[RFC PATCH 02/25] mm/zsmalloc: add utility functions for zsdesc

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

Introduce utility functions for zsdesc to avoid directly accessing fields
of struct page.

zsdesc_page() is defined this way 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 | 120 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 118 insertions(+), 2 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index e2e34992c439..4af9f87cafb7 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -332,6 +332,124 @@ 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 struct zspage *zsdesc_zspage(const struct zsdesc *zsdesc)
+{
+	return (struct zspage *)page_private(zsdesc_page(zsdesc));
+}
+
+static inline int trylock_zsdesc(struct zsdesc *zsdesc)
+{
+	return trylock_page(zsdesc_page(zsdesc));
+}
+
+static inline void unlock_zsdesc(struct zsdesc *zsdesc)
+{
+	return unlock_page(zsdesc_page(zsdesc));
+}
+
+static inline struct zone *zsdesc_zone(struct zsdesc *zsdesc)
+{
+	return page_zone(zsdesc_page(zsdesc));
+}
+
+static inline void wait_on_zsdesc_locked(struct zsdesc *zsdesc)
+{
+	wait_on_page_locked(zsdesc_page(zsdesc));
+}
+
+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);
+}
+
+static inline void *zsdesc_kmap_atomic(struct zsdesc *zsdesc)
+{
+	return kmap_atomic(zsdesc_page(zsdesc));
+}
+
+static inline void zsdesc_set_zspage(struct zsdesc *zsdesc, struct zspage *zspage)
+{
+	set_page_private(zsdesc_page(zsdesc), (unsigned long)zspage);
+}
+
+static inline void zsdesc_set_first(struct zsdesc *zsdesc)
+{
+	SetPagePrivate(zsdesc_page(zsdesc));
+}
+
+static inline bool zsdesc_is_locked(struct zsdesc *zsdesc)
+{
+	return PageLocked(zsdesc_page(zsdesc));
+}
+
+static inline bool zsdesc_is_isolated(struct zsdesc *zsdesc)
+{
+	return PageIsolated(zsdesc_page(zsdesc));
+}
+
+static inline void zsdesc_inc_zone_page_state(struct zsdesc *zsdesc)
+{
+	inc_zone_page_state(zsdesc_page(zsdesc), NR_ZSPAGES);
+}
+
+static inline void zsdesc_dec_zone_page_state(struct zsdesc *zsdesc)
+{
+	dec_zone_page_state(zsdesc_page(zsdesc), NR_ZSPAGES);
+}
+
+static inline struct zsdesc *alloc_zsdesc(gfp_t gfp)
+{
+	struct page *page = alloc_page(gfp);
+
+	zsdesc_inc_zone_page_state(page_zsdesc(page));
+	return page_zsdesc(page);
+}
+
+static inline void free_zsdesc(struct zsdesc *zsdesc)
+{
+	struct page *page = zsdesc_page(zsdesc);
+
+	zsdesc_dec_zone_page_state(page_zsdesc(page));
+	__free_page(page);
+}
+
+static const struct movable_operations zsmalloc_mops;
+
+static inline void zsdesc_set_movable(struct zsdesc *zsdesc)
+{
+	struct page *page = zsdesc_page(zsdesc);
+
+	__SetPageMovable(page, &zsmalloc_mops);
+}
+
 /* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
 static void SetZsHugePage(struct zspage *zspage)
 {
@@ -2012,8 +2130,6 @@ static void dec_zspage_isolation(struct zspage *zspage)
 	zspage->isolated--;
 }
 
-static const struct movable_operations zsmalloc_mops;
-
 static void replace_sub_page(struct size_class *class, struct zspage *zspage,
 				struct page *newpage, struct page *oldpage)
 {
-- 
2.25.1