fix.patch

diff --git a/usr/src/uts/common/fs/zfs/dmu_traverse.c b/usr/src/uts/common/fs/zfs/dmu_traverse.c
index ac93002..a1a0293 100644
--- a/usr/src/uts/common/fs/zfs/dmu_traverse.c
+++ b/usr/src/uts/common/fs/zfs/dmu_traverse.c
@@ -39,6 +39,7 @@
 #include <sys/zfeature.h>

 int32_t zfs_pd_bytes_max = 50 * 1024 * 1024;	/* 50MB */
+boolean_t ignore_hole_birth = B_FALSE;

 typedef struct prefetch_data {
 	kmutex_t pd_mtx;
@@ -254,7 +255,7 @@ traverse_visitbp(traverse_data_t *td, const dnode_phys_t *dnp,
 		 *
 		 * Note that the meta-dnode cannot be reallocated.
 		 */
-		if ((!td->td_realloc_possible ||
+		if (!ignore_hole_birth && (!td->td_realloc_possible ||
 		    zb->zb_object == DMU_META_DNODE_OBJECT) &&
 		    td->td_hole_birth_enabled_txg <= td->td_min_txg)
 			return (0);

The latest rev will cause hole birth to be ignored when sending holes with birth time zero, if the tunable is set. You still get some of the hole birth benefits, just not all of them.