From bf64833d24fb6d57d8a688dcba901500eadc239d Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@dragonflybsd.org>
Date: Mon, 11 Dec 2006 20:55:25 +0000
Subject: [PATCH] Document MADV_SETMAP and MAP_VPAGETABLE.  These functions
 support virtualized page tables for memory mapped regions from userland.

---
 lib/libc/sys/mmap.2 | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/lib/libc/sys/mmap.2 b/lib/libc/sys/mmap.2
index cf0c7b1be0..f823c6cfa4 100644
--- a/lib/libc/sys/mmap.2
+++ b/lib/libc/sys/mmap.2
@@ -31,7 +31,7 @@
 .\"
 .\"	@(#)mmap.2	8.4 (Berkeley) 5/11/95
 .\" $FreeBSD: src/lib/libc/sys/mmap.2,v 1.22.2.12 2002/02/27 03:40:13 dd Exp $
-.\" $DragonFly: src/lib/libc/sys/mmap.2,v 1.4 2005/08/01 03:49:16 swildner Exp $
+.\" $DragonFly: src/lib/libc/sys/mmap.2,v 1.5 2006/12/11 21:55:25 dillon Exp $
 .\"
 .Dd November 17, 2001
 .Dt MMAP 2
@@ -231,6 +231,20 @@ stack top is the starting address returned by the call, plus
 .Fa len
 bytes.  The bottom of the stack at maximum growth is the starting
 address returned by the call.
+.It Dv MAP_VPAGETABLE
+Memory accessed via this map is not linearly mapped and will be governed
+by a virtual page table.  The base address of the virtual page table may
+be set using
+.Xr mcontrol 2
+with MADV_SETMAP.  Virtual page tables work with anonymous memory but there
+is no way to populate the page table so for all intents and purposes
+.Dv MAP_VPAGETABLE
+can only be used when mapping file descriptors.
+.Pp
+Addressable backing store is limited by the range suppored in the virtual
+page table entries.  The kernel may implement a page table abstraction capable
+of addressing a larger range within the backing store then could otherwise
+be mapped into memory.
 .El
 .Pp
 The
-- 
2.11.4.GIT