On Mon, Jun 09, 2025 at 05:08:07PM +0000, Shivank Garg wrote:
> Replace open-coded folio reference count calculations with the
> folio_expected_ref_count() helper to improve code maintainability
> and reduce duplication.
I wonder if there is any opportunity for reducing duplication more broadly?
The migration code has similar helpers (folio_expected_refs) as does
khugepaged (is_refcount_suitable) and vmscan (is_page_cache_freeable).
do_huge_pmd_wp_page() also has an open-coded version of these checks and there
are probably others around the place to.
These could all be converted to a helper that returns all the "extra" references
after taking into account things like mapping, swapcache, etc. depending on
folio.
> No functional changes intended.
>
> Signed-off-by: Shivank Garg <shiva...@amd.com>
> ---
> kernel/events/uprobes.c | 5 +++--
> mm/memfd.c | 4 ++--
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 4c965ba77f9f..c978c8c27340 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -434,10 +434,11 @@ static int __uprobe_write_opcode(struct vm_area_struct
> *vma,
> /*
> * When unregistering, we may only zap a PTE if uffd is disabled and
> * there are no unexpected folio references ...
> + * Expected refs: mappings + swapcache.
> + * We hold one additional reference (+1).
> */
> if (is_register || userfaultfd_missing(vma) ||
> - (folio_ref_count(folio) != folio_mapcount(folio) + 1 +
> - folio_test_swapcache(folio) * folio_nr_pages(folio)))
> + (folio_ref_count(folio) != folio_expected_ref_count(folio) + 1))
> goto remap;
>
> /*
> diff --git a/mm/memfd.c b/mm/memfd.c
> index ab367e61553d..4ed5506221b7 100644
> --- a/mm/memfd.c
> +++ b/mm/memfd.c
> @@ -32,8 +32,8 @@
>
> static bool memfd_folio_has_extra_refs(struct folio *folio)
> {
> - return folio_ref_count(folio) - folio_mapcount(folio) !=
> - folio_nr_pages(folio);
> + /* Expected refs: pagecache + mappings */
> + return folio_ref_count(folio) != folio_expected_ref_count(folio);
> }
>
> static void memfd_tag_pins(struct xa_state *xas)
> --
> 2.43.0
>
>
