[plug] upper RAM size limits in Linux

[Trent Lloyd]

I know that 4G is the upper limit for one process to use I think

I believe that you can use up to 64G overall.

As for glibc/etc I'm pretty sure the '3 gig limit' is for each instance of a program etc.

I could be wrong.. just what i recall off hand.

Cheers,
Trent

On Tue, Dec 02, 2003 at 09:27:19PM +0800, Denis Brown wrote:
> Dear PLUG list members,
> 
> I have a "nice" problem :-)  Am about to order a couple of gritty
> workstations and servers for a medical imaging laboratory.  On the server
> side we're talking dual Xeon 2.8GHz, hardware RAID, initially 0.4TByte
> disk space across three spindles, U320 SCSI and now the question... Budget
> will probably allow up to 4 GByte RAM, possibly more, but isn't 4GByte the
> upper addressable limit anyway given the bus width?   Too late in the
> night for my math cells to function :-(
> 
> On the workstation side, single Xeon 2.8GHz, single SCSI320 drives and ???
> RAM with gigabit links between server(s) and WS(s).   Since this is
> imaging, the more RAM the better but is there a practical upper bound in
> Linux?   I've seen reference to having to specify memory size (in
> lilo.conf???) but I think that was in the Bad Old Days (tm)
> 
> As an example of the sort of memory requirements there was a message on
> one of the imaging lists tonight suggesting that 3GByte swap would be
> appropriate for some functional MRI work - file sizes for a single study
> 500MByte, and we generally average 100 of those from a population to
> create normalised templates for subsequent analysis.   (Do not try this on
> your abacus!)
> 
> I did some Googling but haven't found much on the topic since about Feb
> 2000, when a discussion on the kernel archive talked of brk() having an
> upper bound of 900MByte and mmap() up to 3GByte.   There was some talk in
> the same thread about getting the glibc people to opt for the 3GByte limit
> by default.
> 
> TIA,
> Denis
> 
> 
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