Re: [RFC v2 2/3] atomic: Specify alignment for atomic_t and atomic64_t

[Geert Uytterhoeven]

Hi Finn,

On Wed, 1 Oct 2025 at 03:46, Finn Thain <fthain@xxxxxxxxxxxxxx> wrote:
> On Tue, 30 Sep 2025, Geert Uytterhoeven wrote:
> > > To silence the misalignment WARN from CONFIG_DEBUG_ATOMIC, for 64-bit
> > > atomic operations, for my small m68k .config, it was also necesary to
> > > increase ARCH_SLAB_MINALIGN to 8. However, I'm not advocating a
> >
> > Probably ARCH_SLAB_MINALIGN should be 4 on m68k.  Somehow I thought that
> > was already the case, but it is __alignof__(unsigned long long) = 2.
>
> I agree -- setting ARCH_SLAB_MINALIGN to 4 would be better style, and may
> avoid surprises in future. Right now that won't have any effect because
> that value gets increased to sizeof(void *) by calculate_alignment() and

Ah, so there it happens...

> gets increased to ARCH_KMALLOC_MINALIGN or ARCH_DMA_MINALIGN by
> __kmalloc_minalign().

Thanks for checking!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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