docs/78041: docs for md need further explanation of type swap

[Lars Kristiansen]

>Number:         78041
>Category:       docs
>Synopsis:       docs for md need further explanation of type swap
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Thu Feb 24 22:20:21 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Lars Kristiansen <lars+lister.freebsd at adventuras.no>
>Release:        FreeBSD 5.3-RELEASE i386
>Organization:
Adventuras
>Environment:
System: FreeBSD ladyda.master.local 5.3-RELEASE FreeBSD 5.3-RELEASE #1:
Fri Nov 12 20:41:58 CET 2004
root at ladyda.master.local:/usr/obj/usr/src/sys/GENERIC i386



>Description:
Documentation describes memory disks of type swap as allocated from swap
space which leads to believe they are diskbound.

This description in a mail from Scott Long to freebsd-fs explains otherwise:
 ( http://docs.freebsd.org/cgi/mid.cgi?41E01905.3040200 )
"With the swap option, pages are allocated from the buffer/cache and
held there.  They are only swapped to disk when the system is under
memory pressure, otherwise they stay in RAM."

or this one in a mail from Poul-Henning Kamp:
 ( http://docs.freebsd.org/cgi/mid.cgi?45044.1105365790 )
"Swap-backing is very different from RAM disks in that things get
pushed out of RAM if better use can be made of the pages."



>How-To-Repeat:

>Fix:

############### suggested patch from Lowell Gilbert: ###############
--- src/share/man/man4/md.4.ORIG   Thu Feb 24 11:51:37 2005
+++ src/share/man/man4/md.4        Thu Feb 24 11:51:51 2005
@@ -50,7 +50,7 @@
 This allows for mounting ISO images without the tedious
 detour over actual physical media.
 .It Cm swap
-Backing store is allocated from swap space.
+Backing store is allocated from virtual memory space.
 .El
 .Pp
 For more information, please see
############### end of patch ###############



Note:
Documents which could use corresponding changes includes
 the manpages for md, mdconfig and mdmfs,
and also in this chapter of the handbook:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/disks-virtual.html#DISKS-MD-FREEBSD5




>Release-Note:
>Audit-Trail:
>Unformatted: