[CentOS] x86 uniprocessor 4GB memory

[Bruno Sousa]

Hi there,
I did the question regarding multiple processors, because it seems like i
will be getting na HP ML 350 with 2 Intel Xeon with 4 or 8gb of memory.
But will I be able to use 4gb or more? 

Thanks,
Bruno Sousa

-----Mensagem original-----
De: centos-bounces at centos.org [mailto:centos-bounces at centos.org] Em nome de
James Pearson
Enviada: quinta-feira, 22 de Junho de 2006 17:18
Para: CentOS mailing list
Assunto: Re: [CentOS] x86 uniprocessor 4GB memory

> Hi there,
> 
> It seems like the bios of this machine doesn't have any type of
> configuration regarding the memory mapping.
> I'm already using the kernel-hugemem , but the problem remains.
> What else can be done?
> 
> By the way, if the machine had more than one cpu, the problem would
remain?
> 
> Best regards,
> Bruno Sousa
> 
> -----Mensagem original-----
> De: centos-bounces at centos.org [mailto:centos-bounces at centos.org] Em nome
de
> James Pearson
> Enviada: quinta-feira, 22 de Junho de 2006 15:54
> Para: CentOS mailing list
> Assunto: Re: [CentOS] x86 uniprocessor 4GB memory
> 
> Bruno Sousa wrote:
> 
>>Hi there, 
>>
>>I'm currently using CentOS 4.3 (Server edition) in a HP DC 5100 with the
>>IntelR 915GV chipset, powered by a PIV 3.0GHZ.
>>
>>Now I'm facing a problem, with memory. 
>>
>>I got myself 4GB of memory, the system bios detects it correctly, but in
>>Linux can only see around 3.5gb memory. With the default kernel-smp (I use
>>hyperthread) or with kernel-hugemem , I have the same results.
>>
>>Is there any way to workaround this issue?
> 
> 
> It is probably the 4Gb memory hole issue - various 'things' reserve 
> memory below 4GB so hiding the real memory from the OS.
> 
> Your BIOS may have a mapping option to map some of this hidden real 
> memory to above 4Gb - however, you need to use a hugemem kernel to 
> access this memory.

Having multiple CPUs would make no difference. The hugemem kernel would 
only see this memory if the BIOS could map it to above 4Gb - if the BIOS 
can't, then there is nothing above 4Gb for the hugemem kernel to see.

A newer version of the BIOS _might_ have added this support ...

James Pearson

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