Index: /usr/src/sys/fs/tmpfs/tmpfs_subr.c
===================================================================
--- /usr/src/sys/fs/tmpfs/tmpfs_subr.c	(revision 324624)
+++ /usr/src/sys/fs/tmpfs/tmpfs_subr.c	(working copy)
@@ -65,6 +65,7 @@
 SYSCTL_NODE(_vfs, OID_AUTO, tmpfs, CTLFLAG_RW, 0, "tmpfs file system");
 
 static long tmpfs_pages_reserved = TMPFS_PAGES_MINRESERVED;
+static int tmpfs_inactive_percent = 0;
 
 static int
 sysctl_mem_reserved(SYSCTL_HANDLER_ARGS)
@@ -87,9 +88,30 @@
 	return (0);
 }
 
+static int
+sysctl_inactive_percent(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	int percent;
+
+	percent = *(int *)arg1;
+	error = sysctl_handle_int(oidp, &percent, 0, req);
+	if (error || !req->newptr)
+		return (error);
+	if (percent < 0)
+		percent = 0;
+	if (percent > 100)
+		percent = 100;
+	*(int *)arg1 = percent;
+	return (0);
+}
+
 SYSCTL_PROC(_vfs_tmpfs, OID_AUTO, memory_reserved, CTLTYPE_LONG|CTLFLAG_RW,
     &tmpfs_pages_reserved, 0, sysctl_mem_reserved, "L",
     "Amount of available memory and swap below which tmpfs growth stops");
+SYSCTL_PROC(_vfs_tmpfs, OID_AUTO, inactive_percent, CTLTYPE_INT|CTLFLAG_RW,
+    &tmpfs_inactive_percent, 0, sysctl_inactive_percent, "I",
+    "Percentage of inactive memory to add to free space");
 
 static __inline int tmpfs_dirtree_cmp(struct tmpfs_dirent *a,
     struct tmpfs_dirent *b);
@@ -100,7 +122,9 @@
 {
 	vm_ooffset_t avail;
 
-	avail = swap_pager_avail + vm_cnt.v_free_count - tmpfs_pages_reserved;
+	avail = swap_pager_avail + vm_cnt.v_free_count +
+		(vm_cnt.v_inactive_count / 100 * tmpfs_inactive_percent) -
+		tmpfs_pages_reserved;
 	if (__predict_false(avail < 0))
 		avail = 0;
 	return (avail);