Concuring with Stephen's mail, the way that the RHEL 4 
hugemem kernel worked involved so much register and TLB 
switching that Red Hat reckoned on a 20% performance hit. 
So with RHEL5, the advice is to go 64 bit and reclaim your 
performance hit from using the RHEL 4 hugemem kernel.

Regs,

- Nick

>-----Original Message-----
>From: [log in to unmask]
>[mailto:[log in to unmask]]On Behalf Of
>Stephen John Smoogen
>Sent: 21 January 2008 05:07
>To: markaoki
>Cc: John Summerfield; [log in to unmask]
>Subject: Re: System Configuration Limits for SL5
>
>
>On Jan 20, 2008 12:25 PM, markaoki <[log in to unmask]> wrote:
>> The config limits chart for SL covers only V3 and 4, so I 
>don't know for
>> sure.
>>
>> Red Hat has a chart covering RHEL 3, 4, and 5, indicating a drop in
>> supported
>> maximum per-process memory, from 4gb to 3gb, for V5 over the 
>prior versions:
>> http://www.redhat.com/rhel/compare/
>>
>> I don't see hugemem kernel anywhere, not since SL 4 anyway.
>>
>
>I think the reason is that Red Hat is following Linus's lead on this:
>If you want more than what the base architecture go to 64 bit. While
>you can get 4gb on a 32 bit kernel, there is a non-negligible
>performance hit and a lot of odd things seem to happen that are not
>reproducible.. but thought to be due to the various hacks one has to
>on the chipsets to get it to be more ram than it is supposed to.
>
>
>
>
>-- 
>Stephen J Smoogen. -- CSIRT/Linux System Administrator
>How far that little candle throws his beams! So shines a good deed
>in a naughty world. = Shakespeare. "The Merchant of Venice"
>