large memory support

large memory support

Post by Robert Schweiker » Fri, 21 Feb 2003 10:47:22



I know that Linux can support up to 64GB of memory on an IA32 system,
what I do not know is what I have to turn on to get this capability.

Can anyone tell me the flag or/optin to set during configuration?

Does anyone know whether or not the kernel distributed with the SuSE 7.3
distribution is compiled appropriately to deal with memory > 4GB?

Thanks,
Robert

 
 
 

large memory support

Post by torste » Fri, 21 Feb 2003 11:10:33


Quote:>Can anyone tell me the flag or/optin to set during configuration?

CONFIG_NOHIGHMEM
CONFIG_HIGHMEM4G
CONFIG_HIGHMEM64G

Quote:>Does anyone know whether or not the kernel distributed with the SuSE 7.3
>distribution is compiled appropriately to deal with memory > 4GB?

No.

Here's Why.
Using memory under 1GB allows using an offset bit to a base address.
This offset can be loaded into a cpu register without loading a
full address from memory, consequently, this is the fastest option.

Using memory between 1GB adn 4GB requires a full 32bit address.  The
entire address must be loaded into a register, and this causes cache
misses, which decreases performance.

Above 4GB, you are using 36bit addressing.  Since this method is not
"natively" supported on 32 bit architectures, the machine must read
each parity bit and interpret it as RAM.  This interpreting overhead
causes a performance hit.

Torsten

 
 
 

large memory support

Post by Jhair Tocancipa Trian » Fri, 21 Feb 2003 11:10:38


Quote:Robert Schweikert writes:
> I  know that  Linux can  support up  to 64GB  of memory  on  an IA32
> system, what  I do not know  is what I have  to turn on  to get this
> capability.

Turn on  the 64  GB high memory  support in the  kernel configuration,
recompile and install it.

Quote:> Does anyone know whether or not the kernel distributed with the SuSE
> 7.3  distribution is compiled  appropriately to  deal with  memory >
> 4GB?

I don't know.

--
--Jhair