diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index b800cdd..b9e8a93 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -44,3 +44,9 @@
 	Current threshold on this BDI for reclaimable + writeback
 	memory
 
+min_ratio (read-write)
+
+	Minimal percentage of global dirty threshold allocated to this
+	bdi.  If the value written to this file would make the the sum
+	of all min_ratio values exceed 100, then EINVAL is returned.
+	The default is zero