Re: [RFC/Discussion] mm/damon: Implementation for paused kdamond

[SeongJae Park <sj@kernel.org>]

On Thu, 17 Sep 2026 23:31:53 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> On Mon, 14 Sep 2026 17:28:35 -0700 SJ Park <sj@kernel.org> wrote:
> 
> > On Mon, 14 Sep 2026 23:35:10 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:
> > 
> > > Hi SJ,
> > > 
> > > I noticed that the current implementation for paused kdamond is
> > > periodically applies online parameter updates by kdamond_usleep().
> > > 
> > > I'd like to know if we should change it to waitqueue to achieve a lower
> > > power consumption?
> > 
> > I'd like to make a data driven decision :)
> > 
> > > 
> > > Previous Discussion
> > > ===================
> > > 
> > > I noticed that when you introduced ctx->pause [1], Sashiko asked the
> > > same question, and your response at the time was:
> > > 
> > >     "sample internval is 5ms by default and recommended auto-tuning
> > >     setup makes it hundreds of milliseconds.  So I don't think such
> > >     change is required."
> > > 
> > > I'm curious that, did you think it wasn't neccessary to change it to
> > > waitqueue when it was introduced, or it wasn't neccessary to do so even
> > > after it had been introduced?
> > 
> > I guess I thought so when the quiestion is raised.
> > 
> > > 
> > > Asussmption
> > > ===========
> > > 
> > > This is just my assumption, not a real use case I knew:  When 'pause' is
> > > set on an Android device, user might want DAMON to stop running
> > > completely when the screen is off, thereby reducing the load on the CPU
> > > without losing important information such as regions and age.
> > > 
> > > The current polling may make it harder for the phone to enter idle mode,
> > > resulting in some unnecessary power consumption.
> > > 
> > > However, pause feature is only present in the stable version v7.2 or
> > > higher, and since the latest Android kernel is 6.18, this highly
> > > unlikely will affect any Android users.
> > 
> > If whoever comes with a data that require changes, we can discuss.
> 
> Thank you for your clarify.
> 
> I recently backported the pause feature to my phone.  However, due to
> Android's screen-off mechanisms, I wasn't able to obtain any valid data
> during testing.
> 
> Since we haven't identified any practical issues with the existing pause
> feature, switching to waitqueue isn't neccessary at this time.

Thank you for checking this.  I agree.

> 
> Regarding the documentation, should we explicitly explain the
> relationship between 'pause' and sample_interval in the documentation?
> That way, users can adjust the sample_interval value when using pause
> feature based on their specific use case.

I think that is too much detail for normal users, unless we find a problem from
the lack of the documentation.


Thanks,
SJ

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