[ltp] Re: Ubuntu 32 vrs 64 bit

[Micha Feigin]

On Mon, 15 Dec 2008 16:49:50 +0100
"Adrian Bastholm" <adrian@javaguru.org> wrote:

> The PAE enabled "bigmem" kernels, can they make use of memory which is
> "appropriated" (or in english, made unavailable, stolen) by certain
> motherboards ?
> 
> Adrian
> 
> >
> > As Daniel uses Ubuntu he just can choose Ubuntu's server kernel that
> > has already enabled PAE. That's the way I address 4 GB of RAM on my
> > X200s with Ubuntu 8.10.
> >

But here you start paying all sorts of penaltries that usually justify moving
to a 64bit system. This kernel is more appropriate to 32bit cpus using more
than 2/3 GB ram, not for 64bit cpus.

First of all you can access more than 2 or 3 GB for each process (the process
memory space is limited to 4GB out of which 1 or 2 GB depending on kernel setup
are reserved for the kernel). (this also applies to swap usage with system with
2GB memory of less)

Second problem is that you hit an overhead when accessing this extra memory.

What you are better off doing is running a 64bit kernel and a 32bit userspace
if  you want the 32bit userspace and to be able to use the extra memory (you
are still stuck with the maximum 2GB memory per process though) core2 and amd
64bit run the 32bit processes nativelly and not in emulation mode so you don't
get the performance hit there (unlike ia64)

> > [...]
> >
> > Best
> > Christoph
> > --
> > +++ Typografie-Regeln: http://zvisionwelt.de/downloads.html (1.6)
> >
> > --
> > The linux-thinkpad mailing list home page is at:
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> >
> 
> 
>