diff mbox series

[v7,1/9] mm: Consolidate freeing of typed folios on final folio_put()

Message ID 20250318161823.4005529-2-tabba@google.com
State New
Headers show
Series [v7,1/9] mm: Consolidate freeing of typed folios on final folio_put() | expand

Commit Message

Fuad Tabba March 18, 2025, 4:18 p.m. UTC 
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(-)

Comments

David Hildenbrand April 14, 2025, 10 a.m. UTC | #1 
On 18.03.25 17:18, Fuad Tabba wrote:
> 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>
> ---

As discussed in the last upstream meeting, we should focus on using the 
folio_put() hook only for the post-truncate case where required (e.g., 
re-assemble hugetlb).

For shared->private conversion doing it synchronously (unmap, try 
freezing refcount) and failing if impossible to signal user space to 
retry is a better first approach.

So this patch will be dropped from your series for now, correct?
Fuad Tabba April 14, 2025, 10:15 a.m. UTC | #2 
Hi David,

On Mon, 14 Apr 2025 at 11:00, David Hildenbrand <david@redhat.com> wrote:
>
> On 18.03.25 17:18, Fuad Tabba wrote:
> > 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>
> > ---
>
> As discussed in the last upstream meeting, we should focus on using the
> folio_put() hook only for the post-truncate case where required (e.g.,
> re-assemble hugetlb).
>
> For shared->private conversion doing it synchronously (unmap, try
> freezing refcount) and failing if impossible to signal user space to
> retry is a better first approach.
>
> So this patch will be dropped from your series for now, correct?

Yes it will.

Thanks,
/fuad

> --
> Cheers,
>
> David / dhildenb
>
diff mbox series

Patch

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);