Index: sys/vm/vm_phys.h
===================================================================
--- sys/vm/vm_phys.h
+++ sys/vm/vm_phys.h
@@ -69,6 +69,7 @@
 	vm_paddr_t	start;
 	vm_paddr_t	end;
 	vm_page_t	first_page;
+	int		first_superpage;
 	int		domain;
 	struct vm_freelist (*free_queues)[VM_NFREEPOOL][VM_NFREEORDER_MAX];
 };
@@ -96,6 +97,7 @@
 void vm_phys_free_pages(vm_page_t m, int order);
 void vm_phys_init(void);
 vm_page_t vm_phys_paddr_to_vm_page(vm_paddr_t pa);
+int vm_phys_paddr_to_superpage_index(vm_paddr_t pa);
 void vm_phys_register_domains(int ndomains, struct mem_affinity *affinity,
     int *locality);
 vm_page_t vm_phys_scan_contig(int domain, u_long npages, vm_paddr_t low,
Index: sys/vm/vm_phys.c
===================================================================
--- sys/vm/vm_phys.c
+++ sys/vm/vm_phys.c
@@ -72,6 +72,11 @@
 _Static_assert(sizeof(long) * NBBY >= VM_PHYSSEG_MAX,
     "Too many physsegs.");
 
+#if VM_NRESERVLEVEL > 0
+#define	VM_LEVEL_0_SHIFT	(VM_LEVEL_0_ORDER + PAGE_SHIFT)
+#define	VM_LEVEL_0_SIZE		(1 << VM_LEVEL_0_SHIFT)
+#endif
+
 #ifdef NUMA
 struct mem_affinity __read_mostly *mem_affinity;
 int __read_mostly *mem_locality;
@@ -489,6 +494,10 @@
 {
 	struct vm_freelist *fl;
 	struct vm_phys_seg *end_seg, *prev_seg, *seg, *tmp_seg;
+#if VM_NRESERVLEVEL > 0
+	vm_pindex_t l0_start, l0_end, l0_end_prev;
+	u_long nl0;
+#endif
 	u_long npages;
 	int dom, flind, freelist, oind, pind, segind;
 
@@ -543,6 +552,10 @@
 	 */
 #ifdef VM_PHYSSEG_SPARSE
 	npages = 0;
+#endif
+#if VM_NRESERVLEVEL > 0
+	nl0 = 0;
+	l0_end_prev = 0;
 #endif
 	for (segind = 0; segind < vm_phys_nsegs; segind++) {
 		seg = &vm_phys_segs[segind];
@@ -552,6 +565,17 @@
 #else
 		seg->first_page = PHYS_TO_VM_PAGE(seg->start);
 #endif
+#if VM_NRESERVLEVEL > 0
+		l0_start = seg->start >> VM_LEVEL_0_SHIFT;
+		l0_end = roundup2(seg->end, VM_LEVEL_0_SIZE) >> VM_LEVEL_0_SHIFT;
+		seg->first_superpage = nl0;
+		nl0 += l0_end - l0_start;
+		if (l0_end_prev > l0_start) {
+			seg->first_superpage--;
+			nl0--;
+		}
+		l0_end_prev = l0_end;
+#endif
 #ifdef	VM_FREELIST_LOWMEM
 		if (seg->end <= VM_LOWMEM_BOUNDARY) {
 			flind = vm_freelist_to_flind[VM_FREELIST_LOWMEM];
@@ -910,6 +934,24 @@
 	return (NULL);
 }
 
+#if VM_NRESERVLEVEL > 0
+int
+vm_phys_paddr_to_superpage_index(vm_paddr_t pa)
+{
+	struct vm_phys_seg *seg;
+	int segind;
+
+	for (segind = 0; segind < vm_phys_nsegs; segind++) {
+		seg = &vm_phys_segs[segind];
+		if (pa >= seg->start && pa < seg->end)
+			return (seg->first_superpage +
+			    (pa >> VM_LEVEL_0_SHIFT) -
+			    (seg->start >> VM_LEVEL_0_SHIFT));
+	}
+	panic("pa 0x%lx not within vm_phys_segs", pa);
+}
+#endif
+
 vm_page_t
 vm_phys_fictitious_to_vm_page(vm_paddr_t pa)
 {
Index: sys/vm/vm_reserv.c
===================================================================
--- sys/vm/vm_reserv.c
+++ sys/vm/vm_reserv.c
@@ -1,3 +1,4 @@
+
 /*-
  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
  *
@@ -233,6 +234,8 @@
  */
 static vm_reserv_t vm_reserv_array;
 
+#define PHYS_TO_VM_RESERV(pa) &vm_reserv_array[vm_phys_paddr_to_superpage_index(pa)]
+
 /*
  * The per-domain partially populated reservation queues
  *
@@ -335,7 +338,7 @@
 		paddr = roundup2(seg->start, VM_LEVEL_0_SIZE);
 		while (paddr + VM_LEVEL_0_SIZE > paddr && paddr +
 		    VM_LEVEL_0_SIZE <= seg->end) {
-			rv = &vm_reserv_array[paddr >> VM_LEVEL_0_SHIFT];
+			rv = PHYS_TO_VM_RESERV(paddr);
 			fullpop += rv->popcnt == VM_LEVEL_0_NPAGES;
 			paddr += VM_LEVEL_0_SIZE;
 		}
@@ -497,7 +500,7 @@
 vm_reserv_from_page(vm_page_t m)
 {
 
-	return (&vm_reserv_array[VM_PAGE_TO_PHYS(m) >> VM_LEVEL_0_SHIFT]);
+	return (PHYS_TO_VM_RESERV(VM_PAGE_TO_PHYS(m)));
 }
 
 /*
@@ -1065,7 +1068,7 @@
 		paddr = roundup2(seg->start, VM_LEVEL_0_SIZE);
 		while (paddr + VM_LEVEL_0_SIZE > paddr && paddr +
 		    VM_LEVEL_0_SIZE <= seg->end) {
-			rv = &vm_reserv_array[paddr >> VM_LEVEL_0_SHIFT];
+			rv = PHYS_TO_VM_RESERV(paddr);
 			rv->pages = PHYS_TO_VM_PAGE(paddr);
 			rv->domain = seg->domain;
 			mtx_init(&rv->lock, "vm reserv", NULL, MTX_DEF);
@@ -1400,20 +1403,19 @@
 vm_paddr_t
 vm_reserv_startup(vm_offset_t *vaddr, vm_paddr_t end)
 {
-	vm_paddr_t new_end, high_water;
+	vm_paddr_t new_end;
 	size_t size;
-	int i;
+	int count, i;
 
-	high_water = phys_avail[1];
+	count = 0;
 	for (i = 0; i < vm_phys_nsegs; i++) {
-		if (vm_phys_segs[i].end > high_water)
-			high_water = vm_phys_segs[i].end;
+		count += howmany(vm_phys_segs[i].end, VM_LEVEL_0_SIZE) -
+		    vm_phys_segs[i].start / VM_LEVEL_0_SIZE;
 	}
 
-	/* Skip the first chunk.  It is already accounted for. */
-	for (i = 2; phys_avail[i + 1] != 0; i += 2) {
-		if (phys_avail[i + 1] > high_water)
-			high_water = phys_avail[i + 1];
+	for (i = 0; phys_avail[i + 1] != 0; i += 2) {
+		count += howmany(phys_avail[i + 1], VM_LEVEL_0_SIZE) -
+		    phys_avail[i] / VM_LEVEL_0_SIZE;
 	}
 
 	/*
@@ -1423,7 +1425,7 @@
 	 * number of elements in the reservation array can be greater than the
 	 * number of superpages. 
 	 */
-	size = howmany(high_water, VM_LEVEL_0_SIZE) * sizeof(struct vm_reserv);
+	size = count * sizeof(struct vm_reserv);
 
 	/*
 	 * Allocate and map the physical memory for the reservation array.  The