[plug] upper RAM size limits in Linux

[Nick Bannon]

On Tue, Dec 02, 2003 at 09:31:27PM +0800, Trent Lloyd wrote:
> I know that 4G is the upper limit for one process to use I think
[...]

I think that's 3GB/process, in Linux 2.4.

The i386 is a 32 bit CPU, which can address 4GB of virtual memory.
Fiddling with the memory map takes time and the more you want to
stretch a process' view of the world the more fiddling it takes. The
Xeon has an extra four addressing bits which you use Intel's Physical
Address Extension (PAE) to access, for up to 64GB total.

Linux 2.4 on i386 can disable high memory (fine if you've got <1GB of
physical RAM), enable it to 4GB, or enable it to 64GB. Linux 2.6 on
i386 has a patch by Ingo Molnar to squeeze it up to a full
4GB/process:
http://www.kerneltraffic.org/kernel-traffic/kt20030730_224.html#1

Denis - you can probably get enough of a discount on a Sun V240 server
or Blade 2000 workstation to make it vaguely affordable, and even
borrow one so you can benchmark it.
http://www.sun-catalogue.com/partpricing.xml?site=AU_ENG&id=10606

amd64 (Athlon64/Opteron) is looking like an affordable alternative. A
nice rackmount dual Opteron looks like it's about $3000, plus $500/GB
of PC 2700 ECC Registered DDR RAM. ($444 from crucial.com)
http://www.rainbow-it.co.uk/SearchResults.aspx?txtSearch=Opteron

Nick.

-- 
   Nick Bannon   | "I made this letter longer than usual because
nick-sig at rcpt.to | I lack the time to make it shorter." - Pascal