Index: stable/10/sys/kern/vfs_cache.c
===================================================================
--- stable/10/sys/kern/vfs_cache.c
+++ stable/10/sys/kern/vfs_cache.c
@@ -330,23 +330,27 @@
 	int n_nchash;
 	int count;
 
+retry:
 	n_nchash = nchash + 1;	/* nchash is max index, not count */
 	if (!req->oldptr)
 		return SYSCTL_OUT(req, 0, n_nchash * sizeof(int));
-
-	/* Scan hash tables for applicable entries */
-	for (ncpp = nchashtbl; n_nchash > 0; n_nchash--, ncpp++) {
-		CACHE_RLOCK();
-		count = 0;
-		LIST_FOREACH(ncp, ncpp, nc_hash) {
-			count++;
-		}
+	cntbuf = malloc(n_nchash * sizeof(int), M_TEMP, M_ZERO | M_WAITOK);
+	CACHE_RLOCK();
+	if (n_nchash != nchash + 1) {
 		CACHE_RUNLOCK();
-		error = SYSCTL_OUT(req, &count, sizeof(count));
-		if (error)
-			return (error);
+		free(cntbuf, M_TEMP);
+		goto retry;
 	}
-	return (0);
+	/* Scan hash tables counting entries */
+	for (ncpp = nchashtbl, i = 0; i < n_nchash; ncpp++, i++)
+		LIST_FOREACH(ncp, ncpp, nc_hash)
+			cntbuf[i]++;
+	CACHE_RUNLOCK();
+	for (error = 0, i = 0; i < n_nchash; i++)
+		if ((error = SYSCTL_OUT(req, &cntbuf[i], sizeof(int))) != 0)
+			break;
+	free(cntbuf, M_TEMP);
+	return (error);
 }
 SYSCTL_PROC(_debug_hashstat, OID_AUTO, rawnchash, CTLTYPE_INT|CTLFLAG_RD|
     CTLFLAG_MPSAFE, 0, 0, sysctl_debug_hashstat_rawnchash, "S,int",
@@ -935,6 +939,44 @@
 }
 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nchinit, NULL);
 
+void
+cache_changesize(int newmaxvnodes)
+{
+	struct nchashhead *new_nchashtbl, *old_nchashtbl;
+	u_long new_nchash, old_nchash;
+	struct namecache *ncp;
+	uint32_t hash;
+	int i;
+
+	new_nchashtbl = hashinit(newmaxvnodes * 2, M_VFSCACHE, &new_nchash);
+	/* If same hash table size, nothing to do */
+	if (nchash == new_nchash) {
+		free(new_nchashtbl, M_VFSCACHE);
+		return;
+	}
+	/*
+	 * Move everything from the old hash table to the new table.
+	 * None of the namecache entries in the table can be removed
+	 * because to do so, they have to be removed from the hash table.
+	 */
+	CACHE_WLOCK();
+	old_nchashtbl = nchashtbl;
+	old_nchash = nchash;
+	nchashtbl = new_nchashtbl;
+	nchash = new_nchash;
+	for (i = 0; i <= old_nchash; i++) {
+		while ((ncp = LIST_FIRST(&old_nchashtbl[i])) != NULL) {
+			hash = fnv_32_buf(nc_get_name(ncp), ncp->nc_nlen,
+			    FNV1_32_INIT);
+			hash = fnv_32_buf(&ncp->nc_dvp, sizeof(ncp->nc_dvp),
+			    hash);
+			LIST_REMOVE(ncp, nc_hash);
+			LIST_INSERT_HEAD(NCHHASH(hash), ncp, nc_hash);
+		}
+	}
+	CACHE_WUNLOCK();
+	free(old_nchashtbl, M_VFSCACHE);
+}
 
 /*
  * Invalidate all entries to a particular vnode.
Index: stable/10/sys/kern/vfs_hash.c
===================================================================
--- stable/10/sys/kern/vfs_hash.c
+++ stable/10/sys/kern/vfs_hash.c
@@ -160,3 +160,40 @@
 	vp->v_hash = hash;
 	mtx_unlock(&vfs_hash_mtx);
 }
+
+void
+vfs_hash_changesize(int newmaxvnodes)
+{
+	struct vfs_hash_head *vfs_hash_newtbl, *vfs_hash_oldtbl;
+	u_long vfs_hash_newmask, vfs_hash_oldmask;
+	struct vnode *vp;
+	int i;
+
+	vfs_hash_newtbl = hashinit(newmaxvnodes, M_VFS_HASH,
+		&vfs_hash_newmask);
+	/* If same hash table size, nothing to do */
+	if (vfs_hash_mask == vfs_hash_newmask) {
+		free(vfs_hash_newtbl, M_VFS_HASH);
+		return;
+	}
+	/*
+	 * Move everything from the old hash table to the new table.
+	 * None of the vnodes in the table can be recycled because to
+	 * do so, they have to be removed from the hash table.
+	 */
+	rw_wlock(&vfs_hash_lock);
+	vfs_hash_oldtbl = vfs_hash_tbl;
+	vfs_hash_oldmask = vfs_hash_mask;
+	vfs_hash_tbl = vfs_hash_newtbl;
+	vfs_hash_mask = vfs_hash_newmask;
+	for (i = 0; i <= vfs_hash_oldmask; i++) {
+		while ((vp = LIST_FIRST(&vfs_hash_oldtbl[i])) != NULL) {
+			LIST_REMOVE(vp, v_hashlist);
+			LIST_INSERT_HEAD(
+			    vfs_hash_bucket(vp->v_mount, vp->v_hash),
+			    vp, v_hashlist);
+		}
+	}
+	rw_wunlock(&vfs_hash_lock);
+	free(vfs_hash_oldtbl, M_VFS_HASH);
+}
Index: stable/10/sys/kern/vfs_subr.c
===================================================================
--- stable/10/sys/kern/vfs_subr.c
+++ stable/10/sys/kern/vfs_subr.c
@@ -280,8 +280,25 @@
  * XXX desiredvnodes is historical cruft and should not exist.
  */
 int desiredvnodes;
-SYSCTL_INT(_kern, KERN_MAXVNODES, maxvnodes, CTLFLAG_RW,
-    &desiredvnodes, 0, "Maximum number of vnodes");
+
+static int
+sysctl_update_desiredvnodes(SYSCTL_HANDLER_ARGS)
+{
+	int error, old_desiredvnodes;
+
+	old_desiredvnodes = desiredvnodes;
+	if ((error = sysctl_handle_int(oidp, arg1, arg2, req)) != 0)
+		return (error);
+	if (old_desiredvnodes != desiredvnodes) {
+		vfs_hash_changesize(desiredvnodes);
+		cache_changesize(desiredvnodes);
+	}
+	return (0);
+}
+
+SYSCTL_PROC(_kern, KERN_MAXVNODES, maxvnodes,
+    CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_RW, &desiredvnodes, 0,
+    sysctl_update_desiredvnodes, "I", "Maximum number of vnodes");
 SYSCTL_ULONG(_kern, OID_AUTO, minvnodes, CTLFLAG_RW,
     &wantfreevnodes, 0, "Minimum number of vnodes (legacy)");
 static int vnlru_nowhere;
Index: stable/10/sys/sys/vnode.h
===================================================================
--- stable/10/sys/sys/vnode.h
+++ stable/10/sys/sys/vnode.h
@@ -600,6 +600,7 @@
 typedef int (*vn_get_ino_t)(struct mount *, void *, int, struct vnode **);
 
 /* cache_* may belong in namei.h. */
+void	cache_changesize(int newhashsize);
 #define	cache_enter(dvp, vp, cnp)					\
 	cache_enter_time(dvp, vp, cnp, NULL, NULL)
 void	cache_enter_time(struct vnode *dvp, struct vnode *vp,
@@ -836,6 +837,7 @@
 /* vfs_hash.c */
 typedef int vfs_hash_cmp_t(struct vnode *vp, void *arg);
 
+void vfs_hash_changesize(int newhashsize);
 int vfs_hash_get(const struct mount *mp, u_int hash, int flags, struct thread *td, struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg);
 u_int vfs_hash_index(struct vnode *vp);
 int vfs_hash_insert(struct vnode *vp, u_int hash, int flags, struct thread *td, struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg);