Index: sys/uvm/pmap/pmap_segtab.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/pmap/pmap_segtab.c,v
retrieving revision 1.15
diff -p -u -r1.15 pmap_segtab.c
--- sys/uvm/pmap/pmap_segtab.c	7 Aug 2020 07:19:45 -0000	1.15
+++ sys/uvm/pmap/pmap_segtab.c	17 Aug 2020 04:23:38 -0000
@@ -137,11 +137,11 @@ pmap_check_stp(pmap_segtab_t *stp, const
 #ifdef DEBUG
 	for (size_t i = 0; i < PMAP_SEGTABSIZE; i++) {
 		if (stp->seg_tab[i] != 0) {
-#ifdef DEBUG_NOISY
+//#ifdef DEBUG_NOISY
 			for (size_t j = i; j < PMAP_SEGTABSIZE; j++)
 				printf("%s: pm_segtab.seg_tab[%zu] = %p\n",
 				    caller, j, stp->seg_tab[j]);
-#endif
+//#endif
 			panic("%s: pm_segtab.seg_tab[%zu] != 0 (%p): %s",
 			    caller, i, stp->seg_tab[i], why);
 		}
@@ -210,12 +210,18 @@ pmap_segtab_release(pmap_t pmap, pmap_se
 {
 	pmap_segtab_t *stp = *stp_p;
 
+	UVMHIST_FUNC(__func__);
+	UVMHIST_CALLARGS(pmaphist, "pm=%#jx stpp=%#jx free=%jd",
+	    (uintptr_t)pmap, (uintptr_t)stp_p, free_stp, 0);
+	UVMHIST_LOG(pmaphist, " callback=%jx flags=%jx va=%jx vinc=%jx",
+	    (uintptr_t)callback, flags, (uintptr_t)va, (uintptr_t)vinc);
 	for (size_t i = (va / vinc) & (PMAP_SEGTABSIZE - 1);
 	     i < PMAP_SEGTABSIZE;
 	     i++, va += vinc) {
 #ifdef _LP64
 		if (vinc > NBSEG) {
 			if (stp->seg_seg[i] != NULL) {
+				UVMHIST_LOG(pmaphist, " recursing", 0, 0, 0, 0);
 				pmap_segtab_release(pmap, &stp->seg_seg[i],
 				    true, callback, flags, va, vinc / NSEGPG);
 				KASSERT(stp->seg_seg[i] == NULL);
@@ -255,6 +261,7 @@ pmap_segtab_release(pmap_t pmap, pmap_se
 #endif
 
 		stp->seg_tab[i] = NULL;
+		UVMHIST_LOG(pmaphist, " zeroing tab[%jd]", i, 0, 0, 0);
 	}
 
 	if (free_stp) {
@@ -448,6 +455,10 @@ pmap_pte_reserve(pmap_t pmap, vaddr_t va
 	pmap_segtab_t *stp = pmap->pm_segtab;
 	pt_entry_t *pte;
 
+	UVMHIST_FUNC(__func__);
+	UVMHIST_CALLARGS(pmaphist, "pm=%#jx va=%#jx flags=%jx",
+	    (uintptr_t)pmap, (uintptr_t)va, flags, 0);
+
 	pte = pmap_pte_lookup(pmap, va);
 	if (__predict_false(pte == NULL)) {
 #ifdef _LP64
@@ -513,6 +524,8 @@ pmap_pte_reserve(pmap_t pmap, vaddr_t va
 		*pte_p = pte;
 #endif
 		KASSERT(pte == stp->seg_tab[(va >> SEGSHIFT) & (PMAP_SEGTABSIZE - 1)]);
+		UVMHIST_LOG(pmaphist, " set tab[%jd]=%jx",
+		    (va >> SEGSHIFT) & (PMAP_SEGTABSIZE - 1), pte, 0, 0);
 
 #ifdef DEBUG
 		for (size_t i = 0; i < NPTEPG; i++) {