GFS2: Add an AIL writeback tracepoint

Add a tracepoint for monitoring writeback of the AIL.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 03e0041..ad1f188 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -144,6 +144,7 @@
 	struct list_head *head = &sdp->sd_ail1_list;
 	struct gfs2_ail *ai;
 
+	trace_gfs2_ail_flush(sdp, wbc, 1);
 	spin_lock(&sdp->sd_ail_lock);
 	list_for_each_entry_reverse(ai, head, ai_list) {
 		if (wbc->nr_to_write <= 0)
@@ -151,6 +152,7 @@
 		gfs2_ail1_start_one(sdp, wbc, ai); /* This may drop ail lock */
 	}
 	spin_unlock(&sdp->sd_ail_lock);
+	trace_gfs2_ail_flush(sdp, wbc, 0);
 }
 
 /**