On Fri, Aug 29, 2003 at 02:59:49PM -0700, Steve Madsen wrote:
> Is it possible to use more than 256 MB of system memory with the Broadcom
> SB1250 in 32-bit mode? The memory map I'm looking at shows me that the
> second 256 MB of memory is at physical address 0x80000000. I suspect that
> due to the 2G/2G split in the kernel, I can't use memory this high without
> moving to the 64-bit kernel.
Steve Finney's answer was correct; I'd like to add a few details though.
The explanation you gave isn't exactly right. A 2GB/2GB split would normally
support 2GB of low memory. We don't on MIPS due to the very inconvenient and
unchangable mappings of KSEG0/KSEG1 - something that may have been sweet
in '85 when the address map was designed but not today when 32-bit address
spaces are beginning to be fairly tight.
Highmem works ok in 2.4 as long as you have a reasonably low ratio of
highmem to lowmem. For typical loads that means going beyond 4:1 isn't
sensible but the actual number may vary much based on exact system
configuration or workload.