dm vdo: document log_level parameter

Signed-off-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Author: raeburn

Documentation/admin-guide/device-mapper/vdo.rst

@@ -315,6 +315,13 @@ GB of RAM per 1 TB of window. For sparse indexes, the index requires 1 GB
 of RAM per 10 TB of window. The index configuration is set when the target
 is formatted and may not be modified.
 
+Module Parameters
+=================
+
+The vdo driver has a numeric parameter 'log_level' which controls the
+verbosity of logging from the driver. The default setting is 6
+(LOGLEVEL_INFO and more severe messages).
+
 Run-time Usage
 ==============