Re: 10 GB in Opteron machine

[Jakob Oestergaard <jakob@unthought.net>]

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On Fri, Jul 22, 2005 at 11:31:38AM +0200, Christoph Pleger wrote:
> Hello,
...
> > There is no highmem option for the 64-bit kernel, because it doesn't 
> > need one.
> 
> I have two questions:
> 
> 1. Is it possible to compile a 64-bit kernel on a 32-bit machine (or at
> least on a 64-bit machine with 32-bit software) and if yes, how can I do
> that?

Yes. On Debian Sarge, I have a few wrapper scripts to accomplish it -
all attached to this mail - just untar them in /usr/local/bin on a
standard x86 32-bit Sarge distro.  Use 'kmake' instead of 'make' when
you are working with your kernel source (eg. 'kmake menuconfig', 'kmake
all')

Sarge comes with all the necessary toolchain support to build a 64-bit
kernel.

It should be equally possible on most other distros of course, I just
haven't felt the urge to go waste my time with them :)

> 2. All other software on the machine is 32-bit software. Will that
> software work with a 64-bit kernel?

Yes. You tell your 64-bit kernel to enable 'IA32 Emulation' (under
Executable file formats / Emulations).

This is really the clever way to run a 64-bit system - 99% of what is
commonly run on most systems only gains overhead from the 64-bit address
space - tools like postfix, cron, syslog, apache, ... will not gain from
being native 64-bit.

The kernel however will gain from being 64-bit - and it will easily run
your existing 32-bit apps.

Solaris has done this for ages - maintaining a mostly 32-bit user space,
a 64-bit kernel, and then allowing for certain memory intensive
applications to run natively 64-bit.

It's a nice way to run a Linux based system too, IMO.

-- 

 / jakob


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