kern/53350: fill up a malloc md-disk on 5.1-R causes panic

[David Schultz]

On Sun, Jun 15, 2003, Poul-Henning Kamp wrote:
> The following reply was made to PR kern/53350; it has been noted by GNATS.
> 
> From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> To: Jay Kuri <jay at oneway.com>
> Cc: FreeBSD-gnats-submit at freebsd.org
> Subject: Re: kern/53350: fill up a malloc md-disk on 5.1-R causes panic 
> Date: Sun, 15 Jun 2003 18:24:17 +0200
> 
>  >>Description:
>  >          If you have a 5.1-R system with, say, 256M of ram
>  >and you mdconfig one or several malloc md-devices totalling around 100M,
>  >if you attempt to use them to capacity, the machine will panic.  The
>  >message given is:
>  >
>  > panic: kmem_malloc(4096): kmem_map too small: 108347392 total allocated

Dedicating more than a third of your physical memory to
malloc-backed storage is kind of insane anyway, but you can do it
if you specify a VM_KMEM_SIZE_SCALE of 1 or 2 in your kernel config.

>  It's really very simple:  You ran out of kernel mapped memory ("KVM").
>  
>  Remedy: Don't Do That.
>  
>  See also: malloc(9), md(4)
>  
>  This PR can be closed.

The kmem_map limitations are a FAQ and should probably be
documented as such.