1 files changed, 182 insertions, 0 deletions
diff --git a/mm/zpdesc.h b/mm/zpdesc.h
new file mode 100644
index 000000000000..fa47fece2237
--- /dev/null
+++ b/mm/zpdesc.h
@@ -0,0 +1,182 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* zpdesc.h: zswap.zpool memory descriptor
+ *
+ * Written by Alex Shi <alexs@kernel.org>
+ *	      Hyeonggon Yoo <42.hyeyoo@gmail.com>
+ */
+#ifndef __MM_ZPDESC_H__
+#define __MM_ZPDESC_H__
+
+/*
+ * struct zpdesc -	Memory descriptor for zpool memory.
+ * @flags:		Page flags, mostly unused by zsmalloc.
+ * @lru:		Indirectly used by page migration.
+ * @movable_ops:	Used by page migration.
+ * @next:		Next zpdesc in a zspage in zsmalloc zpool.
+ * @handle:		For huge zspage in zsmalloc zpool.
+ * @zspage:		Points to the zspage this zpdesc is a part of.
+ * @first_obj_offset:	First object offset in zsmalloc zpool.
+ * @_refcount:		The number of references to this zpdesc.
+ *
+ * This struct overlays struct page for now. Do not modify without a good
+ * understanding of the issues. In particular, do not expand into the overlap
+ * with memcg_data.
+ *
+ * Page flags used:
+ * * PG_private identifies the first component page.
+ * * PG_locked is used by page migration code.
+ */
+struct zpdesc {
+	unsigned long flags;
+	struct list_head lru;
+	unsigned long movable_ops;
+	union {
+		struct zpdesc *next;
+		unsigned long handle;
+	};
+	struct zspage *zspage;
+	/*
+	 * Only the lower 24 bits are available for offset, limiting a page
+	 * to 16 MiB. The upper 8 bits are reserved for PGTY_zsmalloc.
+	 *
+	 * Do not access this field directly.
+	 * Instead, use {get,set}_first_obj_offset() helpers.
+	 */
+	unsigned int first_obj_offset;
+	atomic_t _refcount;
+};
+#define ZPDESC_MATCH(pg, zp) \
+	static_assert(offsetof(struct page, pg) == offsetof(struct zpdesc, zp))
+
+ZPDESC_MATCH(flags, flags);
+ZPDESC_MATCH(lru, lru);
+ZPDESC_MATCH(mapping, movable_ops);
+ZPDESC_MATCH(index, next);
+ZPDESC_MATCH(index, handle);
+ZPDESC_MATCH(private, zspage);
+ZPDESC_MATCH(page_type, first_obj_offset);
+ZPDESC_MATCH(_refcount, _refcount);
+#undef ZPDESC_MATCH
+static_assert(sizeof(struct zpdesc) <= sizeof(struct page));
+
+/*
+ * zpdesc_page - The first struct page allocated for a zpdesc
+ * @zp: The zpdesc.
+ *
+ * A convenience wrapper for converting zpdesc to the first struct page of the
+ * underlying folio, to communicate with code not yet converted to folio or
+ * struct zpdesc.
+ *
+ */
+#define zpdesc_page(zp)			(_Generic((zp),			\
+	const struct zpdesc *:		(const struct page *)(zp),	\
+	struct zpdesc *:		(struct page *)(zp)))
+
+/**
+ * zpdesc_folio - The folio allocated for a zpdesc
+ * @zp: The zpdesc.
+ *
+ * Zpdescs are descriptors for zpool memory. The zpool memory itself is
+ * allocated as folios that contain the zpool objects, and zpdesc uses specific
+ * fields in the first struct page of the folio - those fields are now accessed
+ * by struct zpdesc.
+ *
+ * It is occasionally necessary convert to back to a folio in order to
+ * communicate with the rest of the mm. Please use this helper function
+ * instead of casting yourself, as the implementation may change in the future.
+ */
+#define zpdesc_folio(zp)		(_Generic((zp),			\
+	const struct zpdesc *:		(const struct folio *)(zp),	\
+	struct zpdesc *:		(struct folio *)(zp)))
+/**
+ * page_zpdesc - Converts from first struct page to zpdesc.
+ * @p: The first (either head of compound or single) page of zpdesc.
+ *
+ * A temporary wrapper to convert struct page to struct zpdesc in situations
+ * where we know the page is the compound head, or single order-0 page.
+ *
+ * Long-term ideally everything would work with struct zpdesc directly or go
+ * through folio to struct zpdesc.
+ *
+ * Return: The zpdesc which contains this page
+ */
+#define page_zpdesc(p)			(_Generic((p),			\
+	const struct page *:		(const struct zpdesc *)(p),	\
+	struct page *:			(struct zpdesc *)(p)))
+
+static inline void zpdesc_lock(struct zpdesc *zpdesc)
+{
+	folio_lock(zpdesc_folio(zpdesc));
+}
+
+static inline bool zpdesc_trylock(struct zpdesc *zpdesc)
+{
+	return folio_trylock(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_unlock(struct zpdesc *zpdesc)
+{
+	folio_unlock(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_wait_locked(struct zpdesc *zpdesc)
+{
+	folio_wait_locked(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_get(struct zpdesc *zpdesc)
+{
+	folio_get(zpdesc_folio(zpdesc));
+}
+
+static inline void zpdesc_put(struct zpdesc *zpdesc)
+{
+	folio_put(zpdesc_folio(zpdesc));
+}
+
+static inline void *kmap_local_zpdesc(struct zpdesc *zpdesc)
+{
+	return kmap_local_page(zpdesc_page(zpdesc));
+}
+
+static inline unsigned long zpdesc_pfn(struct zpdesc *zpdesc)
+{
+	return page_to_pfn(zpdesc_page(zpdesc));
+}
+
+static inline struct zpdesc *pfn_zpdesc(unsigned long pfn)
+{
+	return page_zpdesc(pfn_to_page(pfn));
+}
+
+static inline void __zpdesc_set_movable(struct zpdesc *zpdesc,
+					const struct movable_operations *mops)
+{
+	__SetPageMovable(zpdesc_page(zpdesc), mops);
+}
+
+static inline void __zpdesc_set_zsmalloc(struct zpdesc *zpdesc)
+{
+	__SetPageZsmalloc(zpdesc_page(zpdesc));
+}
+
+static inline void __zpdesc_clear_zsmalloc(struct zpdesc *zpdesc)
+{
+	__ClearPageZsmalloc(zpdesc_page(zpdesc));
+}
+
+static inline bool zpdesc_is_isolated(struct zpdesc *zpdesc)
+{
+	return PageIsolated(zpdesc_page(zpdesc));
+}
+
+static inline struct zone *zpdesc_zone(struct zpdesc *zpdesc)
+{
+	return page_zone(zpdesc_page(zpdesc));
+}
+
+static inline bool zpdesc_is_locked(struct zpdesc *zpdesc)
+{
+	return folio_test_locked(zpdesc_folio(zpdesc));
+}
+#endif