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Date: Thu, 19 Jun 2003 01:49:47 -0700
From: David Schultz <das@freebsd.org>
To: Peter Losher <Peter_Losher@isc.org>
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cc: current@freebsd.org
Subject: Re: Problems tuning kmem_map on 5.1-REL box.
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On Thu, Jun 19, 2003, Peter Losher wrote:
> On Wed, 18 Jun 2003, David Schultz wrote:
> 
> > To allow the kmem_map to exceed 200 MB, you'll also need to tweak
> > VM_KMEM_SIZE_MAX to (for example) '(1024 * 1024 * 1024)'.  BTW,
> > the formula, which I stole from vmparam.h, is:
> >
> > min(max(VM_KMEM_SIZE, Physical memory/VM_KMEM_SIZE_SCALE), VM_KMEM_SIZE_MAX)
> 
> Looks like I may have found some kind of error, adding this to my kernel
> config:
> 
> # KVM
> options         VM_KMEM_SIZE_SCALE="4"
> options         VM_KMEM_SIZE_MAX="(1024 * 1024 * 1024)"
> 
> (1024MB of KVM, 4096MB/4, 1024MB MAX KVM size)
> 
> Cause the following warning and compile bomb:
> 
> % config KVM_FIX
> WARNING: unknown option `*' removed from ../compile/KVM_FIX/opt_vm.h

This looks like a limitation of config(8).

> Changing the options to:
> 
> # KVM
> options         VM_KMEM_SIZE_SCALE="4"
> options         VM_KMEM_SIZE_MAX="(1024*1024*1024)"
> 
> Configs and compiles cleanly, but panics when rebooting with the new
> kernel:
> 
> kmem_suballoc: bad status return of 3.
> panic: kmem_suballoc

That means there wasn't a large enough contiguous region for the
kmem_map.  I guess I forgot to tell you that you also need to
adjust KVA_PAGES upwards so that the kernel has enough virtual
address space to fit the map.  The following should do:

	options		KVA_PAGES=512