SUMMARY: multiple swap devices and save core during crash

From: mwp.michael (MWP.MICHAEL@MELPN1.CV.COM)
Date: Mon Jul 05 1993 - 00:37:05 CDT

Originally I asked whether a physical swap partition smaller than main RAM
would cause the savemem program (invoked during during crash recovery) to
write past the end of the partition and clobber the next parition on the
system disk. I.E. is the savemem function intelligent enough to stop at the
end of the physical partition?

The answers indicate that if swap space on the system disk is smaller than
physical RAM, your VM is limited to the size of the swap. I have yet to test
Ray's conjecture on the effect of adding extra swap.

Thanks to James and Ray for their responses...

From: James J Dempsey <>

> The question is, during a crash when memory is stored on the swap device,
> if the system disk swap partition is smaller than physical RAM, does the
> writing process guarantee not to write over the end of the partition?
> (i.e., it would only store a portion of RAM on swap if swap on the system
> disk is smaller than physical memory).

I believe the answer to this question is that it doesn't overwrite the
swap space, because it doesn't ever use the physical RAM that you have
that is beyond your swap space.

Evidently there is a way to configure things to use ram (and never use
swap space) on solaris 2.x, but I believe if you have 64MB of RAM and
a 32MB swap partition, your virtual address space will be 32MB.

               --Jim Dempsey--

From: Ray Brownrigg <>
Subject: Re: Multiple swap devices and save core during crash

My feeling would be that if your primary swap space is less than
physical RAM, then only that amount of physical RAM will be used. If
this is all the swap space you have, then it is "well known" that this
is true. The question then becomes, if you add more swap space from a
different partition, will the system then use any extra RAM. My guess
is no.

You could probably test this conjecture, say by setting your primary
swap space to be half your physical RAM, then add another swap
partition, and see if any extra RAM is used. I believe some of the
??stat commands will help you determine this.

Hope this helps,
Ray Brownrigg

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