diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_object.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_object.c
index 9f0f2b437c36..aede315502d9 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_object.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_object.c
@@ -32,7 +32,8 @@
 #include <sys/zfeature.h>
 
 uint64_t
-dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
+dmu_object_alloc_ibs(objset_t *os, dmu_object_type_t ot, int blocksize,
+    int indirect_blockshift,
     dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
 {
 	uint64_t object;
@@ -92,7 +93,8 @@ dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
 			os->os_obj_next = object - 1;
 	}
 
-	dnode_allocate(dn, ot, blocksize, 0, bonustype, bonuslen, tx);
+	dnode_allocate(dn, ot, blocksize, indirect_blockshift,
+	    bonustype, bonuslen, tx);
 	mutex_exit(&os->os_obj_lock);
 
 	dmu_tx_add_new_object(tx, dn);
@@ -101,6 +103,14 @@ dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
 	return (object);
 }
 
+uint64_t
+dmu_object_alloc(objset_t *os, dmu_object_type_t ot, int blocksize,
+    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
+{
+	return (dmu_object_alloc_ibs(os, ot, blocksize, 0,
+	    bonustype, bonuslen, tx));
+}
+
 int
 dmu_object_claim(objset_t *os, uint64_t object, dmu_object_type_t ot,
     int blocksize, dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx)
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/space_map.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/space_map.c
index c6dc0f75140b..7356e3ceea75 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/space_map.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/space_map.c
@@ -54,6 +54,17 @@ SYSCTL_DECL(_vfs_zfs);
  */
 boolean_t zfs_force_some_double_word_sm_entries = B_FALSE;
 
+/*
+ * Override the default indirect block size of 128K, instead using 16K for
+ * spacemaps (2^14 bytes).  This dramatically reduces write inflation since
+ * appending to a spacemap typically has to write one data block (4KB) and one
+ * or two indirect blocks (16K-32K, rather than 128K).
+ */
+int space_map_ibs = 14;
+
+SYSCTL_INT(_vfs_zfs, OID_AUTO, space_map_ibs, CTLFLAG_RWTUN,
+    &space_map_ibs, 0, "Space map indirect block shift");
+
 boolean_t
 sm_entry_is_debug(uint64_t e)
 {
@@ -676,8 +687,8 @@ space_map_write_impl(space_map_t *sm, range_tree_t *rt, maptype_t maptype,
 		 *
 		 * [1] The feature is enabled.
 		 * [2] The offset or run is too big for a single-word entry,
-		 * 	or the vdev_id is set (meaning not equal to
-		 * 	SM_NO_VDEVID).
+		 *	or the vdev_id is set (meaning not equal to
+		 *	SM_NO_VDEVID).
 		 *
 		 * Note that for purposes of testing we've added the case that
 		 * we write two-word entries occasionally when the feature is
@@ -836,7 +847,8 @@ space_map_truncate(space_map_t *sm, int blocksize, dmu_tx_t *tx)
 	 */
 	if ((spa_feature_is_enabled(spa, SPA_FEATURE_SPACEMAP_HISTOGRAM) &&
 	    doi.doi_bonus_size != sizeof (space_map_phys_t)) ||
-	    doi.doi_data_block_size != blocksize) {
+	    doi.doi_data_block_size != blocksize ||
+	    doi.doi_metadata_block_size != 1 << space_map_ibs) {
 		zfs_dbgmsg("txg %llu, spa %s, sm %p, reallocating "
 		    "object[%llu]: old bonus %u, old blocksz %u",
 		    dmu_tx_get_txg(tx), spa_name(spa), sm, sm->sm_object,
@@ -892,8 +904,8 @@ space_map_alloc(objset_t *os, int blocksize, dmu_tx_t *tx)
 		bonuslen = SPACE_MAP_SIZE_V0;
 	}
 
-	object = dmu_object_alloc(os, DMU_OT_SPACE_MAP, blocksize,
-	    DMU_OT_SPACE_MAP_HEADER, bonuslen, tx);
+	object = dmu_object_alloc_ibs(os, DMU_OT_SPACE_MAP, blocksize,
+	    space_map_ibs, DMU_OT_SPACE_MAP_HEADER, bonuslen, tx);
 
 	return (object);
 }
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
index 090d3a63265c..9c542baf5809 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
@@ -356,6 +356,9 @@ typedef struct dmu_buf {
  */
 uint64_t dmu_object_alloc(objset_t *os, dmu_object_type_t ot,
     int blocksize, dmu_object_type_t bonus_type, int bonus_len, dmu_tx_t *tx);
+uint64_t dmu_object_alloc_ibs(objset_t *os, dmu_object_type_t ot, int blocksize,
+    int indirect_blockshift,
+    dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx);
 int dmu_object_claim(objset_t *os, uint64_t object, dmu_object_type_t ot,
     int blocksize, dmu_object_type_t bonus_type, int bonus_len, dmu_tx_t *tx);
 int dmu_object_reclaim(objset_t *os, uint64_t object, dmu_object_type_t ot,