Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_pdaemon.c,v
retrieving revision 1.110
diff -u -p -r1.110 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c	21 Apr 2019 15:32:18 -0000	1.110
+++ uvm/uvm_pdaemon.c	1 Jan 2020 16:05:00 -0000
@@ -915,6 +915,8 @@ uvmpd_scan_queue(void)
 #endif /* defined(VMSWAP) */
 	}
 
+	uvmpdpol_scanfini();
+
 #if defined(VMSWAP)
 	mutex_exit(&uvm_pageqlock);
 	swapcluster_flush(&swc, true);
@@ -1038,17 +1040,39 @@ uvm_estimatepageable(int *active, int *i
 static void
 uvmpd_pool_drain_thread(void *arg)
 {
-	int bufcnt;
+	struct pool *firstpool, *curpool;
+	int bufcnt, lastslept;
+	bool cycled;
 
+	firstpool = NULL;
+	cycled = true;
 	for (;;) {
+		/*
+		 * sleep until awoken by the pagedaemon.
+		 */
 		mutex_enter(&uvmpd_pool_drain_lock);
 		if (!uvmpd_pool_drain_run) {
+			lastslept = hardclock_ticks;
 			cv_wait(&uvmpd_pool_drain_cv, &uvmpd_pool_drain_lock);
+			if (hardclock_ticks != lastslept) {
+				cycled = false;
+				firstpool = NULL;
+			}
 		}
 		uvmpd_pool_drain_run = false;
 		mutex_exit(&uvmpd_pool_drain_lock);
 
 		/*
+		 * rate limit draining, otherwise in desperate circumstances
+		 * this can totally saturate the system with xcall activity.
+		 */
+		if (cycled) {
+			kpause("uvmpdlmt", false, 1, NULL);
+			cycled = false;
+			firstpool = NULL;
+		}
+
+		/*
 		 * kill unused metadata buffers.
 		 */
 		mutex_spin_enter(&uvm_fpageqlock);
@@ -1064,7 +1088,13 @@ uvmpd_pool_drain_thread(void *arg)
 		/*
 		 * drain a pool.
 		 */
-		pool_drain(NULL);
+		(void)pool_drain(&curpool);
+		KASSERT(curpool != NULL);
+		if (firstpool == NULL) {
+			firstpool = curpool;
+		} else if (firstpool == curpool) {
+			cycled = true;
+		}
 	}
 	/*NOTREACHED*/
 }
Index: uvm/uvm_pdpolicy.h
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_pdpolicy.h,v
retrieving revision 1.3
diff -u -p -r1.3 uvm_pdpolicy.h
--- uvm/uvm_pdpolicy.h	21 Feb 2007 23:00:14 -0000	1.3
+++ uvm/uvm_pdpolicy.h	1 Jan 2020 16:05:00 -0000
@@ -51,6 +51,7 @@ void uvmpdpol_anfree(struct vm_anon *);
 
 void uvmpdpol_tune(void);
 void uvmpdpol_scaninit(void);
+void uvmpdpol_scanfini(void);
 struct vm_page *uvmpdpol_selectvictim(void);
 void uvmpdpol_balancequeue(int);
 
Index: uvm/uvm_pdpolicy_clock.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_pdpolicy_clock.c,v
retrieving revision 1.17
diff -u -p -r1.17 uvm_pdpolicy_clock.c
--- uvm/uvm_pdpolicy_clock.c	30 Jan 2012 17:21:52 -0000	1.17
+++ uvm/uvm_pdpolicy_clock.c	1 Jan 2020 16:05:00 -0000
@@ -105,9 +105,8 @@ struct uvmpdpol_globalstate {
 };
 
 struct uvmpdpol_scanstate {
-	bool ss_first;
 	bool ss_anonreact, ss_filereact, ss_execreact;
-	struct vm_page *ss_nextpg;
+	struct vm_page ss_marker;
 };
 
 static struct uvmpdpol_globalstate pdpol_state;
@@ -160,8 +159,18 @@ uvmpdpol_scaninit(void)
 	ss->ss_anonreact = anonreact;
 	ss->ss_filereact = filereact;
 	ss->ss_execreact = execreact;
+	memset(&ss->ss_marker, 0, sizeof(ss->ss_marker));
+	ss->ss_marker.flags = PG_MARKER;
+	TAILQ_INSERT_HEAD(&pdpol_state.s_inactiveq, &ss->ss_marker,
+	    pageq.queue);
+}
+
+void
+uvmpdpol_scanfini(void)
+{
+	struct uvmpdpol_scanstate *ss = &pdpol_scanstate;
 
-	ss->ss_first = true;
+	TAILQ_REMOVE(&pdpol_state.s_inactiveq, &ss->ss_marker, pageq.queue);
 }
 
 struct vm_page *
@@ -177,20 +186,11 @@ uvmpdpol_selectvictim(void)
 		struct vm_anon *anon;
 		struct uvm_object *uobj;
 
-		if (ss->ss_first) {
-			pg = TAILQ_FIRST(&pdpol_state.s_inactiveq);
-			ss->ss_first = false;
-		} else {
-			pg = ss->ss_nextpg;
-			if (pg != NULL && (pg->pqflags & PQ_INACTIVE) == 0) {
-				pg = TAILQ_FIRST(&pdpol_state.s_inactiveq);
-			}
-		}
+		pg = TAILQ_NEXT(&ss->ss_marker, pageq.queue);
 		if (pg == NULL) {
 			break;
 		}
-		ss->ss_nextpg = TAILQ_NEXT(pg, pageq.queue);
-
+		KASSERT((pg->flags & PG_MARKER) == 0);
 		uvmexp.pdscans++;
 
 		/*
@@ -213,6 +213,15 @@ uvmpdpol_selectvictim(void)
 		uobj = pg->uobject;
 
 		/*
+		 * now prepare to move on to the next page.
+		 */
+
+		TAILQ_REMOVE(&pdpol_state.s_inactiveq, &ss->ss_marker,
+		    pageq.queue);
+		TAILQ_INSERT_AFTER(&pdpol_state.s_inactiveq, pg,
+		    &ss->ss_marker, pageq.queue);
+
+		/*
 		 * enforce the minimum thresholds on different
 		 * types of memory usage.  if reusing the current
 		 * page would reduce that type of usage below its
Index: uvm/uvm_pdpolicy_clockpro.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_pdpolicy_clockpro.c,v
retrieving revision 1.17
diff -u -p -r1.17 uvm_pdpolicy_clockpro.c
--- uvm/uvm_pdpolicy_clockpro.c	20 Jun 2011 23:18:58 -0000	1.17
+++ uvm/uvm_pdpolicy_clockpro.c	1 Jan 2020 16:05:00 -0000
@@ -1190,6 +1190,12 @@ uvmpdpol_scaninit(void)
 	ss->ss_nscanned = 0;
 }
 
+void
+uvmpdpol_scanfini(void)
+{
+
+}
+
 struct vm_page *
 uvmpdpol_selectvictim(void)
 {