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10592 misc. metaslab and vdev related ZoL bug fixes
Portions contributed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed by: George Melikov <mail@gmelikov.ru>
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Tony Hutter <hutter2@llnl.gov>
Reviewed by: Kody Kantor <kody.kantor@joyent.com>
Approved by: Dan McDonald <danmcd@joyent.com>

@@ -496,49 +496,66 @@
         ASSERT3P(m1, ==, m2);
 
         return (0);
 }
 
+uint64_t
+metaslab_allocated_space(metaslab_t *msp)
+{
+        return (msp->ms_allocated_space);
+}
+
 /*
  * Verify that the space accounting on disk matches the in-core range_trees.
  */
-void
+static void
 metaslab_verify_space(metaslab_t *msp, uint64_t txg)
 {
         spa_t *spa = msp->ms_group->mg_vd->vdev_spa;
-        uint64_t allocated = 0;
+        uint64_t allocating = 0;
         uint64_t sm_free_space, msp_free_space;
 
         ASSERT(MUTEX_HELD(&msp->ms_lock));
+        ASSERT(!msp->ms_condensing);
 
         if ((zfs_flags & ZFS_DEBUG_METASLAB_VERIFY) == 0)
                 return;
 
         /*
          * We can only verify the metaslab space when we're called
-         * from syncing context with a loaded metaslab that has an allocated
-         * space map. Calling this in non-syncing context does not
-         * provide a consistent view of the metaslab since we're performing
-         * allocations in the future.
+         * from syncing context with a loaded metaslab that has an
+         * allocated space map. Calling this in non-syncing context
+         * does not provide a consistent view of the metaslab since
+         * we're performing allocations in the future.
          */
         if (txg != spa_syncing_txg(spa) || msp->ms_sm == NULL ||
             !msp->ms_loaded)
                 return;
 
-        sm_free_space = msp->ms_size - space_map_allocated(msp->ms_sm) -
-            space_map_alloc_delta(msp->ms_sm);
+        /*
+         * Even though the smp_alloc field can get negative (e.g.
+         * see vdev_checkpoint_sm), that should never be the case
+         * when it come's to a metaslab's space map.
+         */
+        ASSERT3S(space_map_allocated(msp->ms_sm), >=, 0);
 
+        sm_free_space = msp->ms_size - metaslab_allocated_space(msp);
+
         /*
-         * Account for future allocations since we would have already
-         * deducted that space from the ms_freetree.
+         * Account for future allocations since we would have
+         * already deducted that space from the ms_allocatable.
          */
         for (int t = 0; t < TXG_CONCURRENT_STATES; t++) {
-                allocated +=
+                allocating +=
                     range_tree_space(msp->ms_allocating[(txg + t) & TXG_MASK]);
         }
 
-        msp_free_space = range_tree_space(msp->ms_allocatable) + allocated +
+        ASSERT3U(msp->ms_deferspace, ==,
+            range_tree_space(msp->ms_defer[0]) +
+            range_tree_space(msp->ms_defer[1]));
+
+        msp_free_space = range_tree_space(msp->ms_allocatable) + allocating +
             msp->ms_deferspace + range_tree_space(msp->ms_freed);
 
         VERIFY3U(sm_free_space, ==, msp_free_space);
 }
 

@@ -839,10 +856,11 @@
         ASSERT3U(RANGE_TREE_HISTOGRAM_SIZE, >=,
             SPACE_MAP_HISTOGRAM_SIZE + ashift);
 
         for (int m = 0; m < vd->vdev_ms_count; m++) {
                 metaslab_t *msp = vd->vdev_ms[m];
+                ASSERT(msp != NULL);
 
                 /* skip if not active or not a member */
                 if (msp->ms_sm == NULL || msp->ms_group != mg)
                         continue;
 

@@ -1459,11 +1477,208 @@
  * ==========================================================================
  * Metaslabs
  * ==========================================================================
  */
 
+static void
+metaslab_aux_histograms_clear(metaslab_t *msp)
+{
+        /*
+         * Auxiliary histograms are only cleared when resetting them,
+         * which can only happen while the metaslab is loaded.
+         */
+        ASSERT(msp->ms_loaded);
+
+        bzero(msp->ms_synchist, sizeof (msp->ms_synchist));
+        for (int t = 0; t < TXG_DEFER_SIZE; t++)
+                bzero(msp->ms_deferhist[t], sizeof (msp->ms_deferhist[t]));
+}
+
+static void
+metaslab_aux_histogram_add(uint64_t *histogram, uint64_t shift,
+    range_tree_t *rt)
+{
+        /*
+         * This is modeled after space_map_histogram_add(), so refer to that
+         * function for implementation details. We want this to work like
+         * the space map histogram, and not the range tree histogram, as we
+         * are essentially constructing a delta that will be later subtracted
+         * from the space map histogram.
+         */
+        int idx = 0;
+        for (int i = shift; i < RANGE_TREE_HISTOGRAM_SIZE; i++) {
+                ASSERT3U(i, >=, idx + shift);
+                histogram[idx] += rt->rt_histogram[i] << (i - idx - shift);
+
+                if (idx < SPACE_MAP_HISTOGRAM_SIZE - 1) {
+                        ASSERT3U(idx + shift, ==, i);
+                        idx++;
+                        ASSERT3U(idx, <, SPACE_MAP_HISTOGRAM_SIZE);
+                }
+        }
+}
+
 /*
+ * Called at every sync pass that the metaslab gets synced.
+ *
+ * The reason is that we want our auxiliary histograms to be updated
+ * wherever the metaslab's space map histogram is updated. This way
+ * we stay consistent on which parts of the metaslab space map's
+ * histogram are currently not available for allocations (e.g because
+ * they are in the defer, freed, and freeing trees).
+ */
+static void
+metaslab_aux_histograms_update(metaslab_t *msp)
+{
+        space_map_t *sm = msp->ms_sm;
+        ASSERT(sm != NULL);
+
+        /*
+         * This is similar to the metaslab's space map histogram updates
+         * that take place in metaslab_sync(). The only difference is that
+         * we only care about segments that haven't made it into the
+         * ms_allocatable tree yet.
+         */
+        if (msp->ms_loaded) {
+                metaslab_aux_histograms_clear(msp);
+
+                metaslab_aux_histogram_add(msp->ms_synchist,
+                    sm->sm_shift, msp->ms_freed);
+
+                for (int t = 0; t < TXG_DEFER_SIZE; t++) {
+                        metaslab_aux_histogram_add(msp->ms_deferhist[t],
+                            sm->sm_shift, msp->ms_defer[t]);
+                }
+        }
+
+        metaslab_aux_histogram_add(msp->ms_synchist,
+            sm->sm_shift, msp->ms_freeing);
+}
+
+/*
+ * Called every time we are done syncing (writing to) the metaslab,
+ * i.e. at the end of each sync pass.
+ * [see the comment in metaslab_impl.h for ms_synchist, ms_deferhist]
+ */
+static void
+metaslab_aux_histograms_update_done(metaslab_t *msp, boolean_t defer_allowed)
+{
+        spa_t *spa = msp->ms_group->mg_vd->vdev_spa;
+        space_map_t *sm = msp->ms_sm;
+
+        if (sm == NULL) {
+                /*
+                 * We came here from metaslab_init() when creating/opening a
+                 * pool, looking at a metaslab that hasn't had any allocations
+                 * yet.
+                 */
+                return;
+        }
+
+        /*
+         * This is similar to the actions that we take for the ms_freed
+         * and ms_defer trees in metaslab_sync_done().
+         */
+        uint64_t hist_index = spa_syncing_txg(spa) % TXG_DEFER_SIZE;
+        if (defer_allowed) {
+                bcopy(msp->ms_synchist, msp->ms_deferhist[hist_index],
+                    sizeof (msp->ms_synchist));
+        } else {
+                bzero(msp->ms_deferhist[hist_index],
+                    sizeof (msp->ms_deferhist[hist_index]));
+        }
+        bzero(msp->ms_synchist, sizeof (msp->ms_synchist));
+}
+
+/*
+ * Ensure that the metaslab's weight and fragmentation are consistent
+ * with the contents of the histogram (either the range tree's histogram
+ * or the space map's depending whether the metaslab is loaded).
+ */
+static void
+metaslab_verify_weight_and_frag(metaslab_t *msp)
+{
+        ASSERT(MUTEX_HELD(&msp->ms_lock));
+
+        if ((zfs_flags & ZFS_DEBUG_METASLAB_VERIFY) == 0)
+                return;
+
+        /* see comment in metaslab_verify_unflushed_changes() */
+        if (msp->ms_group == NULL)
+                return;
+
+        /*
+         * Devices being removed always return a weight of 0 and leave
+         * fragmentation and ms_max_size as is - there is nothing for
+         * us to verify here.
+         */
+        vdev_t *vd = msp->ms_group->mg_vd;
+        if (vd->vdev_removing)
+                return;
+
+        /*
+         * If the metaslab is dirty it probably means that we've done
+         * some allocations or frees that have changed our histograms
+         * and thus the weight.
+         */
+        for (int t = 0; t < TXG_SIZE; t++) {
+                if (txg_list_member(&vd->vdev_ms_list, msp, t))
+                        return;
+        }
+
+        /*
+         * This verification checks that our in-memory state is consistent
+         * with what's on disk. If the pool is read-only then there aren't
+         * any changes and we just have the initially-loaded state.
+         */
+        if (!spa_writeable(msp->ms_group->mg_vd->vdev_spa))
+                return;
+
+        /* some extra verification for in-core tree if you can */
+        if (msp->ms_loaded) {
+                range_tree_stat_verify(msp->ms_allocatable);
+                VERIFY(space_map_histogram_verify(msp->ms_sm,
+                    msp->ms_allocatable));
+        }
+
+        uint64_t weight = msp->ms_weight;
+        uint64_t was_active = msp->ms_weight & METASLAB_ACTIVE_MASK;
+        boolean_t space_based = WEIGHT_IS_SPACEBASED(msp->ms_weight);
+        uint64_t frag = msp->ms_fragmentation;
+        uint64_t max_segsize = msp->ms_max_size;
+
+        msp->ms_weight = 0;
+        msp->ms_fragmentation = 0;
+        msp->ms_max_size = 0;
+
+        /*
+         * This function is used for verification purposes. Regardless of
+         * whether metaslab_weight() thinks this metaslab should be active or
+         * not, we want to ensure that the actual weight (and therefore the
+         * value of ms_weight) would be the same if it was to be recalculated
+         * at this point.
+         */
+        msp->ms_weight = metaslab_weight(msp) | was_active;
+
+        VERIFY3U(max_segsize, ==, msp->ms_max_size);
+
+        /*
+         * If the weight type changed then there is no point in doing
+         * verification. Revert fields to their original values.
+         */
+        if ((space_based && !WEIGHT_IS_SPACEBASED(msp->ms_weight)) ||
+            (!space_based && WEIGHT_IS_SPACEBASED(msp->ms_weight))) {
+                msp->ms_fragmentation = frag;
+                msp->ms_weight = weight;
+                return;
+        }
+
+        VERIFY3U(msp->ms_fragmentation, ==, frag);
+        VERIFY3U(msp->ms_weight, ==, weight);
+}
+
+/*
  * Wait for any in-progress metaslab loads to complete.
  */
 static void
 metaslab_load_wait(metaslab_t *msp)
 {

@@ -1480,51 +1695,98 @@
 {
         int error = 0;
 
         ASSERT(MUTEX_HELD(&msp->ms_lock));
         ASSERT(msp->ms_loading);
+        ASSERT(!msp->ms_condensing);
 
         /*
-         * 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.
+         * We temporarily drop the lock to unblock other operations while we
+         * are reading the space map. Therefore, metaslab_sync() and
+         * metaslab_sync_done() can run at the same time as we do.
+         *
+         * metaslab_sync() can append to the space map while we are loading.
+         * Therefore we load only entries that existed when we started the
+         * load. Additionally, metaslab_sync_done() has to wait for the load
+         * to complete because there are potential races like metaslab_load()
+         * loading parts of the space map that are currently being appended
+         * by metaslab_sync(). If we didn't, the ms_allocatable would have
+         * entries that metaslab_sync_done() would try to re-add later.
+         *
+         * That's why before dropping the lock we remember the synced length
+         * of the metaslab and read up to that point of the space map,
+         * ignoring entries appended by metaslab_sync() that happen after we
+         * drop the lock.
          */
+        uint64_t length = msp->ms_synced_length;
         mutex_exit(&msp->ms_lock);
 
-        /*
-         * If the space map has not been allocated yet, then treat
-         * all the space in the metaslab as free and add it to ms_allocatable.
-         */
         if (msp->ms_sm != NULL) {
-                error = space_map_load(msp->ms_sm, msp->ms_allocatable,
-                    SM_FREE);
+                error = space_map_load_length(msp->ms_sm, msp->ms_allocatable,
+                    SM_FREE, length);
         } else {
+                /*
+                 * The space map has not been allocated yet, so treat
+                 * all the space in the metaslab as free and add it to the
+                 * ms_allocatable tree.
+                 */
                 range_tree_add(msp->ms_allocatable,
                     msp->ms_start, msp->ms_size);
         }
 
+        /*
+         * We need to grab the ms_sync_lock to prevent metaslab_sync() from
+         * changing the ms_sm and the metaslab's range trees while we are
+         * about to use them and populate the ms_allocatable. The ms_lock
+         * is insufficient for this because metaslab_sync() doesn't hold
+         * the ms_lock while writing the ms_checkpointing tree to disk.
+         */
+        mutex_enter(&msp->ms_sync_lock);
         mutex_enter(&msp->ms_lock);
+        ASSERT(!msp->ms_condensing);
 
-        if (error != 0)
+        if (error != 0) {
+                mutex_exit(&msp->ms_sync_lock);
                 return (error);
+        }
 
         ASSERT3P(msp->ms_group, !=, NULL);
         msp->ms_loaded = B_TRUE;
 
         /*
-         * If the metaslab already has a spacemap, then we need to
-         * remove all segments from the defer tree; otherwise, the
-         * metaslab is completely empty and we can skip this.
+         * The ms_allocatable contains the segments that exist in the
+         * ms_defer trees [see ms_synced_length]. Thus we need to remove
+         * them from ms_allocatable as they will be added again in
+         * metaslab_sync_done().
          */
-        if (msp->ms_sm != NULL) {
                 for (int t = 0; t < TXG_DEFER_SIZE; t++) {
                         range_tree_walk(msp->ms_defer[t],
                             range_tree_remove, msp->ms_allocatable);
                 }
-        }
+
+        /*
+         * Call metaslab_recalculate_weight_and_sort() now that the
+         * metaslab is loaded so we get the metaslab's real weight.
+         *
+         * Unless this metaslab was created with older software and
+         * has not yet been converted to use segment-based weight, we
+         * expect the new weight to be better or equal to the weight
+         * that the metaslab had while it was not loaded. This is
+         * because the old weight does not take into account the
+         * consolidation of adjacent segments between TXGs. [see
+         * comment for ms_synchist and ms_deferhist[] for more info]
+         */
+        uint64_t weight = msp->ms_weight;
+        metaslab_recalculate_weight_and_sort(msp);
+        if (!WEIGHT_IS_SPACEBASED(weight))
+                ASSERT3U(weight, <=, msp->ms_weight);
         msp->ms_max_size = metaslab_block_maxsize(msp);
 
+        spa_t *spa = msp->ms_group->mg_vd->vdev_spa;
+        metaslab_verify_space(msp, spa_syncing_txg(spa));
+        mutex_exit(&msp->ms_sync_lock);
+
         return (0);
 }
 
 int
 metaslab_load(metaslab_t *msp)

@@ -1537,10 +1799,11 @@
          */
         metaslab_load_wait(msp);
         if (msp->ms_loaded)
                 return (0);
         VERIFY(!msp->ms_loading);
+        ASSERT(!msp->ms_condensing);
 
         msp->ms_loading = B_TRUE;
         int error = metaslab_load_impl(msp);
         msp->ms_loading = B_FALSE;
         cv_broadcast(&msp->ms_load_cv);

@@ -1550,14 +1813,33 @@
 
 void
 metaslab_unload(metaslab_t *msp)
 {
         ASSERT(MUTEX_HELD(&msp->ms_lock));
+
+        metaslab_verify_weight_and_frag(msp);
+
         range_tree_vacate(msp->ms_allocatable, NULL, NULL);
         msp->ms_loaded = B_FALSE;
+
         msp->ms_weight &= ~METASLAB_ACTIVE_MASK;
         msp->ms_max_size = 0;
+
+        /*
+         * We explicitly recalculate the metaslab's weight based on its space
+         * map (as it is now not loaded). We want unload metaslabs to always
+         * have their weights calculated from the space map histograms, while
+         * loaded ones have it calculated from their in-core range tree
+         * [see metaslab_load()]. This way, the weight reflects the information
+         * available in-core, whether it is loaded or not
+         *
+         * If ms_group == NULL means that we came here from metaslab_fini(),
+         * at which point it doesn't make sense for us to do the recalculation
+         * and the sorting.
+         */
+        if (msp->ms_group != NULL)
+                metaslab_recalculate_weight_and_sort(msp);
 }
 
 static void
 metaslab_space_update(vdev_t *vd, metaslab_class_t *mc, int64_t alloc_delta,
     int64_t defer_delta, int64_t space_delta)

@@ -1593,10 +1875,17 @@
         ms->ms_new = B_TRUE;
 
         /*
          * We only open space map objects that already exist. All others
          * will be opened when we finally allocate an object for it.
+         *
+         * Note:
+         * When called from vdev_expand(), we can't call into the DMU as
+         * we are holding the spa_config_lock as a writer and we would
+         * deadlock [see relevant comment in vdev_metaslab_init()]. in
+         * that case, the object parameter is zero though, so we won't
+         * call into the DMU.
          */
         if (object != 0) {
                 error = space_map_open(&ms->ms_sm, mos, object, ms->ms_start,
                     ms->ms_size, vd->vdev_ashift);
 

@@ -1604,18 +1893,21 @@
                         kmem_free(ms, sizeof (metaslab_t));
                         return (error);
                 }
 
                 ASSERT(ms->ms_sm != NULL);
+                ASSERT3S(space_map_allocated(ms->ms_sm), >=, 0);
+                ms->ms_allocated_space = space_map_allocated(ms->ms_sm);
         }
 
         /*
-         * We create the main range tree here, but we don't create the
+         * We create the ms_allocatable here, but we don't create the
          * other range trees until metaslab_sync_done().  This serves
          * two purposes: it allows metaslab_sync_done() to detect the
-         * addition of new space; and for debugging, it ensures that we'd
-         * data fault on any attempt to use this metaslab before it's ready.
+         * addition of new space; and for debugging, it ensures that
+         * we'd data fault on any attempt to use this metaslab before
+         * it's ready.
          */
         ms->ms_allocatable = range_tree_create(&metaslab_rt_ops, ms);
         metaslab_group_add(mg, ms);
 
         metaslab_set_fragmentation(ms);

@@ -1627,12 +1919,15 @@
          * does not become available until after this txg has synced.
          * The metaslab's weight will also be initialized when we sync
          * out this txg. This ensures that we don't attempt to allocate
          * from it before we have initialized it completely.
          */
-        if (txg <= TXG_INITIAL)
+        if (txg <= TXG_INITIAL) {
                 metaslab_sync_done(ms, 0);
+                metaslab_space_update(vd, mg->mg_class,
+                    metaslab_allocated_space(ms), 0, 0);
+        }
 
         /*
          * If metaslab_debug_load is set and we're initializing a metaslab
          * that has an allocated space map object then load the space map
          * so that we can verify frees.

@@ -1662,11 +1957,11 @@
         metaslab_group_remove(mg, msp);
 
         mutex_enter(&msp->ms_lock);
         VERIFY(msp->ms_group == NULL);
         metaslab_space_update(vd, mg->mg_class,
-            -space_map_allocated(msp->ms_sm), 0, -msp->ms_size);
+            -metaslab_allocated_space(msp), 0, -msp->ms_size);
 
         space_map_close(msp->ms_sm);
 
         metaslab_unload(msp);
 

@@ -1683,10 +1978,13 @@
         }
         ASSERT0(msp->ms_deferspace);
 
         range_tree_destroy(msp->ms_checkpointing);
 
+        for (int t = 0; t < TXG_SIZE; t++)
+                ASSERT(!txg_list_member(&vd->vdev_ms_list, msp, t));
+
         mutex_exit(&msp->ms_lock);
         cv_destroy(&msp->ms_load_cv);
         mutex_destroy(&msp->ms_lock);
         mutex_destroy(&msp->ms_sync_lock);
         ASSERT3U(msp->ms_allocator, ==, -1);

@@ -1698,11 +1996,11 @@
 
 /*
  * This table defines a segment size based fragmentation metric that will
  * allow each metaslab to derive its own fragmentation value. This is done
  * by calculating the space in each bucket of the spacemap histogram and
- * multiplying that by the fragmetation metric in this table. Doing
+ * multiplying that by the fragmentation metric in this table. Doing
  * this for all buckets and dividing it by the total amount of free
  * space in this metaslab (i.e. the total free space in all buckets) gives
  * us the fragmentation metric. This means that a high fragmentation metric
  * equates to most of the free space being comprised of small segments.
  * Conversely, if the metric is low, then most of the free space is in

@@ -1733,14 +2031,14 @@
         5,      /* 8M   */
         0       /* 16M  */
 };
 
 /*
- * Calclate the metaslab's fragmentation metric. A return value
- * of ZFS_FRAG_INVALID means that the metaslab has not been upgraded and does
- * not support this metric. Otherwise, the return value should be in the
- * range [0, 100].
+ * Calculate the metaslab's fragmentation metric and set ms_fragmentation.
+ * Setting this value to ZFS_FRAG_INVALID means that the metaslab has not
+ * been upgraded and does not support this metric. Otherwise, the return
+ * value should be in the range [0, 100].
  */
 static void
 metaslab_set_fragmentation(metaslab_t *msp)
 {
         spa_t *spa = msp->ms_group->mg_vd->vdev_spa;

@@ -1829,11 +2127,11 @@
         ASSERT(!vd->vdev_removing);
 
         /*
          * The baseline weight is the metaslab's free space.
          */
-        space = msp->ms_size - space_map_allocated(msp->ms_sm);
+        space = msp->ms_size - metaslab_allocated_space(msp);
 
         if (metaslab_fragmentation_factor_enabled &&
             msp->ms_fragmentation != ZFS_FRAG_INVALID) {
                 /*
                  * Use the fragmentation information to inversely scale

@@ -1933,18 +2231,42 @@
  * information is updated in metaslab_sync().
  */
 static uint64_t
 metaslab_weight_from_spacemap(metaslab_t *msp)
 {
-        uint64_t weight = 0;
+        space_map_t *sm = msp->ms_sm;
+        ASSERT(!msp->ms_loaded);
+        ASSERT(sm != NULL);
+        ASSERT3U(space_map_object(sm), !=, 0);
+        ASSERT3U(sm->sm_dbuf->db_size, ==, sizeof (space_map_phys_t));
 
+        /*
+         * Create a joint histogram from all the segments that have made
+         * it to the metaslab's space map histogram, that are not yet
+         * available for allocation because they are still in the freeing
+         * pipeline (e.g. freeing, freed, and defer trees). Then subtract
+         * these segments from the space map's histogram to get a more
+         * accurate weight.
+         */
+        uint64_t deferspace_histogram[SPACE_MAP_HISTOGRAM_SIZE] = {0};
+        for (int i = 0; i < SPACE_MAP_HISTOGRAM_SIZE; i++)
+                deferspace_histogram[i] += msp->ms_synchist[i];
+        for (int t = 0; t < TXG_DEFER_SIZE; t++) {
+                for (int i = 0; i < SPACE_MAP_HISTOGRAM_SIZE; i++) {
+                        deferspace_histogram[i] += msp->ms_deferhist[t][i];
+                }
+        }
+
+        uint64_t weight = 0;
         for (int i = SPACE_MAP_HISTOGRAM_SIZE - 1; i >= 0; i--) {
-                if (msp->ms_sm->sm_phys->smp_histogram[i] != 0) {
-                        WEIGHT_SET_COUNT(weight,
-                            msp->ms_sm->sm_phys->smp_histogram[i]);
-                        WEIGHT_SET_INDEX(weight, i +
-                            msp->ms_sm->sm_shift);
+                ASSERT3U(sm->sm_phys->smp_histogram[i], >=,
+                    deferspace_histogram[i]);
+                uint64_t count =
+                    sm->sm_phys->smp_histogram[i] - deferspace_histogram[i];
+                if (count != 0) {
+                        WEIGHT_SET_COUNT(weight, count);
+                        WEIGHT_SET_INDEX(weight, i + sm->sm_shift);
                         WEIGHT_SET_ACTIVE(weight, 0);
                         break;
                 }
         }
         return (weight);

@@ -1965,11 +2287,11 @@
         ASSERT(MUTEX_HELD(&msp->ms_lock));
 
         /*
          * The metaslab is completely free.
          */
-        if (space_map_allocated(msp->ms_sm) == 0) {
+        if (metaslab_allocated_space(msp) == 0) {
                 int idx = highbit64(msp->ms_size) - 1;
                 int max_idx = SPACE_MAP_HISTOGRAM_SIZE + shift - 1;
 
                 if (idx < max_idx) {
                         WEIGHT_SET_COUNT(weight, 1ULL);

@@ -1987,11 +2309,11 @@
         ASSERT3U(msp->ms_sm->sm_dbuf->db_size, ==, sizeof (space_map_phys_t));
 
         /*
          * If the metaslab is fully allocated then just make the weight 0.
          */
-        if (space_map_allocated(msp->ms_sm) == msp->ms_size)
+        if (metaslab_allocated_space(msp) == msp->ms_size)
                 return (0);
         /*
          * If the metaslab is already loaded, then use the range tree to
          * determine the weight. Otherwise, we rely on the space map information
          * to generate the weight.

@@ -2068,10 +2390,12 @@
          * ensure that we get an accurate maximum size if newly freed space
          * has been added back into the free tree.
          */
         if (msp->ms_loaded)
                 msp->ms_max_size = metaslab_block_maxsize(msp);
+        else
+                ASSERT0(msp->ms_max_size);
 
         /*
          * Segment-based weighting requires space map histogram support.
          */
         if (zfs_metaslab_segment_weight_enabled &&

@@ -2083,10 +2407,19 @@
                 weight = metaslab_space_weight(msp);
         }
         return (weight);
 }
 
+void
+metaslab_recalculate_weight_and_sort(metaslab_t *msp)
+{
+        /* note: we preserve the mask (e.g. indication of primary, etc..) */
+        uint64_t was_active = msp->ms_weight & METASLAB_ACTIVE_MASK;
+        metaslab_group_sort(msp->ms_group, msp,
+            metaslab_weight(msp) | was_active);
+}
+
 static int
 metaslab_activate_allocator(metaslab_group_t *mg, metaslab_t *msp,
     int allocator, uint64_t activation_weight)
 {
         /*

@@ -2467,21 +2800,21 @@
 
 
         VERIFY(txg <= spa_final_dirty_txg(spa));
 
         /*
-         * The only state that can actually be changing concurrently with
-         * metaslab_sync() is the metaslab's ms_allocatable.  No other
-         * thread can be modifying this txg's alloc, freeing,
+         * The only state that can actually be changing concurrently
+         * with metaslab_sync() is the metaslab's ms_allocatable. No
+         * other thread can be modifying this txg's alloc, freeing,
          * freed, or 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.
+         * 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().
+         * 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);
 
         if (msp->ms_sm == NULL) {
                 uint64_t new_object;

@@ -2489,11 +2822,13 @@
                 new_object = space_map_alloc(mos, zfs_metaslab_sm_blksz, tx);
                 VERIFY3U(new_object, !=, 0);
 
                 VERIFY0(space_map_open(&msp->ms_sm, mos, new_object,
                     msp->ms_start, msp->ms_size, vd->vdev_ashift));
+
                 ASSERT(msp->ms_sm != NULL);
+                ASSERT0(metaslab_allocated_space(msp));
         }
 
         if (!range_tree_is_empty(msp->ms_checkpointing) &&
             vd->vdev_checkpoint_sm == NULL) {
                 ASSERT(spa_has_checkpoint(spa));

@@ -2537,10 +2872,15 @@
                 space_map_write(msp->ms_sm, msp->ms_freeing, SM_FREE,
                     SM_NO_VDEVID, tx);
                 mutex_enter(&msp->ms_lock);
         }
 
+        msp->ms_allocated_space += range_tree_space(alloctree);
+        ASSERT3U(msp->ms_allocated_space, >=,
+            range_tree_space(msp->ms_freeing));
+        msp->ms_allocated_space -= range_tree_space(msp->ms_freeing);
+
         if (!range_tree_is_empty(msp->ms_checkpointing)) {
                 ASSERT(spa_has_checkpoint(spa));
                 ASSERT3P(vd->vdev_checkpoint_sm, !=, NULL);
 
                 /*

@@ -2550,18 +2890,17 @@
                  */
                 mutex_exit(&msp->ms_lock);
                 space_map_write(vd->vdev_checkpoint_sm,
                     msp->ms_checkpointing, SM_FREE, SM_NO_VDEVID, tx);
                 mutex_enter(&msp->ms_lock);
-                space_map_update(vd->vdev_checkpoint_sm);
 
                 spa->spa_checkpoint_info.sci_dspace +=
                     range_tree_space(msp->ms_checkpointing);
                 vd->vdev_stat.vs_checkpoint_space +=
                     range_tree_space(msp->ms_checkpointing);
                 ASSERT3U(vd->vdev_stat.vs_checkpoint_space, ==,
-                    -vd->vdev_checkpoint_sm->sm_alloc);
+                    -space_map_allocated(vd->vdev_checkpoint_sm));
 
                 range_tree_vacate(msp->ms_checkpointing, NULL, NULL);
         }
 
         if (msp->ms_loaded) {

@@ -2602,27 +2941,30 @@
          * accounts for all free space. If the space map is not loaded,
          * then we will lose some accuracy but will correct it the next
          * time we load the space map.
          */
         space_map_histogram_add(msp->ms_sm, msp->ms_freeing, tx);
+        metaslab_aux_histograms_update(msp);
 
         metaslab_group_histogram_add(mg, msp);
         metaslab_group_histogram_verify(mg);
         metaslab_class_histogram_verify(mg->mg_class);
 
         /*
          * For sync pass 1, we avoid traversing this txg's free range tree
-         * and instead will just swap the pointers for freeing and
-         * freed. We can safely do this since the freed_tree is
-         * guaranteed to be empty on the initial pass.
+         * and instead will just swap the pointers for freeing and freed.
+         * We can safely do this since the freed_tree is guaranteed to be
+         * empty on the initial pass.
          */
         if (spa_sync_pass(spa) == 1) {
                 range_tree_swap(&msp->ms_freeing, &msp->ms_freed);
+                ASSERT0(msp->ms_allocated_this_txg);
         } else {
                 range_tree_vacate(msp->ms_freeing,
                     range_tree_add, msp->ms_freed);
         }
+        msp->ms_allocated_this_txg += range_tree_space(alloctree);
         range_tree_vacate(alloctree, NULL, NULL);
 
         ASSERT0(range_tree_space(msp->ms_allocating[txg & TXG_MASK]));
         ASSERT0(range_tree_space(msp->ms_allocating[TXG_CLEAN(txg)
             & TXG_MASK]));

@@ -2696,11 +3038,12 @@
         if (free_space <= spa_get_slop_space(spa) || vd->vdev_removing) {
                 defer_allowed = B_FALSE;
         }
 
         defer_delta = 0;
-        alloc_delta = space_map_alloc_delta(msp->ms_sm);
+        alloc_delta = msp->ms_allocated_this_txg -
+            range_tree_space(msp->ms_freed);
         if (defer_allowed) {
                 defer_delta = range_tree_space(msp->ms_freed) -
                     range_tree_space(*defer_tree);
         } else {
                 defer_delta -= range_tree_space(*defer_tree);

@@ -2728,12 +3071,13 @@
         } else {
                 range_tree_vacate(msp->ms_freed,
                     msp->ms_loaded ? range_tree_add : NULL,
                     msp->ms_allocatable);
         }
-        space_map_update(msp->ms_sm);
 
+        msp->ms_synced_length = space_map_length(msp->ms_sm);
+
         msp->ms_deferspace += defer_delta;
         ASSERT3S(msp->ms_deferspace, >=, 0);
         ASSERT3S(msp->ms_deferspace, <=, msp->ms_size);
         if (msp->ms_deferspace != 0) {
                 /*

@@ -2740,23 +3084,24 @@
                  * Keep syncing this metaslab until all deferred frees
                  * are back in circulation.
                  */
                 vdev_dirty(vd, VDD_METASLAB, msp, txg + 1);
         }
+        metaslab_aux_histograms_update_done(msp, defer_allowed);
 
         if (msp->ms_new) {
                 msp->ms_new = B_FALSE;
                 mutex_enter(&mg->mg_lock);
                 mg->mg_ms_ready++;
                 mutex_exit(&mg->mg_lock);
         }
+
         /*
-         * Calculate the new weights before unloading any metaslabs.
-         * This will give us the most accurate weighting.
+         * Re-sort metaslab within its group now that we've adjusted
+         * its allocatable space.
          */
-        metaslab_group_sort(mg, msp, metaslab_weight(msp) |
-            (msp->ms_weight & METASLAB_ACTIVE_MASK));
+        metaslab_recalculate_weight_and_sort(msp);
 
         /*
          * If the metaslab is loaded and we've not tried to load or allocate
          * from it in 'metaslab_unload_delay' txgs, then unload it.
          */

@@ -2779,10 +3124,11 @@
         ASSERT0(range_tree_space(msp->ms_allocating[txg & TXG_MASK]));
         ASSERT0(range_tree_space(msp->ms_freeing));
         ASSERT0(range_tree_space(msp->ms_freed));
         ASSERT0(range_tree_space(msp->ms_checkpointing));
 
+        msp->ms_allocated_this_txg = 0;
         mutex_exit(&msp->ms_lock);
 }
 
 void
 metaslab_sync_reassess(metaslab_group_t *mg)

@@ -4034,11 +4380,11 @@
 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,
     zio_alloc_list_t *zal, zio_t *zio, int allocator)
 {
         dva_t *dva = bp->blk_dva;
-        dva_t *hintdva = hintbp->blk_dva;
+        dva_t *hintdva = (hintbp != NULL) ? hintbp->blk_dva : NULL;
         int error = 0;
 
         ASSERT(bp->blk_birth == 0);
         ASSERT(BP_PHYSICAL_BIRTH(bp) == 0);
 

@@ -4201,18 +4547,20 @@
         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_allocatable, offset, size);
+        if (msp->ms_loaded) {
+                range_tree_verify_not_present(msp->ms_allocatable,
+                    offset, size);
+        }
 
-        range_tree_verify(msp->ms_freeing, offset, size);
-        range_tree_verify(msp->ms_checkpointing, offset, size);
-        range_tree_verify(msp->ms_freed, offset, size);
+        range_tree_verify_not_present(msp->ms_freeing, offset, size);
+        range_tree_verify_not_present(msp->ms_checkpointing, offset, size);
+        range_tree_verify_not_present(msp->ms_freed, offset, size);
         for (int j = 0; j < TXG_DEFER_SIZE; j++)
-                range_tree_verify(msp->ms_defer[j], offset, size);
+                range_tree_verify_not_present(msp->ms_defer[j], offset, size);
         mutex_exit(&msp->ms_lock);
 }
 
 void
 metaslab_check_free(spa_t *spa, const blkptr_t *bp)