Re: [RFC PATCH 0/4] mm/damon/sysfs: support periodic and automated stats update

[Honggyu Kim <honggyu.kim@sk.com>]

On 7/16/2025 11:51 AM, SeongJae Park wrote:
> On Wed, 16 Jul 2025 10:58:06 +0900 Honggyu Kim <honggyu.kim@sk.com> wrote:
> 
>> Hi SeongJae,
>>
>> On 7/16/2025 8:43 AM, SeongJae Park wrote:
>>> On Wed, 16 Jul 2025 07:20:57 +0900 Honggyu Kim <honggyu.kim@sk.com> wrote:
>>>
>>>> Hi SeongJae,
>>>>
>>>> On 7/13/2025 5:46 AM, SeongJae Park wrote:
>>>>> DAMON sysfs interface provides files for reading DAMON internal status
>>>>> including DAMOS stats.  The content of the files are not automatically
>>>>> updated, though.  Users should manually request updates of the contents
>>>>> by writing a special command to 'state' file of each kdamond directory.
>>>>> This interface is good for minimizing overhead, but causes the below
>>>>> problems.

[...snip...]

>>>>> Introduce a new sysfs file, namely refresh_ms, for asking DAMON sysfs
>>>>> interface to repeat the essential contents update with a user-specified
>>>>> time delay.
>>>>
>>>> Thanks for working on this, but I have a few questions.
>>>> 1. Could you please list up what are the "essential contents"?
>>>
>>> Thank you for asking this.  The contents are auto-tuned monitoring intervals,
>>> DAMOS stats, and auto-tuned effective size quota.
>>
>> Thanks, but I meant the specific list of damon knobs refreshed.  If there are
>> too many knobs, then don't have to list them all.
> 
> I guess you are saying about sysfs files?  Yes, I think listing those all is
> unnecessary.

OK. No problem then.

>>> I will add these on the next version cover letter.
>>
>> Thanks.
>>
>>>> 2. Does it mean that it is different from writing "commit" to "state"?
>>>> 3. If not, then is there equivalent action to writing something to "state"?
>>>
>>> "refresh_ms" works same to other DAMON parameter files.  You can set it before
>>> starting DAMON, or "commit" new values (including 0 for turning this refresh
>>> off) in runtime.
>>>
>>> I'm not that confident if I understood your point very well, especially what
>>> "it"s mean.  Let me know if I'm misunderstanding something.
>>
>> I mean writing "commit" to "state" refresh all knobs,
> 
> Assuming "knobs" mean sysfs files, this is incorrect.  Writing "commit" to
> "state" passes the parameters written on appropriate files to running kdamond.
> It doesn't update any sysfs files until a "update_*" keyword is written to the
> "state" file.

I thought writing "commit" to "state" applies config changes and updates all the
readable sysfs files together, but it doesn't.  Thanks for the correction.

> 
>> but it seems "refresh_ms"
>> internally refresh paritial knobs so I was wondering what are refreshed and what
>> aren't.
>>
>> Regarding the "equivalent action", I was also wondering if there is a command
>> that works same as "refresh_ms" internally does among the command below.
>>
>>     update_tuned_intervals
>>     commit_schemes_quota_goals
>>     update_schemes_stats
>>     update_schemes_tried_regions
>>     update_schemes_tried_bytes
>>     clear_schemes_tried_regions
>>     update_schemes_effective_quotas
>>
>> https://docs.kernel.org/admin-guide/mm/damon/usage.html#kdamonds-n
>>
>> In other words, if there is the same command listed above, then users might be
>> able to run a script that regularaly write the command to the current "state"
>> even without this "refresh_ms".  I know having "refresh_ms" is much better
>> though.
> 
> Thank you for this nice question.  Yes.  Enabling "refresh_ms" is roughly same
> to periodically writing
> "update_{tuned_intervals,schemes_stats,schemes_effective_quotas" to "state"
> file.

OK. I get that "refresh_ms" does periodic write the combination of them to
"state" without "update_{schemes_tried_regions,schemes_tried_bytes}.

In other words, it is same as periodic execution of the follows.

   echo update_tuned_intervals > state
   echo update_schemes_stats > state
   echo update_schemes_effective_quotas > state

That makes my question clear.  Thanks for the explanation!

Thanks,
Honggyu

> 
> 
> Thanks,
> SJ
> 
> [...]