linux-kernel - Re: [LSF/MM/BPF TOPIC] Overhauling hot page detection and promotion based on PTE A bit scanning

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Message-ID: <0571919b-52e1-4981-8d34-bcc781c0561a@amd.com>
Date: Fri, 24 Jan 2025 14:32:42 +0530
From: Raghavendra K T <raghavendra.kt@....com>
To: Hyeonggon Yoo <hyeonggon.yoo@...com>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
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 "bharata@....com" <bharata@....com>
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Subject: Re: [LSF/MM/BPF TOPIC] Overhauling hot page detection and promotion
 based on PTE A bit scanning

On 1/24/2025 11:23 AM, Hyeonggon Yoo wrote:
> 
> 
> On 1/23/2025 7:57 PM, Raghavendra K T wrote:
>> Bharata and I would like to propose the following topic for LSFMM.
>>
>> Topic: Overhauling hot page detection and promotion based on PTE A bit 
>> scanning.
[...]
>> Here is the list of potential discussion points:
>> 1. Other improvements and enhancements to PTE A bit scanning approach. 
>> Use of
>> multiple kernel threads, throttling improvements, promotion policies, 
>> per-process
>> opt-in via prctl, virtual vs physical address based scanning, tuning 
>> hot page
>> detection algorithm etc.
> 
> Yuanchu's MGLRU periodic aging series [1] seems quite relevant here,
> you might want to look at it. adding Yuanchu to Cc.

Thank you for pointing that.

> 
> By the way, do you have any reason why you'd prefer opt-in prctl
> over per-memcg control?
>

opt-in prctl came in the MM alignment discussion, and have added that.
per-memcg also definitely makes sense. I am not aware which is the most
used usecase. But adding provision for both with one having more
priority over other may be the way to go.

Overall point here is to save time in unnecessary scanning.
will be adding prctl in the upcoming version to start with.

> [1] https://lore.kernel.org/all/20221214225123.2770216-1- 
> yuanchu@...gle.com/
>