diff --git a/sys/sys/bitset.h b/sys/sys/bitset.h
index 47c4106d4127..6d60e40a3f7e 100644
--- a/sys/sys/bitset.h
+++ b/sys/sys/bitset.h
@@ -286,6 +286,9 @@
 			break;						\
 		}							\
 		__bits = op((p)->__bits[__i]);				\
+		if (__i == __bitset_words(_s) - 1 &&			\
+		    (_s) % _BITSET_BITS != 0)				\
+			__bits &= (1ul << (_s % _BITSET_BITS)) - 1;	\
 	}								\
 	__found != 0;							\
 })
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 5a9d9bb9fbf4..123d3095d869 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -4013,6 +4013,36 @@ slab_alloc_item(uma_keg_t keg, uma_slab_t slab)
 	return (item);
 }
 
+static int
+slab_alloc_items(uma_keg_t keg, uma_slab_t slab, void **bucket, int max)
+{
+	uma_domain_t dom;
+	int count, freei;
+
+	KASSERT(max >= slab->us_freecount,
+	    ("%s: less than %d items in %p", __func__, max, slab));
+	KEG_LOCK_ASSERT(keg, slab->us_domain);
+	dom = &keg->uk_domain[slab->us_domain];
+
+	count = 0;
+	BIT_FOREACH_ISSET(keg->uk_ipers, freei, &slab->us_free) {
+		bucket[count++] = slab_item(slab, keg, freei);
+	}
+	slab->us_freecount = 0;
+	dom->ud_free_items -= count;
+	BIT_ZERO(keg->uk_ipers, &slab->us_free);
+
+	/*
+	 * Move this slab to the full list.  It must be on the partial list, so
+	 * we do not need to update the free slab count.  In particular,
+	 * keg_fetch_slab() always returns slabs on the partial list.
+	 */
+	LIST_REMOVE(slab, us_link);
+	LIST_INSERT_HEAD(&dom->ud_full_slab, slab, us_link);
+
+	return (count);
+}
+
 static int
 zone_import(void *arg, void **bucket, int max, int domain, int flags)
 {
@@ -4032,6 +4062,21 @@ zone_import(void *arg, void **bucket, int max, int domain, int flags)
 	for (i = 0; i < max; ) {
 		if ((slab = keg_fetch_slab(keg, zone, domain, flags)) == NULL)
 			break;
+
+		/*
+		 * As an optimization, try to pull all of the items out of the
+		 * slab at once.
+		 *
+		 * XXXMJ this can and should go further: we can make a copy of
+		 * the bitmap and slab base address, then drop the per-domain
+		 * lock before the loop.
+		 */
+		if (max - i >= slab->us_freecount && keg->uk_reserve == 0 &&
+		    (zone->uz_flags & UMA_ZONE_ROUNDROBIN) == 0) {
+			i += slab_alloc_items(keg, slab, bucket + i, max - i);
+			goto next;
+		}
+
 #ifdef NUMA
 		stripe = howmany(max, vm_ndomains);
 #endif
@@ -4062,6 +4107,7 @@ zone_import(void *arg, void **bucket, int max, int domain, int flags)
 				break;
 #endif
 		} while (slab->us_freecount != 0 && i < max);
+next:
 		KEG_UNLOCK(keg, slab->us_domain);
 
 		/* Don't block if we allocated any successfully. */