MFC r295022:

  nvd: add hw.nvd.delete_max tunable

  The NVMe specification does not define a maximum or optimal delete
  size, so technically max delete size is min(full size of namespace,
  2^32 - 1 LBAs).  A single delete operation for a multi-TB NVMe
  namespace though may take much longer to complete than the nvme(4)
  I/O timeout period.  So choose a sensible default here that is still
  suitably large to minimize the number of overall delete operations.

  This also fixes possible uint32_t overflow on initial TRIM operation
  for zpool create operations for NVMe namespaces with >4G LBAs.

Approved by:	re (glebius)
Sponsored by:	Intel

1 files changed, 11 insertions, 2 deletions

diff --git a/share/man/man4/nvd.4 b/share/man/man4/nvd.4
index 15200a4..4018dd8 100644
--- a/share/man/man4/nvd.4
+++ b/share/man/man4/nvd.4
@@ -1,5 +1,5 @@
 .\"
-.\" Copyright (c) 2012-2014 Intel Corporation
+.\" Copyright (c) 2012-2016 Intel Corporation
 .\" All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
@@ -33,7 +33,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 18, 2014
+.Dd January 28, 2016
 .Dt NVD 4
 .Os
 .Sh NAME
@@ -74,6 +74,15 @@ Note that device nodes from the
 driver are not
 .Xr GEOM 4
 disks and cannot be partitioned.
+.Sh CONFIGURATION
+The
+.Nm
+driver defines a system-wide maximum delete size for NVMe devices.  The
+default is 1GB.  To select a different value, set the following tunable in
+.Xr loader.conf 5 :
+.Bd -literal -offset indent
+hw.nvd.delete_max=<delete size in bytes>
+.Ed
 .Sh SEE ALSO
 .Xr GEOM 4 ,
 .Xr nvme 4 ,