Index: uvm_pglist.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_pglist.c,v
retrieving revision 1.88
diff -p -u -r1.88 uvm_pglist.c
--- uvm_pglist.c	26 Mar 2021 09:35:18 -0000	1.88
+++ uvm_pglist.c	30 Jul 2021 17:04:40 -0000
@@ -386,6 +386,30 @@ uvm_pglistalloc_contig_aggressive(int nu
 
 			for (i = 0; i < acnt; i++) {
 				pg = PHYS_TO_VM_PAGE(spa - alignment + ptoa(i));
+				KASSERTMSG(pg != NULL,
+					   "num %d "
+					   "low 0x%jx high 0x%jx "
+					   "alignment 0x%jx boundary 0x%jx "
+					   "pa 0x%jx upm %p "
+					   "upmstart 0x%jx upmend 0x%jx "
+					   "rlo 0x%jx rhi 0x%jx "
+					   "spa 0x%jx i %d",
+					   num,
+					   (uintmax_t)low,
+					   (uintmax_t)high,
+					   (uintmax_t)alignment,
+					   (uintmax_t)boundary,
+					   (uintmax_t)pa,
+					   (void *)(uintptr_t)upm,
+					   (uintmax_t)
+					   ptoa(uvm_physseg_get_avail_start(upm)),
+					   (uintmax_t)
+					   ptoa(uvm_physseg_get_avail_end(upm)),
+					   (uintmax_t)rlo,
+					   (uintmax_t)rhi,
+					   (uintmax_t)spa,
+					   i);
+
 				if ((pg->flags & PG_PGLCA) == 0) {
 					break;
 				}
@@ -406,6 +430,29 @@ uvm_pglistalloc_contig_aggressive(int nu
 		}
 		for (; run < num; run++) {
 			pg = PHYS_TO_VM_PAGE(spa + ptoa(run));
+				KASSERTMSG(pg != NULL,
+					   "num %d "
+					   "low 0x%jx high 0x%jx "
+					   "alignment 0x%jx boundary 0x%jx "
+					   "pa 0x%jx upm %p "
+					   "upmstart 0x%jx upmend 0x%jx "
+					   "rlo 0x%jx rhi 0x%jx "
+					   "spa 0x%jx run %d",
+					   num,
+					   (uintmax_t)low,
+					   (uintmax_t)high,
+					   (uintmax_t)alignment,
+					   (uintmax_t)boundary,
+					   (uintmax_t)pa,
+					   (void *)(uintptr_t)upm,
+					   (uintmax_t)
+					   ptoa(uvm_physseg_get_avail_start(upm)),
+					   (uintmax_t)
+					   ptoa(uvm_physseg_get_avail_end(upm)),
+					   (uintmax_t)rlo,
+					   (uintmax_t)rhi,
+					   (uintmax_t)spa,
+					   run);
 			if ((pg->flags & PG_PGLCA) == 0) {
 				break;
 			}