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Re: Large memory with netbsd 4

On Wed, Aug 06, 2008 at 08:03:53AM -0700, Paul Goyette wrote:
> On Wed, 6 Aug 2008, Manuel Bouyer wrote:
> >>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 don't think I'm running anything particularly esoteric on this box. 
> It's just a quad-core AMD64 on a ASUS M2N-E motherboard.  Just in case, 
> I've attached my kernel config and dmesg output.

Well, mines are Intel systems, with Intel chipsets.

> >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.
> Hmmm.  I thought the PCI hole got explicitly mapped just _below_ the 4GB 
> boundary.  At least, that was the explanation for why my machine uses 
> only 3.5 GB when I set PHYSMEM_MAX_ADDR=4096

Sorry, I worded it badly. I meant "lives in the top of the fist 4GB".

Manuel Bouyer, LIP6, Universite Paris VI.  
     NetBSD: 26 ans d'experience feront toujours la difference

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