When the kernel decides to move a page to the inactive list, with
uvm_pagedeactivate(), it also remove its pmap references to ensure
the next access will generate a fault.

Diff below moves the pmap_page_protect(9) call inside uvm_pagedeactivate().

This is a baby step towards reducing the contention on the `pageqlock'.

I'm aware that many more improvements are possible.  I'm trying to move
very slowly to not introduce too many changes in behavior and expose
existing bugs.  That's why I'm keeping the existing behavior of always
calling pmap_page_protect(9) inside uvm_pagedeactivate().

Note that currently, one call to uvm_pagedeactivate() is not coupled with
a pmap_page_protect(), the diff below fixes that/makes it coherent.

ok?

Index: uvm/uvm_anon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_anon.c,v
diff -u -p -r1.60 uvm_anon.c
--- uvm/uvm_anon.c	24 Dec 2024 08:39:30 -0000	1.60
+++ uvm/uvm_anon.c	24 Dec 2024 09:40:07 -0000
@@ -202,7 +202,6 @@ uvm_anon_pagein(struct vm_amap *amap, st
 	/*
 	 * Deactivate the page (to put it on a page queue).
 	 */
-	pmap_page_protect(pg, PROT_NONE);
 	uvm_lock_pageq();
 	uvm_pagedeactivate(pg);
 	uvm_unlock_pageq();
Index: uvm/uvm_aobj.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_aobj.c,v
diff -u -p -r1.114 uvm_aobj.c
--- uvm/uvm_aobj.c	24 Dec 2024 08:39:30 -0000	1.114
+++ uvm/uvm_aobj.c	24 Dec 2024 09:40:08 -0000
@@ -930,7 +930,6 @@ uao_flush(struct uvm_object *uobj, voff_
 				continue;
 
 			uvm_lock_pageq();
-			pmap_page_protect(pg, PROT_NONE);
 			uvm_pagedeactivate(pg);
 			uvm_unlock_pageq();
 
Index: uvm/uvm_fault.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_fault.c,v
diff -u -p -r1.157 uvm_fault.c
--- uvm/uvm_fault.c	24 Dec 2024 08:55:48 -0000	1.157
+++ uvm/uvm_fault.c	24 Dec 2024 09:40:08 -0000
@@ -185,7 +185,6 @@ uvmfault_anonflush(struct vm_anon **anon
 		if (pg && (pg->pg_flags & PG_BUSY) == 0) {
 			uvm_lock_pageq();
 			if (pg->wire_count == 0) {
-				pmap_page_protect(pg, PROT_NONE);
 				uvm_pagedeactivate(pg);
 			}
 			uvm_unlock_pageq();
Index: uvm/uvm_map.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_map.c,v
diff -u -p -r1.336 uvm_map.c
--- uvm/uvm_map.c	11 Dec 2024 02:00:32 -0000	1.336
+++ uvm/uvm_map.c	24 Dec 2024 09:40:09 -0000
@@ -4524,11 +4524,6 @@ deactivate_it:
 				uvm_lock_pageq();
 
 				KASSERT(pg->uanon == anon);
-
-				/* zap all mappings for the page. */
-				pmap_page_protect(pg, PROT_NONE);
-
-				/* ...and deactivate the page. */
 				uvm_pagedeactivate(pg);
 
 				uvm_unlock_pageq();
Index: uvm/uvm_page.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_page.c,v
diff -u -p -r1.179 uvm_page.c
--- uvm/uvm_page.c	20 Dec 2024 18:54:12 -0000	1.179
+++ uvm/uvm_page.c	24 Dec 2024 09:40:09 -0000
@@ -1256,7 +1256,7 @@ uvm_pageunwire(struct vm_page *pg)
 }
 
 /*
- * uvm_pagedeactivate: deactivate page -- no pmaps have access to page
+ * uvm_pagedeactivate: deactivate page.
  *
  * => caller must lock page queues
  * => caller must check to make sure page is not wired
@@ -1267,6 +1267,8 @@ uvm_pagedeactivate(struct vm_page *pg)
 {
 	KASSERT(uvm_page_owner_locked_p(pg, FALSE));
 	MUTEX_ASSERT_LOCKED(&uvm.pageqlock);
+
+	pmap_page_protect(pg, PROT_NONE);
 
 	if (pg->pg_flags & PQ_ACTIVE) {
 		TAILQ_REMOVE(&uvm.page_active, pg, pageq);
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
diff -u -p -r1.132 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c	25 Nov 2024 13:37:49 -0000	1.132
+++ uvm/uvm_pdaemon.c	24 Dec 2024 09:40:09 -0000
@@ -1020,7 +1020,6 @@ uvmpd_scan_active(struct uvm_pmalloc *pm
 		 * inactive pages.
 		 */
 		if (inactive_shortage > 0) {
-			pmap_page_protect(p, PROT_NONE);
 			/* no need to check wire_count as pg is "active" */
 			uvm_pagedeactivate(p);
 			uvmexp.pddeact++;
Index: uvm/uvm_vnode.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_vnode.c,v
diff -u -p -r1.137 uvm_vnode.c
--- uvm/uvm_vnode.c	20 Dec 2024 18:49:37 -0000	1.137
+++ uvm/uvm_vnode.c	24 Dec 2024 09:40:09 -0000
@@ -683,7 +683,6 @@ uvn_flush(struct uvm_object *uobj, voff_
 		if (!needs_clean) {
 			if (flags & PGO_DEACTIVATE) {
 				if (pp->wire_count == 0) {
-					pmap_page_protect(pp, PROT_NONE);
 					uvm_pagedeactivate(pp);
 				}
 			} else if (flags & PGO_FREE) {
@@ -809,7 +808,6 @@ ReTry:
 			/* dispose of page */
 			if (flags & PGO_DEACTIVATE) {
 				if (ptmp->wire_count == 0) {
-					pmap_page_protect(ptmp, PROT_NONE);
 					uvm_pagedeactivate(ptmp);
 				}
 			} else if (flags & PGO_FREE &&