physical memory support under RHEL for Opteron

From: Joshua Baker-LePain (jlb17_at_duke.edu)
Date: 03/31/04

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    Date: Wed, 31 Mar 2004 12:12:03 -0500 (EST)
To: redhat-list@redhat.com

    On Wed, 31 Mar 2004 at 12:00pm, redhat-list-request@redhat.com wrote

    > I am just about to order an dual Opteron 248 server to run under RHEL AS.
    >
    > I would like to double check the physical memory supported - we are getting
    > 8 x 2GB PC3200 or PC2700 memory on this server.
    >
    > I have found something a bit obscure on the RH web page:
    > http://www.redhat.com/software/rhel/as/
    > <http://www.redhat.com/software/rhel/as/>
    >
    > in that it said:
    >
    > ** 64GB is the maximum memory size for X86 systems. Maximum memory sizes
    > vary with other architectures.
    >
    > Can anyone confirm
    > a. the maximum memory size for Opterons supported, and
    > b. the maximum usable physical memory per process on user applications

    >From /usr/src/linux-2.4.21-9.EL/Documentation/x86_64/mm.txt on my RHEL3.0
    AMD64 system:

    The paging design used on the x86-64 linux kernel port in 2.4.x provides:

    o per process virtual address space limit of 512 Gigabytes
    o top of userspace stack located at address 0x0000007fffffffff
    o start of the kernel mapping = 0x0000010000000000
    o global RAM per system 508*512GB=254 Terabytes
    o no need of any common code change
    o 512GB of vmalloc/ioremap space

    So I think you're OK with 16GB. ;) FWIW, that systems has 8GB and runs
    wonderfully. Be sure to follow the recommendations in bugs 118152 and
    115438, which fix a couple of memory issues. 

    -- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University
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