Re: -CURRENT kernel panic

On Sun, 7 Mar 2004, Andre Guibert de Bruet wrote:

> On Sun, 7 Mar 2004, Vincent Poy wrote:
> > On Sun, 7 Mar 2004, Andre Guibert de Bruet wrote:
> > > On Sat, 6 Mar 2004, Vincent Poy wrote:
> > > >
> > > > 	I managed to get the system not panicing on bootup if I set the
> > > > VM_KMEM_SIZE_MAX to 384MB.  At 512MB and 768MB, it would panic but anyone
> > > > knows what the default VM_KMEM_SIZE_MAX size is?
> > >
> > > That's the maximum amount of KMEM that your system can have. Let's say for
> > > example that you have a system with 4GB of RAM. You set VM_KMEM_SIZE_MAX
> > > to 1GB but VM_KMEM_SIZE_SCALE to 8 you get:
> > >
> > > VM_KMEM_SIZE_MAX: 1024 MB of KMEM
> > > VM_KMEM_SIZE_SCALE: 512 MB of KMEM (4096/8)
> > >
> > > The algorithm uses the lesser of these two numbers. Remember that a whole
> > > lot of things use the allocated memory so don't skimp! If you don't want
> > > to use the memory in your system, take it out and set it on the desk. ;-)
> >
> > 	Okay, here's a dumb question.  If it uses the less of the two
> > numbers, is there a reason to need to even define the VM_KMEM_SIZE_SCALE
> > since wouldn't by default, it be 1/3rd of your RAM anyways?
>
> The SCALE value is there to protect in the case of systems that might have
> memory amounts that change. If you had a set value for your KMEM which is
> larger than the amount of memory available when RAM is pulled out, your
> kernel would surely not boot. For short, the SCALE value lets you get
> creative with the size assigned to your KMEM.

	Yeah but assuming the SCALE value was the default of 3 and you had
768MB of RAM, your SCALE would still be higher than the KMEM undefined
which is 200MB.

> You might find the following mail interesting:
> http://unix.derkeiler.com/Mailing-Lists/FreeBSD/current/2003-06/1599.html

	Actually, I read that portion already since I saw it in one of
your posts in the archives.

> > > I've found through personal experience and endless hours of experimenting
> > > on fairly busy machines that the following values work for the various RAM
> > > configurations (Lower values may also work depending upon disk, net and
> > > load):
> > >
> > > RAM		KMEM size
> > > 4.0GB		768MB
> > > 3.5GB		768MB
> > > 3.0GB		512MB
> > > 2.5GB 		384MB
> > > 2.0GB		384MB
> > > 1.5GB and below	256MB
> >
> > 	You're right that anything above 384MB using a scale of 2, the
> > kernel would panic as soon as the Real Memory is posted in the boot.  Did
> > this problem actually exist recently because prior to February 28, I was
> > on a September 26, 2003 -CURRENT and it has not had the problem.  I'm
> > using maxusers=512 in the kernel as well as 65536 NMBCLUSTERS, it used to
> > be 32768 but I thought that was what was causing the panic.
>
> This problem has been around since at least June of last year, which is
> the date that I first had a test system with more than 1GB running CURRENT
> (All my production systems still track STABLE).

	When I searched the lists, it seemed to happen for people in
January 2004 and later though.  Maybe the problem wasn't as big though.
June 14, 2003 was when I first installed -CURRENT on the machine and it
originally did have 128MB only but then I got 2 1GB SODIMM's sometime in
early September and the last -current I did was September 26 and the
system had stayed up for atleast a month until I actually rebooted it.  It
wasn't until I did a -CURRENT upgrade beginning with the February 28, 2004
-CURRENT that seemed to have this issue.  Maybe the newer -CURRENT's are
just more sensitive to this problem.  Hopefully this problem eventually
gets fixed though.

> > > As with everything, backup your data, put on your fire-retarding suit, and
> > > YMMV. :-)
> >
> > 	Nah, the kernel one doesn't require backing up the data since the
> > only reason I get the panic is because I'm dumping both / and /usr to
> > another identical drive.  It's only doing the /boot/loader.conf variable
> > for kmem that's scary. ;)
>
> Loader tunables for this type of thing scare me too. I guess we're just
> old school...

	Yeah, since there is no such thing as loading a
/boot/loader.conf.old ;)


Cheers,
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