Configuring virtual memory layout

[Hommel, Thomas (GE EntSol, Intelligent Platforms)]

Hello,
I am trying to figure out how to configure the virtual memory layout in
the kernel.
To increase the size of the Vmalloc area, I have set KERNEL_START to
0xa0000000 and have left LOWMEM_SIZE at 0x30000000. The other parameters
in 'Advanced setup' are unchanged.
This works fine with 512 MB of RAM. However, with 1 GB of RAM installed,
the system shows odd behavior, crashes, faults, ... This seems to be due
to the fact that it then uses 256 MB of high memory.

I played around with HIGHMEM_START, but couldn't get a working setting.

How do these parameters have to be configured correctly? Is there any
documentation for that?

Thanks for your help
Thomas