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

[Michal Koutný]

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.)

Thus I was mainly motivated by bundling this change with cleanup of the
module_param().
I may have misjudged importance/usefulness of the data (not using them
myself).

On Wed, Mar 04, 2026 at 01:56:43AM -0800, Breno Leitao <leitao@xxxxxxxxxx> wrote:
> My goal is to ship a kernel that exposes these detailed io stats by    
> default, without requiring any runtime configuration. The stats should 
> simply be available out of the box.

Does it mean the information is useful to you since early boot and
adjusting the param with a userspace tool in boot sequence is too late?

Michal

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