linux-kernel - Re: [LSF/MM/BPF TOPIC] Unifying sources of page temperature information

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Message-Id: <20250206064624.3225-1-sj@kernel.org>
Date: Wed,  5 Feb 2025 22:46:24 -0800
From: SeongJae Park <sj@...nel.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: SeongJae Park <sj@...nel.org>,
	Bharata B Rao <bharata@....com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Raghavendra K T <raghavendra.kt@....com>,
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Subject: Re: [LSF/MM/BPF TOPIC] Unifying sources of page temperature information - what info is actually wanted?

On Wed, 5 Feb 2025 11:05:29 -0500 Johannes Weiner <hannes@...xchg.org> wrote:

> On Wed, Feb 05, 2025 at 11:54:05AM +0530, Bharata B Rao wrote:
> > On 31-Jan-25 6:39 PM, Jonathan Cameron wrote:
> > > On Fri, 31 Jan 2025 12:28:03 +0000
> > > Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
[...]
> > Here is a compilation of available temperature sources and how the 
> > hot/access data is consumed by different subsystems:
> 
> This is super useful, thanks for collecting this.

Indeed.  Thank you Bharata!

[...]
> For the following table, it might be useful to add *when* the source
> produces this information.  Sampling frequency is a likely challenge:
> consumers have different requirements, and overhead should be limited
> to the minimum required to serve enabled consumers.

+1

> 
> Here is an (incomplete) attempt - sorry about the long lines:
> 
> > And here is an attempt to compile how different subsystems
> > use the above data:
> > ==============================================================
> > Source			Subsystem		Consumption         Activation/Frequency
[...]
> > ==============================================================
> > PTE A bit via		DAMON		LRU activation,                     Continuous sampling (configurable)?
> > rmap walk				hot page promotion,                 (I believe SJ is looking into
> > 					demotion etc                         auto-tuning this).

You're right.  I'm working on auto-tuning of the sampling/aggregation intervals
of DAMON based on its tuning guide theory[1].  Hopefully I will be able to post
an RFC patch series within a couple of weeks.

> > ==============================================================
> > Platform hints		NUMAB		NUMAB=1 Locality based
> > (AMD IBS)				balancing and
> > 					NUMAB=2 hot page
> > 					promotion
> > ==============================================================
> > Device hints		NUMAB		NUMAB=2 hot page
> > 					promotion
> > ==============================================================
> > The last two are listed as possibilities.

I'm also trying to extend DAMON to use PROT_NONE faults and AMD IBS like access
check sources.  Hopefully I will share more details of the plan and experiment
results for the PROT_NONE faults extension by LSFMMBPF.

[1] https://lore.kernel.org/20241202175459.2005526-1-sj@kernel.org


Thanks,
SJ

[...]