diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -1302,7 +1302,7 @@
 static bool	pmap_demote_pde_locked(pmap_t pmap, pd_entry_t *pde,
     vm_offset_t va, struct rwlock **lockp);
 static bool	pmap_demote_pdpe(pmap_t pmap, pdp_entry_t *pdpe,
-    vm_offset_t va);
+    vm_offset_t va, vm_page_t *mp);
 static int	pmap_enter_2mpage(pmap_t pmap, vm_offset_t va, vm_page_t m,
 		    vm_prot_t prot, struct rwlock **lockp);
 static int	pmap_enter_pde(pmap_t pmap, vm_offset_t va, pd_entry_t newpde,
@@ -1311,7 +1311,7 @@
     vm_page_t m, vm_prot_t prot, vm_page_t mpte, struct rwlock **lockp);
 static void pmap_fill_ptp(pt_entry_t *firstpte, pt_entry_t newpte);
 static int pmap_insert_pt_page(pmap_t pmap, vm_page_t mpte, bool promoted,
-    bool allpte_PG_A_set);
+    bool allpte_PG_A_set, void *node);
 static void pmap_invalidate_cache_range_selfsnoop(vm_offset_t sva,
     vm_offset_t eva);
 static void pmap_invalidate_cache_range_all(vm_offset_t sva,
@@ -2541,7 +2541,7 @@
 		 */
 		if ((i == 0 ||
 		    kernphys + ((vm_paddr_t)(i - 1) << PDRSHIFT) < KERNend) &&
-		    pmap_insert_pt_page(kernel_pmap, mpte, false, false))
+		    pmap_insert_pt_page(kernel_pmap, mpte, false, false, NULL))
 			panic("pmap_init: pmap_insert_pt_page failed");
 	}
 	PMAP_UNLOCK(kernel_pmap);
@@ -4153,14 +4153,21 @@
  */
 static __inline int
 pmap_insert_pt_page(pmap_t pmap, vm_page_t mpte, bool promoted,
-    bool allpte_PG_A_set)
+    bool allpte_PG_A_set, void *node)
 {
+	int res;
 
 	PMAP_LOCK_ASSERT(pmap, MA_OWNED);
 	KASSERT(promoted || !allpte_PG_A_set,
 	    ("a zero-filled PTP can't have PG_A set in every PTE"));
 	mpte->valid = promoted ? (allpte_PG_A_set ? VM_PAGE_BITS_ALL : 1) : 0;
-	return (vm_radix_insert(&pmap->pm_root, mpte));
+	if (node == NULL) {
+		res = vm_radix_insert(&pmap->pm_root, mpte);
+	} else {
+		vm_radix_insert_prealloc(&pmap->pm_root, mpte, node);
+		res = 0;
+	}
+	return (res);
 }
 
 /*
@@ -7070,7 +7077,7 @@
 	    ("pmap_promote_pde: page table page's pindex is wrong "
 	    "mpte %p pidx %#lx va %#lx va pde pidx %#lx",
 	    mpte, mpte->pindex, va, pmap_pde_pindex(va)));
-	if (pmap_insert_pt_page(pmap, mpte, true, allpte_PG_A != 0)) {
+	if (pmap_insert_pt_page(pmap, mpte, true, allpte_PG_A != 0, NULL)) {
 		counter_u64_add(pmap_pde_p_failures, 1);
 		CTR2(KTR_PMAP,
 		    "pmap_promote_pde: failure for va %#lx in pmap %p", va,
@@ -7554,9 +7561,11 @@
 {
 	struct spglist free;
 	pd_entry_t oldpde, *pde;
+	void *node;
 	pt_entry_t PG_G, PG_RW, PG_V;
 	vm_page_t mt, pdpg;
 	vm_page_t uwptpg;
+	int rv;
 
 	PG_G = pmap_global_bit(pmap);
 	PG_RW = pmap_rw_bit(pmap);
@@ -7588,6 +7597,13 @@
 		return (KERN_PROTECTION_FAILURE);
 	}
 
+	node = vm_radix_node_alloc(&pmap->pm_root.rt_trie);
+	if (node == NULL) {
+		pmap_abort_ptp(pmap, va, pdpg);
+		return (KERN_RESOURCE_SHORTAGE);
+	}
+	rv = KERN_SUCCESS;
+
 	/*
 	 * If there are existing mappings, either abort or remove them.
 	 */
@@ -7602,7 +7618,8 @@
 				CTR2(KTR_PMAP,
 				    "pmap_enter_pde: no space for va %#lx"
 				    " in pmap %p", va, pmap);
-				return (KERN_NO_SPACE);
+				rv = KERN_NO_SPACE;
+				goto out;
 			} else if (va < VM_MAXUSER_ADDRESS ||
 			    !pmap_every_pte_zero(oldpde & PG_FRAME)) {
 				if (pdpg != NULL)
@@ -7610,7 +7627,8 @@
 				CTR2(KTR_PMAP,
 				    "pmap_enter_pde: failure for va %#lx"
 				    " in pmap %p", va, pmap);
-				return (KERN_FAILURE);
+				rv = KERN_FAILURE;
+				goto out;
 			}
 		}
 		/* Break the existing mapping(s). */
@@ -7645,8 +7663,9 @@
 			 * leave the kernel page table page zero filled.
 			 */
 			mt = PHYS_TO_VM_PAGE(*pde & PG_FRAME);
-			if (pmap_insert_pt_page(pmap, mt, false, false))
+			if (pmap_insert_pt_page(pmap, mt, false, false, node))
 				panic("pmap_enter_pde: trie insert failed");
+			node = NULL;
 		}
 	}
 
@@ -7659,12 +7678,14 @@
 		    VM_ALLOC_WIRED);
 		if (uwptpg == NULL) {
 			pmap_abort_ptp(pmap, va, pdpg);
-			return (KERN_RESOURCE_SHORTAGE);
+			rv = KERN_RESOURCE_SHORTAGE;
+			goto out;
 		}
-		if (pmap_insert_pt_page(pmap, uwptpg, true, false)) {
+		if (pmap_insert_pt_page(pmap, uwptpg, true, false, node)) {
 			pmap_free_pt_page(pmap, uwptpg, false);
 			pmap_abort_ptp(pmap, va, pdpg);
-			return (KERN_RESOURCE_SHORTAGE);
+			rv = KERN_RESOURCE_SHORTAGE;
+			goto out;
 		}
 
 		uwptpg->ref_count = NPTEPG;
@@ -7686,7 +7707,8 @@
 			}
 			CTR2(KTR_PMAP, "pmap_enter_pde: failure for va %#lx"
 			    " in pmap %p", va, pmap);
-			return (KERN_RESOURCE_SHORTAGE);
+			rv = KERN_RESOURCE_SHORTAGE;
+			goto out;
 		}
 		if ((newpde & PG_RW) != 0) {
 			for (mt = m; mt < &m[NBPDR / PAGE_SIZE]; mt++)
@@ -7710,7 +7732,9 @@
 	counter_u64_add(pmap_pde_mappings, 1);
 	CTR2(KTR_PMAP, "pmap_enter_pde: success for va %#lx in pmap %p",
 	    va, pmap);
-	return (KERN_SUCCESS);
+out:
+	vm_radix_node_free(&pmap->pm_root.rt_trie, node);
+	return (rv);
 }
 
 /*
@@ -9614,7 +9638,7 @@
  * Tries to demote a 1GB page mapping.
  */
 static bool
-pmap_demote_pdpe(pmap_t pmap, pdp_entry_t *pdpe, vm_offset_t va)
+pmap_demote_pdpe(pmap_t pmap, pdp_entry_t *pdpe, vm_offset_t va, vm_page_t *mp)
 {
 	pdp_entry_t newpdpe, oldpdpe;
 	pd_entry_t *firstpde, newpde, *pde;
@@ -9631,8 +9655,15 @@
 	oldpdpe = *pdpe;
 	KASSERT((oldpdpe & (PG_PS | PG_V)) == (PG_PS | PG_V),
 	    ("pmap_demote_pdpe: oldpdpe is missing PG_PS and/or PG_V"));
-	pdpg = pmap_alloc_pt_page(pmap, va >> PDPSHIFT,
-	    VM_ALLOC_WIRED | VM_ALLOC_INTERRUPT);
+	if (mp == NULL) {
+		pdpg = pmap_alloc_pt_page(pmap, va >> PDPSHIFT,
+		    VM_ALLOC_WIRED);
+	} else {
+		pdpg = *mp;
+		*mp = NULL;
+		pdpg->pindex = va >> PDPSHIFT;
+		pmap_pt_page_count_adj(pmap, 1);
+	}
 	if (pdpg  == NULL) {
 		CTR2(KTR_PMAP, "pmap_demote_pdpe: failure for va %#lx"
 		    " in pmap %p", va, pmap);
@@ -9846,7 +9877,7 @@
 				tmpva += NBPDP;
 				continue;
 			}
-			if (!pmap_demote_pdpe(kernel_pmap, pdpe, tmpva))
+			if (!pmap_demote_pdpe(kernel_pmap, pdpe, tmpva, NULL))
 				return (ENOMEM);
 		}
 		pde = pmap_pdpe_to_pde(pdpe, tmpva);
@@ -10015,6 +10046,7 @@
 {
 	pdp_entry_t *pdpe;
 	pd_entry_t *pde;
+	vm_page_t m;
 	vm_offset_t va;
 	bool changed;
 
@@ -10023,15 +10055,24 @@
 	KASSERT(powerof2(len), ("pmap_demote_DMAP: len is not a power of 2"));
 	KASSERT((base & (len - 1)) == 0,
 	    ("pmap_demote_DMAP: base is not a multiple of len"));
+	m = NULL;
 	if (len < NBPDP && base < dmaplimit) {
 		va = PHYS_TO_DMAP(base);
 		changed = false;
+
+		/*
+		 * Assume that it is fine to sleep there.  Existing
+		 * only caller of pmap_demote_DMAP() is the
+		 * x86_mr_split_dmap() function.
+		 */
+		m = vm_page_alloc_noobj(VM_ALLOC_WIRED | VM_ALLOC_WAITOK);
+
 		PMAP_LOCK(kernel_pmap);
 		pdpe = pmap_pdpe(kernel_pmap, va);
 		if ((*pdpe & X86_PG_V) == 0)
 			panic("pmap_demote_DMAP: invalid PDPE");
 		if ((*pdpe & PG_PS) != 0) {
-			if (!pmap_demote_pdpe(kernel_pmap, pdpe, va))
+			if (!pmap_demote_pdpe(kernel_pmap, pdpe, va, &m))
 				panic("pmap_demote_DMAP: PDPE failed");
 			changed = true;
 		}
@@ -10049,6 +10090,10 @@
 			pmap_invalidate_page(kernel_pmap, va);
 		PMAP_UNLOCK(kernel_pmap);
 	}
+	if (m != NULL) {
+		vm_page_unwire_noq(m);
+		vm_page_free(m);
+	}
 }
 
 /*
diff --git a/sys/vm/vm_radix.h b/sys/vm/vm_radix.h
--- a/sys/vm/vm_radix.h
+++ b/sys/vm/vm_radix.h
@@ -357,5 +357,8 @@
 	return (VM_RADIX_PCTRIE_REPLACE(&rtree->rt_trie, newpage));
 }
 
+void vm_radix_insert_prealloc(struct vm_radix *rtree, vm_page_t m,
+    void *node);
+
 #endif /* _KERNEL */
 #endif /* !_VM_RADIX_H_ */
diff --git a/sys/vm/vm_radix.c b/sys/vm/vm_radix.c
--- a/sys/vm/vm_radix.c
+++ b/sys/vm/vm_radix.c
@@ -124,3 +124,19 @@
 {
 	uma_zwait(vm_radix_node_zone);
 }
+
+void
+vm_radix_insert_prealloc(struct vm_radix *rtree, vm_page_t m, void *node)
+{
+	struct pctrie *ptree;
+	void *parentp;
+	struct pctrie_node *child, *parent;
+	uint64_t *val;
+
+	ptree = &rtree->rt_trie;
+	val = VM_RADIX_PCTRIE_PTR2VAL(m);
+	child = node;
+	parentp = pctrie_insert_lookup_strict(ptree, val, &parent);
+	if (parentp != NULL)
+		pctrie_insert_node(val, parent, parentp, child);
+}