[PATCH v6 01/10] mm: Consolidate freeing of typed folios on final folio_put()

Fuad Tabba
2025-03-12T17:58:31Z

Some folio types, such as hugetlb, handle freeing their own
folios. Moreover, guest_memfd will require being notified once a
folio's reference count reaches 0 to facilitate shared to private
folio conversion, without the folio actually being freed at that
point.

As a first step towards that, this patch consolidates freeing
folios that have a type. The first user is hugetlb folios. Later
in this patch series, guest_memfd will become the second user of
this.

Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
include/linux/page-flags.h | 15 +++++++++++++++
mm/swap.c | 23 ++++++++++++++++++-----
2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 36d283552f80..6dc2494bd002 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -953,6 +953,21 @@ static inline bool page_has_type(const struct page *page)
return page_mapcount_is_type(data_race(page->page_type));
}

+static inline int page_get_type(const struct page *page)
+{
+ return page->page_type >> 24;
+}
+
+static inline bool folio_has_type(const struct folio *folio)
+{
+ return page_has_type(&folio->page);
+}
+
+static inline int folio_get_type(const struct folio *folio)
+{
+ return page_get_type(&folio->page);
+}
+
#define FOLIO_TYPE_OPS(lname, fname) \
static __always_inline bool folio_test_##fname(const struct folio *folio) \
{ \
diff --git a/mm/swap.c b/mm/swap.c
index fc8281ef4241..47bc1bb919cc 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -94,6 +94,19 @@ static void page_cache_release(struct folio *folio)
unlock_page_lruvec_irqrestore(lruvec, flags);
}

+static void free_typed_folio(struct folio *folio)
+{
+ switch (folio_get_type(folio)) {
+#ifdef CONFIG_HUGETLBFS
+ case PGTY_hugetlb:
+ free_huge_folio(folio);
+ return;
+#endif
+ default:
+ WARN_ON_ONCE(1);
+ }
+}
+
void __folio_put(struct folio *folio)
{
if (unlikely(folio_is_zone_device(folio))) {
@@ -101,8 +114,8 @@ void __folio_put(struct folio *folio)
return;
}

- if (folio_test_hugetlb(folio)) {
- free_huge_folio(folio);
+ if (unlikely(folio_has_type(folio))) {
+ free_typed_folio(folio);
return;
}

@@ -966,13 +979,13 @@ void folios_put_refs(struct folio_batch *folios, unsigned int *refs)
if (!folio_ref_sub_and_test(folio, nr_refs))
continue;

- /* hugetlb has its own memcg */
- if (folio_test_hugetlb(folio)) {
+ if (unlikely(folio_has_type(folio))) {
+ /* typed folios have their own memcg, if any */
if (lruvec) {
unlock_page_lruvec_irqrestore(lruvec, flags);
lruvec = NULL;
}
- free_huge_folio(folio);
+ free_typed_folio(folio);
continue;
}
folio_unqueue_deferred_split(folio);
--
2.49.0.rc0.332.g42c0ae87b1-goog