btrfs: Add noautodefrag mount option.

Btrfs has autodefrag mount option but no pairing noautodefrag option,
which makes it impossible to disable autodefrag without umount.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
index ce487a2a88f8..e87609a4e21c 100644
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -46,10 +46,12 @@ Options with (*) are default options and will not show in the mount options.
         bytes, optionally with a K, M, or G suffix, case insensitive.
         Default is 1MB.
 
+  noautodefrag(*)
   autodefrag
-        Detect small random writes into files and queue them up for the
-        defrag process.  Works best for small files; Not well suited for
-        large database workloads.
+        Disable/enable auto defragmentation.
+        Auto defragmentation detects small random writes into files and queue
+        them up for the defrag process.  Works best for small files;
+        Not well suited for large database workloads.
 
   check_int
   check_int_data