Re: Addressing more than 2 Gig of Memory

Matthew Wilcox (Matthew.Wilcox@genedata.com)
Fri, 30 Jul 1999 23:40:24 +0200

On Fri, Jul 30, 1999 at 03:18:12PM -0500, mikosh@austin.ibm.com wrote:
> >> I understand that there may be a Linux kernel patch available that
> >> increases the maximum amount of addressable memory beyond 2 gigabytes.
> >>
> >> Do you know of such a patch for the 2.2 kernel?
>
> >If you're talking about the 36 bit memory support, such a patch does not
> >exist yet -- to the best of my knowledge it's still in the 'napkin' stage.
>
> Yes, thanks for the response.
>
> But also, is there a patch which provides an unsigned 32 bit memory address
> space for each process? (as opposed to a signed 32 bit address, which I'm
> finding in all the 2.2.x kernel updates)
>
> So the maximum amount of addressable memory would be 4 GB.

I think you must be mistaken; by default Linux supports 3GB of virtual
memory and 1GB (- epsilon = 960MB, iirc) of physical RAM. It's possible
to change that to 2GB + 2GB, but it isn't possible to get 4GB of linear
addressed space on x86. If you need that, get an Alpha.

Even the proposed 36-bit extensions won't allow this -- they merely allow
the system to keep around many more anonymous pages which you can't use
directly. Fortunately, this is exactly what big databases want.

-- 
Matthew Wilcox <willy@bofh.ai>
"Windows and MacOS are products, contrived by engineers in the service of
specific companies. Unix, by contrast, is not so much a product as it is a
painstakingly compiled oral history of the hacker subculture." - N Stephenson


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