diff --git a/zfs/lib/libzpool/dmu_tx.c b/zfs/lib/libzpool/dmu_tx.c
index 18a640d6d0..42ce01d23c 100644
--- a/zfs/lib/libzpool/dmu_tx.c
+++ b/zfs/lib/libzpool/dmu_tx.c
@@ -48,6 +48,8 @@ dmu_tx_create_dd(dsl_dir_t *dd)
 		tx->tx_pool = dd->dd_pool;
 	list_create(&tx->tx_holds, sizeof (dmu_tx_hold_t),
 	    offsetof(dmu_tx_hold_t, txh_node));
+	list_create(&tx->tx_callbacks, sizeof (dmu_callback_t),
+	    offsetof(dmu_callback_t, dcb_node));
 #ifdef ZFS_DEBUG
 	refcount_create(&tx->tx_space_written);
 	refcount_create(&tx->tx_space_freed);
@@ -1020,6 +1022,9 @@ dmu_tx_commit(dmu_tx_t *tx)
 	if (tx->tx_tempreserve_cookie)
 		dsl_dir_tempreserve_clear(tx->tx_tempreserve_cookie, tx);
 
+	if (!list_is_empty(&tx->tx_callbacks))
+		txg_rele_commit_cb(&tx->tx_txgh, &tx->tx_callbacks);
+
 	if (tx->tx_anyobj == FALSE)
 		txg_rele_to_sync(&tx->tx_txgh);
 	list_destroy(&tx->tx_holds);
@@ -1032,6 +1037,8 @@ dmu_tx_commit(dmu_tx_t *tx)
 	refcount_destroy_many(&tx->tx_space_freed,
 	    refcount_count(&tx->tx_space_freed));
 #endif
+	ASSERT(list_is_empty(&tx->tx_callbacks));
+	list_destroy(&tx->tx_callbacks);
 	kmem_free(tx, sizeof (dmu_tx_t));
 }
 
@@ -1039,6 +1046,7 @@ void
 dmu_tx_abort(dmu_tx_t *tx)
 {
 	dmu_tx_hold_t *txh;
+	dmu_callback_t *dcb;
 
 	ASSERT(tx->tx_txg == 0);
 
@@ -1050,6 +1058,16 @@ dmu_tx_abort(dmu_tx_t *tx)
 		if (dn != NULL)
 			dnode_rele(dn, tx);
 	}
+
+	while ((dcb = list_head(&tx->tx_callbacks))) {
+		list_remove(&tx->tx_callbacks, dcb);
+
+		/*
+		 * Call the callback with an error code. The callback will
+		 * call dmu_tx_callback_data_destroy to free the memory.
+		 */
+		dcb->dcb_func(dcb->dcb_data, ECANCELED);
+	}
 	list_destroy(&tx->tx_holds);
 #ifdef ZFS_DEBUG
 	refcount_destroy_many(&tx->tx_space_written,
@@ -1057,6 +1075,7 @@ dmu_tx_abort(dmu_tx_t *tx)
 	refcount_destroy_many(&tx->tx_space_freed,
 	    refcount_count(&tx->tx_space_freed));
 #endif
+	list_destroy(&tx->tx_callbacks);
 	kmem_free(tx, sizeof (dmu_tx_t));
 }
 
@@ -1066,3 +1085,45 @@ dmu_tx_get_txg(dmu_tx_t *tx)
 	ASSERT(tx->tx_txg != 0);
 	return (tx->tx_txg);
 }
+
+void *
+dmu_tx_callback_data_create(size_t bytes)
+{
+	dmu_callback_t *dcb;
+
+	dcb = kmem_alloc(sizeof (dmu_callback_t) + bytes, KM_SLEEP);
+
+	dcb->dcb_magic = DMU_CALLBACK_MAGIC;
+	dcb->dcb_bytes = bytes;
+
+	return &dcb->dcb_data;
+}
+
+int
+dmu_tx_callback_commit_add(dmu_tx_t *tx, dmu_callback_func_t *dcb_func,
+    void *dcb_data)
+{
+	dmu_callback_t *dcb = container_of(dcb_data, dmu_callback_t, dcb_data);
+
+	if (dcb->dcb_magic != DMU_CALLBACK_MAGIC)
+		return (EINVAL);
+
+	dcb->dcb_func = dcb_func;
+
+	list_insert_tail(&tx->tx_callbacks, dcb);
+
+	return (0);
+}
+
+int
+dmu_tx_callback_data_destroy(void *dcb_data)
+{
+	dmu_callback_t *dcb = container_of(dcb_data, dmu_callback_t, dcb_data);
+
+	if (dcb->dcb_magic != DMU_CALLBACK_MAGIC)
+		return (EINVAL);
+
+	kmem_free(dcb, sizeof (dmu_callback_t) + dcb->dcb_bytes);
+
+	return (0);
+}
diff --git a/zfs/lib/libzpool/include/sys/dmu.h b/zfs/lib/libzpool/include/sys/dmu.h
index 3b1e5c8fbc..e4bcdfbe03 100644
--- a/zfs/lib/libzpool/include/sys/dmu.h
+++ b/zfs/lib/libzpool/include/sys/dmu.h
@@ -64,6 +64,7 @@ struct objset_impl;
 typedef struct objset objset_t;
 typedef struct dmu_tx dmu_tx_t;
 typedef struct dsl_dir dsl_dir_t;
+typedef void dmu_callback_func_t(void *dcb_data, int error);
 
 typedef enum dmu_object_type {
 	DMU_OT_NONE,
@@ -429,6 +430,32 @@ int dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how);
 void dmu_tx_wait(dmu_tx_t *tx);
 void dmu_tx_commit(dmu_tx_t *tx);
 
+/*
+ * To add a commit callback, you must first call dmu_tx_callback_data_create().
+ * This will return a pointer to a memory area of size "bytes" (which can be 0,
+ * or just the size of a pointer if there is a large or existing external data
+ * struct to be referenced) that the caller and the callback can use to exchange
+ * data.
+ *
+ * The callback can then be registered by calling dmu_tx_callback_commit_add()
+ * with the pointer returned by dmu_tx_callback_data_create() passed in the
+ * dcb_data argument. The transaction must be already created, but it cannot
+ * be committed or aborted. It can be assigned to a txg or not.
+ *
+ * The callback will be called after the transaction has been safely written
+ * to stable storage and will also be called if the dmu_tx is aborted.
+ * If there is any error which prevents the transaction from being committed
+ * to disk, the callback will be called with a value of error != 0.
+ *
+ * When the callback data is no longer needed, it must be destroyed by the
+ * caller's code with dmu_tx_callback_data_destroy(). This is typically done at
+ * the end of the callback function.
+ */
+void *dmu_tx_callback_data_create(size_t bytes);
+int dmu_tx_callback_commit_add(dmu_tx_t *tx, dmu_callback_func_t *dcb_func,
+    void *dcb_data);
+int dmu_tx_callback_data_destroy(void *dcb_data);
+
 /*
  * Free up the data blocks for a defined range of a file.  If size is
  * zero, the range from offset to end-of-file is freed.
diff --git a/zfs/lib/libzpool/include/sys/dmu_impl.h b/zfs/lib/libzpool/include/sys/dmu_impl.h
index 96ce688e15..f32ab6ad71 100644
--- a/zfs/lib/libzpool/include/sys/dmu_impl.h
+++ b/zfs/lib/libzpool/include/sys/dmu_impl.h
@@ -232,6 +232,19 @@ extern "C" {
 struct objset;
 struct dmu_pool;
 
+#define DMU_CALLBACK_MAGIC 0xca11bac0ca11bacfull
+
+#define container_of(ptr, type, member) \
+    ((type *)((char *)(ptr) - offsetof(type, member)))
+
+typedef struct dmu_callback {
+	list_node_t         dcb_node;    /* linked to tx_callbacks list */
+	uint64_t            dcb_magic;   /* magic number to verify header */
+	dmu_callback_func_t *dcb_func;   /* caller function pointer */
+	size_t              dcb_bytes;   /* caller private data size */
+	char                dcb_data[0]; /* caller private data */
+} dmu_callback_t;
+
 #ifdef	__cplusplus
 }
 #endif
diff --git a/zfs/lib/libzpool/include/sys/dmu_tx.h b/zfs/lib/libzpool/include/sys/dmu_tx.h
index 2727daaaa7..47b9bcaa57 100644
--- a/zfs/lib/libzpool/include/sys/dmu_tx.h
+++ b/zfs/lib/libzpool/include/sys/dmu_tx.h
@@ -59,6 +59,7 @@ struct dmu_tx {
 	txg_handle_t tx_txgh;
 	void *tx_tempreserve_cookie;
 	struct dmu_tx_hold *tx_needassign_txh;
+	list_t tx_callbacks; /* list of dmu_callback_t on this dmu_tx */
 	uint8_t tx_anyobj;
 	int tx_err;
 #ifdef ZFS_DEBUG
@@ -109,6 +110,11 @@ void dmu_tx_abort(dmu_tx_t *tx);
 uint64_t dmu_tx_get_txg(dmu_tx_t *tx);
 void dmu_tx_wait(dmu_tx_t *tx);
 
+void *dmu_tx_callback_data_create(size_t bytes);
+int dmu_tx_callback_commit_add(dmu_tx_t *tx, dmu_callback_func_t *dcb_func,
+    void *dcb_data);
+int dmu_tx_callback_data_destroy(void *dcb_data);
+
 /*
  * These routines are defined in dmu_spa.h, and are called by the SPA.
  */
diff --git a/zfs/lib/libzpool/include/sys/txg.h b/zfs/lib/libzpool/include/sys/txg.h
index 23bdff211b..1349bd4dcb 100644
--- a/zfs/lib/libzpool/include/sys/txg.h
+++ b/zfs/lib/libzpool/include/sys/txg.h
@@ -71,6 +71,7 @@ extern void txg_sync_stop(struct dsl_pool *dp);
 extern uint64_t txg_hold_open(struct dsl_pool *dp, txg_handle_t *txghp);
 extern void txg_rele_to_quiesce(txg_handle_t *txghp);
 extern void txg_rele_to_sync(txg_handle_t *txghp);
+extern void txg_rele_commit_cb(txg_handle_t *txghp, list_t *tx_callbacks);
 extern void txg_suspend(struct dsl_pool *dp);
 extern void txg_resume(struct dsl_pool *dp);
 
diff --git a/zfs/lib/libzpool/include/sys/txg_impl.h b/zfs/lib/libzpool/include/sys/txg_impl.h
index 7413c662b3..a9a7c358b4 100644
--- a/zfs/lib/libzpool/include/sys/txg_impl.h
+++ b/zfs/lib/libzpool/include/sys/txg_impl.h
@@ -37,6 +37,7 @@ struct tx_cpu {
 	kmutex_t	tc_lock;
 	kcondvar_t	tc_cv[TXG_SIZE];
 	uint64_t	tc_count[TXG_SIZE];
+	list_t		tc_callbacks[TXG_SIZE]; /* post-commit callbacks */
 	char		tc_pad[16];
 };
 
diff --git a/zfs/lib/libzpool/include/sys/zap.h b/zfs/lib/libzpool/include/sys/zap.h
index f88cc068bd..687f7fcd75 100644
--- a/zfs/lib/libzpool/include/sys/zap.h
+++ b/zfs/lib/libzpool/include/sys/zap.h
@@ -316,6 +316,11 @@ void zap_cursor_advance(zap_cursor_t *zc);
  */
 uint64_t zap_cursor_serialize(zap_cursor_t *zc);
 
+/*
+ * Advance the cursor to the attribute having the key.
+ */
+int zap_cursor_move_to_key(zap_cursor_t *zc, const char *name, matchtype_t mt);
+
 /*
  * Initialize a zap cursor pointing to the position recorded by
  * zap_cursor_serialize (in the "serialized" argument).  You can also
diff --git a/zfs/lib/libzpool/include/sys/zap_impl.h b/zfs/lib/libzpool/include/sys/zap_impl.h
index 0dc02ab6b0..159ffaf8b0 100644
--- a/zfs/lib/libzpool/include/sys/zap_impl.h
+++ b/zfs/lib/libzpool/include/sys/zap_impl.h
@@ -210,6 +210,7 @@ int fzap_add_cd(zap_name_t *zn,
     uint64_t integer_size, uint64_t num_integers,
     const void *val, uint32_t cd, dmu_tx_t *tx);
 void fzap_upgrade(zap_t *zap, dmu_tx_t *tx);
+int fzap_cursor_move_to_key(zap_cursor_t *zc, zap_name_t *zn);
 
 #ifdef	__cplusplus
 }
diff --git a/zfs/lib/libzpool/txg.c b/zfs/lib/libzpool/txg.c
index 8e99ef7f26..b150ebd3cf 100644
--- a/zfs/lib/libzpool/txg.c
+++ b/zfs/lib/libzpool/txg.c
@@ -26,6 +26,7 @@
 #include <sys/zfs_context.h>
 #include <sys/txg_impl.h>
 #include <sys/dmu_impl.h>
+#include <sys/dmu_tx.h>
 #include <sys/dsl_pool.h>
 #include <sys/callb.h>
 
@@ -57,6 +58,9 @@ txg_init(dsl_pool_t *dp, uint64_t txg)
 		for (i = 0; i < TXG_SIZE; i++) {
 			cv_init(&tx->tx_cpu[c].tc_cv[i], NULL, CV_DEFAULT,
 			    NULL);
+			list_create(&tx->tx_cpu[c].tc_callbacks[i],
+			    sizeof (dmu_callback_t), offsetof(dmu_callback_t,
+			    dcb_node));
 		}
 	}
 
@@ -98,8 +102,11 @@ txg_fini(dsl_pool_t *dp)
 		int i;
 
 		mutex_destroy(&tx->tx_cpu[c].tc_lock);
-		for (i = 0; i < TXG_SIZE; i++)
+		for (i = 0; i < TXG_SIZE; i++) {
 			cv_destroy(&tx->tx_cpu[c].tc_cv[i]);
+			ASSERT(list_is_empty(&tx->tx_cpu[c].tc_callbacks[i]));
+			list_destroy(&tx->tx_cpu[c].tc_callbacks[i]);
+		}
 	}
 
 	kmem_free(tx->tx_cpu, max_ncpus * sizeof (tx_cpu_t));
@@ -245,6 +252,21 @@ txg_rele_to_sync(txg_handle_t *th)
 	th->th_cpu = NULL;	/* defensive */
 }
 
+void
+txg_rele_commit_cb(txg_handle_t *th, list_t *tx_callbacks)
+{
+	dmu_callback_t *dcb;
+	tx_cpu_t *tc = th->th_cpu;
+	int g = th->th_txg & TXG_MASK;
+
+	mutex_enter(&tc->tc_lock);
+	while ((dcb = list_head(tx_callbacks))) {
+		list_remove(tx_callbacks, dcb);
+		list_insert_tail(&tc->tc_callbacks[g], dcb);
+	}
+	mutex_exit(&tc->tc_lock);
+}
+
 static void
 txg_quiesce(dsl_pool_t *dp, uint64_t txg)
 {
@@ -285,7 +307,8 @@ txg_sync_thread(dsl_pool_t *dp)
 {
 	tx_state_t *tx = &dp->dp_tx;
 	callb_cpr_t cpr;
-	uint64_t start, delta;
+	uint64_t timeout, start, delta, timer;
+	int c, target;
 
 	txg_thread_enter(tx, &cpr);
 
@@ -347,6 +370,63 @@ txg_sync_thread(dsl_pool_t *dp)
 		spa_sync(dp->dp_spa, txg);
 		delta = lbolt - start;
 
+		/*
+		 * Call all the callbacks for this txg. The callbacks must
+		 * call dmu_tx_callback_data_destroy to free memory.
+		 */
+		for (c = 0; c < max_ncpus; c++) {
+			dmu_callback_t *dcb;
+			tx_cpu_t *tc = &tx->tx_cpu[c];
+			int g = txg & TXG_MASK;
+			/* No need to lock tx_cpu_t */
+
+			while ((dcb = list_head(&tc->tc_callbacks[g]))) {
+				list_remove(&tc->tc_callbacks[g], dcb);
+				dcb->dcb_func(dcb->dcb_data, 0);
+			}
+		}
+
+		written = dp->dp_space_towrite[txg & TXG_MASK];
+		dp->dp_space_towrite[txg & TXG_MASK] = 0;
+		ASSERT(dp->dp_tempreserved[txg & TXG_MASK] == 0);
+
+		/*
+		 * If the write limit max has not been explicitly set, set it
+		 * to a fraction of available phisical memory (default 1/8th).
+		 * Note that we must inflate the limit because the spa
+		 * inflates write sizes to account for data replication.
+		 * Check this each sync phase to catch changing memory size.
+		 */
+		if (zfs_write_limit_inflated == 0 ||
+		    (zfs_write_limit_shift && zfs_write_limit_max !=
+		    physmem * PAGESIZE >> zfs_write_limit_shift)) {
+			zfs_write_limit_max =
+			    physmem * PAGESIZE >> zfs_write_limit_shift;
+			zfs_write_limit_inflated =
+			    spa_get_asize(dp->dp_spa, zfs_write_limit_max);
+			if (zfs_write_limit_min > zfs_write_limit_inflated)
+				zfs_write_limit_inflated = zfs_write_limit_min;
+		}
+
+		/*
+		 * Attempt to keep the sync time consistant by adjusting the
+		 * amount of write traffic allowed into each transaction group.
+		 */
+		target = zfs_txg_synctime * hz;
+		if (delta > target) {
+			uint64_t old = MIN(dp->dp_write_limit, written);
+
+			dp->dp_write_limit = MAX(zfs_write_limit_min,
+			    old * target / delta);
+		} else if (written >= dp->dp_write_limit &&
+		    delta >> 3 < target >> 3) {
+			uint64_t rescale =
+			    MIN((100 * target) / delta, 200);
+
+			dp->dp_write_limit = MIN(zfs_write_limit_inflated,
+			    written * rescale / 100);
+		}
+
 		mutex_enter(&tx->tx_sync_lock);
 		rw_enter(&tx->tx_suspend, RW_WRITER);
 		tx->tx_synced_txg = txg;
diff --git a/zfs/lib/libzpool/zap.c b/zfs/lib/libzpool/zap.c
index 2989c61536..a9bd189f84 100644
--- a/zfs/lib/libzpool/zap.c
+++ b/zfs/lib/libzpool/zap.c
@@ -1080,6 +1080,29 @@ zap_stats_ptrtbl(zap_t *zap, uint64_t *tbl, int len, zap_stats_t *zs)
 	}
 }
 
+int fzap_cursor_move_to_key(zap_cursor_t *zc, zap_name_t *zn)
+{
+	int err;
+	zap_leaf_t *l;
+	zap_entry_handle_t zeh;
+
+	if (zn->zn_name_orij && strlen(zn->zn_name_orij) > ZAP_MAXNAMELEN)
+		return (E2BIG);
+
+	err = zap_deref_leaf(zc->zc_zap, zn->zn_hash, NULL, RW_READER, &l);
+	if (err != 0)
+		return (err);
+
+	err = zap_leaf_lookup(l, zn, &zeh);
+	if (err != 0)
+		return (err);
+
+	zc->zc_leaf = l;
+	zc->zc_hash = zeh.zeh_hash;
+	zc->zc_cd = zeh.zeh_cd;
+	return 0;
+}
+
 void
 fzap_get_stats(zap_t *zap, zap_stats_t *zs)
 {
diff --git a/zfs/lib/libzpool/zap_micro.c b/zfs/lib/libzpool/zap_micro.c
index 5ac0bb7421..02c13120c4 100644
--- a/zfs/lib/libzpool/zap_micro.c
+++ b/zfs/lib/libzpool/zap_micro.c
@@ -1045,6 +1045,45 @@ zap_cursor_advance(zap_cursor_t *zc)
 	}
 }
 
+int zap_cursor_move_to_key(zap_cursor_t *zc, const char *name, matchtype_t mt)
+{
+	int err = 0;
+	mzap_ent_t *mze;
+	zap_name_t *zn;
+
+	if (zc->zc_zap == NULL) {
+		err = zap_lockdir(zc->zc_objset, zc->zc_zapobj, NULL,
+				RW_READER, TRUE, FALSE, &zc->zc_zap);
+		if (err)
+			return (err);
+	} else {
+		rw_enter(&zc->zc_zap->zap_rwlock, RW_READER);
+	}
+
+	zn = zap_name_alloc(zc->zc_zap, name, mt);
+	if (zn == NULL) {
+		rw_exit(&zc->zc_zap->zap_rwlock);
+		return (ENOTSUP);
+	}
+
+	if (!zc->zc_zap->zap_ismicro) {
+		err = fzap_cursor_move_to_key(zc, zn);
+	} else {
+		mze = mze_find(zn);
+		if (mze == NULL) {
+			err = (ENOENT);
+			goto out;
+		}
+		zc->zc_hash = mze->mze_hash;
+		zc->zc_cd = mze->mze_phys.mze_cd;
+	}
+
+out:
+	zap_name_free(zn);
+	rw_exit(&zc->zc_zap->zap_rwlock);
+	return (err);
+}
+
 int
 zap_get_stats(objset_t *os, uint64_t zapobj, zap_stats_t *zs)
 {