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" >