[comp.unix.ultrix] Swap Space Problems

bemery@nmsu.edu (Bryan Emery) (06/27/91)

I am needing some advice about swap space definitions.

My setup is a DECstation 3100 with Ultrix 4.1.  I have 16 Mb memory and
about 1.8 Gbytes of disk.

The installation guide suggested that I need about 2-3 times the amount of
virtual memory in swap space and that two swap areas is more efficient than
one.  So, I took 16*3=48 Mbytes, divided that by two and set up two 24 Mbyte
partitions for swapping.

In my previous install I just used the Basic Installation and had one 64 Mbyte
partition for swapping.

Now, I am getting lots and lots of memory problems.  For example, when someone
is using SAS on the console in windows, no one else can even login.

Also, when someone is using MATLAB (another software package) and has been 
doing things for a while.  If you get into a terminal window and do:

su userid

to allow another user temporary use of the console, I get:

getwd:  can't open .. -- can't start new shell

I assume these problems are related to not enough available memory which
translates to not enough swap space.

But, I thought (according to the guide) I had plenty.

Any suggestions?  Please respond by e-mail.  Thanks!!

Bryan Emery
Computer Systems Analyst
Lockheed Engineering and Sciences Corp.

alan@shodha.enet.dec.com ( Alan's Home for Wayward Notes File.) (06/28/91)

In article <1623@opus.NMSU.Edu>, bemery@nmsu.edu (Bryan Emery) writes:
> 
> The installation guide suggested that I need about 2-3 times the amount of
> virtual memory in swap space and that two swap areas is more efficient than
> one.  So, I took 16*3=48 Mbytes, divided that by two and set up two 24 Mbyte
> partitions for swapping.

	The suggestion of 2-3 time physical memory is probably good
	for most typical application loads.  There is no way the
	installation guide can predict that you might have an application
	that uses 500 MB (to pick a truly random number) of virtual memory.
	Remember this point.
> 
> Now, I am getting lots and lots of memory problems.  For example, when someone
> is using SAS on the console in windows, no one else can even login.

	"Typical".  Why do I suspect SAS may not be typical...  So
	if you have a spare partition the right size, add more page/
	swap space.  Multiple spindles are good if you actually start
	doing pageing I/O.  If you have access to a shell while SAS 
	is running use pstat(8) and ps(1) to look at page/swap space
	and virtual memory usage.  If either exit with a message that
	resembles "out of core", then you're definately out of page
	and swap space.

> 
> [ Description of a problem with su(1) ].

	This is more likely a permission problem, so look there first
	to make sure.
> 
> I assume these problems are related to not enough available memory which
> translates to not enough swap space.

	The SAS problem almost certainly is.
> 
> But, I thought (according to the guide) I had plenty.
> 
> Any suggestions?  Please respond by e-mail.  Thanks!!

	I'll reply and post both, since it may be of general
	interest.
> 
> Bryan Emery
-- 
Alan Rollow				alan@nabeth.cxn.dec.com

yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille) (06/29/91)

In article <1623@opus.NMSU.Edu> bemery@nmsu.edu (Bryan Emery) writes:
>I am needing some advice about swap space definitions.
>
>My setup is a DECstation 3100 with Ultrix 4.1.  I have 16 Mb memory and
>about 1.8 Gbytes of disk.
>
>The installation guide suggested that I need about 2-3 times the amount of
>virtual memory in swap space and that two swap areas is more efficient than
>one.  So, I took 16*3=48 Mbytes, divided that by two and set up two 24 Mbyte
>partitions for swapping.

48 MB of swap space! That's not sufficient if you use X Windows! (and if
you only have 16 MB of real memory)

We have our DECstations 3100 set up with 125 MB of swap. Things are OK
with that but some of our developpers who are doing a lot of X programs
that use bitmaps, pixmaps and the like are starting to get close to the
upper limit. So now we are going to configure their machines with 200 MB
of swap space.
-- 
  Philip Yzarn de Louraille                 Internet: yzarn@chevron.com
  Research Support Division                 Unix & Open Systems
  Chevron Information & Technology Co.      Tel: (213) 694-9232
  P.O. Box 446, La Habra, CA 90633-0446     Fax: (213) 694-7709