Re: [PATCH v2] blk-cgroup: always display debug stats in io.stat

[Tejun Heo]

Hello,

On Wed, Mar 04, 2026 at 02:28:03PM +0100, Michal Koutný wrote:
> On Tue, Mar 03, 2026 at 07:46:46AM -1000, Tejun Heo <tj@xxxxxxxxxx> wrote:
> > > has not been modularized since commit 32e380aedc3de ("blkcg: make
> > > CONFIG_BLK_CGROUP bool"), making the module parameter a historical
> > > artifact. Readers of the nested-keys format should be able to handle
> > > additional fields.
> > 
> > I'm not sure what the above para means. Module param works just fine for
> > built-in modules on both boot command line and through sysfs.
> 
> Yeah, it works but BLK_CGROUP is not a module/built-in it's config
> option affecting builds. I find the module_param() in blk-cgroup.c to be
> a residual, I admit it's convenient way how to expose a tunable to
> userspace.
> 
> (Contemporary way of implementing the option could also be a cgroupfs
> mount option/feature or maybe sysctl for which tooling is available.)

I don't konw whether I'm the only one doing it but I use moduleparams as an
easy way to get non-API boot and runtime toggles whether the target code is
actually module or not. It's easy to use and the params are in a pretty gray
area in terms of API stability, so if you wanna throw in a debug option, it
works.

Thanks.

-- 
tejun