Re: [PATCH 2/2] mm/damon: skip deactivated schemes in watermark checks and add fallback sleep

[SJ Park <sj@kernel.org>]

On Sun,  9 Aug 2026 05:55:54 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> Hi SJ,
> 
> On Fri,  7 Aug 2026 07:07:39 -0700 SJ Park <sj@kernel.org> wrote:
> 
> > This is an intended implementation.
> > 
> > When all schemes are deactivated by watermarks, DAMON stops monitoring.  It was
> > implemented in the way because we didn't want DAMON consumes system resource in
> > the case.  But, later it turned out DAMON's resource consumption is really
> > negligible.  Rather, it is turned out that it makes DAMON runs with stale
> > history when it is activated again.  Particularly, regions have 'age' and their
> > start/end addresses that was emerged before the deactivation.  Those are
> > meaningless and could even cause wrong DAMOS decisions.
> > 
> > We don't want that anymore.  For a case the user really want DAMON completely
> > stops, we introduced 'pause'.  For max_nr_snapshot-based deactivation, we don't
> > intend to completely stop DAMON.
> > 
> > Maybe the documentation can be updated to further clarify this.
> 
> Wait, according to the documentation and the code, DAMON will still stop
> monitoring when all schemes is deactivated.

That's correct.

[...]
> Should this be changed to monitoring will not stop?

No.  The change you mentioning will be unexpected behavioral change.

> 
> Also this patch (0002) add a new function named damos_is_deactivated(),
> it checks both wmarks.activated and max_nr_snapshot conditions, and I
> replace the wmarks.activated-only with this new function.

Let's distinguish watermarks based deactivation and max_nr_snapshots based
deactivation.  They are completely different things and have different
behaviors.  The current documentation may confused you.

> 
> I am sorry if my commit message has caused you any misunderstanding.

No worry.  The current poor documentation is the one to blame in my opinion.


Thanks,
SJ

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