Tweak the code that wakes up uvm_pmalloc sleepers in the page daemin.

Although there are open questions about whether we should flag failures with
UVM_PMA_FAIL or not, we really should only wake up a sleeper if we unlink
the pma.  For now only do that if pages were actually freed in the requested
region.

Prompted by:

CID 1453061 Logically dead code

which should be fixed by this commit.

ok (and together with) beck@

sys/uvm/uvm_pdaemon.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_pdaemon.c,v 1.85 2019/12/30 23:58:38 jsg Exp $	*/
+/*	$OpenBSD: uvm_pdaemon.c,v 1.86 2020/04/04 22:08:02 kettenis Exp $	*/
 /*	$NetBSD: uvm_pdaemon.c,v 1.23 2000/08/20 10:24:14 bjh21 Exp $	*/
 
 /* 
@@ -210,7 +210,6 @@ uvm_pageout(void *arg)
 {
 	struct uvm_constraint_range constraint;
 	struct uvm_pmalloc *pma;
-	int work_done;
 	int npages = 0;
 
 	/* ensure correct priority and set paging parameters... */
@@ -223,7 +222,6 @@ uvm_pageout(void *arg)
 
 	for (;;) {
 		long size;
-	  	work_done = 0; /* No work done this iteration. */
 
 		uvm_lock_fpageq();
 		if (!uvm_nowait_failed && TAILQ_EMPTY(&uvm.pmr_control.allocs)) {
@@ -282,7 +280,6 @@ uvm_pageout(void *arg)
 		    ((uvmexp.free - BUFPAGES_DEFICIT) < uvmexp.freetarg) ||
 		    ((uvmexp.inactive + BUFPAGES_INACT) < uvmexp.inactarg)) {
 			uvmpd_scan();
-			work_done = 1; /* XXX we hope... */
 		}
 
 		/*
@@ -296,15 +293,18 @@ uvm_pageout(void *arg)
 		}
 
 		if (pma != NULL) {
+			/* 
+			 * XXX If UVM_PMA_FREED isn't set, no pages
+			 * were freed.  Should we set UVM_PMA_FAIL in
+			 * that case?
+			 */
 			pma->pm_flags &= ~UVM_PMA_BUSY;
-			if (!work_done)
-				pma->pm_flags |= UVM_PMA_FAIL;
-			if (pma->pm_flags & (UVM_PMA_FAIL | UVM_PMA_FREED)) {
+			if (pma->pm_flags & UVM_PMA_FREED) {
 				pma->pm_flags &= ~UVM_PMA_LINKED;
 				TAILQ_REMOVE(&uvm.pmr_control.allocs, pma,
 				    pmq);
+				wakeup(pma);
 			}
-			wakeup(pma);
 		}
 		uvm_unlock_fpageq();