Subject: Re: HIGHMEM

From: Jon Anders Haugum <[email-masked]>
Date: Tue, 7 Dec 2004 11:29:04 +0100 (CET)

> In 2.4 the support for CONFIG_DISCONTIG and CONFIG_NUMA are a bit tangled
> with each other because IP27 is the only platform to uses these features and
> it needs both.  Other than that you can also just setup your system as 0x0 -
> 0x10000000 being RAM, 0x10000000 - 0x20000000 being reserved memory and
> 0x20000000 - 0x30000000 being highmem.  Which works but is a bit wasteful.
>
> Issue #2 is that we don't support the combination of CONFIG_DISCONTIG and
> CONFIG_HIGHMEM.  And highmem is a lobotomized solution for lobotomized
> silicon anyway.  You have a 64-bit processor - use it's capabilities :-)
>
> Issue #3 - As I recall the TX4937's H3 core is suffering from cache aliases.
> Handling those efficiently for highmem is not easily possible and so we
> don't even try.  More recent kernels will refuse to enable highmem on such
> cache configurations but something like 2.4.18 which by now is an almost 3
> year old antique doesn't know about that and will happily crash.
>
> I recommend you should go for a 64-bit kernel instead.  And 64-bit support
> is certainly better in 2.6 than in 2.4.  Especially the area of 32-bit
> binary compatibility has been improved significantly.

What about on a processor like the AMD au1550?

I've tried the latest from 2.4 branch in cvs, and I haven't been 
successful in geting past INIT either...

Can I place all the memory from address 0x20000000 to get more than 
256Meg?

-- 
Jon Anders Haugum

---

From: Ralf Baechle <[email-masked]>
Date: Wed, 15 Dec 2004 15:18:49 +0100

> Can I place all the memory from address 0x20000000 to get more than 

Yes, that should just work on Alchemy.

  Ralf