f2fs: add a tracepoint for f2fs_write_{meta,node,data}_pages

This patch adds a tracepoint for f2fs_write_{meta,node,data}_pages to trace when
pages are fsyncing/flushing.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index b997d55..21bfafa 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -860,6 +860,8 @@
 	int ret;
 	long diff;
 
+	trace_f2fs_writepages(mapping->host, wbc, DATA);
+
 	/* deal with chardevs and other special file */
 	if (!mapping->a_ops->writepage)
 		return 0;