OpenZFS 7614, 9064 - zfs device evacuation/removal

OpenZFS 7614 - zfs device evacuation/removal
OpenZFS 9064 - remove_mirror should wait for device removal to complete

This project allows top-level vdevs to be removed from the storage pool
with "zpool remove", reducing the total amount of storage in the pool.
This operation copies all allocated regions of the device to be removed
onto other devices, recording the mapping from old to new location.
After the removal is complete, read and free operations to the removed
(now "indirect") vdev must be remapped and performed at the new location
on disk.  The indirect mapping table is kept in memory whenever the pool
is loaded, so there is minimal performance overhead when doing operations
on the indirect vdev.

The size of the in-memory mapping table will be reduced when its entries
become "obsolete" because they are no longer used by any block pointers
in the pool.  An entry becomes obsolete when all the blocks that use
it are freed.  An entry can also become obsolete when all the snapshots
that reference it are deleted, and the block pointers that reference it
have been "remapped" in all filesystems/zvols (and clones).  Whenever an
indirect block is written, all the block pointers in it will be "remapped"
to their new (concrete) locations if possible.  This process can be
accelerated by using the "zfs remap" command to proactively rewrite all
indirect blocks that reference indirect (removed) vdevs.

Note that when a device is removed, we do not verify the checksum of
the data that is copied.  This makes the process much faster, but if it
were used on redundant vdevs (i.e. mirror or raidz vdevs), it would be
possible to copy the wrong data, when we have the correct data on e.g.
the other side of the mirror.

At the moment, only mirrors and simple top-level vdevs can be removed
and no removal is allowed if any of the top-level vdevs are raidz.

Porting Notes:

* Avoid zero-sized kmem_alloc() in vdev_compact_children().

    The device evacuation code adds a dependency that
    vdev_compact_children() be able to properly empty the vdev_child
    array by setting it to NULL and zeroing vdev_children.  Under Linux,
    kmem_alloc() and related functions return a sentinel pointer rather
    than NULL for zero-sized allocations.

* Remove comment regarding "mpt" driver where zfs_remove_max_segment
  is initialized to SPA_MAXBLOCKSIZE.

  Change zfs_condense_indirect_commit_entry_delay_ticks to
  zfs_condense_indirect_commit_entry_delay_ms for consistency with
  most other tunables in which delays are specified in ms.

* ZTS changes:

    Use set_tunable rather than mdb
    Use zpool sync as appropriate
    Use sync_pool instead of sync
    Kill jobs during test_removal_with_operation to allow unmount/export
    Don't add non-disk names such as "mirror" or "raidz" to $DISKS
    Use $TEST_BASE_DIR instead of /tmp
    Increase HZ from 100 to 1000 which is more common on Linux

    removal_multiple_indirection.ksh
        Reduce iterations in order to not time out on the code
        coverage builders.

    removal_resume_export:
        Functionally, the test case is correct but there exists a race
        where the kernel thread hasn't been fully started yet and is
        not visible.  Wait for up to 1 second for the removal thread
        to be started before giving up on it.  Also, increase the
        amount of data copied in order that the removal not finish
        before the export has a chance to fail.

* MMP compatibility, the concept of concrete versus non-concrete devices
  has slightly changed the semantics of vdev_writeable().  Update
  mmp_random_leaf_impl() accordingly.

* Updated dbuf_remap() to handle the org.zfsonlinux:large_dnode pool
  feature which is not supported by OpenZFS.

* Added support for new vdev removal tracepoints.

* Test cases removal_with_zdb and removal_condense_export have been
  intentionally disabled.  When run manually they pass as intended,
  but when running in the automated test environment they produce
  unreliable results on the latest Fedora release.

  They may work better once the upstream pool import refectoring is
  merged into ZoL at which point they will be re-enabled.

Authored by: Matthew Ahrens <[email protected]>
Reviewed-by: Alex Reece <[email protected]>
Reviewed-by: George Wilson <[email protected]>
Reviewed-by: John Kennedy <[email protected]>
Reviewed-by: Prakash Surya <[email protected]>
Reviewed by: Richard Laager <[email protected]>
Reviewed by: Tim Chase <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Approved by: Garrett D'Amore <[email protected]>
Ported-by: Tim Chase <[email protected]>
Signed-off-by: Tim Chase <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/7614
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/f539f1eb
Closes #6900

1 files changed, 520 insertions, 119 deletions

diff --git a/module/zfs/metaslab.c b/module/zfs/metaslab.c
index 6320fd388..25090f089 100644
--- a/module/zfs/metaslab.c
+++ b/module/zfs/metaslab.c
@@ -33,6 +33,7 @@
 #include <sys/zio.h>
 #include <sys/spa_impl.h>
 #include <sys/zfeature.h>
+#include <sys/vdev_indirect_mapping.h>
 
 #define	WITH_DF_BLOCK_ALLOCATOR
 
@@ -47,7 +48,8 @@
  */
 unsigned long metaslab_aliquot = 512 << 10;
 
-uint64_t metaslab_gang_bang = SPA_MAXBLOCKSIZE + 1;	/* force gang blocks */
+/* force gang blocks */
+unsigned long metaslab_gang_bang = SPA_MAXBLOCKSIZE + 1;
 
 /*
  * The in-core space map representation is more compact than its on-disk form.
@@ -169,6 +171,11 @@ int metaslab_bias_enabled = B_TRUE;
 
 
 /*
+ * Enable/disable remapping of indirect DVAs to their concrete vdevs.
+ */
+boolean_t zfs_remap_blkptr_enable = B_TRUE;
+
+/*
  * Enable/disable segment-based metaslab selection.
  */
 int zfs_metaslab_segment_weight_enabled = B_TRUE;
@@ -202,6 +209,8 @@ uint64_t metaslab_trace_max_entries = 5000;
 
 static uint64_t metaslab_weight(metaslab_t *);
 static void metaslab_set_fragmentation(metaslab_t *);
+static void metaslab_free_impl(vdev_t *, uint64_t, uint64_t, uint64_t);
+static void metaslab_check_free_impl(vdev_t *, uint64_t, uint64_t);
 
 #ifdef _METASLAB_TRACING
 kmem_cache_t *metaslab_alloc_trace_cache;
@@ -323,7 +332,7 @@ metaslab_class_histogram_verify(metaslab_class_t *mc)
 		 * Skip any holes, uninitialized top-levels, or
 		 * vdevs that are not in this metalab class.
 		 */
-		if (tvd->vdev_ishole || tvd->vdev_ms_shift == 0 ||
+		if (!vdev_is_concrete(tvd) || tvd->vdev_ms_shift == 0 ||
 		    mg->mg_class != mc) {
 			continue;
 		}
@@ -358,10 +367,10 @@ metaslab_class_fragmentation(metaslab_class_t *mc)
 		metaslab_group_t *mg = tvd->vdev_mg;
 
 		/*
-		 * Skip any holes, uninitialized top-levels, or
-		 * vdevs that are not in this metalab class.
+		 * Skip any holes, uninitialized top-levels,
+		 * or vdevs that are not in this metalab class.
 		 */
-		if (tvd->vdev_ishole || tvd->vdev_ms_shift == 0 ||
+		if (!vdev_is_concrete(tvd) || tvd->vdev_ms_shift == 0 ||
 		    mg->mg_class != mc) {
 			continue;
 		}
@@ -406,7 +415,7 @@ metaslab_class_expandable_space(metaslab_class_t *mc)
 		vdev_t *tvd = rvd->vdev_child[c];
 		metaslab_group_t *mg = tvd->vdev_mg;
 
-		if (tvd->vdev_ishole || tvd->vdev_ms_shift == 0 ||
+		if (!vdev_is_concrete(tvd) || tvd->vdev_ms_shift == 0 ||
 		    mg->mg_class != mc) {
 			continue;
 		}
@@ -505,6 +514,8 @@ metaslab_group_alloc_update(metaslab_group_t *mg)
 	boolean_t was_initialized;
 
 	ASSERT(vd == vd->vdev_top);
+	ASSERT3U(spa_config_held(mc->mc_spa, SCL_ALLOC, RW_READER), ==,
+	    SCL_ALLOC);
 
 	mutex_enter(&mg->mg_lock);
 	was_allocatable = mg->mg_allocatable;
@@ -615,7 +626,7 @@ metaslab_group_activate(metaslab_group_t *mg)
 	metaslab_class_t *mc = mg->mg_class;
 	metaslab_group_t *mgprev, *mgnext;
 
-	ASSERT(spa_config_held(mc->mc_spa, SCL_ALLOC, RW_WRITER));
+	ASSERT3U(spa_config_held(mc->mc_spa, SCL_ALLOC, RW_WRITER), !=, 0);
 
 	ASSERT(mc->mc_rotor != mg);
 	ASSERT(mg->mg_prev == NULL);
@@ -641,13 +652,22 @@ metaslab_group_activate(metaslab_group_t *mg)
 	mc->mc_rotor = mg;
 }
 
+/*
+ * Passivate a metaslab group and remove it from the allocation rotor.
+ * Callers must hold both the SCL_ALLOC and SCL_ZIO lock prior to passivating
+ * a metaslab group. This function will momentarily drop spa_config_locks
+ * that are lower than the SCL_ALLOC lock (see comment below).
+ */
 void
 metaslab_group_passivate(metaslab_group_t *mg)
 {
 	metaslab_class_t *mc = mg->mg_class;
+	spa_t *spa = mc->mc_spa;
 	metaslab_group_t *mgprev, *mgnext;
+	int locks = spa_config_held(spa, SCL_ALL, RW_WRITER);
 
-	ASSERT(spa_config_held(mc->mc_spa, SCL_ALLOC, RW_WRITER));
+	ASSERT3U(spa_config_held(spa, SCL_ALLOC | SCL_ZIO, RW_WRITER), ==,
+	    (SCL_ALLOC | SCL_ZIO));
 
 	if (--mg->mg_activation_count != 0) {
 		ASSERT(mc->mc_rotor != mg);
@@ -657,7 +677,23 @@ metaslab_group_passivate(metaslab_group_t *mg)
 		return;
 	}
 
+	/*
+	 * The spa_config_lock is an array of rwlocks, ordered as
+	 * follows (from highest to lowest):
+	 *	SCL_CONFIG > SCL_STATE > SCL_L2ARC > SCL_ALLOC >
+	 *	SCL_ZIO > SCL_FREE > SCL_VDEV
+	 * (For more information about the spa_config_lock see spa_misc.c)
+	 * The higher the lock, the broader its coverage. When we passivate
+	 * a metaslab group, we must hold both the SCL_ALLOC and the SCL_ZIO
+	 * config locks. However, the metaslab group's taskq might be trying
+	 * to preload metaslabs so we must drop the SCL_ZIO lock and any
+	 * lower locks to allow the I/O to complete. At a minimum,
+	 * we continue to hold the SCL_ALLOC lock, which prevents any future
+	 * allocations from taking place and any changes to the vdev tree.
+	 */
+	spa_config_exit(spa, locks & ~(SCL_ZIO - 1), spa);
 	taskq_wait_outstanding(mg->mg_taskq, 0);
+	spa_config_enter(spa, locks & ~(SCL_ZIO - 1), spa, RW_WRITER);
 	metaslab_group_alloc_update(mg);
 
 	mgprev = mg->mg_prev;
@@ -1269,6 +1305,12 @@ metaslab_load(metaslab_t *msp)
 	ASSERT(!msp->ms_loading);
 
 	msp->ms_loading = B_TRUE;
+	/*
+	 * Nobody else can manipulate a loading metaslab, so it's now safe
+	 * to drop the lock.  This way we don't have to hold the lock while
+	 * reading the spacemap from disk.
+	 */
+	mutex_exit(&msp->ms_lock);
 
 	/*
 	 * If the space map has not been allocated yet, then treat
@@ -1281,6 +1323,8 @@ metaslab_load(metaslab_t *msp)
 		range_tree_add(msp->ms_tree, msp->ms_start, msp->ms_size);
 
 	success = (error == 0);
+
+	mutex_enter(&msp->ms_lock);
 	msp->ms_loading = B_FALSE;
 
 	if (success) {
@@ -1318,6 +1362,7 @@ metaslab_init(metaslab_group_t *mg, uint64_t id, uint64_t object, uint64_t txg,
 
 	ms = kmem_zalloc(sizeof (metaslab_t), KM_SLEEP);
 	mutex_init(&ms->ms_lock, NULL, MUTEX_DEFAULT, NULL);
+	mutex_init(&ms->ms_sync_lock, NULL, MUTEX_DEFAULT, NULL);
 	cv_init(&ms->ms_load_cv, NULL, CV_DEFAULT, NULL);
 	ms->ms_id = id;
 	ms->ms_start = id << vd->vdev_ms_shift;
@@ -1329,7 +1374,7 @@ metaslab_init(metaslab_group_t *mg, uint64_t id, uint64_t object, uint64_t txg,
 	 */
 	if (object != 0) {
 		error = space_map_open(&ms->ms_sm, mos, object, ms->ms_start,
-		    ms->ms_size, vd->vdev_ashift, &ms->ms_lock);
+		    ms->ms_size, vd->vdev_ashift);
 
 		if (error != 0) {
 			kmem_free(ms, sizeof (metaslab_t));
@@ -1347,7 +1392,7 @@ metaslab_init(metaslab_group_t *mg, uint64_t id, uint64_t object, uint64_t txg,
 	 * data fault on any attempt to use this metaslab before it's ready.
 	 */
 	ms->ms_tree = range_tree_create_impl(&rt_avl_ops, &ms->ms_size_tree,
-	    metaslab_rangesize_compare, &ms->ms_lock, 0);
+	    metaslab_rangesize_compare, 0);
 	metaslab_group_add(mg, ms);
 
 	metaslab_set_fragmentation(ms);
@@ -1416,6 +1461,7 @@ metaslab_fini(metaslab_t *msp)
 	mutex_exit(&msp->ms_lock);
 	cv_destroy(&msp->ms_load_cv);
 	mutex_destroy(&msp->ms_lock);
+	mutex_destroy(&msp->ms_sync_lock);
 
 	kmem_free(msp, sizeof (metaslab_t));
 }
@@ -1780,14 +1826,11 @@ metaslab_weight(metaslab_t *msp)
 	ASSERT(MUTEX_HELD(&msp->ms_lock));
 
 	/*
-	 * This vdev is in the process of being removed so there is nothing
+	 * If this vdev is in the process of being removed, there is nothing
 	 * for us to do here.
 	 */
-	if (vd->vdev_removing) {
-		ASSERT0(space_map_allocated(msp->ms_sm));
-		ASSERT0(vd->vdev_ms_shift);
+	if (vd->vdev_removing)
 		return (0);
-	}
 
 	metaslab_set_fragmentation(msp);
 
@@ -1922,10 +1965,13 @@ metaslab_group_preload(metaslab_group_t *mg)
 	}
 
 	mutex_enter(&mg->mg_lock);
+
 	/*
 	 * Load the next potential metaslabs
 	 */
 	for (msp = avl_first(t); msp != NULL; msp = AVL_NEXT(t, msp)) {
+		ASSERT3P(msp->ms_group, ==, mg);
+
 		/*
 		 * We preload only the maximum number of metaslabs specified
 		 * by metaslab_preload_limit. If a metaslab is being forced
@@ -1952,7 +1998,7 @@ metaslab_group_preload(metaslab_group_t *mg)
  *
  * 2. The minimal on-disk space map representation is zfs_condense_pct/100
  * times the size than the free space range tree representation
- * (i.e. zfs_condense_pct = 110 and in-core = 1MB, minimal = 1.1.MB).
+ * (i.e. zfs_condense_pct = 110 and in-core = 1MB, minimal = 1.1MB).
  *
  * 3. The on-disk size of the space map should actually decrease.
  *
@@ -2049,7 +2095,7 @@ metaslab_condense(metaslab_t *msp, uint64_t txg, dmu_tx_t *tx)
 	 * a relatively inexpensive operation since we expect these trees to
 	 * have a small number of nodes.
 	 */
-	condense_tree = range_tree_create(NULL, NULL, &msp->ms_lock);
+	condense_tree = range_tree_create(NULL, NULL);
 	range_tree_add(condense_tree, msp->ms_start, msp->ms_size);
 
 	/*
@@ -2082,7 +2128,6 @@ metaslab_condense(metaslab_t *msp, uint64_t txg, dmu_tx_t *tx)
 
 	mutex_exit(&msp->ms_lock);
 	space_map_truncate(sm, tx);
-	mutex_enter(&msp->ms_lock);
 
 	/*
 	 * While we would ideally like to create a space map representation
@@ -2099,6 +2144,7 @@ metaslab_condense(metaslab_t *msp, uint64_t txg, dmu_tx_t *tx)
 	range_tree_destroy(condense_tree);
 
 	space_map_write(sm, msp->ms_tree, SM_FREE, tx);
+	mutex_enter(&msp->ms_lock);
 	msp->ms_condensing = B_FALSE;
 }
 
@@ -2148,10 +2194,14 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
 	 * The only state that can actually be changing concurrently with
 	 * metaslab_sync() is the metaslab's ms_tree.  No other thread can
 	 * be modifying this txg's alloctree, freeingtree, freedtree, or
-	 * space_map_phys_t. Therefore, we only hold ms_lock to satify
-	 * space map ASSERTs. We drop it whenever we call into the DMU,
-	 * because the DMU can call down to us (e.g. via zio_free()) at
-	 * any time.
+	 * space_map_phys_t.  We drop ms_lock whenever we could call
+	 * into the DMU, because the DMU can call down to us
+	 * (e.g. via zio_free()) at any time.
+	 *
+	 * The spa_vdev_remove_thread() can be reading metaslab state
+	 * concurrently, and it is locked out by the ms_sync_lock.  Note
+	 * that the ms_lock is insufficient for this, because it is dropped
+	 * by space_map_write().
 	 */
 
 	tx = dmu_tx_create_assigned(spa_get_dsl(spa), txg);
@@ -2163,11 +2213,11 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
 		VERIFY3U(new_object, !=, 0);
 
 		VERIFY0(space_map_open(&msp->ms_sm, mos, new_object,
-		    msp->ms_start, msp->ms_size, vd->vdev_ashift,
-		    &msp->ms_lock));
+		    msp->ms_start, msp->ms_size, vd->vdev_ashift));
 		ASSERT(msp->ms_sm != NULL);
 	}
 
+	mutex_enter(&msp->ms_sync_lock);
 	mutex_enter(&msp->ms_lock);
 
 	/*
@@ -2183,13 +2233,15 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
 	    metaslab_should_condense(msp)) {
 		metaslab_condense(msp, txg, tx);
 	} else {
+		mutex_exit(&msp->ms_lock);
 		space_map_write(msp->ms_sm, alloctree, SM_ALLOC, tx);
 		space_map_write(msp->ms_sm, msp->ms_freeingtree, SM_FREE, tx);
+		mutex_enter(&msp->ms_lock);
 	}
 
 	if (msp->ms_loaded) {
 		/*
-		 * When the space map is loaded, we have an accruate
+		 * When the space map is loaded, we have an accurate
 		 * histogram in the range tree. This gives us an opportunity
 		 * to bring the space map's histogram up-to-date so we clear
 		 * it first before updating it.
@@ -2257,6 +2309,7 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
 		dmu_write(mos, vd->vdev_ms_array, sizeof (uint64_t) *
 		    msp->ms_id, sizeof (uint64_t), &object, tx);
 	}
+	mutex_exit(&msp->ms_sync_lock);
 	dmu_tx_commit(tx);
 }
 
@@ -2286,23 +2339,19 @@ metaslab_sync_done(metaslab_t *msp, uint64_t txg)
 		for (int t = 0; t < TXG_SIZE; t++) {
 			ASSERT(msp->ms_alloctree[t] == NULL);
 
-			msp->ms_alloctree[t] = range_tree_create(NULL, msp,
-			    &msp->ms_lock);
+			msp->ms_alloctree[t] = range_tree_create(NULL, NULL);
 		}
 
 		ASSERT3P(msp->ms_freeingtree, ==, NULL);
-		msp->ms_freeingtree = range_tree_create(NULL, msp,
-		    &msp->ms_lock);
+		msp->ms_freeingtree = range_tree_create(NULL, NULL);
 
 		ASSERT3P(msp->ms_freedtree, ==, NULL);
-		msp->ms_freedtree = range_tree_create(NULL, msp,
-		    &msp->ms_lock);
+		msp->ms_freedtree = range_tree_create(NULL, NULL);
 
 		for (int t = 0; t < TXG_DEFER_SIZE; t++) {
 			ASSERT(msp->ms_defertree[t] == NULL);
 
-			msp->ms_defertree[t] = range_tree_create(NULL, msp,
-			    &msp->ms_lock);
+			msp->ms_defertree[t] = range_tree_create(NULL, NULL);
 		}
 
 		vdev_space_update(vd, 0, 0, msp->ms_size);
@@ -2312,7 +2361,7 @@ metaslab_sync_done(metaslab_t *msp, uint64_t txg)
 
 	uint64_t free_space = metaslab_class_get_space(spa_normal_class(spa)) -
 	    metaslab_class_get_alloc(spa_normal_class(spa));
-	if (free_space <= spa_get_slop_space(spa)) {
+	if (free_space <= spa_get_slop_space(spa) || vd->vdev_removing) {
 		defer_allowed = B_FALSE;
 	}
 
@@ -2383,19 +2432,33 @@ metaslab_sync_done(metaslab_t *msp, uint64_t txg)
 			metaslab_unload(msp);
 	}
 
+	ASSERT0(range_tree_space(msp->ms_alloctree[txg & TXG_MASK]));
+	ASSERT0(range_tree_space(msp->ms_freeingtree));
+	ASSERT0(range_tree_space(msp->ms_freedtree));
+
 	mutex_exit(&msp->ms_lock);
 }
 
 void
 metaslab_sync_reassess(metaslab_group_t *mg)
 {
+	spa_t *spa = mg->mg_class->mc_spa;
+
+	spa_config_enter(spa, SCL_ALLOC, FTAG, RW_READER);
 	metaslab_group_alloc_update(mg);
 	mg->mg_fragmentation = metaslab_group_fragmentation(mg);
 
 	/*
-	 * Preload the next potential metaslabs
+	 * Preload the next potential metaslabs but only on active
+	 * metaslab groups. We can get into a state where the metaslab
+	 * is no longer active since we dirty metaslabs as we remove a
+	 * a device, thus potentially making the metaslab group eligible
+	 * for preloading.
 	 */
-	metaslab_group_preload(mg);
+	if (mg->mg_activation_count > 0) {
+		metaslab_group_preload(mg);
+	}
+	spa_config_exit(spa, SCL_ALLOC, FTAG);
 }
 
 static uint64_t
@@ -2875,7 +2938,7 @@ int ditto_same_vdev_distance_shift = 3;
 /*
  * Allocate a block for the specified i/o.
  */
-static int
+int
 metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize,
     dva_t *dva, int d, dva_t *hintdva, uint64_t txg, int flags,
     zio_alloc_list_t *zal)
@@ -2921,10 +2984,11 @@ metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize,
 
 		/*
 		 * It's possible the vdev we're using as the hint no
-		 * longer exists (i.e. removed). Consult the rotor when
+		 * longer exists or its mg has been closed (e.g. by
+		 * device removal).  Consult the rotor when
 		 * all else fails.
 		 */
-		if (vd != NULL) {
+		if (vd != NULL && vd->vdev_mg != NULL) {
 			mg = vd->vdev_mg;
 
 			if (flags & METASLAB_HINTBP_AVOID &&
@@ -3116,18 +3180,228 @@ next:
 	return (SET_ERROR(ENOSPC));
 }
 
+void
+metaslab_free_concrete(vdev_t *vd, uint64_t offset, uint64_t asize,
+    uint64_t txg)
+{
+	metaslab_t *msp;
+	ASSERTV(spa_t *spa = vd->vdev_spa);
+
+	ASSERT3U(txg, ==, spa->spa_syncing_txg);
+	ASSERT(vdev_is_concrete(vd));
+	ASSERT3U(spa_config_held(spa, SCL_ALL, RW_READER), !=, 0);
+	ASSERT3U(offset >> vd->vdev_ms_shift, <, vd->vdev_ms_count);
+
+	msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+
+	VERIFY(!msp->ms_condensing);
+	VERIFY3U(offset, >=, msp->ms_start);
+	VERIFY3U(offset + asize, <=, msp->ms_start + msp->ms_size);
+	VERIFY0(P2PHASE(offset, 1ULL << vd->vdev_ashift));
+	VERIFY0(P2PHASE(asize, 1ULL << vd->vdev_ashift));
+
+	metaslab_check_free_impl(vd, offset, asize);
+	mutex_enter(&msp->ms_lock);
+	if (range_tree_space(msp->ms_freeingtree) == 0) {
+		vdev_dirty(vd, VDD_METASLAB, msp, txg);
+	}
+	range_tree_add(msp->ms_freeingtree, offset, asize);
+	mutex_exit(&msp->ms_lock);
+}
+
+/* ARGSUSED */
+void
+metaslab_free_impl_cb(uint64_t inner_offset, vdev_t *vd, uint64_t offset,
+    uint64_t size, void *arg)
+{
+	uint64_t *txgp = arg;
+
+	if (vd->vdev_ops->vdev_op_remap != NULL)
+		vdev_indirect_mark_obsolete(vd, offset, size, *txgp);
+	else
+		metaslab_free_impl(vd, offset, size, *txgp);
+}
+
+static void
+metaslab_free_impl(vdev_t *vd, uint64_t offset, uint64_t size,
+    uint64_t txg)
+{
+	spa_t *spa = vd->vdev_spa;
+
+	ASSERT3U(spa_config_held(spa, SCL_ALL, RW_READER), !=, 0);
+
+	if (txg > spa_freeze_txg(spa))
+		return;
+
+	if (spa->spa_vdev_removal != NULL &&
+	    spa->spa_vdev_removal->svr_vdev == vd &&
+	    vdev_is_concrete(vd)) {
+		/*
+		 * Note: we check if the vdev is concrete because when
+		 * we complete the removal, we first change the vdev to be
+		 * an indirect vdev (in open context), and then (in syncing
+		 * context) clear spa_vdev_removal.
+		 */
+		free_from_removing_vdev(vd, offset, size, txg);
+	} else if (vd->vdev_ops->vdev_op_remap != NULL) {
+		vdev_indirect_mark_obsolete(vd, offset, size, txg);
+		vd->vdev_ops->vdev_op_remap(vd, offset, size,
+		    metaslab_free_impl_cb, &txg);
+	} else {
+		metaslab_free_concrete(vd, offset, size, txg);
+	}
+}
+
+typedef struct remap_blkptr_cb_arg {
+	blkptr_t *rbca_bp;
+	spa_remap_cb_t rbca_cb;
+	vdev_t *rbca_remap_vd;
+	uint64_t rbca_remap_offset;
+	void *rbca_cb_arg;
+} remap_blkptr_cb_arg_t;
+
+void
+remap_blkptr_cb(uint64_t inner_offset, vdev_t *vd, uint64_t offset,
+    uint64_t size, void *arg)
+{
+	remap_blkptr_cb_arg_t *rbca = arg;
+	blkptr_t *bp = rbca->rbca_bp;
+
+	/* We can not remap split blocks. */
+	if (size != DVA_GET_ASIZE(&bp->blk_dva[0]))
+		return;
+	ASSERT0(inner_offset);
+
+	if (rbca->rbca_cb != NULL) {
+		/*
+		 * At this point we know that we are not handling split
+		 * blocks and we invoke the callback on the previous
+		 * vdev which must be indirect.
+		 */
+		ASSERT3P(rbca->rbca_remap_vd->vdev_ops, ==, &vdev_indirect_ops);
+
+		rbca->rbca_cb(rbca->rbca_remap_vd->vdev_id,
+		    rbca->rbca_remap_offset, size, rbca->rbca_cb_arg);
+
+		/* set up remap_blkptr_cb_arg for the next call */
+		rbca->rbca_remap_vd = vd;
+		rbca->rbca_remap_offset = offset;
+	}
+
+	/*
+	 * The phys birth time is that of dva[0].  This ensures that we know
+	 * when each dva was written, so that resilver can determine which
+	 * blocks need to be scrubbed (i.e. those written during the time
+	 * the vdev was offline).  It also ensures that the key used in
+	 * the ARC hash table is unique (i.e. dva[0] + phys_birth).  If
+	 * we didn't change the phys_birth, a lookup in the ARC for a
+	 * remapped BP could find the data that was previously stored at
+	 * this vdev + offset.
+	 */
+	vdev_t *oldvd = vdev_lookup_top(vd->vdev_spa,
+	    DVA_GET_VDEV(&bp->blk_dva[0]));
+	vdev_indirect_births_t *vib = oldvd->vdev_indirect_births;
+	bp->blk_phys_birth = vdev_indirect_births_physbirth(vib,
+	    DVA_GET_OFFSET(&bp->blk_dva[0]), DVA_GET_ASIZE(&bp->blk_dva[0]));
+
+	DVA_SET_VDEV(&bp->blk_dva[0], vd->vdev_id);
+	DVA_SET_OFFSET(&bp->blk_dva[0], offset);
+}
+
 /*
- * Free the block represented by DVA in the context of the specified
- * transaction group.
+ * If the block pointer contains any indirect DVAs, modify them to refer to
+ * concrete DVAs.  Note that this will sometimes not be possible, leaving
+ * the indirect DVA in place.  This happens if the indirect DVA spans multiple
+ * segments in the mapping (i.e. it is a "split block").
+ *
+ * If the BP was remapped, calls the callback on the original dva (note the
+ * callback can be called multiple times if the original indirect DVA refers
+ * to another indirect DVA, etc).
+ *
+ * Returns TRUE if the BP was remapped.
  */
-static void
-metaslab_free_dva(spa_t *spa, const dva_t *dva, uint64_t txg, boolean_t now)
+boolean_t
+spa_remap_blkptr(spa_t *spa, blkptr_t *bp, spa_remap_cb_t callback, void *arg)
 {
-	uint64_t vdev = DVA_GET_VDEV(dva);
+	remap_blkptr_cb_arg_t rbca;
+
+	if (!zfs_remap_blkptr_enable)
+		return (B_FALSE);
+
+	if (!spa_feature_is_enabled(spa, SPA_FEATURE_OBSOLETE_COUNTS))
+		return (B_FALSE);
+
+	/*
+	 * Dedup BP's can not be remapped, because ddt_phys_select() depends
+	 * on DVA[0] being the same in the BP as in the DDT (dedup table).
+	 */
+	if (BP_GET_DEDUP(bp))
+		return (B_FALSE);
+
+	/*
+	 * Gang blocks can not be remapped, because
+	 * zio_checksum_gang_verifier() depends on the DVA[0] that's in
+	 * the BP used to read the gang block header (GBH) being the same
+	 * as the DVA[0] that we allocated for the GBH.
+	 */
+	if (BP_IS_GANG(bp))
+		return (B_FALSE);
+
+	/*
+	 * Embedded BP's have no DVA to remap.
+	 */
+	if (BP_GET_NDVAS(bp) < 1)
+		return (B_FALSE);
+
+	/*
+	 * Note: we only remap dva[0].  If we remapped other dvas, we
+	 * would no longer know what their phys birth txg is.
+	 */
+	dva_t *dva = &bp->blk_dva[0];
+
 	uint64_t offset = DVA_GET_OFFSET(dva);
 	uint64_t size = DVA_GET_ASIZE(dva);
-	vdev_t *vd;
+	vdev_t *vd = vdev_lookup_top(spa, DVA_GET_VDEV(dva));
+
+	if (vd->vdev_ops->vdev_op_remap == NULL)
+		return (B_FALSE);
+
+	rbca.rbca_bp = bp;
+	rbca.rbca_cb = callback;
+	rbca.rbca_remap_vd = vd;
+	rbca.rbca_remap_offset = offset;
+	rbca.rbca_cb_arg = arg;
+
+	/*
+	 * remap_blkptr_cb() will be called in order for each level of
+	 * indirection, until a concrete vdev is reached or a split block is
+	 * encountered. old_vd and old_offset are updated within the callback
+	 * as we go from the one indirect vdev to the next one (either concrete
+	 * or indirect again) in that order.
+	 */
+	vd->vdev_ops->vdev_op_remap(vd, offset, size, remap_blkptr_cb, &rbca);
+
+	/* Check if the DVA wasn't remapped because it is a split block */
+	if (DVA_GET_VDEV(&rbca.rbca_bp->blk_dva[0]) == vd->vdev_id)
+		return (B_FALSE);
+
+	return (B_TRUE);
+}
+
+/*
+ * Undo the allocation of a DVA which happened in the given transaction group.
+ */
+void
+metaslab_unalloc_dva(spa_t *spa, const dva_t *dva, uint64_t txg)
+{
 	metaslab_t *msp;
+	vdev_t *vd;
+	uint64_t vdev = DVA_GET_VDEV(dva);
+	uint64_t offset = DVA_GET_OFFSET(dva);
+	uint64_t size = DVA_GET_ASIZE(dva);
+
+	ASSERT(DVA_IS_VALID(dva));
+	ASSERT3U(spa_config_held(spa, SCL_ALL, RW_READER), !=, 0);
 
 	if (txg > spa_freeze_txg(spa))
 		return;
@@ -3140,91 +3414,51 @@ metaslab_free_dva(spa_t *spa, const dva_t *dva, uint64_t txg, boolean_t now)
 		return;
 	}
 
-	msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+	ASSERT(!vd->vdev_removing);
+	ASSERT(vdev_is_concrete(vd));
+	ASSERT0(vd->vdev_indirect_config.vic_mapping_object);
+	ASSERT3P(vd->vdev_indirect_mapping, ==, NULL);
 
 	if (DVA_GET_GANG(dva))
 		size = vdev_psize_to_asize(vd, SPA_GANGBLOCKSIZE);
 
-	mutex_enter(&msp->ms_lock);
-
-	if (now) {
-		range_tree_remove(msp->ms_alloctree[txg & TXG_MASK],
-		    offset, size);
+	msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
 
-		VERIFY(!msp->ms_condensing);
-		VERIFY3U(offset, >=, msp->ms_start);
-		VERIFY3U(offset + size, <=, msp->ms_start + msp->ms_size);
-		VERIFY3U(range_tree_space(msp->ms_tree) + size, <=,
-		    msp->ms_size);
-		VERIFY0(P2PHASE(offset, 1ULL << vd->vdev_ashift));
-		VERIFY0(P2PHASE(size, 1ULL << vd->vdev_ashift));
-		range_tree_add(msp->ms_tree, offset, size);
-		msp->ms_max_size = metaslab_block_maxsize(msp);
-	} else {
-		VERIFY3U(txg, ==, spa->spa_syncing_txg);
-		if (range_tree_space(msp->ms_freeingtree) == 0)
-			vdev_dirty(vd, VDD_METASLAB, msp, txg);
-		range_tree_add(msp->ms_freeingtree, offset, size);
-	}
+	mutex_enter(&msp->ms_lock);
+	range_tree_remove(msp->ms_alloctree[txg & TXG_MASK],
+	    offset, size);
 
+	VERIFY(!msp->ms_condensing);
+	VERIFY3U(offset, >=, msp->ms_start);
+	VERIFY3U(offset + size, <=, msp->ms_start + msp->ms_size);
+	VERIFY3U(range_tree_space(msp->ms_tree) + size, <=,
+	    msp->ms_size);
+	VERIFY0(P2PHASE(offset, 1ULL << vd->vdev_ashift));
+	VERIFY0(P2PHASE(size, 1ULL << vd->vdev_ashift));
+	range_tree_add(msp->ms_tree, offset, size);
 	mutex_exit(&msp->ms_lock);
 }
 
 /*
- * Intent log support: upon opening the pool after a crash, notify the SPA
- * of blocks that the intent log has allocated for immediate write, but
- * which are still considered free by the SPA because the last transaction
- * group didn't commit yet.
+ * Free the block represented by DVA in the context of the specified
+ * transaction group.
  */
-static int
-metaslab_claim_dva(spa_t *spa, const dva_t *dva, uint64_t txg)
+void
+metaslab_free_dva(spa_t *spa, const dva_t *dva, uint64_t txg)
 {
 	uint64_t vdev = DVA_GET_VDEV(dva);
 	uint64_t offset = DVA_GET_OFFSET(dva);
 	uint64_t size = DVA_GET_ASIZE(dva);
-	vdev_t *vd;
-	metaslab_t *msp;
-	int error = 0;
+	vdev_t *vd = vdev_lookup_top(spa, vdev);
 
 	ASSERT(DVA_IS_VALID(dva));
+	ASSERT3U(spa_config_held(spa, SCL_ALL, RW_READER), !=, 0);
 
-	if ((vd = vdev_lookup_top(spa, vdev)) == NULL ||
-	    (offset >> vd->vdev_ms_shift) >= vd->vdev_ms_count)
-		return (SET_ERROR(ENXIO));
-
-	msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
-
-	if (DVA_GET_GANG(dva))
+	if (DVA_GET_GANG(dva)) {
 		size = vdev_psize_to_asize(vd, SPA_GANGBLOCKSIZE);
-
-	mutex_enter(&msp->ms_lock);
-
-	if ((txg != 0 && spa_writeable(spa)) || !msp->ms_loaded)
-		error = metaslab_activate(msp, METASLAB_WEIGHT_SECONDARY);
-
-	if (error == 0 && !range_tree_contains(msp->ms_tree, offset, size))
-		error = SET_ERROR(ENOENT);
-
-	if (error || txg == 0) {	/* txg == 0 indicates dry run */
-		mutex_exit(&msp->ms_lock);
-		return (error);
 	}
 
-	VERIFY(!msp->ms_condensing);
-	VERIFY0(P2PHASE(offset, 1ULL << vd->vdev_ashift));
-	VERIFY0(P2PHASE(size, 1ULL << vd->vdev_ashift));
-	VERIFY3U(range_tree_space(msp->ms_tree) - size, <=, msp->ms_size);
-	range_tree_remove(msp->ms_tree, offset, size);
-
-	if (spa_writeable(spa)) {	/* don't dirty if we're zdb(1M) */
-		if (range_tree_space(msp->ms_alloctree[txg & TXG_MASK]) == 0)
-			vdev_dirty(vd, VDD_METASLAB, msp, txg);
-		range_tree_add(msp->ms_alloctree[txg & TXG_MASK], offset, size);
-	}
-
-	mutex_exit(&msp->ms_lock);
-
-	return (0);
+	metaslab_free_impl(vd, offset, size, txg);
 }
 
 /*
@@ -3275,6 +3509,122 @@ metaslab_class_throttle_unreserve(metaslab_class_t *mc, int slots, zio_t *zio)
 	mutex_exit(&mc->mc_lock);
 }
 
+static int
+metaslab_claim_concrete(vdev_t *vd, uint64_t offset, uint64_t size,
+    uint64_t txg)
+{
+	metaslab_t *msp;
+	spa_t *spa = vd->vdev_spa;
+	int error = 0;
+
+	if (offset >> vd->vdev_ms_shift >= vd->vdev_ms_count)
+		return (ENXIO);
+
+	ASSERT3P(vd->vdev_ms, !=, NULL);
+	msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+
+	mutex_enter(&msp->ms_lock);
+
+	if ((txg != 0 && spa_writeable(spa)) || !msp->ms_loaded)
+		error = metaslab_activate(msp, METASLAB_WEIGHT_SECONDARY);
+
+	if (error == 0 && !range_tree_contains(msp->ms_tree, offset, size))
+		error = SET_ERROR(ENOENT);
+
+	if (error || txg == 0) {	/* txg == 0 indicates dry run */
+		mutex_exit(&msp->ms_lock);
+		return (error);
+	}
+
+	VERIFY(!msp->ms_condensing);
+	VERIFY0(P2PHASE(offset, 1ULL << vd->vdev_ashift));
+	VERIFY0(P2PHASE(size, 1ULL << vd->vdev_ashift));
+	VERIFY3U(range_tree_space(msp->ms_tree) - size, <=, msp->ms_size);
+	range_tree_remove(msp->ms_tree, offset, size);
+
+	if (spa_writeable(spa)) {	/* don't dirty if we're zdb(1M) */
+		if (range_tree_space(msp->ms_alloctree[txg & TXG_MASK]) == 0)
+			vdev_dirty(vd, VDD_METASLAB, msp, txg);
+		range_tree_add(msp->ms_alloctree[txg & TXG_MASK], offset, size);
+	}
+
+	mutex_exit(&msp->ms_lock);
+
+	return (0);
+}
+
+typedef struct metaslab_claim_cb_arg_t {
+	uint64_t	mcca_txg;
+	int		mcca_error;
+} metaslab_claim_cb_arg_t;
+
+/* ARGSUSED */
+static void
+metaslab_claim_impl_cb(uint64_t inner_offset, vdev_t *vd, uint64_t offset,
+    uint64_t size, void *arg)
+{
+	metaslab_claim_cb_arg_t *mcca_arg = arg;
+
+	if (mcca_arg->mcca_error == 0) {
+		mcca_arg->mcca_error = metaslab_claim_concrete(vd, offset,
+		    size, mcca_arg->mcca_txg);
+	}
+}
+
+int
+metaslab_claim_impl(vdev_t *vd, uint64_t offset, uint64_t size, uint64_t txg)
+{
+	if (vd->vdev_ops->vdev_op_remap != NULL) {
+		metaslab_claim_cb_arg_t arg;
+
+		/*
+		 * Only zdb(1M) can claim on indirect vdevs.  This is used
+		 * to detect leaks of mapped space (that are not accounted
+		 * for in the obsolete counts, spacemap, or bpobj).
+		 */
+		ASSERT(!spa_writeable(vd->vdev_spa));
+		arg.mcca_error = 0;
+		arg.mcca_txg = txg;
+
+		vd->vdev_ops->vdev_op_remap(vd, offset, size,
+		    metaslab_claim_impl_cb, &arg);
+
+		if (arg.mcca_error == 0) {
+			arg.mcca_error = metaslab_claim_concrete(vd,
+			    offset, size, txg);
+		}
+		return (arg.mcca_error);
+	} else {
+		return (metaslab_claim_concrete(vd, offset, size, txg));
+	}
+}
+
+/*
+ * Intent log support: upon opening the pool after a crash, notify the SPA
+ * of blocks that the intent log has allocated for immediate write, but
+ * which are still considered free by the SPA because the last transaction
+ * group didn't commit yet.
+ */
+static int
+metaslab_claim_dva(spa_t *spa, const dva_t *dva, uint64_t txg)
+{
+	uint64_t vdev = DVA_GET_VDEV(dva);
+	uint64_t offset = DVA_GET_OFFSET(dva);
+	uint64_t size = DVA_GET_ASIZE(dva);
+	vdev_t *vd;
+
+	if ((vd = vdev_lookup_top(spa, vdev)) == NULL) {
+		return (SET_ERROR(ENXIO));
+	}
+
+	ASSERT(DVA_IS_VALID(dva));
+
+	if (DVA_GET_GANG(dva))
+		size = vdev_psize_to_asize(vd, SPA_GANGBLOCKSIZE);
+
+	return (metaslab_claim_impl(vd, offset, size, txg));
+}
+
 int
 metaslab_alloc(spa_t *spa, metaslab_class_t *mc, uint64_t psize, blkptr_t *bp,
     int ndvas, uint64_t txg, blkptr_t *hintbp, int flags,
@@ -3304,7 +3654,7 @@ metaslab_alloc(spa_t *spa, metaslab_class_t *mc, uint64_t psize, blkptr_t *bp,
 		    txg, flags, zal);
 		if (error != 0) {
 			for (d--; d >= 0; d--) {
-				metaslab_free_dva(spa, &dva[d], txg, B_TRUE);
+				metaslab_unalloc_dva(spa, &dva[d], txg);
 				metaslab_group_alloc_decrement(spa,
 				    DVA_GET_VDEV(&dva[d]), zio, flags);
 				bzero(&dva[d], sizeof (dva_t));
@@ -3342,8 +3692,13 @@ metaslab_free(spa_t *spa, const blkptr_t *bp, uint64_t txg, boolean_t now)
 
 	spa_config_enter(spa, SCL_FREE, FTAG, RW_READER);
 
-	for (int d = 0; d < ndvas; d++)
-		metaslab_free_dva(spa, &dva[d], txg, now);
+	for (int d = 0; d < ndvas; d++) {
+		if (now) {
+			metaslab_unalloc_dva(spa, &dva[d], txg);
+		} else {
+			metaslab_free_dva(spa, &dva[d], txg);
+		}
+	}
 
 	spa_config_exit(spa, SCL_FREE, FTAG);
 }
@@ -3428,6 +3783,49 @@ metaslab_fastwrite_unmark(spa_t *spa, const blkptr_t *bp)
 	spa_config_exit(spa, SCL_VDEV, FTAG);
 }
 
+/* ARGSUSED */
+static void
+metaslab_check_free_impl_cb(uint64_t inner, vdev_t *vd, uint64_t offset,
+    uint64_t size, void *arg)
+{
+	if (vd->vdev_ops == &vdev_indirect_ops)
+		return;
+
+	metaslab_check_free_impl(vd, offset, size);
+}
+
+static void
+metaslab_check_free_impl(vdev_t *vd, uint64_t offset, uint64_t size)
+{
+	metaslab_t *msp;
+	ASSERTV(spa_t *spa = vd->vdev_spa);
+
+	if ((zfs_flags & ZFS_DEBUG_ZIO_FREE) == 0)
+		return;
+
+	if (vd->vdev_ops->vdev_op_remap != NULL) {
+		vd->vdev_ops->vdev_op_remap(vd, offset, size,
+		    metaslab_check_free_impl_cb, NULL);
+		return;
+	}
+
+	ASSERT(vdev_is_concrete(vd));
+	ASSERT3U(offset >> vd->vdev_ms_shift, <, vd->vdev_ms_count);
+	ASSERT3U(spa_config_held(spa, SCL_ALL, RW_READER), !=, 0);
+
+	msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
+
+	mutex_enter(&msp->ms_lock);
+	if (msp->ms_loaded)
+		range_tree_verify(msp->ms_tree, offset, size);
+
+	range_tree_verify(msp->ms_freeingtree, offset, size);
+	range_tree_verify(msp->ms_freedtree, offset, size);
+	for (int j = 0; j < TXG_DEFER_SIZE; j++)
+		range_tree_verify(msp->ms_defertree[j], offset, size);
+	mutex_exit(&msp->ms_lock);
+}
+
 void
 metaslab_check_free(spa_t *spa, const blkptr_t *bp)
 {
@@ -3440,15 +3838,13 @@ metaslab_check_free(spa_t *spa, const blkptr_t *bp)
 		vdev_t *vd = vdev_lookup_top(spa, vdev);
 		uint64_t offset = DVA_GET_OFFSET(&bp->blk_dva[i]);
 		uint64_t size = DVA_GET_ASIZE(&bp->blk_dva[i]);
-		metaslab_t *msp = vd->vdev_ms[offset >> vd->vdev_ms_shift];
 
-		if (msp->ms_loaded)
-			range_tree_verify(msp->ms_tree, offset, size);
+		if (DVA_GET_GANG(&bp->blk_dva[i]))
+			size = vdev_psize_to_asize(vd, SPA_GANGBLOCKSIZE);
+
+		ASSERT3P(vd, !=, NULL);
 
-		range_tree_verify(msp->ms_freeingtree, offset, size);
-		range_tree_verify(msp->ms_freedtree, offset, size);
-		for (int j = 0; j < TXG_DEFER_SIZE; j++)
-			range_tree_verify(msp->ms_defertree[j], offset, size);
+		metaslab_check_free_impl(vd, offset, size);
 	}
 	spa_config_exit(spa, SCL_VDEV, FTAG);
 }
@@ -3502,4 +3898,9 @@ MODULE_PARM_DESC(zfs_metaslab_segment_weight_enabled,
 module_param(zfs_metaslab_switch_threshold, int, 0644);
 MODULE_PARM_DESC(zfs_metaslab_switch_threshold,
 	"segment-based metaslab selection maximum buckets before switching");
+
+/* CSTYLED */
+module_param(metaslab_gang_bang, ulong, 0644);
+MODULE_PARM_DESC(metaslab_gang_bang,
+	"blocks larger than this size are forced to be gang blocks");
 #endif /* _KERNEL && HAVE_SPL */