Re: [RFC PATCH 0/5] mm/damon: Add node_sys_bp quota goal metric for

[SeongJae Park <sj@kernel.org>]

On Tue,  3 Feb 2026 22:06:40 -0800 SeongJae Park <sj@kernel.org> wrote:

> On Wed,  4 Feb 2026 11:25:35 +0900 Yunjeong Mun <yunjeong.mun@sk.com> wrote:
> 
> > On Fri, Jan 23, 2026 at 05:50:43PM -0800, SeongJae Park wrote:
[...]
> > > IIRC, SK hynix people also confused with the behavior when they experimented
> > > migrate_{hot,cold} action with NODE_MEM_USED_BP goal based quota auto-tuning,
> > > but using only a single scheme that does migration in a single direction.
> > > Because this is at least second time it made confusion, if you need, maybe I
> > > can try to add a feature for making DAMOS immediately stops after the goal is
> > > satisfied.  Let me know if such new feature can be useful for you.  Cc-ing SK
> > > hynix people (Honggyu and Yunjeong) so that they can correct me if my memory is
> > > broken, or answer if the new feature I described here can be useful for them.
> > > 
> > 
> > Yes, you're absolutely right. Currently, esz(effective size) starts from 0 and 
> > esz gradually increases as `current` approaches `target`.
> > Once `current` reaches `target`,  `esz` then begins to decrease.
> > 
> > However, we observed that even after `current` hits `target`, 
> > migration still continues relatively aggressively - because `esz`  remains high, 
> > and it takes time for it to decrease.
> > 
> > To address this, we previously suggested that initializing `esz`  at `target`
> > (or something suitably large value, rather than 0) and letting it gradually 
> > decrease as `current` gets closer to  `target`.  
> > This would allow for stronger migration when `current` is far form `target`, 
> > and gradually weaken migration as `current` approaches `target`.
> > 
> > Such a feature would be useful for us to experiment with tiered memory system :)
> 
> Thank you for confirming, Yunjeong.  I now agree this is what really need to be
> implemented.  And I agree your suggestion makes sense for the use case.  I want
> to take sufficient time for good design of it, though.  I will share update as
> soon as I get some idea.

I just posted an RFC patch series for this:
https://lore.kernel.org/20260212062314.69961-1-sj@kernel.org


Thanks,
SJ

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