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surajc 10-13-2006 04:01 AM

Do not seem to be able to use more than 1GB RAM
Hi all,

We currently use 2.4.20 kernel, (the normal RH 9). We have a PC with 4GB RAM. When RH was installed, we got three kernels options to boot up with - uniprocessor, SMP and bigmem kernels. BTW, we use a 3.0GHZ Pentium Xeon Dual Core processor. Now, my questions are:

1. What are the differences between the three kernels

2. Though when we do cat /proc/meminfo and see all the 4GB RAM, we are not able to use them. Our software runs both from kernel space and someone the user space, but mainly on the kernel space, and for some reason, we want to use only the UP kernel. Is there a way to change something on the UP kernel to make use of all the 4GB RAM on the box?

Thanks a lot.

Simon Bridge 10-13-2006 04:12 AM

You cannot access more than 1GB of RAM because your kernel is too old perhaps?

You do know that RH9 is very legacy - to get the most out of your hardware you should consider a more up-to-date distro. If you like the RedHat way, you may like Fedora Core ... this will be much much easier than upgrading RH9.

surajc 10-13-2006 04:24 AM

Yeah, its legacy stuff, but still, RH 9 is to be used...
Thanks for the reply Simon.

Yeah, we do know that RH 9 is legacy stuff, but currently we are bound to use that for some strange reason, which I currently do not know. We wanted to know that if RH 9 UP kernel allows to usemore than 1 GB address spaces, or do we have to use the SMP kernel or the bigmem kernel?


cs-cam 10-13-2006 06:19 AM

You have to use the bigmem kernel. Chances are the configs won't be too different if all 3 shipped with the distro so I doubt you'd notice any differences other than all your memory being used correctly :)

surajc 10-13-2006 11:16 AM

So, UP kernel can use only 1GB RAM?
So, what you mean is that, the UP kernel can use only one GB RAM, though it can list out all the 4GB available? :scratch:

I thought the bigmem kernel is required only if more than 4GB memory was used.

What about the SMP kernel? How much memory can it use?

cs-cam 10-13-2006 06:56 PM

I have no idea about what the kernels actually support, I don't have the distro in front of me to have a look....

The default memory options in a vanilla kernel won't read more than 1GB, I've never been in the position to have a problem with that so I don't know what it'll show if you have more than what is supported. I'm just basing my comments on the fact that you are having problems with your memory not being used, ergo use the bigmem kernel.

If you want any more detailed information than that you're going to need to either look into it yourself by looking in /boot or /usr/src for kernel configs, booting each kernel individually and checking /proc/config.gz or looking in the Redhat documentation. For RH9 there probably won't be any docs left on the Redhat site in which case you go to the person who made the decision to use an out of date distro and inform them it is now their job to find the problem.

surajc 10-13-2006 09:55 PM

Thanks a lot!

I think this is quite enough information for me. The reason why we haven't quite gone to the latest kernel is it requires lot of porting effort. It is currently being done, but it is going to take a while. Until then, we are trying to live with what is available.

Anyway, thanks again.

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