[rescue] sun3/50 swap

[Dave McGuire]

On August 12, schaecsn wrote:
> I do have a SunOS4.1.1U1 question (sun 3/50).
> 
> My machine crashes under "heavy" load, e.g. 3..5 simultaneous compilier
> runs.
> I think the reason is I do have no virtual memory available.
...
> both, top and monitor are supplementary software. they do confirm that I
> don't have virtual memory.

  SunOS requires swap space...there's no way to configure an
unmodified SunOS4 kernel to boot without swap space.

> but at boot time I get:
> 
> swap on sd0b fstype spec size 47880K
> dump on sd0b fstype spec size 47856K

  Yup, this is correct behavior, and it indicates exactly what you think
it does.

> and sun's "pstat -T" reports:
>
> 112/310 files
> 172/177 inodes
>  36/ 58 processes
> 4224/47872 swap

  Same here.

> so, any idea if I do have swap enabled or not? If I do have it enabled

  You definitely do.  The last line of your "pstat -T" output
indicates that you're using 4M of swap space out of an available 47M.

> how come that my machine crashes all the time under heavy load? I have
> fresh installation!

  This is pretty odd.  I must admit I don't have any great ideas right
off the top of my head...and I've seen just about every possible
failure mode of SunOS4 on Sun3 hardware.  By "crashing" I assume you
mean the kernel panics and dumps...if this is the case, are you able
to capture the panic message on the console?  This would be most
helpful in diagnosing the problem.  Please look into this if you can
and I will try to help further.

  Unless you have one of those 3rd party memory expansion boards, you
have only 4MB of physical RAM on a 3/50.  That means your machine is
going to swap a *lot* under even a small load.  Regardless of your
crashing problem you would do well to aggressively trim your kernel
configuration to get your kernel size down.

> My understanding is that swap gets enabled automatically. I don't need
> an entry in /etc/fstab.

  This is correct.  Under SunOS4, the primary swap device is
built into the kernel by statements in the kernel config file.
Additional swap space can be added by creating swap files and using
the program "swapon".

  Though this doesn't seem related to your problem, there is one thing
to keep in mind regarding SunOS4 and swap space.  In all
circumstances, you need to have swap space that is equal to or greater
than the size of your physical memory.  For some unknown reason,
SunOS4 prevents the use of any physical memory that isn't "backed" by
swap space...so if you've got 4MB in your 3/50 and 3MB of swap space,
you've only got 6MB of physical/virtual memory available.  Though I've
confirmed this experimentally time and time again, I've never managed
to figure out why, but this is the behavior.

        -Dave

-- 
Dave McGuire
Laurel, MD