1 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-dm b/Documentation/ABI/testing/sysfs-block-dm
index 87ca5691e29b..ac4b6fe245d9 100644
--- a/Documentation/ABI/testing/sysfs-block-dm
+++ b/Documentation/ABI/testing/sysfs-block-dm
@@ -23,3 +23,17 @@ Description:	Device-mapper device suspend state.
                 Contains the value 1 while the device is suspended.
                 Otherwise it contains 0. Read-only attribute.
 Users:          util-linux, device-mapper udev rules
+
+What:           /sys/block/dm-<num>/dm/rq_based_seq_io_merge_deadline
+Date:           March 2015
+KernelVersion:  4.1
+Contact:        dm-devel@redhat.com
+Description:    Allow control over how long a request that is a
+                reasonable merge candidate can be queued on the request
+                queue.  The resolution of this deadline is in
+                microseconds (ranging from 1 to 100000 usecs).
+                Setting this attribute to 0 (the default) will disable
+                request-based DM's merge heuristic and associated extra
+                accounting.  This attribute is not applicable to
+                bio-based DM devices so it will only ever report 0 for
+                them.