Re: [RFC PATCH 0/2] DAMON: add priority-based scheme application control

[SeongJae Park <sj@kernel.org>]

On Fri, 26 Sep 2025 11:23:33 +0800 Enze Li <lienze@kylinos.cn> wrote:

> Hello SJ,
> 
> On Mon, Sep 22 2025 at 06:01:32 AM -0700, SeongJae Park wrote:
> 
> > Hello Enze,
> >
> > On Mon, 22 Sep 2025 18:10:20 +0800 Enze Li <lienze@kylinos.cn> wrote:
> >
> >> This patchset introduces a priority mechanism for DAMON's scheme
> >> application, allowing users to specify the relative importance of
> >> monitored processes.  The changes ensure that higher-priority targets
> >> receive more frequent memory management operations while maintaining
> >> fairness across all monitored processes.
> >
> > Thank you for this patchset.
> >
> > There are features for monitoring target-based DAMOS filtering
> > (DAMOS_FILTER_TYPE_TARGET) and per-scheme applying time interval
> > (apply_interval_us).  Couldn't those be used for your purpose?
> >
> 
> Sorry for the delay.  I've been testing it for the past few days.

No worry, take your time! :)

> 
> The combination of schemes and filters does indeed emulate a
> priority-like mechanism quite effectively.  This is a fantastic feature!
> It's exactly what I needed for managing my workload's priorities.

Thank you for letting me know it works for you!

[...]
> I've been wondering, though -- for users seeking a simpler interface,
> could we allow them to define a basic priority value and let the kernel
> handle the resource distribution automatically?  This would require the
> DAMON system to intelligently translate a user-defined priority value
> into appropriate internal operations based on current system resources.
> WDYT?

I agree the priority based interface could be better and easier to use than the
target filter + apply_interval combination, for some people.  That said, the
user interface for achieving the same goal already exists.  I think adding
another user interface here could be a duplicate that only increases maintenace
burden.  Particularly because we need to support every user interface of the
kernel for long term, the burden may be not that cheap.

And I think the kernel ABI is not necessarily the only single place that can be
modified to help users.  Users are recommended to use DAMON user-space tool
(damo) rather than directly using DAMON sysfs ABI.  So I think we could add
priority based interface as another wrapper of the target filter +
apply_interval combination, on DAMON user-space tool.


Thanks,
SJ

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