Maximum Memory available to Kernel

Florenz Kley florenz.kley at sap.com
Wed Jan 15 20:25:01 CST 2003


hi Philip,

--On Tuesday, January 14, 2003 09:45:32 -0600 Philip_Olenick at dell.com wrote:

> Hi, I need to understand, using IA32 architecture (Dell PE platforms),
> what is the maximum amount of memory that the Linux Kernels can address?
> Per RH 7.3? RH8.0? Advanced Server 2.1?

as pointed out elsewhere, 64GB is the max RAM you could put in a box and 
have the Linux kernel configured to see it. However, a sensible limit seems 
to be somewhere between 20-40 GB, because adminstration tables, that keep 
track of what's in the shared mem grow with the amount of RAM. Those tables 
have to be kept in a certain memory area, and decrease the amount of shared 
mem that can be adressed by a process contiguously. Depending on you 
application, one would have to balance those two against each other. 
However, this is not really important below ~ 32 GB of RAM.

There is a performance penalty when using kernels that can see more tha 4GB 
of RAM, but it's rather an academic question, when the requirement is "more 
RAM".

> I have clients looking for Servers with 8GB memory support. I know, no
> issue with IA64 - but unfortunately, DELL have no current IA64 based
> Server available...

no issue with ia32, too. All currently shipping machines, that support 8GB 
or more of RAM, can use it nicely with Linux.

There are happy SAP customers running their systems on machines with more 
than 8GB RAM. Nice performance.

regards,
Florenz

-- 
florenz.kley at sap.com
Dell Computer Corporation at the SAP LinuxLab




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