mm: kill frontswap

The only user of frontswap is zswap, and has been for a long time.  Have
swap call into zswap directly and remove the indirection.

[hannes@cmpxchg.org: remove obsolete comment, per Yosry]
  Link: https://lkml.kernel.org/r/20230719142832.GA932528@cmpxchg.org
[fengwei.yin@intel.com: don't warn if none swapcache folio is passed to zswap_load]
  Link: https://lkml.kernel.org/r/20230810095652.3905184-1-fengwei.yin@intel.com
Link: https://lkml.kernel.org/r/20230717160227.GA867137@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

4 files changed, 37 insertions, 105 deletions

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
deleted file mode 100644
index eaa0ac5f9003..000000000000
--- a/include/linux/frontswap.h
+++ /dev/null
@@ -1,91 +0,0 @@
-/* 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 *, bool *); /* load a page */
-	void (*invalidate_page)(unsigned, pgoff_t); /* page no longer needed */
-	void (*invalidate_area)(unsigned); /* swap type just swapoff'ed */
-};
-
-int frontswap_register_ops(const struct frontswap_ops *ops);
-
-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 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 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);
-}
-
-#endif /* _LINUX_FRONTSWAP_H */
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 456546443f1f..bb5adc604144 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -302,10 +302,6 @@ struct swap_info_struct {
 	struct file *swap_file;		/* seldom referenced */
 	unsigned int old_block_size;	/* seldom referenced */
 	struct completion comp;		/* 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
 	spinlock_t lock;		/*
 					 * protect map scan related fields like
 					 * swap_map, lowest_bit, highest_bit,
@@ -630,11 +626,6 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 }
 #endif
 
-#ifdef CONFIG_ZSWAP
-extern u64 zswap_pool_total_size;
-extern atomic_t zswap_stored_pages;
-#endif
-
 #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
 void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp);
 static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index 7ed529a77c5b..99e3ed469e88 100644
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -2,11 +2,6 @@
 #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 struct swap_info_struct *swap_info[];
 extern unsigned long generic_max_swapfile_size(void);
 unsigned long arch_max_swapfile_size(void);
 
diff --git a/include/linux/zswap.h b/include/linux/zswap.h
new file mode 100644
index 000000000000..850c377d9b6d
--- /dev/null
+++ b/include/linux/zswap.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_ZSWAP_H
+#define _LINUX_ZSWAP_H
+
+#include <linux/types.h>
+#include <linux/mm_types.h>
+
+extern u64 zswap_pool_total_size;
+extern atomic_t zswap_stored_pages;
+
+#ifdef CONFIG_ZSWAP
+
+bool zswap_store(struct page *page);
+bool zswap_load(struct page *page);
+void zswap_invalidate(int type, pgoff_t offset);
+void zswap_swapon(int type);
+void zswap_swapoff(int type);
+
+#else
+
+static inline bool zswap_store(struct page *page)
+{
+	return false;
+}
+
+static inline bool zswap_load(struct page *page)
+{
+	return false;
+}
+
+static inline void zswap_invalidate(int type, pgoff_t offset) {}
+static inline void zswap_swapon(int type) {}
+static inline void zswap_swapoff(int type) {}
+
+#endif
+
+#endif /* _LINUX_ZSWAP_H */