From: Martin Pieuchot <mpi@grenadille.net>
Subject: uvm_fault: loaned pages leftovers
To: tech@openbsd.org
Date: Fri, 3 Jan 2025 16:39:33 +0100

OpenBSD's UVM doesn't have support for loaned pages.  Diff below removes
dead code related to such pages.

I've been hitting this hard on my 24 CPUs amd64.  ok?

Index: uvm/uvm_fault.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_fault.c,v
diff -u -p -r1.158 uvm_fault.c
--- uvm/uvm_fault.c	27 Dec 2024 12:04:40 -0000	1.158
+++ uvm/uvm_fault.c	1 Jan 2025 15:31:38 -0000
@@ -321,16 +321,9 @@ uvmfault_anonget(struct uvm_faultinfo *u
 			 * The last unlock must be an atomic unlock and wait
 			 * on the owner of page.
 			 */
-			if (pg->uobject) {
-				/* Owner of page is UVM object. */
-				uvmfault_unlockall(ufi, amap, NULL);
-				uvm_pagewait(pg, pg->uobject->vmobjlock,
-				    "anonget1");
-			} else {
-				/* Owner of page is anon. */
-				uvmfault_unlockall(ufi, NULL, NULL);
-				uvm_pagewait(pg, anon->an_lock, "anonget2");
-			}
+			KASSERT(pg->uobject == NULL);
+			uvmfault_unlockall(ufi, NULL, NULL);
+			uvm_pagewait(pg, anon->an_lock, "anonget");
 		} else {
 			/*
 			 * No page, therefore allocate one.
@@ -998,8 +997,6 @@ uvm_fault_upper(struct uvm_faultinfo *uf
 	 * if it fails (!OK) it will unlock everything for us.
 	 * if it succeeds, locks are still valid and locked.
 	 * also, if it is OK, then the anon's page is on the queues.
-	 * if the page is on loan from a uvm_object, then anonget will
-	 * lock that object for us if it does not fail.
 	 */
 	error = uvmfault_anonget(ufi, amap, anon);
 	switch (error) {