Index: sys/mbuf.h
===================================================================
RCS file: /dump/FreeBSD-CVS/src/sys/sys/mbuf.h,v
retrieving revision 1.71
diff -u -r1.71 mbuf.h
--- sys/mbuf.h	2001/02/17 05:35:56	1.71
+++ sys/mbuf.h	2001/03/08 22:18:46
@@ -37,6 +37,9 @@
 #ifndef _SYS_MBUF_H_
 #define	_SYS_MBUF_H_
 
+#define MBUF_VMGUARD
+#define MCLUSTER_VMGUARD
+
 #include <sys/mutex.h>	/* XXX */
 
 /*
@@ -277,6 +280,26 @@
 		wakeup_one(&(m_wid)); 					\
 } while (0)
 
+#ifdef MCLUSTER_VMGUARD
+#define MEXT_PREADDREF_HOOK(m) do {					\
+	mtx_lock(&mclfree.m_mtx);					\
+	if (m->m_ext.ref_cnt->refcnt == 1 &&				\
+	    m->m_ext.ext_type == EXT_CLUSTER)				\
+		mcl_guard(m);						\
+	mtx_unlock(&mclfree.m_mtx); 					\
+} while (0)
+#define MEXT_POSTREMREF_HOOK(m) do {					\
+	mtx_lock(&mclfree.m_mtx);					\
+	if (m->m_ext.ref_cnt->refcnt == 1 &&				\
+	    m->m_ext.ext_type == EXT_CLUSTER)				\
+		mcl_unguard(m);						\
+	mtx_unlock(&mclfree.m_mtx); 					\
+} while (0)
+#else
+#define MEXT_PREADDREF_HOOK(m)
+#define MEXT_POSTREMREF_HOOK(m)
+#endif
+
 /*
  * mbuf external reference count management macros:
  *
@@ -293,9 +316,13 @@
 #define MEXT_REM_REF(m) do {						\
 	KASSERT((m)->m_ext.ref_cnt->refcnt > 0, ("m_ext refcnt < 0"));	\
 	atomic_subtract_int(&((m)->m_ext.ref_cnt->refcnt), 1);		\
+	MEXT_POSTREMREF_HOOK(m);					\
 } while(0)
 
-#define MEXT_ADD_REF(m) atomic_add_int(&((m)->m_ext.ref_cnt->refcnt), 1)
+#define MEXT_ADD_REF(m) do {						\
+	MEXT_PREADDREF_HOOK(m);						\
+	atomic_add_int(&((m)->m_ext.ref_cnt->refcnt), 1);		\
+} while(0)
 
 #define _MEXT_ALLOC_CNT(m_cnt, how) do {				\
 	union mext_refcnt *__mcnt;					\
@@ -678,6 +705,10 @@
 struct	mbuf *m_pulldown(struct mbuf *, int, int, int *);
 struct	mbuf *m_pullup(struct mbuf *, int);
 struct	mbuf *m_split(struct mbuf *,int,int);
+#ifdef MCLUSTER_VMGUARD
+void	mcl_guard(struct mbuf *m);
+void	mcl_unguard(struct mbuf *m);
+#endif
 #endif /* _KERNEL */
 
 #endif /* !_SYS_MBUF_H_ */
Index: kern/uipc_mbuf.c
===================================================================
RCS file: /dump/FreeBSD-CVS/src/sys/kern/uipc_mbuf.c,v
retrieving revision 1.69
diff -u -r1.69 uipc_mbuf.c
--- kern/uipc_mbuf.c	2001/02/21 09:24:13	1.69
+++ kern/uipc_mbuf.c	2001/03/08 22:42:10
@@ -47,6 +47,11 @@
 #include <vm/vm.h>
 #include <vm/vm_kern.h>
 #include <vm/vm_extern.h>
+#if defined(MBUF_VMGUARD) || defined(MCLUSTER_VMGUARD)
+#include <sys/lock.h>
+#include <vm/pmap.h>
+#include <vm/vm_map.h>
+#endif
 
 static void mbinit(void *);
 SYSINIT(mbuf, SI_SUB_MBUF, SI_ORDER_FIRST, mbinit, NULL)
@@ -253,7 +258,11 @@
 		return (0);
 	}
 
+#ifdef MBUF_VMGUARD
+	nbytes = nmb * PAGE_SIZE * 2;
+#else
 	nbytes = round_page(nmb * MSIZE);
+#endif
 
 	mtx_unlock(&mmbfree.m_mtx);
 	p = (caddr_t)kmem_malloc(mb_map, nbytes, M_NOWAIT);
@@ -270,7 +279,9 @@
 	if (p == NULL)
 		return (0);
 
+#ifndef MBUF_VMGUARD
 	nmb = nbytes / MSIZE;
+#endif
 
 	/*
 	 * We don't let go of the mutex in order to avoid a race.
@@ -278,9 +289,22 @@
 	 * with grabbing the mbuf from the free list.
 	 */
 	for (i = 0; i < nmb; i++) {
+#ifdef MBUF_VMGUARD
+		struct mbuf *m;
+
+		m = (struct mbuf *)(p + PAGE_SIZE - MSIZE);
+		m->m_next = mmbfree.m_head;
+		mmbfree.m_head = m;
+		mtx_unlock(&mmbfree.m_mtx);
+		vm_map_protect(mb_map, (vm_offset_t)p + PAGE_SIZE,
+		    (vm_offset_t)p + 2 * PAGE_SIZE, VM_PROT_NONE, 0);
+		mtx_lock(&mmbfree.m_mtx);
+		p += 2 * PAGE_SIZE;
+#else
 		((struct mbuf *)p)->m_next = mmbfree.m_head;
 		mmbfree.m_head = (struct mbuf *)p;
 		p += MSIZE;
+#endif
 	}
 	mbstat.m_mbufs += nmb;
 	mbtypes[MT_FREE] += nmb;
@@ -373,11 +397,17 @@
 		return (0);
 	}
 
+#ifdef MCLUSTER_VMGUARD
+	npg = ncl * 2;
+#else
 	npg = ncl;
+#endif
 	mtx_unlock(&mclfree.m_mtx);
 	p = (caddr_t)kmem_malloc(mb_map, ctob(npg),
 				 how == M_TRYWAIT ? M_WAITOK : M_NOWAIT);
+#ifndef MCLUSTER_VMGUARD
 	ncl = ncl * PAGE_SIZE / MCLBYTES;
+#endif
 	mtx_lock(&mclfree.m_mtx);
 
 	/*
@@ -393,9 +423,22 @@
 	 * We don't let go of the mutex in order to avoid a race.
 	 */
 	for (i = 0; i < ncl; i++) {
+#ifdef MCLUSTER_VMGUARD
+		union mcluster *q;
+
+		q = (union mcluster *)(p + PAGE_SIZE - MCLBYTES);
+		q->mcl_next = mclfree.m_head;
+		mclfree.m_head = q;
+		mtx_unlock(&mclfree.m_mtx);
+		vm_map_protect(mb_map, (vm_offset_t)p + PAGE_SIZE,
+		    (vm_offset_t)p + 2 * PAGE_SIZE, VM_PROT_NONE, 0);
+		mtx_lock(&mclfree.m_mtx);
+		p += 2 * PAGE_SIZE;
+#else
 		((union mcluster *)p)->mcl_next = mclfree.m_head;
 		mclfree.m_head = (union mcluster *)p;
 		p += MCLBYTES;
+#endif
 		mbstat.m_clfree++;
 	}
 	mbstat.m_clusters += ncl;
@@ -434,6 +477,29 @@
 
 	return (p);
 }
+
+#ifdef MCLUSTER_VMGUARD
+void
+mcl_guard(m)
+	struct mbuf *m;
+{
+	vm_offset_t p = (vm_offset_t)m->m_ext.ext_buf + MCLBYTES - PAGE_SIZE;
+	mtx_unlock(&mclfree.m_mtx);
+	vm_map_protect(mb_map, p, p + PAGE_SIZE, VM_PROT_READ, 0);
+	mtx_lock(&mclfree.m_mtx);
+}
+
+void
+mcl_unguard(m)
+	struct mbuf *m;
+{
+	vm_offset_t p = (vm_offset_t)m->m_ext.ext_buf + MCLBYTES - PAGE_SIZE;
+	mtx_unlock(&mclfree.m_mtx);
+	vm_map_protect(mb_map, p, p + PAGE_SIZE, VM_PROT_READ | VM_PROT_WRITE,
+	    0);
+	mtx_lock(&mclfree.m_mtx);
+}
+#endif
 
 /*
  * m_reclaim: drain protocols in hopes to free up some resources...