Re: M68k backend has landed in LLVM - NetBSD support

On Tue, 9 Nov 2021, John Klos wrote:

>> Bitsavers has all of the Motorola manuals online, in 
>> <http://www.bitsavers.org/components/motorola/68000/>. You'll want the 
>> 68851, 68030, 68040, and 68060 manuals.
>
> I have several of these (M68030, M68060 books), and they're great references, 
> but they really don't help with understanding the NetBSD pmap. I'm learning, 
> but it's a slow process.
>
>> Probably the simplest possible change beyond switching to 8KB pages would 
>> be to increase the size of the root. Even if it's only increased statically 
>> (say based on a kernel config parameter -- you aren't going to make use of 
>> 4GB of virtual address space on an 8MB system) it doesn't take much to 
>> enable vastly more VM.
>
> Increase the size of the root? I don't follow... Would love to hear more, 
> though :)

   Increase the size of the level0 (root) table.  It's currently only one 
page, and the way it was set up requires the root table to be contiguous 
physical pages.  I think there wasn't a way to ensure allocation of 
multiple contiguous pages in the past - I don't know if that has changed.

   I had done some work on a way to increase the size of the root table, as 
well as using a pool for the tables.  I'm currently checking if my changes 
still build.

Mike

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Michael L. Hitch                        [email protected]
Operations Consulting,  Information Technology Center
Montana State University, Bozeman, MT     USA