_rdev_t *rdev;
+	struct blk_plug plug;
 
 	md_check_recovery(mddev);
-	
+
+	blk_start_plug(&plug);
 	for (;;) {
 		char b[BDEVNAME_SIZE];
 
···
 		}
 		cond_resched();
 	}
+	blk_finish_plug(&plug);
 }
 
 

drivers/md/raid10.c

···
 	conf_t *conf = mddev->private;
 	struct list_head *head = &conf->retry_list;
 	mdk_rdev_t *rdev;
+	struct blk_plug plug;
 
 	md_check_recovery(mddev);
 
+	blk_start_plug(&plug);
 	for (;;) {
 		char b[BDEVNAME_SIZE];
 
···
 		}
 		cond_resched();
 	}
+	blk_finish_plug(&plug);
 }
 
 

drivers/md/raid5.c

···
 	struct stripe_head *sh;
 	raid5_conf_t *conf = mddev->private;
 	int handled;
+	struct blk_plug plug;
 
 	pr_debug("+++ raid5d active\n");
 
 	md_check_recovery(mddev);
 
+	blk_start_plug(&plug);
 	handled = 0;
 	spin_lock_irq(&conf->device_lock);
 	while (1) {
···
 	spin_unlock_irq(&conf->device_lock);
 
 	async_tx_issue_pending_all();
+	blk_finish_plug(&plug);
 
 	pr_debug("--- raid5d inactive\n");
 }