Subject: Re: [PATCH 00/10 net-next] Convert CONFIG_IPV6 to built-in and remove stubs

From: Krzysztof Kozlowski <[email-masked]>
Date: Tue, 10 Mar 2026 21:02:40 +0100

On 10/03/2026 00:18, Jakub Kicinski wrote:
> On Mon, 9 Mar 2026 11:26:08 +0100 Krzysztof Kozlowski wrote:
>> Heh, I just checked, that's 6 MB module on arm64 which apparently you
>> want to put into the kernel!
> 
> Pretty sure you get 6MB because you have DEBUG_INFO enabled?

Yeah, that was defconfig with KASAN, not full debug info. defconfig
comes with deduced debug info.  In one of other email threads I
corrected that actual size on distro kernel is much smaller, e.g.
200-400 kB depending on arch or distro settings.

> IMO "I have full debug info but I care about kernel size" is
> internally inconsistent.

My argument is that many of arm64 devices I work with have fixed
partition sizes, come with their own bootloader which uses separate
fixed-size boot partition. I still want to be able to load arm64
defconfig into that boot partition. If it does not fit, I need to tweak
defconfig, e.g. disable some options.

I find it valid usecase and I was disagreeing here with that cloud-only
or big-machines-only approach.

> 
> Here is the top line of bloatometer without debug info:
> 
>   add/remove: 1769/7 grow/shrink: 86/0 up/down: 374521/-228 (374293)
> 
> The vmlinux increases by 200kB with IPv6 built in.
> Not a very dramatic increase.
> 
> Please note that opening any dual-stack socket will cause the IPv6
> module to get loaded. And opening a dual-stack socket will fail if 
> IPv6 is blacklisted. So I find it quite hard to believe that other
> that deeply embedded systems with custom configs there are systems
> out there which don't end up with IPv6 loaded. Whether they have 
> a single IPv6 address configured or not.

Yes, Ubuntu for that reasons does not have it even as module.

This should be used as *the* argument for these changes.

> 
> And if we stop supporting =m we can actually turn a bunch of indirect
> calls into static inlines so in practice the memory use on real system
> will be lower! 
> 
> Please be reasonable, this is objectively the right move.

I am very reasonable, just need to hear reasons. Just to remind - none
of the machines I have, none of the routers, none of the mobile phones
on 4G and 5G receive IPv6 so they don't actually need it. Not having
IPv6 built-in is therefore a valid use case.

Best regards,
Krzysztof