[RFC PATCH v2 02/21] mm/zsmalloc: add utility functions for zsdesc

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

Introduce basic utility functions for zsdesc to avoid directly accessing
fields of struct page. More helpers will be defined later.

zsdesc_page() is defined with _Generic to preserve constness.
page_zsdesc() does not call compound_head() because zsdesc is always
a base page.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
---
 mm/zsmalloc.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 2204bea4f289..11c203e79c39 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -293,6 +293,39 @@ ZSDESC_MATCH(_refcount, _refcount);
 #undef ZSDESC_MATCH
 static_assert(sizeof(struct zsdesc) <= sizeof(struct page));
 
+#define zsdesc_page(zdesc) (_Generic((zdesc),				\
+		const struct zsdesc *:	(const struct page *)zdesc,	\
+		struct zsdesc *:	(struct page *)zdesc))
+
+static inline struct zsdesc *page_zsdesc(struct page *page)
+{
+	return (struct zsdesc *)page;
+}
+
+static inline unsigned long zsdesc_pfn(const struct zsdesc *zsdesc)
+{
+	return page_to_pfn(zsdesc_page(zsdesc));
+}
+
+static inline struct zsdesc *pfn_zsdesc(unsigned long pfn)
+{
+	return page_zsdesc(pfn_to_page(pfn));
+}
+
+static inline void zsdesc_get(struct zsdesc *zsdesc)
+{
+	struct folio *folio = (struct folio *)zsdesc;
+
+	folio_get(folio);
+}
+
+static inline void zsdesc_put(struct zsdesc *zsdesc)
+{
+	struct folio *folio = (struct folio *)zsdesc;
+
+	folio_put(folio);
+}
+
 /* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
 static void SetZsHugePage(struct zspage *zspage)
 {
-- 
2.41.0