btrfs: Add nodiscard mount option.

Add nodiscard mount option to disable discard with remount option.

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, 2 deletions

diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
index e87609a4e21c..7254cf501391 100644
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -98,9 +98,12 @@ Options with (*) are default options and will not show in the mount options.
         can be avoided.  Especially useful when trying to mount a multi-device
         setup as root.  May be specified multiple times for multiple devices.
 
+  nodiscard(*)
   discard
-        Issue frequent commands to let the block device reclaim space freed by
-        the filesystem.  This is useful for SSD devices, thinly provisioned
+        Disable/enable discard mount option.
+        Discard issues frequent commands to let the block device reclaim space
+        freed by the filesystem.
+        This is useful for SSD devices, thinly provisioned
         LUNs and virtual machine images, but may have a significant
         performance impact.  (The fstrim command is also available to
         initiate batch trims from userspace).