f2fs: add fsync_mode=nobarrier for non-atomic files

For non-atomic files, this patch adds an option to give nobarrier which
doesn't issue flush commands to the device.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 0e39c77..44a2e32 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -308,7 +308,7 @@
 	remove_ino_entry(sbi, ino, APPEND_INO);
 	clear_inode_flag(inode, FI_APPEND_WRITE);
 flush_out:
-	if (!atomic)
+	if (!atomic && F2FS_OPTION(sbi).fsync_mode != FSYNC_MODE_NOBARRIER)
 		ret = f2fs_issue_flush(sbi, inode->i_ino);
 	if (!ret) {
 		remove_ino_entry(sbi, ino, UPDATE_INO);