Re: [PATCH 00/10] sh: remove NUMA and SPARSEMEM support

[Arnd Bergmann]

On Mon, Apr 13, 2026, at 12:46, Mike Rapoport wrote:
>
> NUMA support for SuperH was introduced a long time ago by commit
> b241cb0c885e ("sh: Support for multiple nodes.")
>
> 	"... for boards with many different memory blocks that are
> 	 otherwise unused (SH7722/SH7785 URAM and so forth)"
>
> In reality, this added 128K of memory on sh7722 and sh7785 and 256K on
> shx3 at the expense of all the NUMA related code in the kernel.
>
> For build of v7.0-rc7 with defconfig and the same configuration with
> CONFIG_NUMA disabled, bloat-o-meter reports difference of ~76k. Disabling
> CONFIG_SPARSMEM on top increases the difference to ~94k. And that's only
> overhead in code and static data that does not take into the account data
> structures allocated at run time.
>
> And all this overhead has been there for nothing for almost 8 years
> because since commit ac21fc2dcb40 ("sh: switch to NO_BOOTMEM")
> those additional "nodes" could not be used by the core MM because the
> maximal pfn for ZONE_NORMAL was cut out at the end of the normal memory.

I had looked at it when you asked me about it last year, and I can
confirm that agree with all your findings and the resulting patches.

Whole series

Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>

Two very minor points:

* It looks like you left the 'config SYS_SUPPORTS_NUMA' symbol
  in Kconfig, which no longer does anything, so this should probably
  be removed in patch 9 along with the lines that select it.

* It appears that after your series, RISC-V is the only remaining
  architecture that supports NUMA in 32-bit mode, which I think
  we should not allow as a configuration, given that this would
  run into untested code and no hardware exists for it.
  Apparently commit 4f0e8eef772e ("riscv: Add numa support for
  riscv64 platform") intended this to only be for 64-bit targets
  but did not add a Kconfig dependency for CONFIG_64BIT (or
  CONFIG_SMP, which was added later).

        Arnd