linux-kernel - Re: [PATCH v2 15/17] mm/damon: handle device-exclusive entries correctly in damon_folio_mkold

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Message-Id: <20250211070002.6005-1-sj@kernel.org>
Date: Mon, 10 Feb 2025 23:00:02 -0800
From: SeongJae Park <sj@...nel.org>
To: David Hildenbrand <david@...hat.com>
Cc: SeongJae Park <sj@...nel.org>,
	linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linux-mm@...ck.org,
	nouveau@...ts.freedesktop.org,
	linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	damon@...ts.linux.dev,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jérôme Glisse <jglisse@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Alex Shi <alexs@...nel.org>,
	Yanteng Si <si.yanteng@...ux.dev>,
	Karol Herbst <kherbst@...hat.com>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...nel.org>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jann Horn <jannh@...gle.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Peter Xu <peterx@...hat.com>,
	Alistair Popple <apopple@...dia.com>,
	Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2 15/17] mm/damon: handle device-exclusive entries correctly in damon_folio_mkold_one()

On Mon, 10 Feb 2025 20:37:57 +0100 David Hildenbrand <david@...hat.com> wrote:

> Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
> we can return with a device-exclusive entry from page_vma_mapped_walk().
> 
> damon_folio_mkold_one() is not prepared for that and calls
> damon_ptep_mkold() with PFN swap PTEs. Teach damon_ptep_mkold() to deal
> with these PFN swap PTEs. Note that device-private entries are so far not
> applicable on that path, as damon_get_folio() filters out non-lru
> folios.
> 
> Should we just skip PFN swap PTEs completely? Possible, but it seems
> straight forward to just handle it correctly.
> 
> Note that we could currently only run into this case with
> device-exclusive entries on THPs. We still adjust the mapcount on
> conversion to device-exclusive; this makes the rmap walk
> abort early for small folios, because we'll always have
> !folio_mapped() with a single device-exclusive entry. We'll adjust the
> mapcount logic once all page_vma_mapped_walk() users can properly
> handle device-exclusive entries.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

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