UMA_MD_SMALL_ALLOC

[Peter Grehan]

Hi Nathan,

> In doing the G5 port, I have a problem with the UMA_MD_SMALL_ALLOC 
> option. Because the G5 does not have BAT, this is broken. Even if we 
> were to emulate it with pages, this is not a useful thing to have, since 
> the point of the option would be defeated. But removing it would 
> pessimize the G3/G4 port (the AIM code also panics late in boot without 
> it, but that is a separate issue).
> 
> There doesn't seem to be a way to twiddle it at runtime, which is a 
> major problem if we want to have a single kernel running on all OEA 
> machines. So I'm not sure what to do. Thoughts?

  A long time ago I talked to Alan Cox about modifying this option so it 
could be done at run-time, and he seemed agreeable. The mips port has a 
similar issue in that only the lower 512MB of RAM is direct-mapped, so a 
run-time decision would help them too (though it would be based on free 
pages and not processor variant).

> Also, an update on the G5 port: the PMAP stuff is done to the point 
> where the kernel boots all the way to panicing about not having a PIC, 
> which is late in the boot process and implies that only device support 
> remains. Trap handling is up and running as well. And (with the 
> exception of UMA_MD_SMALL_ALLOC) the same kernel also boots on my G3.

  Fantastic ! Post some patches, I'll give it a try.

  Have you changed the sync_icache code to dynamically switch to 128 
bytes for the G5 ?

later,

Peter.