Index: share/man/man9/bus_dma.9
===================================================================
--- share/man/man9/bus_dma.9
+++ share/man/man9/bus_dma.9
@@ -53,7 +53,7 @@
 .\" $FreeBSD$
 .\" $NetBSD: bus_dma.9,v 1.25 2002/10/14 13:43:16 wiz Exp $
 .\"
-.Dd July 17, 2013
+.Dd July 12, 2018
 .Dt BUS_DMA 9
 .Os
 .Sh NAME
@@ -424,9 +424,13 @@
 .It Fa nsegments
 Number of discontinuities (scatter/gather segments) allowed
 in a DMA mapped region.
-If there is no restriction,
-.Dv BUS_SPACE_UNRESTRICTED
-may be specified.
+Even if your device has no restriction on the number of segments, passing a
+maximal value is nonsensical.
+.Nm
+will allocate
+.Fa nsegments
+worth of segments, even if they will not all be used.
+So users should compute a reasonable number of segments for their DMA region.
 .It Fa maxsegsz
 Maximum size, in bytes, of a segment in any DMA mapped region associated
 with