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

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Message-ID: <Z6XXf5OaLe9ZaN02@casper.infradead.org>
Date: Fri, 7 Feb 2025 09:50:55 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Bharata B Rao <bharata@....com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Raghavendra K T <raghavendra.kt@....com>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, lsf-pc@...ts.linux-foundation.org,
	gourry@...rry.net, nehagholkar@...a.com, abhishekd@...a.com,
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	sj@...nel.org, david@...hat.com, k.shutemov@...il.com,
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	rppt@...nel.org, dave.hansen@...el.com
Subject: Re: [LSF/MM/BPF TOPIC] Unifying sources of page temperature
 information - what info is actually wanted?

On Wed, Feb 05, 2025 at 11:54:05AM +0530, Bharata B Rao wrote:
> Here is a compilation of available temperature sources and how the
> hot/access data is consumed by different subsystems:
> 
> PA-Physical address available
> VA-Virtual address available
> AA-Access time available
> NA-accessing Node info available
> 
> I have left the slot blank for those which I am not sure about.
> ==================================================
> Temperature		PA	VA	AA	NA
> source
> ==================================================
> PROT_NONE faults	Y	Y	Y	Y
> --------------------------------------------------
> folio_mark_accessed()	Y		Y	Y
> --------------------------------------------------
> PTE A bit		Y	Y	N	N
> --------------------------------------------------
> Platform hints		Y	Y	Y	Y
> (AMD IBS)
> --------------------------------------------------
> Device hints		Y
> (CXL HMU)
> ==================================================
> 
> And here is an attempt to compile how different subsystems
> use the above data:
> ==============================================================
> Source			Subsystem		Consumption
> ==============================================================
> PROT_NONE faults	NUMAB		NUMAB=1 locality based
> via process pgtable			balancing
> walk					NUMAB=2 hot page
> 					promotion
> ==============================================================
> folio_mark_accessed()	FS/filemap/GUP	LRU list activation
> ==============================================================
> PTE A bit via		Reclaim:LRU	LRU list activation,	
> rmap walk				deactivation/demotion
> ==============================================================
> PTE A bit via		Reclaim:MGLRU	LRU list activation,	
> rmap walk and process			deactivation/demotion
> pgtable walk
> ==============================================================
> PTE A bit via		DAMON		LRU activation,
> rmap walk				hot page promotion,
> 					demotion etc
> ==============================================================
> 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.
> 
> Feel free to correct/clarify and add more.

There's PG_young / PG_idle as well.