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

(oops, missed that earlier)

On Mon, Apr 13, 2026 at 01:14:49PM +0200, Arnd Bergmann wrote:
> 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 <[email protected]>

Thanks!
 
> 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.

I think it better fits patch 1 that removes CONFIG_NUMA, patch 9 is about
SPARSEMEM.
 
> * 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).

I can send a patch to RISC-V for it.
 
>         Arnd

-- 
Sincerely yours,
Mike.