Re: [REGRESSION] kernfs: empty cgroup rmdir latency after delete-notification changes

[Tejun Heo]

Hello,

On Sun, Sep 13, 2026 at 10:43:04PM +0800, Chengfeng Lin wrote:
> I found an increase in empty cgroup removal latency across 507d8ce13f5b
> ("kernfs: Don't set_nlink for directories being removed") and eea5d2bb34ba
> ("kernfs: Send IN_DELETE_SELF and IN_IGNORED"). With sched_ext disabled,
> rmdir() went from about 6.5 us to 9.6 us, an increase of 46-47%.
> The result held in two independent runs.

I don't want to make cgroup removal unnecessarily expensive but at the same
time it's not an operation that I consider to be a hot path, so as long as
the operaiton can finish in a reasonable amount of time and single digit us
definitely is, performance of rmdir usually isn't something which is high in
priority. Can you please detail why this matters for you?

Thanks.

-- 
tejun