Fix a performance problem with the new getnewbuf() code: in an outofspace

condition ( bufspace > hibufspace ), an inappropriate scan of the empty
queue was performed looking for buffer space to free up.

Submitted by:	Matthew Dillon <dillon@apollo.backplane.com>

1 files changed, 30 insertions, 26 deletions

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 3cc6b94..58d463b 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -11,7 +11,7 @@
  * 2. Absolutely no warranty of function or purpose is made by the author
  *		John S. Dyson.
  *
- * $Id: vfs_bio.c,v 1.203 1999/03/19 10:17:44 bde Exp $
+ * $Id: vfs_bio.c,v 1.204 1999/04/05 19:38:30 julian Exp $
  */
 
 /*
@@ -1132,6 +1132,29 @@ getnewbuf(struct vnode *vp, daddr_t blkno,
 	int countawrites = 0;
 	
 restart:
+	/*
+	 * Calculate whether we are out of buffer space.  This state is
+	 * recalculated on every restart.  If we are out of space, we
+	 * have to turn off defragmentation.  The outofspace code will
+	 * defragment too, but the looping conditionals will be messed up
+	 * if both outofspace and defrag are on.
+	 */
+
+	outofspace = 0;
+	if (bufspace >= hibufspace) {
+		if ((curproc->p_flag & P_FLSINPROG) == 0 ||
+		    bufspace >= maxbufspace
+		) {
+			outofspace = 1;
+			defrag = 0;
+		}
+	}
+
+	/*
+	 * defrag state is semi-persistant.  1 means we are flagged for
+	 * defragging.  -1 means we actually defragged something.
+	 */
+	/* nop */
 
 	/*
 	 * Setup for scan.  If we do not have enough free buffers,
@@ -1139,6 +1162,9 @@ restart:
 	 *
 	 * If we are in the middle of a flush, we can dip into the
 	 * emergency reserve.
+	 *
+	 * If we are out of space, we skip trying to scan QUEUE_EMPTY
+	 * because those buffers are, well, empty.
 	 */
 
 	if ((curproc->p_flag & P_FLSINPROG) == 0 &&
@@ -1148,7 +1174,9 @@ restart:
 		nbp = NULL;
 	} else {
 		nqindex = QUEUE_EMPTY;
-		if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY])) == NULL) {
+		if (outofspace || 
+		    (nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY])) == NULL
+		) {
 			nqindex = QUEUE_AGE;
 			nbp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
 			if (nbp == NULL) {
@@ -1159,30 +1187,6 @@ restart:
 	}
 
 	/*
-	 * Calculate whether we are out of buffer space.  This state is
-	 * recalculated on every restart.  If we are out of space, we
-	 * have to turn off defragmentation.  The outofspace code will
-	 * defragment too, but the looping conditionals will be messed up
-	 * if both outofspace and defrag are on.
-	 */
-
-	outofspace = 0;
-	if (bufspace >= hibufspace) {
-		if ((curproc->p_flag & P_FLSINPROG) == 0 ||
-		    bufspace >= maxbufspace
-		) {
-			outofspace = 1;
-			defrag = 0;
-		}
-	}
-
-	/*
-	 * defrag state is semi-persistant.  1 means we are flagged for
-	 * defragging.  -1 means we actually defragged something.
-	 */
-	/* nop */
-
-	/*
 	 * Run scan, possibly freeing data and/or kva mappings on the fly
 	 * depending.
 	 */