Re: HIGHMEM

[Matt Domsch]

On Fri, Feb 13, 2004 at 08:05:14AM -0800, Martin J. Bligh wrote:
> >> We have two Dell Poweredge servers, an older one (PowerEdge 6300) and a
> >> newer one (PowerEdge 6400). Both servers have 4GB RAM, but the Linux
> >> kernel uses about 500MB less memory in the newer machine.
> > 
> > I may be talking through my hat, but I think that in this case you
> > need to select the option for support of 64G highmem.  If I recall,
> > "4G highmem" refers not to the total amount to the memory, but to the
> > highest physical address that can be accessed.
> 
> That's exactly correct. Whether the gain of 500MB of RAM is worth the
> overhead of PAE is another question ... but that's how to do it ;-)

If the chipset and BIOS can't remap the physical RAM out of the
address space needed by the PCI devices and into PAE space, then PAE
doesn't buy you anything.  You need chipset support for RAM remapping,
which doesn't exist on the servers mentioned.

Thanks,
Matt

-- 
Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com
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