Index: share/man/man4/numa.4
===================================================================
--- share/man/man4/numa.4
+++ share/man/man4/numa.4
@@ -24,15 +24,15 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd July 10, 2018
+.Dd October 5, 2018
 .Dt NUMA 4
 .Os
 .Sh NAME
 .Nm NUMA
 .Nd Non-Uniform Memory Access
 .Sh SYNOPSIS
-.Cd options SMP
-.Cd options MAXMEMDOM=16
+.Cd options MAXMEMDOM
+.Cd options NUMA
 .Pp
 .In sys/cpuset.h
 .In sys/bus.h
@@ -47,14 +47,26 @@
 depends upon which processor the memory or device is attached to.
 Accessing memory local to a processor is faster than accessing memory
 that is connected to one of the other processors.
+.Fx
+implements NUMA-aware memory allocation policies.
+By default it attempts to ensure that allocations are balanced across
+each domain.
+Users may override the default domain selection policy using
+.Xr cpuset 1 .
 .Pp
 .Nm
-is enabled when the
+support is enabled when the
 .Cd NUMA
-option is used in a kernel configuration
-file and the
+option is specified in the kernel configuration file.
+Each platform defines the
 .Cd MAXMEMDOM
-option is set to a value greater than 1.
+constant, which specifies the maximum number of supported NUMA domains.
+This constant may be specified in the kernel configuration file.
+.Nm
+support can be disabled at boot time by setting the
+.Va vm.ndomains
+tunable to 1.
+Other values for this tunable are currently ignored.
 .Pp
 Thread and process
 .Nm
@@ -128,7 +140,7 @@
 .Fx 11.0
 and were removed in
 .Fx 12.0 .
-Current implementation appeared in
+The current implementation appeared in
 .Fx 12.0 .
 .Pp
 .Sh AUTHORS
Index: sys/arm64/arm64/mp_machdep.c
===================================================================
--- sys/arm64/arm64/mp_machdep.c
+++ sys/arm64/arm64/mp_machdep.c
@@ -576,11 +576,12 @@
 		return (FALSE);
 
 	/* Try to read the numa node of this cpu */
-	if (OF_getencprop(node, "numa-node-id", &domain, sizeof(domain)) > 0) {
-		__pcpu[id].pc_domain = domain;
-		if (domain < MAXMEMDOM)
-			CPU_SET(id, &cpuset_domain[domain]);
-	}
+	if (vm_ndomains > 1 &&
+	    OF_getencprop(node, "numa-node-id", &domain, sizeof(domain)) <= 0)
+		domain = 0;
+	__pcpu[id].pc_domain = domain;
+	if (domain < MAXMEMDOM)
+		CPU_SET(id, &cpuset_domain[domain]);
 
 	return (TRUE);
 }
Index: sys/kern/kern_cpuset.c
===================================================================
--- sys/kern/kern_cpuset.c
+++ sys/kern/kern_cpuset.c
@@ -457,6 +457,12 @@
 	struct domainset *ndomain;
 	int i, j, max;
 
+	KASSERT(domain->ds_cnt <= vm_ndomains,
+	    ("invalid domain count in domainset %p", domain));
+	KASSERT(domain->ds_policy != DOMAINSET_POLICY_PREFER ||
+	    domain->ds_prefer < vm_ndomains,
+	    ("invalid preferred domain in domains %p", domain));
+
 	mtx_lock_spin(&cpuset_lock);
 	LIST_FOREACH(ndomain, &cpuset_domains, ds_link)
 		if (domainset_equal(ndomain, domain))
Index: sys/vm/vm_phys.c
===================================================================
--- sys/vm/vm_phys.c
+++ sys/vm/vm_phys.c
@@ -597,11 +597,22 @@
     int *locality)
 {
 #ifdef NUMA
-	int i;
+	int i, n;
 
-	vm_ndomains = ndomains;
-	mem_affinity = affinity;
-	mem_locality = locality;
+	/*
+	 * For now the only override value that we support is 1, which
+	 * effectively disables NUMA-awareness in the allocators.
+	 */
+	n = ndomains;
+	TUNABLE_INT_FETCH("vm.ndomains", &n);
+	if (n == 1)
+		ndomains = 1;
+
+	if (ndomains > 1) {
+		vm_ndomains = ndomains;
+		mem_affinity = affinity;
+		mem_locality = locality;
+	}
 
 	for (i = 0; i < vm_ndomains; i++)
 		DOMAINSET_SET(i, &all_domains);
Index: sys/x86/acpica/srat.c
===================================================================
--- sys/x86/acpica/srat.c
+++ sys/x86/acpica/srat.c
@@ -535,11 +535,7 @@
 		if (!cpu->enabled)
 			panic("SRAT: CPU with APIC ID %u is not known",
 			    pc->pc_apic_id);
-#ifdef NUMA
-		pc->pc_domain = cpu->domain;
-#else
-		pc->pc_domain = 0;
-#endif
+		pc->pc_domain = vm_ndomains > 1 ? cpu->domain : 0;
 		CPU_SET(i, &cpuset_domain[pc->pc_domain]);
 		if (bootverbose)
 			printf("SRAT: CPU %u has memory domain %d\n", i,
@@ -564,7 +560,7 @@
 
 	for (i = 0; i < ndomain; i++) {
 		if (domain_pxm[i] == pxm)
-			return (i);
+			return (vm_ndomains > 1 ? i : 0);
 	}
 
 	return (-1);