f2fs: add tracepoint for f2fs_issue_flush

This patch adds a tracepoint for f2fs_issue_flush.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index e016b97..5a53a0a 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -239,6 +239,9 @@
 	struct flush_cmd_control *fcc = SM_I(sbi)->cmd_control_info;
 	struct flush_cmd cmd;
 
+	trace_f2fs_issue_flush(sbi->sb, test_opt(sbi, NOBARRIER),
+					test_opt(sbi, FLUSH_MERGE));
+
 	if (test_opt(sbi, NOBARRIER))
 		return 0;