[CentOS] How to check server kernel support 32 Gb RAM (X86,

Mon Mar 30 18:24:57 UTC 2009
John R Pierce <pierce at hogranch.com>

> we have CENTOS 4.7 (X86) on DELL server, I already put 32 GB RAM on it.  I can use "top" or "free" to check memory and it did show 32 GB.
> I check REDHAT site and found it say:
> The "SMP" kernel supports a maximum of 16GB of main memory. Systems with more than 16GB of main memory use the "Hugemem" kernel.
> I use "uname -r" to check kernel and it show:
> # uname -r
> 2.6.9-78.0.13.ELsmp
> It did NOT show "Hugemem", does this server kernel support 32 GB or not?  If NOT how can I change kernel to "hugeme"?

Dare we ask why this isn't a 64bit server?    using 32gb of memory on a processor architecture that can
only directly address 4GB at a time is kind of brutal, unless this server is handling a rather large number
of connection sessions at the same time.    For instance, a 32bit database server will have a max of about 
2.5GB of shared memory usable.

to install the hugemem kernel, 
	yum install kernel-hugemem
reboot, and test this by selecting it in the grub menu, then adjust /boot/grub.conf to suit.

read the release notes carefully on hugemem, its a very high overhead thing, as the kernel runs in a private
memory space seperate from the applications, so all kernel<->user transfers are complex and slow.