OpenZFS 9102 - zfs should be able to initialize storage devices

PROBLEM
========

The first access to a block incurs a performance penalty on some platforms
(e.g. AWS's EBS, VMware VMDKs). Therefore we recommend that volumes are
"thick provisioned", where supported by the platform (VMware). This can
create a large delay in getting a new virtual machines up and running (or
adding storage to an existing Engine). If the thick provision step is
omitted, write performance will be suboptimal until all blocks on the LUN
have been written.

SOLUTION
=========

This feature introduces a way to 'initialize' the disks at install or in the
background to make sure we don't incur this first read penalty.

When an entire LUN is added to ZFS, we make all space available immediately,
and allow ZFS to find unallocated space and zero it out. This works with
concurrent writes to arbitrary offsets, ensuring that we don't zero out
something that has been (or is in the middle of being) written. This scheme
can also be applied to existing pools (affecting only free regions on the
vdev). Detailed design:
        - new subcommand:zpool initialize [-cs] <pool> [<vdev> ...]
                - start, suspend, or cancel initialization
        - Creates new open-context thread for each vdev
        - Thread iterates through all metaslabs in this vdev
        - Each metaslab:
                - select a metaslab
                - load the metaslab
                - mark the metaslab as being zeroed
                - walk all free ranges within that metaslab and translate
                  them to ranges on the leaf vdev
                - issue a "zeroing" I/O on the leaf vdev that corresponds to
                  a free range on the metaslab we're working on
                - continue until all free ranges for this metaslab have been
                  "zeroed"
                - reset/unmark the metaslab being zeroed
                - if more metaslabs exist, then repeat above tasks.
                - if no more metaslabs, then we're done.

        - progress for the initialization is stored on-disk in the vdev’s
          leaf zap object. The following information is stored:
                - the last offset that has been initialized
                - the state of the initialization process (i.e. active,
                  suspended, or canceled)
                - the start time for the initialization

        - progress is reported via the zpool status command and shows
          information for each of the vdevs that are initializing

Porting notes:
- Added zfs_initialize_value module parameter to set the pattern
  written by "zpool initialize".
- Added zfs_vdev_{initializing,removal}_{min,max}_active module options.

Authored by: George Wilson <george.wilson@delphix.com>
Reviewed by: John Wren Kennedy <john.kennedy@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: loli10K <ezomori.nozomu@gmail.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Richard Lowe <richlowe@richlowe.net>
Signed-off-by: Tim Chase <tim@chase2k.com>
Ported-by: Tim Chase <tim@chase2k.com>

OpenZFS-issue: https://www.illumos.org/issues/9102
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/c3963210eb
Closes #8230

include/sys/fs/zfs.h

@@ -775,6 +775,13 @@ typedef struct zpool_load_policy {
 #define	VDEV_ALLOC_BIAS_SPECIAL		"special"
 #define	VDEV_ALLOC_BIAS_DEDUP		"dedup"
 
+#define	VDEV_LEAF_ZAP_INITIALIZE_LAST_OFFSET	\
+	"com.delphix:next_offset_to_initialize"
+#define	VDEV_LEAF_ZAP_INITIALIZE_STATE	\
+	"com.delphix:vdev_initialize_state"
+#define	VDEV_LEAF_ZAP_INITIALIZE_ACTION_TIME	\
+	"com.delphix:vdev_initialize_action_time"
+
 /*
  * This is needed in userland to report the minimum necessary device size.
  */
@@ -988,10 +995,15 @@ typedef struct vdev_stat {
 	uint64_t	vs_read_errors;		/* read errors		*/
 	uint64_t	vs_write_errors;	/* write errors		*/
 	uint64_t	vs_checksum_errors;	/* checksum errors	*/
+	uint64_t	vs_initialize_errors;	/* initializing errors	*/
 	uint64_t	vs_self_healed;		/* self-healed bytes	*/
 	uint64_t	vs_scan_removing;	/* removing?	*/
 	uint64_t	vs_scan_processed;	/* scan processed bytes	*/
 	uint64_t	vs_fragmentation;	/* device fragmentation */
+	uint64_t	vs_initialize_bytes_done; /* bytes initialized */
+	uint64_t	vs_initialize_bytes_est; /* total bytes to initialize */
+	uint64_t	vs_initialize_state;	/* vdev_initialzing_state_t */
+	uint64_t	vs_initialize_action_time; /* time_t */
 	uint64_t	vs_checkpoint_space;    /* checkpoint-consumed space */
 	uint64_t	vs_resilver_deferred;	/* resilver deferred	*/
 	uint64_t	vs_slow_ios;		/* slow IOs */
@@ -1023,7 +1035,6 @@ typedef struct vdev_stat_ex {
 #define	VDEV_L_HISTO_BUCKETS 37		/* Latency histo buckets */
 #define	VDEV_RQ_HISTO_BUCKETS 25	/* Request size histo buckets */
 
-
 	/* Amount of time in ZIO queue (ns) */
 	uint64_t vsx_queue_histo[ZIO_PRIORITY_NUM_QUEUEABLE]
 	    [VDEV_L_HISTO_BUCKETS];
@@ -1050,6 +1061,16 @@ typedef struct vdev_stat_ex {
 
 } vdev_stat_ex_t;
 
+/*
+ * Initialize functions.
+ */
+typedef enum pool_initialize_func {
+	POOL_INITIALIZE_DO,
+	POOL_INITIALIZE_CANCEL,
+	POOL_INITIALIZE_SUSPEND,
+	POOL_INITIALIZE_FUNCS
+} pool_initialize_func_t;
+
 /*
  * DDT statistics.  Note: all fields should be 64-bit because this
  * is passed between kernel and userland as an nvlist uint64 array.
@@ -1094,6 +1115,14 @@ typedef struct ddt_histogram {
 #define	ZVOL_PROP_NAME		"name"
 #define	ZVOL_DEFAULT_BLOCKSIZE	8192
 
+typedef enum {
+	VDEV_INITIALIZE_NONE,
+	VDEV_INITIALIZE_ACTIVE,
+	VDEV_INITIALIZE_CANCELED,
+	VDEV_INITIALIZE_SUSPENDED,
+	VDEV_INITIALIZE_COMPLETE
+} vdev_initializing_state_t;
+
 /*
  * /dev/zfs ioctl numbers.
  *
@@ -1184,6 +1213,7 @@ typedef enum zfs_ioc {
 	ZFS_IOC_REMAP,				/* 0x5a4c */
 	ZFS_IOC_POOL_CHECKPOINT,		/* 0x5a4d */
 	ZFS_IOC_POOL_DISCARD_CHECKPOINT,	/* 0x5a4e */
+	ZFS_IOC_POOL_INITIALIZE,		/* 0x5a4f */
 
 	/*
 	 * Linux - 3/64 numbers reserved.
@@ -1277,6 +1307,12 @@ typedef enum {
  */
 #define	ZPOOL_HIDDEN_ARGS	"hidden_args"
 
+/*
+ * The following are names used when invoking ZFS_IOC_POOL_INITIALIZE.
+ */
+#define	ZPOOL_INITIALIZE_COMMAND	"initialize_command"
+#define	ZPOOL_INITIALIZE_VDEVS		"initialize_vdevs"
+
 /*
  * Flags for ZFS_IOC_VDEV_SET_STATE
  */