On Mon, 10 Feb 2025 20:37:57 +0100 David Hildenbrand [off-list ref] 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 <redacted>

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


Thanks,
SJ

[...]