xnu-2782.30.5.tar.gz

[apple/xnu.git] / bsd / man / man2 / munmap.2

diff --git a/bsd/man/man2/munmap.2 b/bsd/man/man2/munmap.2
index b32a122f25cbb7139b3a36d08894a860a5cc962d..73a929e088b66f9e2de396184d20b45ce156d121 100644 (file)
--- a/bsd/man/man2/munmap.2
+++ b/bsd/man/man2/munmap.2
@@ -1,3 +1,26 @@
+.\"
+.\" Copyright (c) 2008 Apple Inc.  All rights reserved.
+.\"
+.\" @APPLE_LICENSE_HEADER_START@
+.\" 
+.\" This file contains Original Code and/or Modifications of Original Code
+.\" as defined in and that are subject to the Apple Public Source License
+.\" Version 2.0 (the 'License'). You may not use this file except in
+.\" compliance with the License. Please obtain a copy of the License at
+.\" http://www.opensource.apple.com/apsl/ and read it before using this
+.\" file.
+.\" 
+.\" The Original Code and all software distributed under the License are
+.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+.\" Please see the License for the specific language governing rights and
+.\" limitations under the License.
+.\" 
+.\" @APPLE_LICENSE_HEADER_END@
+.\"
+.\"

 .\"    $NetBSD: munmap.2,v 1.5 1995/02/27 12:35:03 cgd Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"    $NetBSD: munmap.2,v 1.5 1995/02/27 12:35:03 cgd Exp $
 .\"
 .\" Copyright (c) 1991, 1993


@@ -33,7 +56,7 @@
 .\"
 .\"    @(#)munmap.2    8.2 (Berkeley) 4/15/94
 .\"
 .\"
 .\"    @(#)munmap.2    8.2 (Berkeley) 4/15/94
 .\"

-.Dd April 15, 1994
+.Dd October 16, 2008

 .Dt MUNMAP 2
 .Os
 .Sh NAME
 .Dt MUNMAP 2
 .Os
 .Sh NAME


@@ -53,6 +76,32 @@ system call
 deletes the mappings for the specified address range,
 causing further references to addresses within the range
 to generate invalid memory references.
 deletes the mappings for the specified address range,
 causing further references to addresses within the range
 to generate invalid memory references.

+.Sh DIRTY PAGE HANDLING
+How
+.Fn munmap
+handles a dirty page, depends on what type of memory is being unmapped:
+.Pp
+.Bl -tag -width "[System V Shared]"
+.It Bq Anonymous
+If the memory is anonymous memory and if the last reference is going
+away, then the contents are discarded by definition of anonymous memory.
+.It Bq System V Shared
+If the memory mapping was created using System V shared memory, then 
+the contents persist until the System V memory region is destroyed or 
+the system is rebooted.
+.It Bq File mapping
+If the mapping maps data from a file (MAP_SHARED), then the memory will 
+eventually be written back to disk if it's dirty.  This will happen 
+automatically at some point in the future (implementation dependent).
+Note: to force the memory to be written back to the disk, use 
+.Xr msync 2 .
+.El
+.Pp
+If there are still other references to the memory when the munmap is 
+done, then nothing is done to the memory itself and it may be swapped 
+out if need be. The memory will continue to persist until the last 
+reference goes away (except for System V shared memory in which case, 
+see above).

 .Sh RETURN VALUES
 Upon successful completion,
 .Nm munmap
 .Sh RETURN VALUES
 Upon successful completion,
 .Nm munmap