Differences between the SMP and BIGSMP Kernels
Novell Cool Solutions: Tip
Reader Rating 
from 19 ratings
|
Digg This -
Slashdot This
Updated: 4 Nov 2008 |
Updated by: Anders Johansson
Applies to:
- SUSE Linux Enterprise Server 9
- SUSE Linux Enterprise Server 10
- SUSE Linux Enterprise Server 11
A 64 bit system is capable of handling a very large amount of memory, but a 32 bit system is by default only able to handle 4GB. A workaround for this was provided by Intel when they introduced the physical address extension, or pae.
With pae, a 32 bit system is able to handle up to 64GB RAM, in theory. In practice however, the system should not be used with more than 48GB. For more information on the certified amount of memory please have a look at the kernel limits document at http://www.novell.com/products/linuxenterpriseserver/kernel_limits.html.
The YaST installation system should detect which kernel is the correct one for your system, but in case you add memory after installation, and you exceed 4GB, you should switch from kernel-smp to kernel-bigsmp to enable pae.
In SUSE distributions, pae is only enabled for smp kernels.
Note that in some systems, the BIOS will occupy some part of the memory address space, which means that if you have exactly 4GB RAM in the system, you will have more addressable memory, since you also need to be able to work with the BIOS address ranges, so even if you have 4GB you may still need the bigsmp kernel.
For xen, the pae enabled kernel is simply called kernel-xenpae.
In SLES11 (or in openSUSE versions 11.0 and later), all kernels are smp capable, and the kernel for pae systems is then only called kernel-pae.
Reader Comments
- Hinweis auf SLES oder SuSE 9.X/10.X währe hilfreich. (Gilt es für alle SUSE-Kernel?)
- While interesting I still have other questions. Why on a 4GB machine is bigsmp chosen by default even though the machine only has 2 physical CPUs? Why on a machine with 2GB RAM when we upgrade to 4GB is only 3GB and a bit seen, when you say support is there for 4GB? What is the highmem/lowmem split for each of these kernels?
- Is this only for the 32-bit kernel or both 32/64-bit
- Looking at the related package descriptions the bigsmp kernel is suitable for 32 Bit architectures only. Is that true? If yes : What is to be done on 64Bit architectures to get PAE support?
- Need to distinguish 32-bit and 64-bit.....
- how about an instruction how to switch between kernels (e.g. after installing more RAM)?
Novell Cool Solutions (corporate web communities) are produced by WebWise Solutions. www.webwiseone.com