blk-wbt: allow reset of default latency through sysfs

Allow a write of '-1' to reset the default latency target for
a given device. This removes knowledge of the different default
settings for rotational vs non-rotational from user space.

Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index 14235e72a702..51642159aedb 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -188,7 +188,9 @@ wb_lat_usec (RW)
 If the device is registered for writeback throttling, then this file shows
 the target minimum read latency. If this latency is exceeded in a given
 window of time (see wb_window_usec), then the writeback throttling will start
-scaling back writes.
+scaling back writes. Writing a value of '0' to this file disables the
+feature. Writing a value of '-1' to this file resets the value to the
+default setting.
 
 
 Jens Axboe <jens.axboe@oracle.com>, February 2009