memory limitaion for 32 bit Redhat

[ran_li]

Hello List,

Is there a way I tell how big memeory below system support? Is there a 4G limitation? We want to see if we could add more memory to the existing system. Thanks for any comments.

Server: HP Proliant BL25
CPU: AMD Opteron Processor 275
OS: Red Hat Enterprise Linux AS release 4
Kernel: 2.6.9-11.ELsmp
Uname -a: Linux host1 2.6.9-11.ELsmp #1 SMP Fri May 20 18:26:27 EDT 2005 i686 athlon i386 GNU/Linux

[Ivan Ferreira]

The system can go up to 32 GB RAM and Red Hat AS support unlimited memory.

[ran_li]

Thanks for the comment. Is this specified by the hardware vendor? I need to convince the support team to add more memory, they are the god of the system and told me this hardware/OS combination only supports 4G memory.

Regards!

[Sac_3]

Hi Ran li,

I agree with Ivan.

Your Q: Is this specified by the hardware vendor..?
A. Yes.Here is the detailed explanation given by vendor:

1024 MB or 2048 MB PC3200 Registered ECC 400MHz DDR memory, 2 x 1 Interleaved Memory, 8 DIMM slots,expandable to 16 GB (using optional PC3200 DDR) or 32 GB max (using optional PC2700 DDR)

To know more about the hadware: Pls Go through the below link:

http://www.jacob-computer.de/content/datenblatt/114365_1.pdf

P.S : Best way of thanking in this forum is to assign points :o)....

Regards.
SaC

[ran_li]

Thanks for the URL, I m one step close.

I read below on Redhat knowledge base, not sure if I can use the same kernel (athlon) while still have memory upgraded.

http://kbase.redhat.com/faq/FAQ_79_7899.shtm

Issue:
Why is my Opteron-based server detect only 4GB of memory when using the athlon kernel in a 32-bit version of Red Enterprise Linux 3?

Resolution:
The athlon kernel is the 32-bit mode kernel for AMD64 or Opteron CPU. It only supports up to 4GB of memory. For instances that requires more than 4GB memory support, the x86 hugemem kernel can be used. However, by going beyond the kernel limits it would break KMI and creates a 5% performance penalty.

With that, it would be best to initially install the 64-bit Red Hat Enterprise Linux 3 version operating system on an Opteron based server. The x86-64 kernel supports up to 64GB memory.

[Sac_3]

As suggested in Redhat Kbase, installing the required memory and upgrading to hugemem kernel (to have the system/OS detect the installed memory) Shud b fine.

SaC

[ran_li]

Then I believe I could not add any more memory to the system, because we could not upgrade the system to 64-bit, coud not even change the kernel (under certain policy).

Thanks for your comments.

Regards!

[Heironimus]

The RHEL4 "smp" kernel that you're already running should be able to recognize up to 16GB.

On a 32-bit system no single process can see more than 4GB. However, you can run multiple processes that each see 4GB.

[ran_li]

Thanks for the reply.

My understanding is if you have SMP with i686 system you are able to take this advantage. My case however is SMP with athlon kernel so it's kind of impossible.

http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin-guide/ch-kernel.html

Red Hat Enterprise Linux contains the following kernel packages (some may not apply to your architecture):

kernel â Contains the kernel and the following key features:
> Uniprocessor support for x86 and Athlon systems (can be run on a multi-processor system, but only one processor is utilized)
> Multi-processor support for all other architectures
> For x86 systems, only the first 4 GB of RAM is used; use the kernel-hugemem package for x86 systems with over 4 GB of RAM

kernel-devel â Contains the kernel headers and makefiles sufficient to build modules against the kernel package.

kernel-hugemem â (only for i686 systems) In addition to the options enabled for the kernel package, the key configuration options are as follows:
> Support for more than 4 GB of RAM (up to 64 GB for x86)
>> Note: kernel-hugemem is required for memory configurations higher than 16 GB.
> PAE (Physical Address Extension) or 3 level paging on x86 processors that support PAE
> Support for multiple processors
> 4GB/4GB split â 4GB of virtual address space for the kernel and almost 4GB for each user process on x86 systems

kernel-hugemem-devel â Contains the kernel headers and makefiles sufficient to build modules against the kernel-hugemem package.

kernel-smp â Contains the kernel for multi-processor systems. The following are the key features:
> Multi-processor support
> Support for more than 4 GB of RAM (up to 16 GB for x86)
> PAE (Physical Address Extension) or 3 level paging on x86 processors that support PAE

... ...

[Vitaly Karasik_1]

>My understanding is if you have SMP with >i686 system you are able to take this >advantage. My case however is SMP with >athlon kernel so it's kind of impossible.

I think you're wrong. Your kernel-smp works well with your AMD Optheron CPU, right? So your system will be able to use >4GB RAM.

[ran_li]

Your comment is correct, it can work well with 4G however my question here is whether is can support any more memory (4G+)or not(w/ existing kernel).

Regards!

[Steven E. Protter]

Shalom,

You need a hugemem kernel to support more memory. Most smp features are built into that kernel.

SEP

[Vitaly Karasik_1]

as far as I understand from RH docs, kernel-smp is enough for working with up to 16GB RAM.

kernel-hugemem has some overhead; most gurus don't recommend to use it on systems with <16GB RAM.

[ran_li]

Again I totally agree with you but my processor is AMD Opteron, that will make things different.

If the processor is x86 then Hugmem kernel is not necessary for the memory 16G or less, because it can take advantage of PAE also available for x86 processors only.

kernel-smp: Contains the kernel for multi-processor systems. The following are the key features:
> Multi-processor support
> Support for more than 4 GB of RAM (up to 16 GB for x86)
> PAE (Physical Address Extension) or 3 level paging on x86 processors that support PAE

[Vitaly Karasik_1]

I was under impression what Opteron support PAE...
Do you see "pae" flag into /poc/cpuinfo?

[ran_li]

Thanks of the follow up.

Yes there is a pae flag in /proc/cpuinfo

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscal
l nx mmxext lm 3dnowext 3dnow pni

Does it mean the memory can be upgraded (4G+) on this 32-bit SMP Kernel with the processor type athlon?

The question then would be what is the maximum for Opteron. Redhat doc only mention up to 16G for x86 CPU.

Too bad I don't have a test box.

Regards!

[Matti_Kurkela · Accepted solution]

We have two Proliant DL585 servers here with AMD Opteron 880 CPUs, a 32-bit RedHat ES 4 and 16 GB memory. /proc/cpuinfo indicates "pae" on the CPUs, and all the memory is accessible to the OS. The kernel version is currently 2.6.9-55.ELsmp.

Works fine, although the use of the PAE mechanism to overcome the 4 GB limit is less efficient than using a real 64-bit OS.

At the time the system was built, the application vendor officially supported 32-bit OSs only. We built the testing and production systems using 32-bit version of the OS, to be 100% sure we can get support if necessary.

The development machines have been running a 64-bit version of the OS from the very beginning, so we're pretty confident that our applications will work as-is even after the upgrade to 64-bit :-)

As far as I understand, when running in 32-bit mode, Athlons and Opterons are effectively x86 CPUs too. That's the entire point of the 32-bit compatibility mode.

MK

[Vitaly Karasik_1]

>Does it mean the memory can be upgraded >(4G+) on this 32-bit SMP Kernel with the >processor type athlon?

as far as I understand, yes.


The question then would be what is the maximum for Opteron. Redhat doc only mention up to 16G for x86 CPU.

kernel-hugemem supports >16GB RAM, isn't it?

[ran_li]

I meant with SMP kernel. Anyway I got the point.

Thanks very much to you all and all of your comments.

Regards!

[Heironimus]

RHEL3 used an older kernel and there was an athlon-specific build, but there is no athlon kernel for RHEL4. RHEL4 uses a very different kernel than 3 did (based on Linux 2.6 rather than 2.4), and you use the same package for AMD and Intel chips.

[Steven E. Protter]

I thought you wanted to go beyond 16 GB. My writing was poor, but hugemem is generally used to get beyond 16 GB of ram, thouth RHCS the cluster suite requires it to be installed to run the suite.

The processor should not be a factor.

Also the kernel itself indicates an update level of Red Hat that is probably update 1.

You might find update 4 or update 5 more stable.

SEP

[ran_li]

It is good to know RHEL 4 makes no difference between Intel and AMD chips from memory support point of view.

I just want to see if it can be upgraded to 8G, so SMP kernel should be good enough although it is recommended to either upgrade system to 64-bit or use Hugemem kernel instead which we could not do in a short period of time.

Thanks!