f2fs: add iostat support for flush

In this patch, it adds to account flush count.
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1192,6 +1192,7 @@ enum iostat_type {
 
 	/* other */
 	FS_DISCARD_IO,			/* discard */
+	FS_FLUSH_IO,			/* flush */
 	NR_IO_TYPE,
 };
 

fs/f2fs/iostat.c

@@ -80,6 +80,7 @@ int __maybe_unused iostat_info_seq_show(struct seq_file *seq, void *offset)
 	/* print other IOs */
 	seq_puts(seq, "[OTHER]\n");
 	IOSTAT_INFO_SHOW("fs discard", FS_DISCARD_IO);
+	IOSTAT_INFO_SHOW("fs flush", FS_FLUSH_IO);
 
 	return 0;
 }

fs/f2fs/segment.c

@@ -506,6 +506,8 @@ static int __submit_flush_wait(struct f2fs_sb_info *sbi,
 
 	trace_f2fs_issue_flush(bdev, test_opt(sbi, NOBARRIER),
 				test_opt(sbi, FLUSH_MERGE), ret);
+	if (!ret)
+		f2fs_update_iostat(sbi, NULL, FS_FLUSH_IO, 0);
 	return ret;
 }