o Make the reservation of KVA space for kernel map entries a function

of the KVA space's size in addition to the amount of physical memory
   and reduce it by a factor of two.

Under the old formula, our reservation amounted to one kernel map entry
per virtual page in the KVA space on a 4GB i386.

sys/vm/vm_map.c

@@ -263,7 +263,8 @@ vmspace_alloc(min, max)
 void
 vm_init2(void) 
 {
-	uma_zone_set_obj(kmapentzone, &kmapentobj, cnt.v_page_count / 4);
+	uma_zone_set_obj(kmapentzone, &kmapentobj, min(cnt.v_page_count,
+	    (VM_MAX_KERNEL_ADDRESS - KERNBASE) / PAGE_SIZE) / 8);
 	vmspace_zone = uma_zcreate("VMSPACE", sizeof(struct vmspace), NULL,
 #ifdef INVARIANTS
 	    vmspace_zdtor,