v4.19.13 snapshot.
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
new file mode 100644
index 0000000..011965c
--- /dev/null
+++ b/include/linux/frontswap.h
@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_FRONTSWAP_H
+#define _LINUX_FRONTSWAP_H
+
+#include <linux/swap.h>
+#include <linux/mm.h>
+#include <linux/bitops.h>
+#include <linux/jump_label.h>
+
+struct frontswap_ops {
+ void (*init)(unsigned); /* this swap type was just swapon'ed */
+ int (*store)(unsigned, pgoff_t, struct page *); /* store a page */
+ int (*load)(unsigned, pgoff_t, struct page *); /* load a page */
+ void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
+ void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
+ struct frontswap_ops *next; /* private pointer to next ops */
+};
+
+extern void frontswap_register_ops(struct frontswap_ops *ops);
+extern void frontswap_shrink(unsigned long);
+extern unsigned long frontswap_curr_pages(void);
+extern void frontswap_writethrough(bool);
+#define FRONTSWAP_HAS_EXCLUSIVE_GETS
+extern void frontswap_tmem_exclusive_gets(bool);
+
+extern bool __frontswap_test(struct swap_info_struct *, pgoff_t);
+extern void __frontswap_init(unsigned type, unsigned long *map);
+extern int __frontswap_store(struct page *page);
+extern int __frontswap_load(struct page *page);
+extern void __frontswap_invalidate_page(unsigned, pgoff_t);
+extern void __frontswap_invalidate_area(unsigned);
+
+#ifdef CONFIG_FRONTSWAP
+extern struct static_key_false frontswap_enabled_key;
+
+static inline bool frontswap_enabled(void)
+{
+ return static_branch_unlikely(&frontswap_enabled_key);
+}
+
+static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+ return __frontswap_test(sis, offset);
+}
+
+static inline void frontswap_map_set(struct swap_info_struct *p,
+ unsigned long *map)
+{
+ p->frontswap_map = map;
+}
+
+static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
+{
+ return p->frontswap_map;
+}
+#else
+/* all inline routines become no-ops and all externs are ignored */
+
+static inline bool frontswap_enabled(void)
+{
+ return false;
+}
+
+static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+ return false;
+}
+
+static inline void frontswap_map_set(struct swap_info_struct *p,
+ unsigned long *map)
+{
+}
+
+static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
+{
+ return NULL;
+}
+#endif
+
+static inline int frontswap_store(struct page *page)
+{
+ if (frontswap_enabled())
+ return __frontswap_store(page);
+
+ return -1;
+}
+
+static inline int frontswap_load(struct page *page)
+{
+ if (frontswap_enabled())
+ return __frontswap_load(page);
+
+ return -1;
+}
+
+static inline void frontswap_invalidate_page(unsigned type, pgoff_t offset)
+{
+ if (frontswap_enabled())
+ __frontswap_invalidate_page(type, offset);
+}
+
+static inline void frontswap_invalidate_area(unsigned type)
+{
+ if (frontswap_enabled())
+ __frontswap_invalidate_area(type);
+}
+
+static inline void frontswap_init(unsigned type, unsigned long *map)
+{
+#ifdef CONFIG_FRONTSWAP
+ __frontswap_init(type, map);
+#endif
+}
+
+#endif /* _LINUX_FRONTSWAP_H */