diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index 1ad51b5afdaa..41c4a1edfb50 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -1,4 +1,41 @@
-/*	$NetBSD: uipc_mbuf.c,v 1.41 1999/04/25 03:03:03 simonb Exp $	*/
+/*	$NetBSD: uipc_mbuf.c,v 1.42 1999/04/26 22:04:28 thorpej Exp $	*/
+
+/*-
+ * Copyright (c) 1999 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
+ * NASA Ames Research Center.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by the NetBSD
+ *	Foundation, Inc. and its contributors.
+ * 4. Neither the name of The NetBSD Foundation nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
 
 /*
  * Copyright (c) 1982, 1986, 1988, 1991, 1993
@@ -51,9 +88,12 @@
 #include <net/if.h>
 
 #include <vm/vm.h>
+#include <vm/vm_kern.h>
 
 #include <uvm/uvm_extern.h>
 
+#include <sys/sysctl.h>
+
 struct	pool mbpool;		/* mbuf pool */
 struct	pool mclpool;		/* mbuf cluster pool */
 
@@ -63,11 +103,12 @@ int	max_protohdr;
 int	max_hdr;
 int	max_datalen;
 
-extern	vm_map_t mb_map;
-
 void	*mclpool_alloc __P((unsigned long, int, int));
 void	mclpool_release __P((void *, unsigned long, int));
 
+const char *mclpool_warnmsg =
+    "WARNING: mclpool limit reached; increase NMBCLUSTERS";
+
 /*
  * Initialize the mbuf allcator.
  */
@@ -75,9 +116,8 @@ void
 mbinit()
 {
 
-	/* XXX malloc types! */
-	pool_init(&mbpool, MSIZE, 0, 0, 0, "mbpl", 0, NULL, NULL, 0);
-	pool_init(&mclpool, MCLBYTES, 0, 0, 0, "mclpl", 0, mclpool_alloc,
+	pool_init(&mbpool, msize, 0, 0, 0, "mbpl", 0, NULL, NULL, 0);
+	pool_init(&mclpool, mclbytes, 0, 0, 0, "mclpl", 0, mclpool_alloc,
 	    mclpool_release, 0);
 
 	/*
@@ -85,14 +125,88 @@ mbinit()
 	 * mbuf clusters the kernel is to support.  Log the limit
 	 * reached message max once a minute.
 	 */
-	pool_sethardlimit(&mclpool, nmbclusters,
-	    "WARNING: mclpool limit reached; increase NMBCLUSTERS", 60);
-	
+	pool_sethardlimit(&mclpool, nmbclusters, mclpool_warnmsg, 60);
+
 	/*
-	 * XXX Consider setting a low-water mark here.  That will help
-	 * e.g. pagedaemon on diskless systems as it scrambles to clean
-	 * pages in memory starvation situations.
+	 * Set a low water mark for both mbufs and clusters.  This should
+	 * help ensure that they can be allocated in a memory starvation
+	 * situation.  This is important for e.g. diskless systems which
+	 * must allocate mbufs in order for the pagedaemon to clean pages.
 	 */
+	pool_setlowat(&mbpool, mblowat);
+	pool_setlowat(&mclpool, mcllowat);
+}
+
+int
+sysctl_dombuf(name, namelen, oldp, oldlenp, newp, newlen)
+	int *name;
+	u_int namelen;
+	void *oldp;
+	size_t *oldlenp;
+	void *newp;
+	size_t newlen;
+{
+	int error, newval;
+
+	/* All sysctl names at this level are terminal. */
+	if (namelen != 1)
+		return (ENOTDIR);		/* overloaded */
+
+	switch (name[0]) {
+	case MBUF_MSIZE:
+		return (sysctl_rdint(oldp, oldlenp, newp, msize));
+	case MBUF_MCLBYTES:
+		return (sysctl_rdint(oldp, oldlenp, newp, mclbytes));
+	case MBUF_NMBCLUSTERS:
+		/*
+		 * If we have direct-mapped pool pages, we can adjust this
+		 * number on the fly.  If not, we're limited by the size
+		 * of mb_map, and cannot change this value.
+		 *
+		 * Note: we only allow the value to be increased, never
+		 * decreased.
+		 */
+		if (mb_map == NULL) {
+			newval = nmbclusters;
+			error = sysctl_int(oldp, oldlenp, newp, newlen,
+			    &newval);
+			if (error != 0)
+				return (error);
+			if (newp != NULL) {
+				if (newval >= nmbclusters) {
+					nmbclusters = newval;
+					pool_sethardlimit(&mclpool,
+					    nmbclusters, mclpool_warnmsg, 60);
+				} else
+					error = EINVAL;
+			}
+			return (error);
+		} else
+			return (sysctl_rdint(oldp, oldlenp, newp, nmbclusters));
+	case MBUF_MBLOWAT:
+	case MBUF_MCLLOWAT:
+		/* New value must be >= 0. */
+		newval = (name[0] == MBUF_MBLOWAT) ? mblowat : mcllowat;
+		error = sysctl_int(oldp, oldlenp, newp, newlen, &newval);
+		if (error != 0)
+			return (error);
+		if (newp != NULL) {
+			if (newval >= 0) {
+				if (name[0] == MBUF_MBLOWAT) {
+					mblowat = newval;
+					pool_setlowat(&mbpool, newval);
+				} else {
+					mcllowat = newval;
+					pool_setlowat(&mclpool, newval);
+				}
+			} else
+				error = EINVAL;
+		}
+		return (error);
+	default:
+		return (EOPNOTSUPP);
+	}
+	/* NOTREACHED */
 }
 
 void *