Re: [MiNT] Virtual Memory

[Jo Even Skarstein <joska@online.no>]

On Fri, 2013-01-11 at 10:42 -0500, Mark Duckworth wrote:

> I really don't know what I'm doing but I am going to make an honest 
> effort to attempt to implement kernel support for virtual memory.  I 

As Adam has already explained, the big, big problem here is how to get
this working properly with programs that use the AES and VDI. These
absolutely requires that both the system (AES and VDI) and clients use
the same memory space. Also, how does MiNT knows which page(s) can be
swapped and which can't (e.g. interrupt- or traphandlers)?

It can be solved like Adam says by reserving a memory space (shared with
the OS) for current applications, and put a new flag in the header for
executables that are "VM-clean". But I worry about performance. Adapting
the AES/VDI and clients to a VM model would require a whole new API. The
RSC/OBJECT-tree would either have to be replaced with something new, or
be accessed by the client through some API. Same with the shared AES/VDI
structures. This will cost in terms of speed. I fear that AES/VDI
applications would be restricted to "non-VM" also in the future.

Sven Karlsson implemented virtual memory in MiNT 1.14 (or maybe it was
in an early 1.15? I really can't remember, it's 15 years ago or so) but
it really didn't work that well. I suggest you study his implementation
to see what went wrong.

Jo Even