Re: [PATCH 1/4] mm/damon: defensively skip zone device folios in damon_get_folio()

[SJ Park <sj@kernel.org>]

Hi Gregory,


On Tue, 28 Jul 2026 15:47:11 -0400 Gregory Price <gourry@gourry.net> wrote:

> All DAMON physical- and virtual-address operations obtain their folios
> through damon_get_folio(). That helper already excludes ZONE_DEVICE
> memory implicitly via pfn_to_online_page() and folio_test_lru(), but
> this is inconsistent with other callers in mm/ which test explicitly.
> 
> Add an explicit folio_is_zone_device() rejection in damon_get_folio()
> so the guarantee lives in one place and covers every caller uniformly,
> consistent with other mm walkers that reject zone device folios.

Thank you for checking this and sharing this nice patch!

However, I'm not very sure adding a call that not really required for only
making it looks consistent with others is the right choice.  I'm especially
concerned if this will confuse future readers including myself.

If this is a hardening purpose, we have CONFIG_DAMON_DEBUG_SANITY for the
purpose.  What about using it with a good comment explaining why we doing that?


Thanks,
SJ

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