Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!snorkelwacker!bloom-beacon!eng.sun.COM!dshr
From: dshr@eng.sun.COM (David Rosenthal)
Newsgroups: comp.windows.x
Subject: Re: window manager swapping (was Re: Another R5 wish)
Message-ID: <9009251613.AA19362@devnull.Eng.Sun.COM>
Date: 25 Sep 90 16:02:38 GMT
Sender: root@athena.mit.edu (Wizard A. Root)
Organization: The Internet
Lines: 37

> Quoting from the man page:
>     "If an executable file is set up for  sharing  (this  is  the
>      default)  then  mode 01000 (save text image after execution)
>      prevents the system from abandoning the swap-space image  of
>      the program-text portion of the file when its last user ter-
>      minates."
> 
> In other words, it won't get swapped out.  The con is that it'll always
> be there, but you'd probably want to keep the window manager in memory
> anyway.
> 
Even in old,  pre-virtual-memory,  Unix systems like the one you seem
to have got the man page from the sticky bit had no influence on
whether or not the program was swapped out while it was running.  It
controlled whether starting up a new version of the process could get
its image from swap space or from the file system.  Getting it from
swap was typically faster.  The con was that the image consumed swap
space (not memory) all the time whether or not a process was running
that image.  Since the window manager is started once and runs
continually,  the sticky bit is irrelevant even in swap-based systems.

In modern virtual-memory Unix systems the sticky bit on files typically
has no effect.  Swapping a process (which in this context means pushing
its u-area to swap and unloading all its mappings) saves very little
resource,  so it isn't common.  And since the image is moved to and from
disk by random page faults rather than by a single contiguous I/O,  there
is no performance advantage to getting the image pages from swap rather
than the file system.

To decrease the time needed to get the window manager started,  set
its process priority higher (nice).  This normally has no effect on the
priority the system places on satisfying the winodw manager's page
faults,  but it will ensure that the system won't run any other
process when it could be running the window manager,  and thus the
page faults will be detected earlier than they would otherwise be.

	David.