Re: Large memory with netbsd 4

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Aug 05, 2008 at 08:18:54AM -0700, Paul Goyette wrote:
> On Wed, 6 Aug 2008, Simon Burge wrote:
> 
> >>My question is simple, is there any chance that the ammount of memory
> >>can actually crash
> >>the machine ?
> >>
> >>Thanks in advance for your answer.
> >
> >You don't give any specifics like architecture and CPU type/model.  I've
> >used netbsd-4 with the amd64 port on a machine with 16GB of RAM without
> >any problems.
> 
> Hmmm, I'm running -current on a machine with 8GB of RAM, and had to 
> disable the top 4GB to avoid lots of random crashes.  IIRC, someone on 
> this list indicated that there was an "issue" with DMA bounce buffers 
> above the 4GB boundary point.

A specific device may have issues with memory above 4GB, but I don't
think the bus_dma code in general has. I've been running amd64
on systems with more than 4GB without troubles.

> 
> I've actually been watching for any hint of a commit that might address 
> this problem so I can turn on the rest of my memory.
> 
> Having said that, I've had no problems running with 4GB (at least, no 
> problems related to the amount of memory).

With 4GB enabled, you're likely to use a physical segment above the 4GB limit,
as the PCI bus lives in the top 4GB physical address space.

-- 
Manuel Bouyer, LIP6, Universite Paris VI.           
Manuel.Bouyer%lip6.fr@localhost
     NetBSD: 26 ans d'experience feront toujours la difference
--