On Wed, Mar 6, 2024, at 17:22, Arnd Bergmann wrote:
> On Wed, Mar 6, 2024, at 16:31, Andreas Larsson wrote:
> On a relate note, it does seem odd to have such a small
> lowmem area, and I wonder if that could be extended.
> The 192MB lowmem limit comes from
>
> #define SRMMU_MAXMEM 0x0c000000
>
> but I don't understand if that is a hardware limitation
> or a design choice that can be changed, and if it is
> even valid on leon or only on the old sun machines.
I had another look and found that this is a result of
arch/sparc/include/asm/page_32.h:#define PAGE_OFFSET 0xf0000000
which gives 3840MiB to userspace addresses, leaving only
256MiB for kernel lowmem and vmalloc space, which is
less than any other architectures.
I still don't know the history behind this choice, but I
see this was already configured the same when arch/sparc/
was originally merged. You can probably change it to a more
sensible 0xc0000000 or 0x80000000 like on other
architectures and run without highmem on anything with
less than 2GB of total RAM.
How much RAM do Leon machines have typically, or at the
maximum?
Arnd
