[CentOS] To PAE or not to PAE...

Thu Jul 22 18:28:51 UTC 2010
JohnS <jses27 at gmail.com>

On Thu, 2010-07-22 at 17:58 +0000, Joseph L. Casale wrote:
> >What is a program supposed to do to get at "that extra RAM" then ?
> >Just curious ;-)
> AFAIK, it must be specifically compiled for it...

A PAE enabled Kernel:

NO.  It is dependent on the mmap() call in the program as in how the
memory allocation is done in it.
 dmesg | grep Memory
Memory: 2070724k/2097024k available (2254k kernel code, 25172k reserved,
1149k data, 272k init, 1179520k highmem)

 cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size=2048MB: write-back, count=1
reg01: base=0xfc000000 (4032MB), size=  64MB: uncachable, count=1
reg02: base=0xfd000000 (4048MB), size=   8MB: write-combining, count=1

Total of Memory Array(s)
Attributes : Total Installed Capacity
Value      : 2048  MB

Attributes : Total Installed Capacity Available to the OS
Value      : 2024  MB

For as performance wise some would be amazed at what a 32bit machine on
pae can do (prog dependent).  Memory allocation is faster than a X86_64.
IE locking spin lock...  Don't be confused there is a point to stop and
go 64Bit only.