linux-kernel - [RFC PATCH v2 26/51] mm: Consolidate freeing of typed folios on final folio

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Message-ID: <3a897dc919d25951816cba95dd53bfeb2ea6e581.1747264138.git.ackerleytng@google.com>
Date: Wed, 14 May 2025 16:42:05 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
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Subject: [RFC PATCH v2 26/51] mm: Consolidate freeing of typed folios on final folio_put()

From: Fuad Tabba <tabba@...gle.com>

Some folio types, such as hugetlb, handle freeing their own folios.

The guestmem_hugetlb folio, to be introduced in a later patch,
requires extra handling as part of the freeing process.

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, guestmem_hugetlb will become the second user of this.

Suggested-by: David Hildenbrand <david@...hat.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Fuad Tabba <tabba@...gle.com>
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Change-Id: I881dc58ca89603ddd1e8e1ccca8f5dbfc80c43be
---
 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 e6a21b62dcce..9dd60fb8c33f 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -985,6 +985,21 @@ 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 77b2d5997873..d0a5971787c4 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;
 	}
 
@@ -964,13 +977,13 @@ 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);
-- 
2.49.0.1045.g170613ef41-goog