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Date:      Mon, 24 Mar 2003 11:59:50 -0600
From:      Mike Meyer <mwm-dated-1048960792.251d4a@mired.org>
To:        The Anarcat <anarcat@anarcat.ath.cx>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: crashdumping on massive amounts of RAM
Message-ID:  <15999.18326.297880.599596@guru.mired.org>
In-Reply-To: <20030324174332.GB831@lenny.anarcat.ath.cx>
References:  <20030324174332.GB831@lenny.anarcat.ath.cx>

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In <20030324174332.GB831@lenny.anarcat.ath.cx>, The Anarcat <anarcat@anarcat.ath.cx> typed:
> I am fortunate enough to have a box with a lot (by my standards) of
> RAM:
> 
> real memory  = 1207877632 (1151 MB)
> avail memory = 1166782464 (1112 MB)
> 
> Now the problem I have is I'd like to debug the panic()s I'm seeing
> now and then on this box, since I'm running 5.0. :) But it seems I
> need at least as much swap as I need RAM to do this.
> 
> So I just want to make sure there is no other way to crashdump this
> RAM than making a gigantic 1GB swap area. The worst is that I really
> don't need 1GB of *swap*!! 1GB of RAM is fine. All processes run in
> main memory, but 1GB of swap? That would *suck*. ;) I have 250MB right
> now and I already think it's too much.
> 
> Any brilliant ideas to work around this?

Yes - enable the kernel debugging option (DDB) on the kernel, and
debug the running system when it panics.

As for your swap partition - the same thing happens when you run out
of virtual memory either way: processes start dieing. Having a little
swap lets you get a warning of that because you'll start paging things
out which would otherwise live in memory. Unless you're planning on
setting up a warning system that watches for paging activity and
notifies you so you can do something about it, there's probably not
much point in having 250MB of swap on a system with a gigabyte of
ram. In your shoes, I'd seriously consider running without swap.

On the other hand, disk space is so cheap that I always have lots of
swap. Something about the days when I used to recompile LISP systems
on memory-starved machines....

	<mike
-- 
Mike Meyer <mwm@mired.org>		http://www.mired.org/consulting.html
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

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