Re: [RESEND PATCH v2 0/3] mm/damon: Introduce a huge page collapsing mechanism using auto tuning

[SJ Park]

Hello Asier,

On Tue, 14 Jul 2026 15:01:13 +0000 <gutierrez.asier@xxxxxxxxxxxxxxxxxxx> wrote:

> From: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>
> 
> Overview
> ========
> 
> This patch set introduces a new autotuning which allows to collapse
> hot regions into hugepages.

I sincerely appreciate your continued work on this.  But, I have to say I'm
holding review of this series for below reason...

> 
> Motivation
> ==========
> 
> Since TLB is a bottleneck for many systems[1], a way to optimize TLB
> misses (or hits) is to use huge pages. Unfortunately, using "always"
> in THP leads to memory fragmentation and memory waste. For this reason,
> most application guides and system administrators suggest to disable THP.
> 
> Currently DAMON has DAMOS_HUGEPAGE, DAMOS_NONHUGEPAGE and DAMOS_COLLAPSE.
> However, there is no way to tune the settings. It will collapse all the
> hot regions that meet the access pattern. If the server is a bare metal
> database or big data server, this will also lead to eventual fragmentation.
> 
> Additionally, currently THP is set globally. Ideally, there should be a
> way to control which tasks can use huge pages.

You told me [1] you will rephrase the above.  But I show no change from the
previous version.

Asier, this is a repeated pattern that makes me reviewing this series very
difficult and tiresome.  I don't really want to waste our time on repeating
same words.  I know you did this great job so far and you can make it well
completed.  Could you please thoroughly and carefully review "all" previous
discussions, address all the comments and resend the new version?

Particularly, please note that I also asked [2] you a question about Sashiko
review, and I'm still waiting for your answer.  If you don't have a very good
and confident answer, I'd recommend simply adding the zero-case check.

To avoid wasting our time repeating same words, I skip reviewing the remainder
of this version of the series.  I will review the next version.

[1] https://lore.kernel.org/b786294f-0ba5-4b05-b956-d902c358dd88@xxxxxxxxxxxxxxxxxxx
[2] https://lore.kernel.org/20260617041515.98906-1-sj@xxxxxxxxxx


Thanks,
SJ

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