Re: [RFC PATCH v2 0/8] mm: Hot page tracking and promotion infrastructure

[Vinicius Petrucci]

Hi David,

On Tue, Sep 16, 2025 at 1:28 PM David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> I've been pretty focused on the promotion story here rather than demotion
> because of how responsive it needs to be.  Harvesting the page table
> accessed bits or waiting on a sliding window through NUMA Balancing (even
> NUMAB=2) is not as responsive as needed for very fast promotion to top
> tier memory, hence things like the CHMU (or PEBS or IBS etc).

First, thanks for sharing your thoughts on the promotion
responsiveness challenges, definitely a critical aspect for tiering
strategies.

We recently put together a preliminary report using our experimental
HW that I believe could be relevant to the ongoing discussions:
A Limits Study of Memory-side Tiering Telemetry:
https://arxiv.org/abs/2508.09351

It's essentially an initial step toward quantifying the benefits of
HMU on the memory side, aiming to compare promotion quality (e.g.,
hotness coverage and accuracy) across HMU, PEBS-based promotion, and
NUMA balancing (promotion path).
Hopefully, this kind of work can help us better understand some of the
trade-offs being discussed, support more data-driven comparisons, and
spark more fruitful discussions...

Best,
Vinicius