linux-kernel - Re: [RFC PATCH v0 2/2] mm: sched: Batch-migrate misplaced pages

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Message-ID: <20250528122513.4rxzkia7lge7du5p@ed.ac.uk>
Date: Wed, 28 May 2025 13:25:13 +0100
From: Karim Manaouil <kmanaouil.dev@...il.com>
To: Zi Yan <ziy@...dia.com>
Cc: David Hildenbrand <david@...hat.com>, Bharata B Rao <bharata@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Jonathan.Cameron@...wei.com, dave.hansen@...el.com,
	gourry@...rry.net, hannes@...xchg.org, mgorman@...hsingularity.net,
	mingo@...hat.com, peterz@...radead.org, raghavendra.kt@....com,
	riel@...riel.com, rientjes@...gle.com, sj@...nel.org,
	weixugc@...gle.com, willy@...radead.org,
	ying.huang@...ux.alibaba.com, dave@...olabs.net,
	nifan.cxl@...il.com, joshua.hahnjy@...il.com,
	xuezhengchu@...wei.com, yiannis@...corp.com,
	akpm@...ux-foundation.org
Subject: Re: [RFC PATCH v0 2/2] mm: sched: Batch-migrate misplaced pages

On Mon, May 26, 2025 at 10:20:39AM -0400, Zi Yan wrote:
> On 26 May 2025, at 5:29, David Hildenbrand wrote:
> > PFN scanning can be faster than walking lists, but I suspect it depends on how many pages there really are to be migrated ... and some other factors :)
> 
> Yes. LRU list is good since it restricts the scanning range, but PFN scanning
> itself does not have it. PFN scanning with some filter mechanism might work
> and that filter mechanism is a way of marking to-be-migrated pages. Of course,
> a quick re-evaluation of the to-be-migrated pages right before a migration
> would avoid unnecessary work like we discussed above.

PFN scanning could be faster because of prefetching, but it pollutes the
caches, which may not be nice to the application running on that cpu
core before we transitioned to kernel space.

-- 
~karim