Merge branch 'linus' into x86/i8259

[sfrench/cifs-2.6.git] / Documentation / filesystems / ext4.txt

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 560f88dc7090dadcfd7c2db4fc6821c64b8da3fe..0c5086db835262828edd6b377bee4affb4b6da6f 100644 (file)
--- 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.