---

yaml
---
r: 97857
b: refs/heads/master
c: 571640c
h: refs/heads/master
i:
  97855: 2a18671
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 034772b068be62a79470d6c1b81b01fbe27793ac
+refs/heads/master: 571640cad3fda6475da45d91cf86076f1f86bd9b

trunk/Documentation/filesystems/ext4.txt

@@ -139,8 +139,16 @@ commit=nrsec	(*)	Ext4 can be told to sync all its data and metadata
 			Setting it to very large values will improve
 			performance.
 
-barrier=1		This enables/disables barriers.  barrier=0 disables
-			it, barrier=1 enables it.
+barrier=<0|1(*)>	This enables/disables the use of write barriers in
+			the jbd code.  barrier=0 disables, barrier=1 enables.
+			This also requires an IO stack which can support
+			barriers, and if jbd gets an error on a barrier
+			write, it will disable again with a warning.
+			Write barriers enforce proper on-disk ordering
+			of journal commits, making volatile disk write caches
+			safe to use, at some performance penalty.  If
+			your disks are battery-backed in one way or another,
+			disabling barriers may safely improve performance.
 
 orlov		(*)	This enables the new Orlov block allocator. It is
 			enabled by default.

trunk/fs/ext4/super.c

@@ -671,6 +671,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	unsigned long def_mount_opts;
 	struct super_block *sb = vfs->mnt_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	journal_t *journal = sbi->s_journal;
 	struct ext4_super_block *es = sbi->s_es;
 
 	def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
@@ -729,8 +730,13 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 		seq_printf(seq, ",commit=%u",
 			   (unsigned) (sbi->s_commit_interval / HZ));
 	}
-	if (test_opt(sb, BARRIER))
-		seq_puts(seq, ",barrier=1");
+	/*
+	 * We're changing the default of barrier mount option, so
+	 * let's always display its mount state so it's clear what its
+	 * status is.
+	 */
+	seq_puts(seq, ",barrier=");
+	seq_puts(seq, test_opt(sb, BARRIER) ? "1" : "0");
 	if (test_opt(sb, JOURNAL_ASYNC_COMMIT))
 		seq_puts(seq, ",journal_async_commit");
 	if (test_opt(sb, NOBH))
@@ -1909,6 +1915,7 @@ static int ext4_fill_super (struct super_block *sb, void *data, int silent)
 	sbi->s_resgid = le16_to_cpu(es->s_def_resgid);
 
 	set_opt(sbi->s_mount_opt, RESERVATION);
+	set_opt(sbi->s_mount_opt, BARRIER);
 
 	/*
 	 * turn on extents feature by default in ext4 filesystem