Re: [PATCH 00/10 net-next] Convert CONFIG_IPV6 to built-in and remove stubs
From: Fernando Fernandez Mancera
Date: Mon Mar 09 2026 - 09:12:15 EST
On 3/9/26 1:43 PM, Krzysztof Kozlowski wrote:
On 09/03/2026 12:38, Fernando Fernandez Mancera wrote:
On 3/9/26 11:22 AM, Krzysztof Kozlowski wrote:
On 09/03/2026 03:19, Fernando Fernandez Mancera wrote:
Historically, the Linux kernel has supported compiling the IPv6 stack as
a loadable module. While this made sense in the early days of IPv6
adoption, modern deployments and distributions overwhelmingly either
build IPv6 directly into the kernel (CONFIG_IPV6=y) or disable it
entirely (CONFIG_IPV6=n). The modular IPv6 use-case provides little to
no practical benefit today.
It does. We all use generic kernels, thus it is one configuration for
all boards and some setups have IPv6 and some not. The ones without IPv6
just don't use that module.
While I understand this, I would like to clarify that IMHO IPv6 isn't a
secondary protocol and it is fundamental to modern networking. This is
Not for end user devices. None of my devices - neither routers, nor
embedded boards, nor mobile phone from 5G provider - receive IPv6
address, thus for them it is not fundamental.
I am not so sure about this. Many if not most modern routers provide IPv6 support and as I said it is enabled as built-in in openWRT since [1]. For mobile phones they probably use IPv6 when connected to routers but even 5G providers are using IPv6. They are working on IPv6-only deployments with NAT64 too [2].
[1] https://github.com/openwrt/openwrt/commit/0c8f0186d58468024db96a5ab0ca36a4d400d408
[2] https://www.ietf.org/archive/id/draft-ma-v6ops-5g-ipv6only-01.html
I agree it is fundamental for your cloud machines and network backbone
which you are targeting, but this patchset completely ignores other
users calling their use-cases "little practical benefit"! Try running
Amiga machine...
There is no even bloatometer stats for these defconfigs so we can see
the impact.
Sure. I can provide them.
why I believe it should be built-in by default. Currently OpenWRT,
Debian ARM and others already ships the kernel with CONFIG_IPV6=y. I
know that Alpine and Yocto doesn't do that for arm64.
Maybe there are other reasons why distro should not choose it as module
(like module load calls on ipv6 packets) but that was not explained here.
Arch Linux Rpi kernel on arm64 has IPV6=6 and the module itself is 650
kB. That's noticeable for smaller arm64 boards.
For arm it would be even more noticeable as some have 256 MB RAM like
first Rpi.
I guess the most critical one here is Yocto but if the developer of the
embedded device is sure they won't use IPv6 at all, they should turn it off.
At the same time, Alpine ships software that enable IPV6 and is
frequently loaded as a module. So the only remaining concern would be
the boot partition size. I don't really have a solution for that problem.
I think that the infrastructure for allowing IPV6=m is bug-prone and it
impacts performance. Forcing the use of indirect function calls in core
networking, Netfilter or BPF datapaths seems like a heavy tax to me.
Also, with these generic kernels (so again all machines are using same
ones, e.g. distro) users can easily blacklist the module.
FWIW; users can still boot with kernel command line parameter
ipv6.disable=1 and then IPV6 will be administratively disabled.
It's not the same. You enabled it on amiga_defconfig and do you
understand what sort of machine is that? The newest have 16 MB RAM, many
much less like 2 MB, and ipv6 module on m68k is 400 kB, so pretty
significant change.
Fair enough. Of course I am not familiar with all the architectures affected. This feedback is more than welcome and it might make a lot of sense to disable IPv6 on Amiga and probably different architectures. By the way if by Amiga you mean [3] then I believe it should be disabled.
[3] https://en.wikipedia.org/wiki/Amiga
Thanks,
Fernando.