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Date: Thu, 30 Sep 2004 10:03:45 -0600
From: Scott Long <scottl@FreeBSD.org>
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To: Claus Guttesen <cguttesen@yahoo.dk>
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cc: freebsd-current@FreeBSD.org
Subject: Re: unable to install beta6 [amd64] on Dell 2850 with 4 GB
	RAM,workaround
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Claus Guttesen wrote:
>>The AMR driver cannot handle >4GB of RAM.  Even
>>though you only have 
>>4GB, your chipset is remapping part of it to the
>>
>>>4GB region.  The 
>>
>>driver incorrectly interfaces with busdma and cannot
>>handle this
>>scenario very well.  The panic is to be expected. 
>>You can verify
>>this by setting the tunable 'hw.physmem' in the
>>loader to some
>>value under 4GB to artifically limit the amount of
>>RAM that the OS
>>sees.
> 
> 
> Added hw.physmem=4G to /boot/loader.conf and it seems
> to solve the issue. Dmesg now tells me that I have
> 
> real memory  = 3489398784 (3327 MB)
> avail memory = 3367739392 (3211 MB)
> 
> It seems that it does ignore some RAM, but is this the
> correct behaviour?
> 
> Without hw.physmem I get
> 
> real memory  = 5100273664 (4864 MB)
> avail memory = 4125847552 (3934 MB)
> 
> So it appears to perform an incorrect probing of
> memory.
> 
> Thank you.
> Claus
> 

That's not always the case.  The system might be excluding a large
part of the address space for some reason and mapping the RAM around
it.  Can you send a verbose dmesg to me in private?

Scott