Re: [PATCH] mm/damon: reject zero sampling interval

[SeongJae Park <sj@kernel.org>]

Hi Karthikeyan and Sang-Heon,

On Thu, 17 Sep 2026 18:00:13 +0000 Karthikeyan KS <karthiproffesional@gmail.com> wrote:

> Hi Sang-Heon, Hi SJ,
> 
> > I think SJ already commented on a similar patch. please refer to [1]
> >
> > [1] https://lore.kernel.org/all/20260722094304.3132750-1-dayou5941@163.com/

Thank you for pointing this out, Sang-Heon!

> 
> Thanks, missed that thread. Same objection applies to mine.
> 
> > Can't we keep supporting zero sample interval and fix the warning
> > or the real bug instead?
> 
> I measured a few floors for kdamond_usleep():
> 
>   floor    kdamond CPU (3s)   vs sample_us=5000
>   1us      84%                28x
>   100us    42%                14x
>   1000us   12%                ~3x
>   5000us   ~2%                1x (matches control)
> 
> 5000us is damon_new_ctx()'s own default, and at that floor the spin
> is just gone.
> 
> Would you rather we just document sample_us=0 as accepted/expected
> behavior, or clamp it to that default inside damon_set_attrs()?

I'd prefer adding a comment saying zero sampling interval is accepted.  I think
damon_attr kernel-doc comment is a good place for adding that.


Thanks,
SJ

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