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

[Breno Leitao <leitao@debian.org>]

Hello Tejun,

On Tue, Mar 03, 2026 at 07:46:46AM -1000, Tejun Heo wrote:
> On Tue, Mar 03, 2026 at 06:11:15AM -0800, Breno Leitao wrote:

> > Before (without blkcg_debug_stats enabled):
> >   253:0 rbytes=6273024 wbytes=0 rios=20 wios=0 dbytes=0 dios=0 cost.usage=0
> >
> > After:
> >   253:0 rbytes=6273024 wbytes=0 rios=20 wios=0 dbytes=0 dios=0 cost.usage=0 cost.wait=0 cost.indebt=0 cost.indelay=0
>
> Given that they haven't changed for a long time, maybe it's okay to expose
> them by default, but why? This is something which can be toggled on easily
> at any time.

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.

> What's the benefit of exposing these extra numbers which
> probably don't mean much for most people?

My original plan was to introduce a Kconfig option for this. In v1 (about a
month ago), Michal suggested removing the toggle entirely and always exposing
the stats, which seemed reasonable to me and received no objections, so I
went ahead with that approach.

To be clear: is your position that we should not support building a kernel
that always exposes the detailed stats in io.stat?

Thanks for your review,
--breno