32-bit HIGHMEM and game console downstreams
Ash Logan
ash at heyquark.com
Tue Sep 16 11:57:00 AEST 2025
On 13/9/25 23:52, Arnd Bergmann wrote:
Hi Arnd! Thanks for your reply.
> Like most other machines, this one is probably fine with a combination
> of a custom LOWMEM_SIZE setting and using zram-highmem, even if we
> end up removing support for highmem page cache.
Good shout - I'm now testing a 2G/2G split which allows for 1536MiB
lowmem. I know that's a somewhat aggressive setting for userspace, so
we'll see if anything breaks. I read Rasbian shipped similar kernels and
had issues with Wine, though that's not a common use case on PowerPC ^^
> The smaller devices are probable getting problematic sooner, 96MB
> in the Wii is already really tight and this only gets worse over
> time.
The maintainer of that downstream claims to be able to boot modern
text-mode distros on the GameCube' 24MB, which I find really impressive!
> Just to be clear: there is no general 32-bit deprecation going on. When
> I talked about phasing out 32-bit platforms over time, that is purely
> going to be those that have no users left, or the few ones that are
> causing more work than they are worth. E.g. The ppc405 ones got
> removed recently (after many years of discussion) because they were
> making ppc440 maintenance harder and had no known users.
>
> Highmem does get in the way, but unless more -mm folks make a strong
> argument in favor of removing it all, it's more likely that we'll
> go with Willy's suggestion of keeping highmem on page cache (anon
> and file mappings) than just keeling zram, and even that would
> still work.
That's good to hear. I would like to have the page cache, though I'm
still going to try and maximise lowmem as well.
Thanks,
Ash
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