Tuesday, July 27, 2010

SMP & Hugemem kernels

SMP Kernels: Symmetric multi processing Kernel

The Linux installer installs SMP kernels if during install time it detects
multiple CPUs in the system that is for a box with
a) more than one real CPU

b) a dual core CPU or a CPU with HyperThreading (HT) enabled.

If one has any of the above mentioned types of system and then removes the SMP kernel(s), then the system will only be able to use one of the CPUs.

Hugemem kernel:

‘hugemem’ was just a (Redhat) name for a kernel with HIGHMEM64G (thus PAE).

Depends on the motherboard, but 64 Gig is the limit.

From Red Hat Enterprise Linux 3 includes a new kernel known as the hugemem
kernel. This kernel supports a 4GB per process user space (versus 3GB
for the other kernels), and a 4GB direct kernel space. Using this kernel
allows Red Hat Enterprise Linux to run on systems with up to 64GB of
main memory. The hugemem kernel is required in order to use all the
memory in system configurations containing more than 16GB of memory. The
hugemem kernel can also benefit configurations running with less memory
(if running an application that could benefit from the larger per
process user space, for example.)

The HUGEMEM kernel options are only relevant to the 32 bit kernels.


On a 64-Bit system, hugemem kernel doesn't apply at all.

With a 64-bit kernel, a 32-bit application gets a full 4GB user address space and a 64-bit application gets much more than that.

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