Index: sys/kern/vfs_subr.c
===================================================================
--- sys/kern/vfs_subr.c
+++ sys/kern/vfs_subr.c
@@ -492,7 +492,16 @@
 static void *
 buf_trie_alloc(struct pctrie *ptree)
 {
-	return (uma_zalloc_smr(buf_trie_zone, M_NOWAIT));
+	void *res;
+
+	/* Spin to accommodate potential SMR free latency. */
+	for (;;) {
+		res = uma_zalloc_smr(buf_trie_zone, M_NOWAIT);
+		if (__predict_true(res != NULL))
+			break;
+		smr_synchronize(buf_trie_smr);
+	}
+	return (res);
 }
 
 static void
@@ -677,7 +686,8 @@
 	    NULL, NULL, pctrie_zone_init, NULL, UMA_ALIGN_PTR, 
 	    UMA_ZONE_NOFREE | UMA_ZONE_SMR);
 	buf_trie_smr = uma_zone_get_smr(buf_trie_zone);
-	uma_prealloc(buf_trie_zone, nbuf);
+	/* XXX: slop */
+	uma_prealloc(buf_trie_zone, nbuf * 3 / 2);
 
 	vnodes_created = counter_u64_alloc(M_WAITOK);
 	recycles_count = counter_u64_alloc(M_WAITOK);