Re: PROBLEM: Linux 2.6.0-test11 only lets me use 1GB out of 2GB ram.

Raul Miller
2003-12-11T14:41:53Z

> On Thu, Dec 11, 2003 at 12:33:39AM -0500, Ed Sweetman wrote:
> > I thought highmem wasn't necesarily needed for memory <=2GB? Highmem
> > incurs some performance hits doesn't it and so the urge to move to it
> > with only 2GB is not very attractive. Anyways i'm just interested in if
> > that's the case or not since 2GB is easy to get to these days and i had
> > heard that highmem could be avoided passed the 1GB barrier.

On Wed, Dec 10, 2003 at 09:41:11PM -0800, William Lee Irwin III wrote:
> You're probably thinking of 2:2 split patches.
>
> 2:2 splits are at least technically ABI violations, which is probably
> why this isn't merged etc. Applications sensitive to it are uncommon.
>
> Yes, the SVR4 i386 ELF/ABI spec literally mandates 0xC0000000 as the
> top of the process address space.

Apologies if I'm asking about the obvious, but...

[1] isn't 0xC0000000 at 3GB?
[2] Even if ELF did restrict a user process to 1GB (which I'm pretty
sure it doesn't), wouldn't the kernel still be able to manage 2GB of
user memory?

Probably my real question is: "what's this about 2:2 split patches"?

Basically, I thought "linux supports 2GB ram" had been been the case
since the dark ages. It's hard for me to comprehend how highmem, or 64
bit cpus, could have much to do with a 1GB limit.

[In my fantasies, I was thinking that the system came up with only 1GB of
the memory easily usable, and that the lack of support for my hardware
meant that it couldn't be properly reconfigured. But I recognize that
I haven't spent the time researching this to see if in fact this is
the case.]

I am in the process of bringing up an cross compilation environment for
amd64 -- I need to do that anyways -- and I'll try building a real 64
bit kernel to see if that helps any. If that doesn't, I guess I'll try
a couple 4G highmem kernels (one 64 bit, one 32 bit). If nothing else,
that will eat up some time...

Thanks,

--
Raul Miller
moth@magenta.com