Re: Subtle MM bug

[Andrea Arcangeli]

On Mon, Jan 08, 2001 at 02:00:19PM -0800, Wayne Whitney wrote:
> I'd ask if this jives with your theory:  if I configure the linux kernel
> to be able to use 2GB of RAM, then the 870MB limit becomes much lower, to
> 230MB.

It's because the virtual address space for userspace tasks gets reduced
from 3G to 2G to give an additional giga of direct mapping to the kernel.

Also the other limit you hit (at around 800mbyte) is partly because
of the too low userspace virtual address space.

You can use this hack by me to allow the tasks to grow up to 3.5G per task on
IA32 on 2.4.0 (equivalent hack exists for 2.2.19pre6aa1 with bigmem, btw it
makes sense also without bigmem if you have lots of swap, that's all about
virtual memory not physical RAM).  However it doesn't work with PAE enabled
yet.

	ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/patches/v2.4/2.4.0-test11-pre5/per-process-3.5G-IA32-no-PAE-1

If you run your program on any 64bit architecture (in 64bit userspace mode)
supported by linux, you won't run into those per-process address space limits.

Andrea