diff --git a/sys/fs/nfsclient/nfs_clbio.c.append2 b/sys/fs/nfsclient/nfs_clbio.c
--- a/sys/fs/nfsclient/nfs_clbio.c.append2
+++ b/sys/fs/nfsclient/nfs_clbio.c
@@ -1001,12 +1001,25 @@
 	if (uio->uio_resid == 0)
 		return (0);
 
+	/*
+	 * If the file in not mmap()'d, do IO_APPEND writing via a
+	 * synchronous direct write.  This can result in a significant
+	 * performance improvement.
+	 * If the file is mmap()'d, this cannot be done, since there
+	 * is no way to maintain consistency between the file on the
+	 * NFS server and the file's mmap()'d pages.
+	 */
+	NFSLOCKNODE(np);
 	if (vp->v_type == VREG && ((newnfs_directio_enable && (ioflag &
-	    IO_DIRECT)) || (ioflag & IO_APPEND))) {
+	    IO_DIRECT)) || ((ioflag & IO_APPEND) &&
+	    ((np->n_flag & NMMAPPED) == 0 || vp->v_object == NULL ||
+	    !vm_is_object_active(vp->v_object))))) {
+		NFSUNLOCKNODE(np);
 		if ((ioflag & IO_APPEND) != 0)
 			ioflag |= IO_SYNC;
 		return nfs_directio_write(vp, uio, cred, ioflag);
 	}
+	NFSUNLOCKNODE(np);
 
 	/*
 	 * Maybe this should be above the vnode op call, but so long as
diff --git a/sys/fs/nfsclient/nfs_clvnops.c.append2 b/sys/fs/nfsclient/nfs_clvnops.c
--- a/sys/fs/nfsclient/nfs_clvnops.c.append2
+++ b/sys/fs/nfsclient/nfs_clvnops.c
@@ -154,6 +154,7 @@
 static vop_listextattr_t nfs_listextattr;
 static vop_deleteextattr_t nfs_deleteextattr;
 static vop_lock1_t	nfs_lock;
+static vop_mmapped_t	nfs_mmapped;
 
 /*
  * Global vfs data structures for nfs
@@ -201,6 +202,7 @@
 	.vop_setextattr =	nfs_setextattr,
 	.vop_listextattr =	nfs_listextattr,
 	.vop_deleteextattr =	nfs_deleteextattr,
+	.vop_mmapped =		nfs_mmapped,
 };
 VFS_VOP_VECTOR_REGISTER(newnfs_vnodeops_nosig);
 
@@ -4576,4 +4578,19 @@
 		break;
 	}
 	return (error);
+}
+
+/*
+ * Mark the vnode as mmap()'d.
+ */
+static int
+nfs_mmapped(struct vop_mmapped_args *ap)
+{
+	struct nfsnode *np;
+
+	np = VTONFS(ap->a_vp);
+	NFSLOCKNODE(np);
+	np->n_flag |= NMMAPPED;
+	NFSUNLOCKNODE(np);
+	return (0);
 }
diff --git a/sys/fs/nfsclient/nfsnode.h.append2 b/sys/fs/nfsclient/nfsnode.h
--- a/sys/fs/nfsclient/nfsnode.h.append2
+++ b/sys/fs/nfsclient/nfsnode.h
@@ -167,6 +167,7 @@
 #define	NDSCOMMIT	0x00100000  /* Commit is done via the DS. */
 #define	NVNSETSZSKIP	0x00200000  /* Skipped vnode_pager_setsize() */
 #define	NMIGHTBELOCKED	0x00400000  /* Might be file locked. */
+#define	NMMAPPED	0x00800000  /* Has been mmap()'d. */
 
 /*
  * Convert between nfsnode pointers and vnode pointers
diff --git a/sys/vm/vm_extern.h.append2 b/sys/vm/vm_extern.h
--- a/sys/vm/vm_extern.h.append2
+++ b/sys/vm/vm_extern.h
@@ -131,6 +131,7 @@
     vm_page_t ma[], int npages, int req_class);
 u_int vm_active_count(void);
 u_int vm_inactive_count(void);
+bool vm_is_object_active(vm_object_t obj);
 u_int vm_laundry_count(void);
 u_int vm_wait_count(void);
 #endif				/* _KERNEL */
diff --git a/sys/vm/vm_meter.c.append2 b/sys/vm/vm_meter.c
--- a/sys/vm/vm_meter.c.append2
+++ b/sys/vm/vm_meter.c
@@ -150,8 +150,8 @@
  * has very low overhead and is good enough for the advisory
  * vm.vmtotal sysctl.
  */
-static bool
-is_object_active(vm_object_t obj)
+bool
+vm_is_object_active(vm_object_t obj)
 {
 
 	return (obj->ref_count > obj->shadow_count);
@@ -268,7 +268,7 @@
 		}
 		total.t_vm += object->size;
 		total.t_rm += object->resident_page_count;
-		if (is_object_active(object)) {
+		if (vm_is_object_active(object)) {
 			total.t_avm += object->size;
 			total.t_arm += object->resident_page_count;
 		}
@@ -276,7 +276,7 @@
 			/* shared object */
 			total.t_vmshr += object->size;
 			total.t_rmshr += object->resident_page_count;
-			if (is_object_active(object)) {
+			if (vm_is_object_active(object)) {
 				total.t_avmshr += object->size;
 				total.t_armshr += object->resident_page_count;
 			}