diff --git a/sys/kern/subr_vmem.c b/sys/kern/subr_vmem.c
index e5509be7c20c..c71d4bec4327 100644
--- a/sys/kern/subr_vmem.c
+++ b/sys/kern/subr_vmem.c
@@ -691,9 +691,11 @@ vmem_startup(void)
 	/*
 	 * Reserve enough tags to allocate new tags.  We allow multiple
 	 * CPUs to attempt to allocate new tags concurrently to limit
-	 * false restarts in UMA.
+	 * false restarts in UMA.  vmem_bt_alloc() allocates from a per-domain
+	 * arena, which may involve importing a range from the kernel arena,
+	 * so we need to keep at least 2 * BT_MAXALLOC tags reserved.
 	 */
-	uma_zone_reserve(vmem_bt_zone, BT_MAXALLOC * (mp_ncpus + 1) / 2);
+	uma_zone_reserve(vmem_bt_zone, 2 * BT_MAXALLOC * mp_ncpus);
 	uma_zone_set_allocf(vmem_bt_zone, vmem_bt_alloc);
 #endif
 }
diff --git a/sys/vm/vm_kern.c b/sys/vm/vm_kern.c
index 07f3a9913727..c04310d8cbb8 100644
--- a/sys/vm/vm_kern.c
+++ b/sys/vm/vm_kern.c
@@ -125,7 +125,7 @@ SYSCTL_ULONG(_vm, OID_AUTO, max_kernel_address, CTLFLAG_RD,
 #define	KVA_QUANTUM_SHIFT	(VM_LEVEL_0_ORDER + PAGE_SHIFT)
 #else
 /* On non-superpage architectures want large import sizes. */
-#define	KVA_QUANTUM_SHIFT	(10 + PAGE_SHIFT)
+#define	KVA_QUANTUM_SHIFT	(8 + PAGE_SHIFT)
 #endif
 #define	KVA_QUANTUM		(1 << KVA_QUANTUM_SHIFT)