Pool allocation classes

Allocation Classes add the ability to have allocation classes in a
pool that are dedicated to serving specific block categories, such
as DDT data, metadata, and small file blocks. A pool can opt-in to
this feature by adding a 'special' or 'dedup' top-level VDEV.

Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Alek Pinchuk <apinchuk@datto.com>
Reviewed-by: Håkan Johansson <f96hajo@chalmers.se>
Reviewed-by: Andreas Dilger <andreas.dilger@chamcloud.com>
Reviewed-by: DHE <git@dehacked.net>
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: Gregor Kopka <gregor@kopka.net>
Reviewed-by: Kash Pande <kash@tripleback.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Don Brady <don.brady@delphix.com>
Closes #5182

include/sys/vdev_impl.h

@@ -21,6 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
+ * Copyright (c) 2017, Intel Corporation.
  */
 
 #ifndef _SYS_VDEV_IMPL_H
@@ -140,6 +141,14 @@ struct vdev_queue {
 	kmutex_t	vq_lock;
 };
 
+typedef enum vdev_alloc_bias {
+	VDEV_BIAS_NONE,
+	VDEV_BIAS_LOG,		/* dedicated to ZIL data (SLOG) */
+	VDEV_BIAS_SPECIAL,	/* dedicated to ddt, metadata, and small blks */
+	VDEV_BIAS_DEDUP		/* dedicated to dedup metadata */
+} vdev_alloc_bias_t;
+
+
 /*
  * On-disk indirect vdev state.
  *
@@ -236,6 +245,7 @@ struct vdev {
 	boolean_t	vdev_ishole;	/* is a hole in the namespace	*/
 	kmutex_t	vdev_queue_lock; /* protects vdev_queue_depth	*/
 	uint64_t	vdev_top_zap;
+	vdev_alloc_bias_t vdev_alloc_bias; /* metaslab allocation bias	*/
 
 	/* pool checkpoint related */
 	space_map_t	*vdev_checkpoint_sm;	/* contains reserved blocks */