f2fs: add a tracepoint for f2fs_read_data_page

This patch adds a tracepoint for f2fs_read_data_page to trace when page is
readed by user.

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 b3655dc..cadd28f 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -720,6 +720,8 @@
 	struct inode *inode = page->mapping->host;
 	int ret;
 
+	trace_f2fs_readpage(page, DATA);
+
 	/* If the file has inline data, try to read it directlly */
 	if (f2fs_has_inline_data(inode))
 		ret = f2fs_read_inline_data(inode, page);