linux-kernel - Re: [PATCH -next] cgroup: increase maximum subsystem count from 16 to 32

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Message-ID: <asryf3kk6c337l33faqpeznk7d4a3rxblzmqrawxffq7sfbaf7@5yfzzdroltjq>
Date: Thu, 29 Jan 2026 10:23:07 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: tj@...nel.org, hannes@...xchg.org, rostedt@...dmis.org, 
	mhiramat@...nel.org, mathieu.desnoyers@...icios.com, inwardvessel@...il.com, 
	shakeel.butt@...ux.dev, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, lujialin4@...wei.com
Subject: Re: [PATCH -next] cgroup: increase maximum subsystem count from 16
 to 32

On Thu, Jan 29, 2026 at 06:31:33AM +0000, Chen Ridong <chenridong@...weicloud.com> wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> The current cgroup subsystem limit of 16 is insufficient, as the number of
> subsystems has already reached this maximum.

Indeed. But some of them are legacy (and some novel). Do you really need
one kernel image with every subsys config enabled?

> Attempting to add new subsystems beyond this limit results in boot
> failures.

That sounds like BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16) doesn't trigger
during build for you. Is the macro broken?

> This patch increases the maximum number of supported cgroup subsystems from
> 16 to 32, providing adequate headroom for future subsystem additions.

It may be needed one day but I'd suggest binding this change with
introduction of actual new controller.


(As we have some CONFIG_*_V1 options that default to N, I'm thinking
about switching config's default to N as well (like:
CONFIG_CGROUP_CPUACCT CONFIG_CGROUP_DEVICE CONFIG_CGROUP_FREEZER
CONFIG_CGROUP_DEBGU), arch/x86/configs/x86_64_defconfig is not exactly
pinnacle of freshness :-/)


Thanks,
Michal

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