Always back the buffer cache off on any page daemon wakeup. This avoids

a few problems noticed by phessler@ and beck@ where certain allocations
would repeatedly wake the page daemon even though the page daemon's targets
were met already so it didn't do any work. We can avoid this problem when
the buffer cache has pages to throw away by always doing so any time
the page daemon is woken, rather than only when we are under the free
page target.
ok phessler@ deraadt@

1 files changed, 14 insertions, 22 deletions

diff --git a/sys/uvm/uvm_pdaemon.c b/sys/uvm/uvm_pdaemon.c
index 47f85afc638..d85750a839d 100644
--- a/sys/uvm/uvm_pdaemon.c
+++ b/sys/uvm/uvm_pdaemon.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_pdaemon.c,v 1.60 2012/11/07 17:50:49 beck Exp $	*/
+/*	$OpenBSD: uvm_pdaemon.c,v 1.61 2012/12/10 22:42:54 beck Exp $	*/
 /*	$NetBSD: uvm_pdaemon.c,v 1.23 2000/08/20 10:24:14 bjh21 Exp $	*/
 
 /* 
@@ -208,6 +208,7 @@ uvm_pageout(void *arg)
 	 */
 
 	for (;;) {
+		long size;
 	  	work_done = 0; /* No work done this iteration. */
 
 		uvm_lock_fpageq();
@@ -242,31 +243,22 @@ uvm_pageout(void *arg)
 		}
 
 		/*
-		 * get pages from the buffer cache, or scan if needed
+		 * Reclaim pages from the buffer cache if possible.
+		 */
+		size = 0;
+		if (pma != NULL)
+			size += pma->pm_size >> PAGE_SHIFT;
+		if (uvmexp.free - BUFPAGES_DEFICIT < uvmexp.freetarg)
+			size += uvmexp.freetarg - uvmexp.free -
+			    BUFPAGES_DEFICIT;
+		(void) bufbackoff(&constraint, size * 2);
+
+		/*
+		 * Scan if needed to meet our targets.
 		 */
 		if (pma != NULL ||
 		    ((uvmexp.free - BUFPAGES_DEFICIT) < uvmexp.freetarg) ||
 		    ((uvmexp.inactive + BUFPAGES_INACT) < uvmexp.inactarg)) {
-			u_int64_t free, size;
-			free = uvmexp.free - BUFPAGES_DEFICIT;
-			/* start with the size of what we are asking for */
-			size = pma ? pma->pm_size : 0;
-			/*
-			 * If we below our target, add twice the amount
-			 * we are below the target to what we will ask
-			 * the buffer cache to give back. We then ask
-			 * the buffer cache to give us free pages by
-			 * backing off.
-			 */
-			if (uvmexp.freetarg - free > 0)
-				size += (uvmexp.freetarg - free) * 2;
-			(void) bufbackoff(&constraint, size);
-			/*
-			 * Now we scan to ensure we meet all our targets,
-			 * we will not swap at this point, unless the buffer
-			 * cache could not back off enough for us to meet
-			 * our free page targets.
-			 */
 			uvmpd_scan();
 			work_done = 1; /* XXX we hope... */
 		}