One of the problems with the PA linux implementation is the upward
growing stack.  On most architectures, the virtual process space is
divided into


| unmapped | exec and heap |  mappings and stack |
                   TASK_UNMAPPED_BASE        TASK_SIZE


The mappings grow up from the start and the stack grows down from the
end of the area. If they ever meet, the process segfaults.

On palinux, we have an upward growing stack, so we have to size the
stack so when it reaches its ulimit, it hits the top of the area.  This
means that large stack limits cut into the mappable area (and also that
we have to impose a hard limit of 1GB on the stack size otherwise the
user could remove the ability to map processes entirely by setting the
stack limit too high).

The proposal to fix this is to start the stack growing upwards from
TASK_UNMAPPED_BASE and have the mappings grow downwards from TASK_SIZE. 
This should allow us to behave in exactly the same manner as x86 and not
have an arbitrary limit on the stack size.

The attached patch (against 2.5.70-pa1) does this, if you'd like to
comment on it or try it out.

James