Re: HIGHMEM

["Martin J. Bligh" <mbligh@aracnet.com>]

> 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.

Ah, didn't realise you had a hardware problem as well ;-)

M.