Index: sys/kern/subr_vmem.c
===================================================================
--- sys/kern/subr_vmem.c
+++ sys/kern/subr_vmem.c
@@ -244,9 +244,6 @@
 static struct vmem transient_arena_storage;
 /* kernel and kmem arenas are aliased for backwards KPI compat. */
 vmem_t *kernel_arena = &kernel_arena_storage;
-#if VM_NRESERVLEVEL > 0
-vmem_t *kernel_rwx_arena = NULL;
-#endif
 vmem_t *kmem_arena = &kernel_arena_storage;
 vmem_t *buffer_arena = &buffer_arena_storage;
 vmem_t *transient_arena = &transient_arena_storage;
Index: sys/vm/vm_kern.h
===================================================================
--- sys/vm/vm_kern.h
+++ sys/vm/vm_kern.h
@@ -70,7 +70,6 @@
 extern vm_map_t exec_map;
 extern vm_map_t pipe_map;
 extern struct vmem *kernel_arena;
-extern struct vmem *kernel_rwx_arena;
 extern struct vmem *kmem_arena;
 extern struct vmem *buffer_arena;
 extern struct vmem *transient_arena;
Index: sys/vm/vm_kern.c
===================================================================
--- sys/vm/vm_kern.c
+++ sys/vm/vm_kern.c
@@ -669,7 +669,7 @@
 }
 
 /*
- * Import kva into the kernel arena.
+ * Import KVA from the kernel map into the kernel arena.
  */
 static int
 kva_import(void *unused, vmem_size_t size, int flags, vmem_addr_t *addrp)
@@ -691,22 +691,20 @@
 	return (0);
 }
 
-#if VM_NRESERVLEVEL > 0
 /*
- * Import a superpage from the normal kernel arena into the special
- * arena for allocations with different permissions.
+ * Import KVA from a parent arena into a per-domain arena.  Imports must be
+ * KVA_QUANTUM-aligned and a multiple of KVA_QUANTUM in size.
  */
 static int
-kernel_rwx_alloc(void *arena, vmem_size_t size, int flags, vmem_addr_t *addrp)
+kva_import_domain(void *arena, vmem_size_t size, int flags, vmem_addr_t *addrp)
 {
 
 	KASSERT((size % KVA_QUANTUM) == 0,
-	    ("kernel_rwx_alloc: Size %jd is not a multiple of %d",
+	    ("kva_import_domain: Size %jd is not a multiple of %d",
 	    (intmax_t)size, (int)KVA_QUANTUM));
 	return (vmem_xalloc(arena, size, KVA_QUANTUM, 0, 0, VMEM_ADDR_MIN,
 	    VMEM_ADDR_MAX, flags, addrp));
 }
-#endif
 
 /*
  * 	kmem_init:
@@ -744,30 +742,30 @@
 	vmem_init(kernel_arena, "kernel arena", 0, 0, PAGE_SIZE, 0, 0);
 	vmem_set_import(kernel_arena, kva_import, NULL, NULL, KVA_QUANTUM);
 
-#if VM_NRESERVLEVEL > 0
-	/*
-	 * In an architecture with superpages, maintain a separate arena
-	 * for allocations with permissions that differ from the "standard"
-	 * read/write permissions used for memory in the kernel_arena.
-	 */
-	kernel_rwx_arena = vmem_create("kernel rwx arena", 0, 0, PAGE_SIZE,
-	    0, M_WAITOK);
-	vmem_set_import(kernel_rwx_arena, kernel_rwx_alloc,
-	    (vmem_release_t *)vmem_xfree, kernel_arena, KVA_QUANTUM);
-#endif
-
 	for (domain = 0; domain < vm_ndomains; domain++) {
+		/*
+		 * Initialize the per-domain arenas.  These are used to color
+		 * the KVA space in a way that ensures that virtual large pages
+		 * are backed by memory from the same physical domain, which
+		 * maximizes the potential for superpage promotion.
+		 */
 		vm_dom[domain].vmd_kernel_arena = vmem_create(
 		    "kernel arena domain", 0, 0, PAGE_SIZE, 0, M_WAITOK);
 		vmem_set_import(vm_dom[domain].vmd_kernel_arena,
-		    (vmem_import_t *)vmem_alloc, NULL, kernel_arena,
-		    KVA_QUANTUM);
+		    kva_import_domain, NULL, kernel_arena, KVA_QUANTUM);
+
+		/*
+		 * In architectures with superpages, maintain separate arenas
+		 * for allocations with permissions that differ from the
+		 * "standard" read/write permissions used for kernel memory,
+		 * so as not to inhibit superpage promotion.
+		 */
 #if VM_NRESERVLEVEL > 0
 		vm_dom[domain].vmd_kernel_rwx_arena = vmem_create(
 		    "kernel rwx arena domain", 0, 0, PAGE_SIZE, 0, M_WAITOK);
 		vmem_set_import(vm_dom[domain].vmd_kernel_rwx_arena,
-		    kernel_rwx_alloc, (vmem_release_t *)vmem_xfree,
-		    vm_dom[domain].vmd_kernel_arena, KVA_QUANTUM);
+		    kva_import_domain, (vmem_release_t *)vmem_xfree,
+		    kernel_arena, KVA_QUANTUM);
 #endif
 	}
 }