[ltp] Re: Ubuntu 32 vrs 64 bit

[Christoph Bier]

Micha Feigin schrieb am 15.12.2008 19:11:

> 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)

Thanks for your explanation! I did not know about that.

Best
Christoph
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