On Fri, Dec 04, 2020 at 02:23:29PM -0500, Peter Xu wrote: > If we see [1]: > > if (!pte_present && !pte_none && pte_swp_uffd_wp && not_anonymous_vma && !is_migration_entry) > > Then it's fundamentally the same as: > > swp_entry(0, _UFFD_SWP_UFFD_WP) && !vma_is_anonymous(vma) Yes conceptually it's the same, but in practice it's different value in the raw pte if you set swp_offset to _UFFD_SWP_UFFD_WP. Setting swp_offset to _UFFD_SWP_UFFD_WP is just confusing, it's better magic type 1 offset 0 then to even touch _UFFD_SWP_UFFD_WP if you reserve the magic value in the swap entry. pte_swp_uffd_wp or _UFFD_SWP_UFFD_WP are the raw pte value. swp_entry(0, _UFFD_SWP_UFFD_WP) is not the raw pte value, and it has to be first converted to the raw pte value with swp_entry_to_pte, so the _UFFD_SWP_UFFD_WP gets shifted left. If we use _UFFD_SWP_UFFD_WP it looks much cleaner to keep it in the pte, not in the swp entry, since then you can use the already existing methods that only can take in input the pte_t (not the swp_entry_t). Thanks, Andrea
