Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4

* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
  ext4: enable barriers by default
  jbd2: Fix barrier fallback code to re-lock the buffer head
  ext4: Display the journal_async_commit mount option in /proc/mounts
  jbd2: If a journal checksum error is detected, propagate the error to ext4
  jbd2: Fix memory leak when verifying checksums in the journal
  ext4: fix online resize bug
  ext4: Fix uninit block group initialization with FLEX_BG
  ext4: Fix use of uninitialized data with debug enabled.

1 files changed, 10 insertions, 2 deletions

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 560f88dc7090..0c5086db8352 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/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.