v4.19.13 snapshot.
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
new file mode 100644
index 0000000..e06febf
--- /dev/null
+++ b/include/linux/swapfile.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SWAPFILE_H
+#define _LINUX_SWAPFILE_H
+
+/*
+ * these were static in swapfile.c but frontswap.c needs them and we don't
+ * want to expose them to the dozens of source files that include swap.h
+ */
+extern spinlock_t swap_lock;
+extern struct plist_head swap_active_head;
+extern struct swap_info_struct *swap_info[];
+extern int try_to_unuse(unsigned int, bool, unsigned long);
+extern unsigned long generic_max_swapfile_size(void);
+extern unsigned long max_swapfile_size(void);
+
+#endif /* _LINUX_SWAPFILE_H */