f2fs: add nobarrier mount option

This patch adds a mount option, nobarrier, in f2fs.
The assumption in here is that file system keeps the IO ordering, but
doesn't care about cache flushes inside the storages.

Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Conflicts:
	Documentation/filesystems/f2fs.txt

Change-Id: I2947cb10128efcf5647eff432d5fd959b2d2f5bc
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index 351229f..5b45d40 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -122,6 +122,11 @@
 inline_xattr           Enable the inline xattrs feature.
 inline_data            Enable the inline data feature: New created small(<~3.4k)
                        files can be written into inode block.
+nobarrier              This option can be used if underlying storage guarantees
+                       its cached data should be written to the novolatile area.
+		       If this option is set, no cache_flush commands are issued
+		       but f2fs still guarantees the write ordering of all the
+		       data writes.
 
 ================================================================================
 DEBUGFS ENTRIES
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 5c1e50a..954a1e7 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -140,7 +140,10 @@
 	/* change META to META_FLUSH in the checkpoint procedure */
 	if (type >= META_FLUSH) {
 		io->fio.type = META_FLUSH;
-		io->fio.rw = WRITE_FLUSH_FUA | REQ_META | REQ_PRIO;
+		if (test_opt(sbi, NOBARRIER))
+			io->fio.rw = WRITE_FLUSH | REQ_META | REQ_PRIO;
+		else
+			io->fio.rw = WRITE_FLUSH_FUA | REQ_META | REQ_PRIO;
 	}
 	__submit_merged_bio(io);
 	up_write(&io->io_rwsem);
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c791143..7be81a9 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -42,6 +42,7 @@
 #define F2FS_MOUNT_INLINE_XATTR		0x00000080
 #define F2FS_MOUNT_INLINE_DATA		0x00000100
 #define F2FS_MOUNT_FLUSH_MERGE		0x00000200
+#define F2FS_MOUNT_NOBARRIER		0x00000400
 
 #define clear_opt(sbi, option)	(sbi->mount_opt.opt &= ~F2FS_MOUNT_##option)
 #define set_opt(sbi, option)	(sbi->mount_opt.opt |= F2FS_MOUNT_##option)
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 3461bc1..c5eeb44 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -266,6 +266,9 @@
 	struct flush_cmd_control *fcc = SM_I(sbi)->cmd_control_info;
 	struct flush_cmd cmd;
 
+	if (test_opt(sbi, NOBARRIER))
+		return 0;
+
 	if (!test_opt(sbi, FLUSH_MERGE))
 		return blkdev_issue_flush(sbi->sb->s_bdev, GFP_KERNEL, NULL);
 
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 022c865..dbb99a6 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -52,6 +52,7 @@
 	Opt_inline_xattr,
 	Opt_inline_data,
 	Opt_flush_merge,
+	Opt_nobarrier,
 	Opt_err,
 };
 
@@ -69,6 +70,7 @@
 	{Opt_inline_xattr, "inline_xattr"},
 	{Opt_inline_data, "inline_data"},
 	{Opt_flush_merge, "flush_merge"},
+	{Opt_nobarrier, "nobarrier"},
 	{Opt_err, NULL},
 };
 
@@ -339,6 +341,9 @@
 		case Opt_flush_merge:
 			set_opt(sbi, FLUSH_MERGE);
 			break;
+		case Opt_nobarrier:
+			set_opt(sbi, NOBARRIER);
+			break;
 		default:
 			f2fs_msg(sb, KERN_ERR,
 				"Unrecognized mount option \"%s\" or missing value",
@@ -544,6 +549,8 @@
 		seq_puts(seq, ",inline_data");
 	if (!f2fs_readonly(sbi->sb) && test_opt(sbi, FLUSH_MERGE))
 		seq_puts(seq, ",flush_merge");
+	if (test_opt(sbi, NOBARRIER))
+		seq_puts(seq, ",nobarrier");
 	seq_printf(seq, ",active_logs=%u", sbi->active_logs);
 
 	return 0;