Date: Mon, 24 Mar 2003 13:45:55 -0500 From: The Anarcat <anarcat@anarcat.ath.cx> To: Mike Meyer <mwm@mired.org> Cc: freebsd-questions@freebsd.org Subject: Re: crashdumping on massive amounts of RAM Message-ID: <20030324184555.GD831@lenny.anarcat.ath.cx> In-Reply-To: <15999.18326.297880.599596@guru.mired.org> References: <20030324174332.GB831@lenny.anarcat.ath.cx> <15999.18326.297880.599596@guru.mired.org>
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On Mon Mar 24, 2003 at 11:59:50AM -0600, Mike Meyer wrote:
> In <20030324174332.GB831@lenny.anarcat.ath.cx>, The Anarcat <anarcat@anar=
cat.ath.cx> typed:
> > I am fortunate enough to have a box with a lot (by my standards) of
> > RAM:
> >=20
> > real memory =3D 1207877632 (1151 MB)
> > avail memory =3D 1166782464 (1112 MB)
> >=20
> > 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.
> >=20
> > 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.
> >=20
> > Any brilliant ideas to work around this?
>=20
> Yes - enable the kernel debugging option (DDB) on the kernel, and
> debug the running system when it panics.
The only problem I see with that is with non-reproducable panics, if I
don't debug *everything* properly the first time, I might not be able
to get back all the data I need.
Also, what usually happens is that the victim sends a basic backtrace
and a developper then asks to print *b or something like that, which
is not possible once the panic is over. :)
> 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.
I've considered it, but I found that I've been able to run over 1GB of
mem, so the 250MB is handy to handle exceptional situations as the
disk slows down allocation.
> 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....
Eh. It's a 40GB disk and I really considered putting 1GB of it for
swap.
A.
--=20
Nothing incites to money-crimes like great poverty or great wealth.
- Mark Twain
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