Memory Support for Hugemem Kernel

[Cliff Lim Kok Hwee]

Hi Forum,

If using a HP Proliant server has 8GB of RAM, does it need the hugemem kernel?

Redhat AS 4.0 and running 32bits only not 64bits.

My finding mention that only >16GB RAM requires hugemen kernel for 32bits.

If required how does I upgrade to hugemem kernel?

Thanks/cliff

[njia_1]

Hi Cliff

Linux supports up to 4 GB (~2^32 bytes) of memory on 32-bit
architectures and 64 GB (~2^36 bytes) on x86 with PAE. No other
operating system can support more on 32-bit since it is a limitation of
the hardware.
On 64-bit systems, Linux supports up to 16 EB (~2^64 bytes) of memory,
which is about 16 million times more than the 1 TB limit of MS.

Linux kernel 2.4 allows 32 CPUs for 32-bit arches and 64 CPUs on 64-bit
arches. However, this limit is (was?) being removed in 2.5, so you can
have up to 32767 CPUs, which should be enough for you right now.

PAE was introduced in Pentium Pro processor and should be very well supported by now. Have you actually tried to install RHEL 4 yet ? I strongly suggest that you go ahead with installation maybe few times, that will hopefully answer your question

thanks

[Stuart Browne]

The base kernel installation should be good for up to 4GB of memory.

CONFIG_HIGHMEM4G=y

If you are using more than that however, there should be the 'kernel-hugemem-*.rpm' packages on the installation media.

If you've already got the OS installed, but not using all of the available memory, and not using the 'hugemem' series of kernel, then you can also get the other kernels using 'up2date'.

[Simon Hargrave]

You do not need the hugemem kernel for 8Gb, it is require for >16Gb as you say.

However for reference, to install the hugemem kernel you need the RPM from your RedHat Enterprise media: -

kernel-hugemem-2.4.21-27.EL.i686.rpm (for example)

rpm -ivh this, then it will be added to your boot menu. Once installed you can use up2date to bring down a later version if one exists, in line with your patching strategy.

[Simon Hargrave]

Just to clarify, from the release notes: -

http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/release-notes/as-x86/

A server on the normal kernel can use up to 16Gb without the hugemem kernel. The hugemem kernel lets INDIVIDUAL processes use 4Gb of memory rather than the usual 3Gb. I think this is where the 4/16Gb confusion comes from.

Unless your processes explicitly need to use 4Gb EACH, then you don't need the hugemem kernel. If you don't need it and you install it anyway you can have reduced performance due to the overheads the hugemem kernel has.