Re: Memory tiering with DAMON/DAMOS auto-tuning

[SJ Park <sj@kernel.org>]

On Mon, 28 Sep 2026 20:02:43 +0300 Anton Gavriliuk <antosha20xx@gmail.com> wrote:

> > Thank you for sharing your use case and question!
> 
> Thank you for your quick response and your answer/comments.
> 
> We already had memory tiering implemented at hardware level 5-7 years
> ago with Intel's Optane PEM when configured in Memory Mode.
> Now we do the same thing at Linux level :-)

Interesting!

> I'm new at DAMON/DAMOS, there are lots of new tunables to me.

Indeed there are.  I'd recommend starting with existing DAMON-based memory
tiering solutions including SK Hynix HMSDK and my auto-tune based memory
tiering script [1] and ask questions to the authors.

> 
> > The example memory tiering script [1] uses 4% as intervals goal.  Is there a
> > reason to use 97% as the goal instead?
> 
> Oohhh... I moved to 5%.

I understand you mean 4%?

> 
> > Is the above node_mum_used_bp what you really want?  That means you want to
> > promote hot pages from node 2 to node 0, until the node 0 memory utilization
> > becomes 99.7%.  That overlaps with the demotion goal (50% free memory of node
> > 0) quite a lot.  I'd suggest smaller overlap, say, 50.3%, to keep healthy
> > circulation of hot/cold pages while not consuming too much resource under
> > stabilized access pattern.
> 
> > DAMOS quota auto-tuning supports two tuner algorithms [2], consistent and
> > temporal.  As the documentation [2] explains, 'consistent' tuner assumes it
> > should keep applying the action in a level to keep the goal achieved.  In this
> > case, for example, the demotion scheme assumes there will be continued
> > promotion and therefore it keeps demoting.  If there is no appropriate
> > promotion, it could result in demoting more than expected amount.
> 
> So let me firstly understand what I really want to test :-)

Sure, and please feel free to ask any question in any ways.  If you prefer to,
you could also ask questions privately to me or use DAMON Beer/Coffee/Tea Chat
series [2].

[1] https://github.com/damonitor/damo/blob/next/scripts/mem_tier.sh
[2] https://docs.google.com/document/d/1v43Kcj3ly4CYqmAkMaZzLiM2GEnWfgdGbZAH3mi2vpM/edit?usp=sharing


Thanks,
SJ

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