Index: sys/vm/vm_page.c
===================================================================
--- sys/vm/vm_page.c
+++ sys/vm/vm_page.c
@@ -2997,6 +2997,16 @@
 	    (count < npages && req_class == VM_ALLOC_INTERRUPT))
 		return (false);
 
+	/*
+	 * The caller will attempt an allocation after some runs have been
+	 * reclaimed and added to the vm_phys buddy lists.  To ensure that runs
+	 * are not fragmented, round up the requested length to the next power
+	 * of 2 and ensure that each run is self-aligned.
+	 */
+	npages = 1 << flsl(npages - 1);
+	if (alignment < ptoa(npages))
+		alignment = ptoa(npages);
+
 	/*
 	 * Scan up to three times, relaxing the restrictions ("options") on
 	 * the reclamation of reservations and superpages each time.