ext3: make default data ordering mode configurable

This makes the defautl ext3 data ordering mode (when no explicit
ordering is set) configurable, so as to allow people to default to
'data=writeback' and get the resulting latency improvements.

This is a non-issue if a filesystem has been explicitly set to some
ordering (with 'tune2fs').

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 26 insertions, 1 deletions

diff --git a/fs/ext3/Kconfig b/fs/ext3/Kconfig
index 8e0cfe44b0fc..fb3c1a21b135 100644
--- a/fs/ext3/Kconfig
+++ b/fs/ext3/Kconfig
@@ -28,6 +28,25 @@ config EXT3_FS
           To compile this file system support as a module, choose M here: the
           module will be called ext3.
 
+config EXT3_DEFAULTS_TO_ORDERED
+        bool "Default to 'data=ordered' in ext3 (legacy option)"
+        depends on EXT3_FS
+        help
+          If a filesystem does not explicitly specify a data ordering
+          mode, and the journal capability allowed it, ext3 used to
+          historically default to 'data=ordered'.
+
+          That was a rather unfortunate choice, because it leads to all
+          kinds of latency problems, and the 'data=writeback' mode is more
+          appropriate these days.
+
+          You should probably always answer 'n' here, and if you really
+          want to use 'data=ordered' mode, set it in the filesystem itself
+          with 'tune2fs -o journal_data_ordered'.
+
+          But if you really want to enable the legacy default, you can do
+          so by answering 'y' to this question.
+
 config EXT3_FS_XATTR
         bool "Ext3 extended attributes"
         depends on EXT3_FS
diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 9e5b8e387e1e..599dbfe504c3 100644
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -44,6 +44,12 @@
 #include "acl.h"
 #include "namei.h"
 
+#ifdef CONFIG_EXT3_DEFAULTS_TO_ORDERED
+  #define EXT3_MOUNT_DEFAULT_DATA_MODE EXT3_MOUNT_ORDERED_DATA
+#else
+  #define EXT3_MOUNT_DEFAULT_DATA_MODE EXT3_MOUNT_WRITEBACK_DATA
+#endif
+
 static int ext3_load_journal(struct super_block *, struct ext3_super_block *,
                              unsigned long journal_devnum);
 static int ext3_create_journal(struct super_block *, struct ext3_super_block *,
@@ -1919,7 +1925,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
                    cope, else JOURNAL_DATA */
                 if (journal_check_available_features
                     (sbi->s_journal, 0, 0, JFS_FEATURE_INCOMPAT_REVOKE))
-                        set_opt(sbi->s_mount_opt, ORDERED_DATA);
+                        set_opt(sbi->s_mount_opt, DEFAULT_DATA_MODE);
                 else
                         set_opt(sbi->s_mount_opt, JOURNAL_DATA);
                 break;