Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout

Geert Uytterhoeven
2025-09-19T07:17:53Z

Hi Arnd,

On Thu, 18 Sept 2025 at 15:13, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wed, Sep 17, 2025, at 14:59, Jason Gunthorpe wrote:
> > On Tue, Sep 09, 2025 at 11:23:37PM +0200, Arnd Bergmann wrote:
> >
> >> I'm still collecting information about which of the remaining highmem
> >> users plan to keep updating their kernels and for what reason.
> >
> > On this topic of removing some parts of highmem, can we say goodbye to
> > kmap_high_get()? Only ARM uses it and only for
> > !cache_is_vipt_nonaliasing() systems.
>
> Good idea. I think we are almost there, just need to verify that
> there is actually no impact for existing users. I already knew
> that there is very little highmem usage on ARMv6 and earlier, but
> I tried to recheck all platforms that might be affected:

> * Microchip SAM9x7 is the newest ARMv5 chip, clearly does
> get kernel updates, and the only one I can think of with
> DDR3 support, but seems to be limited to 256MB total memory.

Are they limited to DDR3?

IIRC, someone (you? ;-) told me at ELCE that Microchip keeps on spinning
new variants of old SoCs, to accommodate the changing DDR landscape
and market. So perhaps they also accept larger RAM sizes?

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds