Re: [PATCH 1/2] cgroup/dmem: add per-region event counters

[Hongfu Li]

Hi, Tejun
Thanks for the review comments.

> > Add dmem.events to report hierarchical low/max event counts per DMEM
> > region.  Increment counters on dmem.max allocation failures and
> > dmem.low protection events.  The file is available for non-root cgroups
> > only.
> 
> Please don't double space in descs or comments. Also, maybe it's obvious but
> it'd help if you list why and how this is useful. Why do we want to add
> this?

I'll fix the double spacing in the commit message and comments.

As for the motivation: dmem already exposes per-region limits and current
usage, but not how often those limits actually matter at runtime. Without
event counters, it's hard to tell whether allocation failures come from
this cgroup, a parent limit, or pressure elsewhere in the hierarchy.
dmem.events provides that visibility for tuning dmem.low/dmem.max and
diagnosing recurring device memory pressure.

I'll expand the commit message to cover this.
 
> > +  dmem.events
> > +	A read-only file that reports the number of times each cgroup
> > +	has hit its configured memory limits.  The format lists each
> > +	region on a single line, followed by the event counters::
> > +
> > +	  drm/0000:03:00.0/vram0 low 0 max 3
> > +	  drm/0000:03:00.0/stolen low 0 max 0
> 
> This isn't a supported file format. Please read the documentation on allowed
> formats.

Thanks for catching this. I'll switch dmem.events to nested-keyed format (region low=N max=M).

Thanks again for the valuable feedback.

Best regards,
Hongfu