Re: problem with fsck under 1.3, can't install

[Ignatios Souvatzis <ignatios%theory.cs.uni-bonn.de@localhost>]

> In article <199801161650.RAA01752%cauchy.cs.uni-bonn.de@localhost>,
>       Ignatios Souvatzis <ignatios%theory.cs.uni-bonn.de@localhost> writes:
> > Because you can tell the bootloader to pretend you have less memory (say, 
> > only 40 Megs: -m40960, like me on my BIG machine) ...
> 
> If the kernel can't handle more than 64MB it shouldn't try do use it
> without any special option to "loadbsd".

It's no fixed limit. Its rather like:

SUm of:
        kernel text+data+bss+symbols
        +bootloaderoptions
        +I/O space
        +dynamically allocated structures.

The latter is variable, and partially (due to the disk buffer cache being
scaled with memory, per default) memory size dependend.
But a graphics board with a big address space (e.g. cv64/3d) might cause
the same problem.

You can work aorund this by using less memory to a certain extend, or by
taking out some graphics board (or SHUTUPing it).

Its not easily detectable by the kernel before its too late, because the
kernel must start the MMU at the very beginning, and the current pmap
implementation uses a fixed size of the upper level of the page table.
(BTW, the i386 had a similar problem until very recently, too... can you
spell "NKPDE"?) 

Somebody would have to rewreite the pmap to have all those tables variable
sized, to fix the problem.

> 
> > ... and build a kernel with a bigger table easily...
> 
> Easily? It's not even documented which parameters you have to tweak.
> There should at least be a "MACHINE_WITH_LOTS_OF_RAM" option.

loadbsd -h will happily tell you this. I guess the INSTALL document should
give a hint.
> 
> > ... while people on a 68030/16 machine with 8 megs
> > would need much longer to build a kernel which doesn't take 2 megs away.
> 
> People with such machines will probably drop Unix on Amiga sooner or later.

No. People with such machine wrote half of the Amiga support for NetBSD (later
they got more memory...). And it really helps that the standard kernel only
takes away less from their memory.

        -is