64 Bit Linux shows 4GB... was Using all of 4GB RAM...

[Bill Davidsen]

Alan Cox wrote:
>> Then why does it say 32-bit operating systems?  64-bit operating systems
>> have baseline memory demands too.
> 
> What is usually going on in those cases is that with 4GB RAM you need
> some space for PCI etc below the 4GB boundary, that means part of the RAM
> has to be mapped above the 4GB boundary which most 32bit OS can't reach
> (hugemem Linux kernels can but there is a big performance cost to such
> antics)
> 
You probably understand this better than I do, but I have never been able to 
find enough performance difference in PAE vs. default kernels to worry me, at 
least using my normal applications. I have measured run times and CPU (back 
around 2.6.22) and found the overhead was "measurable but not noticeable," down 
in the "few percent" range. I suspect you have something bigger in mind when you 
say "big performance cost," so could you expand on that? Is there some type of 
use which would trigger performance issues not more than compensated by using 
RAM instead of swapping?

I'm writing this in a VM running FC9 under a native "2.6.22.14-72.fc6PAE" kernel 
which is heavily used in native mode using all 4GB memory. I did measure this 
against both the non-PAE 32 bit kernel and x86_64 kernel for desktop, gimp, and 
kernel builds.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot