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Re: Announcing Red Hat Enterprise Linux 4 (Nahant) Beta 2 Public Availability



On Mon, 2004-11-08 at 13:18 -0500, nahant-beta-list redhat com wrote:
>  * For the 32-bit x86 architecture, Red Hat Enterprise Linux 4 
>    Beta 2 includes an optional 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. 
>    The hugemem kernel is required in order to use all the 
>    memory in 32-bit x86 system configurations containing more 
>    than 16GB of memory.


for those who wonder... in beta 1, the 4G/4G feature was enabled by
default in all kernels so no extra kernel was needed at all.
However this feature causes RHEL to run slower inside vmware (an
artifact of the virtualisation technique used), as reported on this list
only a few days ago.

The 4G of userspace address space are very useful for applications like
Oracle, DB2, Domino, Java, Fortran and generally applications that use
many threads. The 4G of kernel address space are useful from 1Gb of ram
onwards (less kmap's needed) but more so from 12Gb onwards (because by
then the 1Gb of lowmem in the non-4g/4g kernel really starts hurting the
vm algorithms).
 

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