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>

Documentation/filesystems/f2fs.txt

@@ -126,6 +126,11 @@ flush_merge	       Merge concurrent cache_flush commands as much as possible
                        to eliminate redundant command issues. If the underlying
 		       device handles the cache_flush command relatively slowly,
 		       recommend to enable this option.
+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

fs/f2fs/data.c

@@ -139,7 +139,10 @@ void f2fs_submit_merged_bio(struct f2fs_sb_info *sbi,
 	/* 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);

fs/f2fs/f2fs.h

@@ -41,6 +41,7 @@
 #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)

fs/f2fs/segment.c

@@ -239,6 +239,9 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
 	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);
 

fs/f2fs/super.c

@@ -52,6 +52,7 @@ enum {
 	Opt_inline_xattr,
 	Opt_inline_data,
 	Opt_flush_merge,
+	Opt_nobarrier,
 	Opt_err,
 };
 
@@ -69,6 +70,7 @@ static match_table_t f2fs_tokens = {
 	{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 @@ static int parse_options(struct super_block *sb, char *options)
 		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 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		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;