mm: frontswap: cleanup code

After allowing tmem backends to build/run as modules, frontswap_enabled
always true if defined CONFIG_FRONTSWAP.  But frontswap_test() depends on
whether backend is registered, mv it into frontswap.c using fronstswap_ops
to make the decision.

frontswap_set/clear are not used outside frontswap, so don't export them.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andor Daam <andor.daam@googlemail.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Florian Schmaus <fschmaus@gmail.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Stefan Hengelein <ilendir@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 30 insertions, 27 deletions

diff --git a/mm/frontswap.c b/mm/frontswap.c
index e44c9cbd1443..2760b0f98822 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -27,14 +27,6 @@
 static struct frontswap_ops *frontswap_ops __read_mostly;
 
 /*
- * This global enablement flag reduces overhead on systems where frontswap_ops
- * has not been registered, so is preferred to the slower alternative: a
- * function call that checks a non-global.
- */
-bool frontswap_enabled __read_mostly;
-EXPORT_SYMBOL(frontswap_enabled);
-
-/*
  * If enabled, frontswap_store will return failure even on success.  As
  * a result, the swap subsystem will always write the page to swap, in
  * effect converting frontswap into a writethrough cache.  In this mode,
@@ -128,8 +120,6 @@ struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
         struct frontswap_ops *old = frontswap_ops;
         int i;
 
-        frontswap_enabled = true;
-
         for (i = 0; i < MAX_SWAPFILES; i++) {
                 if (test_and_clear_bit(i, need_init))
                         ops->init(i);
@@ -183,9 +173,21 @@ void __frontswap_init(unsigned type)
 }
 EXPORT_SYMBOL(__frontswap_init);
 
-static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
+bool __frontswap_test(struct swap_info_struct *sis,
+                                pgoff_t offset)
+{
+        bool ret = false;
+
+        if (frontswap_ops && sis->frontswap_map)
+                ret = test_bit(offset, sis->frontswap_map);
+        return ret;
+}
+EXPORT_SYMBOL(__frontswap_test);
+
+static inline void __frontswap_clear(struct swap_info_struct *sis,
+                                pgoff_t offset)
 {
-        frontswap_clear(sis, offset);
+        clear_bit(offset, sis->frontswap_map);
         atomic_dec(&sis->frontswap_pages);
 }
 
@@ -204,18 +206,20 @@ int __frontswap_store(struct page *page)
         struct swap_info_struct *sis = swap_info[type];
         pgoff_t offset = swp_offset(entry);
 
-        if (!frontswap_ops) {
-                inc_frontswap_failed_stores();
+        /*
+         * Return if no backend registed.
+         * Don't need to inc frontswap_failed_stores here.
+         */
+        if (!frontswap_ops)
                 return ret;
-        }
 
         BUG_ON(!PageLocked(page));
         BUG_ON(sis == NULL);
-        if (frontswap_test(sis, offset))
+        if (__frontswap_test(sis, offset))
                 dup = 1;
         ret = frontswap_ops->store(type, offset, page);
         if (ret == 0) {
-                frontswap_set(sis, offset);
+                set_bit(offset, sis->frontswap_map);
                 inc_frontswap_succ_stores();
                 if (!dup)
                         atomic_inc(&sis->frontswap_pages);
@@ -248,18 +252,18 @@ int __frontswap_load(struct page *page)
         struct swap_info_struct *sis = swap_info[type];
         pgoff_t offset = swp_offset(entry);
 
-        if (!frontswap_ops)
-                return ret;
-
         BUG_ON(!PageLocked(page));
         BUG_ON(sis == NULL);
-        if (frontswap_test(sis, offset))
+        /*
+         * __frontswap_test() will check whether there is backend registered
+         */
+        if (__frontswap_test(sis, offset))
                 ret = frontswap_ops->load(type, offset, page);
         if (ret == 0) {
                 inc_frontswap_loads();
                 if (frontswap_tmem_exclusive_gets_enabled) {
                         SetPageDirty(page);
-                        frontswap_clear(sis, offset);
+                        __frontswap_clear(sis, offset);
                 }
         }
         return ret;
@@ -274,11 +278,11 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
 {
         struct swap_info_struct *sis = swap_info[type];
 
-        if (!frontswap_ops)
-                return;
-
         BUG_ON(sis == NULL);
-        if (frontswap_test(sis, offset)) {
+        /*
+         * __frontswap_test() will check whether there is backend registered
+         */
+        if (__frontswap_test(sis, offset)) {
                 frontswap_ops->invalidate_page(type, offset);
                 __frontswap_clear(sis, offset);
                 inc_frontswap_invalidates();
@@ -435,7 +439,6 @@ static int __init init_frontswap(void)
         debugfs_create_u64("invalidates", S_IRUGO,
                                 root, &frontswap_invalidates);
 #endif
-        frontswap_enabled = 1;
         return 0;
 }