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

mcclnx mcc mcclnx at yahoo.com.tw
Mon Mar 30 19:32:47 UTC 2009


The reason we did not use 64 bits O.S. due to we still have some problem run 64 bit ORACLE on X86_64.

I have another question:
  since server we have is "SMP" how come it can show 32 GB RAM on application like "top" and "free"?

Thanks.

--- 09/3/30 (一),John R Pierce <pierce at hogranch.com> 寫道:

> 寄件者: John R Pierce <pierce at hogranch.com>
> 主旨: Re: [CentOS] How to check server kernel support 32 Gb RAM (X86,
> 收件者: centos at centos.org
> 日期: 2009 3 30 一 下午 2:24
> > 
> > 
> > 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.
> http://www.centos.org/docs/4/html/release-notes/as-x86/
> 
> 
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> 


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