Large memory support in Linux

[Lennart Sorensen]

On Tue, Jan 22, 2008 at 04:06:00PM -0500, Asaf Maruf wrote:
> Hello
> 
> What is the maximum memory supported by the current Linux kernel? Will i
> have to use the HUGEMEM kernel for a large memory configuration of 64G+ or
> 128G+.

If you use x86 (i386-i686/k7/etc) then you need HIGHMEM4GB if you
have more than 900MB, you need HIGHMEM64GB if you have more than about
3GB ram (basically if you have any memory mapped higher than 4GB address).
x86 32bit can't addres more than 64GB no matter what you do.

If you run amd64 (x86_64) then you don't have to worry about it.
Maximum address range is at least 40bit on Opterons, while at least some
Xeon's were limited to 36bit (64GB).  Not sure what the current physical
address range on the modern Xeons is now.  I see IBM says one of their
Xeon servers can run 512GB so that would be at least 39bit.

So if the machine is 64bit capable, and can accept that much ram, then
32bit linux with HIGHMEM64G can use about 63GB of the ram.  64bit linux
can use all of it with the standard config, since it doesn't have any
settings for memory space.

--
Len Sorensen
--
The Toronto Linux Users Group.      Meetings: http://gtalug.org/
TLUG requests: Linux topics, No HTML, wrap text below 80 columns
How to UNSUBSCRIBE: http://gtalug.org/wiki/Mailing_lists