Merge tag 'stable/frontswap.v16-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/mm

Pull frontswap feature from Konrad Rzeszutek Wilk:
 "Frontswap provides a "transcendent memory" interface for swap pages.
  In some environments, dramatic performance savings may be obtained
  because swapped pages are saved in RAM (or a RAM-like device) instead
  of a swap disk.  This tag provides the basic infrastructure along with
  some changes to the existing backends."

Fix up trivial conflict in mm/Makefile due to removal of swap token code
changing a line next to the new frontswap entry.

This pull request came in before the merge window even opened, it got
delayed to after the merge window by me just wanting to make sure it had
actual users.  Apparently IBM is using this on their embedded side, and
Jan Beulich says that it's already made available for SLES and OpenSUSE
users.

Also acked by Rik van Riel, and Konrad points to other people liking it
too.  So in it goes.

By Dan Magenheimer (4) and Konrad Rzeszutek Wilk (2)
via Konrad Rzeszutek Wilk
* tag 'stable/frontswap.v16-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/mm:
  frontswap: s/put_page/store/g s/get_page/load
  MAINTAINER: Add myself for the frontswap API
  mm: frontswap: config and doc files
  mm: frontswap: core frontswap functionality
  mm: frontswap: core swap subsystem hooks and headers
  mm: frontswap: add frontswap header file

3 files changed, 144 insertions, 0 deletions

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
new file mode 100644
index 000000000000..0e4e2eec5c1d
--- /dev/null
+++ b/include/linux/frontswap.h
@@ -0,0 +1,127 @@
+#ifndef _LINUX_FRONTSWAP_H
+#define _LINUX_FRONTSWAP_H
+
+#include <linux/swap.h>
+#include <linux/mm.h>
+#include <linux/bitops.h>
+
+struct frontswap_ops {
+        void (*init)(unsigned);
+        int (*store)(unsigned, pgoff_t, struct page *);
+        int (*load)(unsigned, pgoff_t, struct page *);
+        void (*invalidate_page)(unsigned, pgoff_t);
+        void (*invalidate_area)(unsigned);
+};
+
+extern bool frontswap_enabled;
+extern struct frontswap_ops
+        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);
+
+extern void __frontswap_init(unsigned type);
+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
+
+static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+        bool ret = false;
+
+        if (frontswap_enabled && sis->frontswap_map)
+                ret = test_bit(offset, sis->frontswap_map);
+        return ret;
+}
+
+static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
+{
+        if (frontswap_enabled && sis->frontswap_map)
+                set_bit(offset, sis->frontswap_map);
+}
+
+static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
+{
+        if (frontswap_enabled && sis->frontswap_map)
+                clear_bit(offset, sis->frontswap_map);
+}
+
+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 */
+
+#define frontswap_enabled (0)
+
+static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
+{
+        return false;
+}
+
+static inline void frontswap_set(struct swap_info_struct *sis, pgoff_t offset)
+{
+}
+
+static inline void frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
+{
+}
+
+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)
+{
+        int ret = -1;
+
+        if (frontswap_enabled)
+                ret = __frontswap_store(page);
+        return ret;
+}
+
+static inline int frontswap_load(struct page *page)
+{
+        int ret = -1;
+
+        if (frontswap_enabled)
+                ret = __frontswap_load(page);
+        return ret;
+}
+
+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)
+{
+        if (frontswap_enabled)
+                __frontswap_init(type);
+}
+
+#endif /* _LINUX_FRONTSWAP_H */
diff --git a/include/linux/swap.h b/include/linux/swap.h
index b6661933e252..c84ec68eaec9 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -197,6 +197,10 @@ struct swap_info_struct {
         struct block_device *bdev;      /* swap device or bdev of swap file */
         struct file *swap_file;         /* seldom referenced */
         unsigned int old_block_size;    /* seldom referenced */
+#ifdef CONFIG_FRONTSWAP
+        unsigned long *frontswap_map;   /* frontswap in-use, one bit per page */
+        atomic_t frontswap_pages;       /* frontswap pages in-use counter */
+#endif
 };
 
 struct swap_list_t {
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
new file mode 100644
index 000000000000..e282624e8c10
--- /dev/null
+++ b/include/linux/swapfile.h
@@ -0,0 +1,13 @@
+#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 swap_list_t swap_list;
+extern struct swap_info_struct *swap_info[];
+extern int try_to_unuse(unsigned int, bool, unsigned long);
+
+#endif /* _LINUX_SWAPFILE_H */