[PATCH 01/10 net-next] ipv6: convert CONFIG_IPV6 to built-in only and clean up Kconfigs

[Geert Uytterhoeven]

On Tue, 10 Mar 2026 at 20:58, Arnd Bergmann <arnd at arndb.de> wrote:
> On Tue, Mar 10, 2026, at 20:40, Kolbjørn Barmen wrote:
> > On Mon, 9 Mar 2026, Krzysztof Kozlowski wrote:
> >> On 09/03/2026 03:19, Fernando Fernandez Mancera wrote:
> >>
> >> It must stay module for me. Alternatively, drop it, but then some users
> >> will be really affected.
> >
> > I agree. If anything I would prefer to see IPv4 be made optional (and
> > modular) as well, and not as something IPv6 depends on, it's (AFAIK)
> > impossible today to build an IPv6-only Linux kernel.
>
> My first feeling was that this is a bad idea as well. On the other hand

Exactly my feeling. That's why I stayed quiet for a while, and gave
it some thought...

> I found that the default changed from =m to -y over 10 years ago, all
> recent distros listed in https://github.com/nyrahul/linux-kernel-configs
> use that default (the only two exceptions are board specific builds
> of Debian and Ubuntu for linux-5.x).

Thanks, that is something I was wondering too.

Obviously the world is moving the IPv6 (but having IPv6=m doesn't
preclude that!).  From the other side, there is a trend to have as much
as possible in modules instead of built-in.  A larger base kernel not
only has impact on memory usage (and loading modules has, too), but
also on e.g. boot partitions.  Various platform-specific limitations
may be at play (boot loader size limits, boot partition size limits,
base kernel must fit in the first memory block on systems with many
small discontiguous memory blocks, ...).

But apparently even the Android gki_defconfig (which is not on the
page mentioned above?) has IPv6 built-in.

Back to the numbers:
  - base kernel: atari_defconfig (CONFIG_IPv6=m)
  - with this series, CONFIG_IPv6=n: -22 KiB
  - with this series, CONFIG_IPv6=y: +246 KiB
Note that I ignored any defconfig changes in these series.
The size impact is almost the same for v1 and v2, but only v2 boots.

Each new kernel release increases kernel size by ca. 30-40 KiB on
average.  So a one-time increase of 246 KiB is not unsurmountable,
and slightly less than the increase between v6.14 and v6.19...

Gr{oetje,eeting}s,

                        Geert


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