Re: [Hampshire] [Hardware] - 64 bit Fedora

> (*) Below about 940MiB, 32-bit x86 is perfectly happy. Up to 3-4GiB,
> you need a different memory model in the kernel, which slows things
> down a little. Above 4GiB, you need yet _another_ memory model, which
> in theory will go up to 64GiB, but in practice gets harder and harder
> to manage as you increase the RAM(**). Current Athlon64 machines, in
> 64-bit mode, will handle up to 16TiB of RAM (44 bits of addressing
> space), if you can find a box that will take that much. :)
>
> (**) Someone on linux-kernel this week claimed that anyone running
> more than 12GiB of RAM on 32-bit x86 needed their head testing. As you
> increase the RAM, the amount of space needed to manage that RAM also
> increases, and the whole thing gets out of hand quite fast.
>
>
Hmm, it depends a lot on what the systems are actually doing - we're
running a whole bunch of servers with 16GB on Red Hat EL 4 (Red Hat
don't recommend going over 16GB without using the "hugemem" kernel), and
they're fine with the 32-bit kernel. We've even got several (Oracle
application servers) with 18 and even 24GB, and they're also fine. The
only lowmem exhaustion we've seen was with a buggy earlier version of
OCFS2 file system that had a known lowmem leak.

YMMV

Peter