[PATCH RFC] mm: simplify frontswap_init()

[Cesar Eduardo Barros]

The function frontswap_init() uses the passed parameter only to check
for the presence of the frontswap_map. It is also passed down to
frontswap_ops.init(), but all implementations of it in the kernel ignore
the parameter.

Do the check for frontswap_map in the caller instead and remove the
parameter from frontswap_init() and frontswap_ops.init().

Also, __frontswap_init() was exported, but its only caller (via an
inline function) is mm/swapfile.c, which cannot be built as a module.
Remove the unnecessary export.

Signed-off-by: Cesar Eduardo Barros <cesarb@xxxxxxxxxx>
---

Not even compile tested, just a quick patch to show what I was thinking
of, but feel free to apply if you think it is good.

I might write another patch to move it outside the lock later, but I
would have to read the frontswap code more carefully first.

 drivers/staging/ramster/zcache-main.c |  2 +-
 drivers/staging/zcache/zcache-main.c  |  2 +-
 drivers/xen/tmem.c                    |  2 +-
 include/linux/frontswap.h             |  8 ++++----
 mm/frontswap.c                        | 10 ++--------
 mm/swapfile.c                         |  3 ++-
 6 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/staging/ramster/zcache-main.c b/drivers/staging/ramster/zcache-main.c
index a09dd5c..b3f01c9 100644
--- a/drivers/staging/ramster/zcache-main.c
+++ b/drivers/staging/ramster/zcache-main.c
@@ -1610,7 +1610,7 @@ static void zcache_frontswap_flush_area(unsigned type)
 	}
 }
 
-static void zcache_frontswap_init(unsigned ignored)
+static void zcache_frontswap_init(void)
 {
 	/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
 	if (zcache_frontswap_poolid < 0)
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 52b43b7..cb67635 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1903,7 +1903,7 @@ static void zcache_frontswap_flush_area(unsigned type)
 	}
 }
 
-static void zcache_frontswap_init(unsigned ignored)
+static void zcache_frontswap_init(void)
 {
 	/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
 	if (zcache_frontswap_poolid < 0)
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index 144564e..7156ff0 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -343,7 +343,7 @@ static void tmem_frontswap_flush_area(unsigned type)
 		(void)xen_tmem_flush_object(pool, oswiz(type, ind));
 }
 
-static void tmem_frontswap_init(unsigned ignored)
+static void tmem_frontswap_init(void)
 {
 	struct tmem_pool_uuid private = TMEM_POOL_PRIVATE_UUID;
 
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 3044254..6374c80 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -6,7 +6,7 @@
 #include <linux/bitops.h>
 
 struct frontswap_ops {
-	void (*init)(unsigned);
+	void (*init)(void);
 	int (*store)(unsigned, pgoff_t, struct page *);
 	int (*load)(unsigned, pgoff_t, struct page *);
 	void (*invalidate_page)(unsigned, pgoff_t);
@@ -22,7 +22,7 @@ extern void frontswap_writethrough(bool);
 #define FRONTSWAP_HAS_EXCLUSIVE_GETS
 extern void frontswap_tmem_exclusive_gets(bool);
 
-extern void __frontswap_init(unsigned type);
+extern void __frontswap_init(void);
 extern int __frontswap_store(struct page *page);
 extern int __frontswap_load(struct page *page);
 extern void __frontswap_invalidate_page(unsigned, pgoff_t);
@@ -120,10 +120,10 @@ static inline void frontswap_invalidate_area(unsigned type)
 		__frontswap_invalidate_area(type);
 }
 
-static inline void frontswap_init(unsigned type)
+static inline void frontswap_init(void)
 {
 	if (frontswap_enabled)
-		__frontswap_init(type);
+		__frontswap_init();
 }
 
 #endif /* _LINUX_FRONTSWAP_H */
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 2890e67..d13661b 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -115,16 +115,10 @@ EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
 /*
  * Called when a swap device is swapon'd.
  */
-void __frontswap_init(unsigned type)
+void __frontswap_init(void)
 {
-	struct swap_info_struct *sis = swap_info[type];
-
-	BUG_ON(sis == NULL);
-	if (sis->frontswap_map == NULL)
-		return;
-	frontswap_ops.init(type);
+	frontswap_ops.init();
 }
-EXPORT_SYMBOL(__frontswap_init);
 
 static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
 {
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 088daf4..28c26bd 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1479,7 +1479,8 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
 {
 	spin_lock(&swap_lock);
 	_enable_swap_info(p, prio, swap_map, frontswap_map);
-	frontswap_init(p->type);
+	if (frontswap_map)
+		frontswap_init();
 	spin_unlock(&swap_lock);
 }
 
-- 
1.7.11.7

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