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/fs/zfs.h

@@ -26,6 +26,7 @@
  * Copyright (c) 2013, 2017 Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
  * Copyright (c) 2017 Datto Inc.
+ * Copyright (c) 2017, Intel Corporation.
  */
 
 /* Portions Copyright 2010 Robert Milkowski */
@@ -181,6 +182,7 @@ typedef enum {
 	ZFS_PROP_KEY_GUID,
 	ZFS_PROP_KEYSTATUS,
 	ZFS_PROP_REMAPTXG,		/* not exposed to the user */
+	ZFS_PROP_SPECIAL_SMALL_BLOCKS,
 	ZFS_NUM_PROPS
 } zfs_prop_t;
 
@@ -713,6 +715,7 @@ typedef struct zpool_load_policy {
 #define	ZPOOL_CONFIG_MMP_TXG		"mmp_txg"	/* not stored on disk */
 #define	ZPOOL_CONFIG_MMP_HOSTNAME	"mmp_hostname"	/* not stored on disk */
 #define	ZPOOL_CONFIG_MMP_HOSTID		"mmp_hostid"	/* not stored on disk */
+#define	ZPOOL_CONFIG_ALLOCATION_BIAS	"alloc_bias"	/* not stored on disk */
 
 /*
  * The persistent vdev state is stored as separate values rather than a single
@@ -759,6 +762,14 @@ typedef struct zpool_load_policy {
 #define	VDEV_TOP_ZAP_POOL_CHECKPOINT_SM \
 	"com.delphix:pool_checkpoint_sm"
 
+#define	VDEV_TOP_ZAP_ALLOCATION_BIAS \
+	"org.zfsonlinux:allocation_bias"
+
+/* vdev metaslab allocation bias */
+#define	VDEV_ALLOC_BIAS_LOG		"log"
+#define	VDEV_ALLOC_BIAS_SPECIAL		"special"
+#define	VDEV_ALLOC_BIAS_DEDUP		"dedup"
+
 /*
  * This is needed in userland to report the minimum necessary device size.
  */