Index: head/sys/fs/nfs/nfsport.h
===================================================================
--- head/sys/fs/nfs/nfsport.h
+++ head/sys/fs/nfs/nfsport.h
@@ -950,7 +950,7 @@
 };
 
 #ifndef NFS_MAXBSIZE
-#define	NFS_MAXBSIZE	MAXBSIZE
+#define	NFS_MAXBSIZE	MAXBCACHEBUF
 #endif
 
 /*
Index: head/sys/fs/nfsclient/nfs_clvfsops.c
===================================================================
--- head/sys/fs/nfsclient/nfs_clvfsops.c
+++ head/sys/fs/nfsclient/nfs_clvfsops.c
@@ -201,16 +201,16 @@
 	}
 	if (nmp->nm_rsize > maxio || nmp->nm_rsize == 0)
 		nmp->nm_rsize = maxio;
-	if (nmp->nm_rsize > MAXBSIZE)
-		nmp->nm_rsize = MAXBSIZE;
+	if (nmp->nm_rsize > NFS_MAXBSIZE)
+		nmp->nm_rsize = NFS_MAXBSIZE;
 	if (nmp->nm_readdirsize > maxio || nmp->nm_readdirsize == 0)
 		nmp->nm_readdirsize = maxio;
 	if (nmp->nm_readdirsize > nmp->nm_rsize)
 		nmp->nm_readdirsize = nmp->nm_rsize;
 	if (nmp->nm_wsize > maxio || nmp->nm_wsize == 0)
 		nmp->nm_wsize = maxio;
-	if (nmp->nm_wsize > MAXBSIZE)
-		nmp->nm_wsize = MAXBSIZE;
+	if (nmp->nm_wsize > NFS_MAXBSIZE)
+		nmp->nm_wsize = NFS_MAXBSIZE;
 
 	/*
 	 * Calculate the size used for io buffers.  Use the larger
Index: head/sys/kern/vfs_bio.c
===================================================================
--- head/sys/kern/vfs_bio.c
+++ head/sys/kern/vfs_bio.c
@@ -805,6 +805,7 @@
 	struct buf *bp;
 	int i;
 
+	CTASSERT(MAXBCACHEBUF >= MAXBSIZE);
 	mtx_init(&bqclean, "bufq clean lock", NULL, MTX_DEF);
 	mtx_init(&bqdirty, "bufq dirty lock", NULL, MTX_DEF);
 	mtx_init(&rbreqlock, "runningbufspace lock", NULL, MTX_DEF);
@@ -846,8 +847,8 @@
 	 * by the system.
 	 */
 	maxbufspace = (long)nbuf * BKVASIZE;
-	hibufspace = lmax(3 * maxbufspace / 4, maxbufspace - MAXBSIZE * 10);
-	lobufspace = hibufspace - MAXBSIZE;
+	hibufspace = lmax(3 * maxbufspace / 4, maxbufspace - MAXBCACHEBUF * 10);
+	lobufspace = hibufspace - MAXBCACHEBUF;
 
 	/*
 	 * Note: The 16 MiB upper limit for hirunningspace was chosen
@@ -857,9 +858,9 @@
 	 * The lower 1 MiB limit is the historical upper limit for
 	 * hirunningspace.
 	 */
-	hirunningspace = lmax(lmin(roundup(hibufspace / 64, MAXBSIZE),
+	hirunningspace = lmax(lmin(roundup(hibufspace / 64, MAXBCACHEBUF),
 	    16 * 1024 * 1024), 1024 * 1024);
-	lorunningspace = roundup((hirunningspace * 2) / 3, MAXBSIZE);
+	lorunningspace = roundup((hirunningspace * 2) / 3, MAXBCACHEBUF);
 
 /*
  * Limit the amount of malloc memory since it is wired permanently into
@@ -3073,8 +3074,9 @@
 	KASSERT((flags & (GB_UNMAPPED | GB_KVAALLOC)) != GB_KVAALLOC,
 	    ("GB_KVAALLOC only makes sense with GB_UNMAPPED"));
 	ASSERT_VOP_LOCKED(vp, "getblk");
-	if (size > MAXBSIZE)
-		panic("getblk: size(%d) > MAXBSIZE(%d)\n", size, MAXBSIZE);
+	if (size > MAXBCACHEBUF)
+		panic("getblk: size(%d) > MAXBCACHEBUF(%d)\n", size,
+		    MAXBCACHEBUF);
 	if (!unmapped_buf_allowed)
 		flags &= ~(GB_UNMAPPED | GB_KVAALLOC);
 
Index: head/sys/sys/param.h
===================================================================
--- head/sys/sys/param.h
+++ head/sys/sys/param.h
@@ -233,10 +233,19 @@
  *		and may be made smaller at the risk of not being able to use
  *		filesystems which require a block size exceeding MAXBSIZE.
  *
+ * MAXBCACHEBUF - Maximum size of a buffer in the buffer cache.  This must
+ *		be >= MAXBSIZE and can be set differently for different
+ *		architectures by defining it in <machine/param.h>.
+ *		Making this larger allows NFS to do larger reads/writes.
+ *
  * BKVASIZE -	Nominal buffer space per buffer, in bytes.  BKVASIZE is the
  *		minimum KVM memory reservation the kernel is willing to make.
  *		Filesystems can of course request smaller chunks.  Actual 
  *		backing memory uses a chunk size of a page (PAGE_SIZE).
+ *		The default value here can be overridden on a per-architecture
+ *		basis by defining it in <machine/param.h>.  This should
+ *		probably be done to increase its value, when MAXBCACHEBUF is
+ *		defined as a larger value in <machine/param.h>.
  *
  *		If you make BKVASIZE too small you risk seriously fragmenting
  *		the buffer KVM map which may slow things down a bit.  If you
@@ -248,7 +257,12 @@
  *		normal UFS filesystem.
  */
 #define MAXBSIZE	65536	/* must be power of 2 */
+#ifndef	MAXBCACHEBUF
+#define	MAXBCACHEBUF	MAXBSIZE /* must be a power of 2 >= MAXBSIZE */
+#endif
+#ifndef	BKVASIZE
 #define BKVASIZE	16384	/* must be power of 2 */
+#endif
 #define BKVAMASK	(BKVASIZE-1)
 
 /*