[PATCH v2 13/17] mm/page_idle: handle device-exclusive entries correctly in page_idle_clear_pte_refs_one()

[SeongJae Park]

On Mon, 10 Feb 2025 20:37:55 +0100 David Hildenbrand <david at redhat.com> wrote:

> Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
> we can return with a device-exclusive entry from page_vma_mapped_walk().
> 
> page_idle_clear_pte_refs_one() is not prepared for that, so let's
> teach it what to do with these PFN swap PTEs. Note that device-private
> entries are so far not applicable on that path, as page_idle_get_folio()
> filters out non-lru folios.
> 
> Should we just skip PFN swap PTEs completely? Possible, but it seems
> straight forward to just handle them 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.
> 
> Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
> Signed-off-by: David Hildenbrand <david at redhat.com>

Reviewed-by: SeongJae Park <sj at kernel.org>


Thanks,
SJ

[...]