2 files changed, 32 insertions, 4 deletions

diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index 0e4e2eec5c1d..30442547b9e6 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -19,6 +19,8 @@ extern struct frontswap_ops
 extern void frontswap_shrink(unsigned long);
 extern unsigned long frontswap_curr_pages(void);
 extern void frontswap_writethrough(bool);
+#define FRONTSWAP_HAS_EXCLUSIVE_GETS
+extern void frontswap_tmem_exclusive_gets(bool);
 
 extern void __frontswap_init(unsigned type);
 extern int __frontswap_store(struct page *page);
diff --git a/mm/frontswap.c b/mm/frontswap.c
index 6b3e71a2cd48..2890e67d6026 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -44,6 +44,13 @@ EXPORT_SYMBOL(frontswap_enabled);
  */
 static bool frontswap_writethrough_enabled __read_mostly;
 
+/*
+ * If enabled, the underlying tmem implementation is capable of doing
+ * exclusive gets, so frontswap_load, on a successful tmem_get must
+ * mark the page as no longer in frontswap AND mark it dirty.
+ */
+static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
+
 #ifdef CONFIG_DEBUG_FS
 /*
  * Counters available via /sys/kernel/debug/frontswap (if debugfs is
@@ -97,6 +104,15 @@ void frontswap_writethrough(bool enable)
 EXPORT_SYMBOL(frontswap_writethrough);
 
 /*
+ * Enable/disable frontswap exclusive gets (see above).
+ */
+void frontswap_tmem_exclusive_gets(bool enable)
+{
+        frontswap_tmem_exclusive_gets_enabled = enable;
+}
+EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
+
+/*
  * Called when a swap device is swapon'd.
  */
 void __frontswap_init(unsigned type)
@@ -174,8 +190,13 @@ int __frontswap_load(struct page *page)
         BUG_ON(sis == NULL);
         if (frontswap_test(sis, offset))
                 ret = frontswap_ops.load(type, offset, page);
-        if (ret == 0)
+        if (ret == 0) {
                 inc_frontswap_loads();
+                if (frontswap_tmem_exclusive_gets_enabled) {
+                        SetPageDirty(page);
+                        frontswap_clear(sis, offset);
+                }
+        }
         return ret;
 }
 EXPORT_SYMBOL(__frontswap_load);
@@ -263,6 +284,11 @@ static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
         return ret;
 }
 
+/*
+ * Used to check if it's necessory and feasible to unuse pages.
+ * Return 1 when nothing to do, 0 when need to shink pages,
+ * error code when there is an error.
+ */
 static int __frontswap_shrink(unsigned long target_pages,
                                 unsigned long *pages_to_unuse,
                                 int *type)
@@ -275,7 +301,7 @@ static int __frontswap_shrink(unsigned long target_pages,
         if (total_pages <= target_pages) {
                 /* Nothing to do */
                 *pages_to_unuse = 0;
-                return 0;
+                return 1;
         }
         total_pages_to_unuse = total_pages - target_pages;
         return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
@@ -292,7 +318,7 @@ static int __frontswap_shrink(unsigned long target_pages,
 void frontswap_shrink(unsigned long target_pages)
 {
         unsigned long pages_to_unuse = 0;
-        int type, ret;
+        int uninitialized_var(type), ret;
 
         /*
          * we don't want to hold swap_lock while doing a very
@@ -302,7 +328,7 @@ void frontswap_shrink(unsigned long target_pages)
         spin_lock(&swap_lock);
         ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
         spin_unlock(&swap_lock);
-        if (ret == 0 && pages_to_unuse)
+        if (ret == 0)
                 try_to_unuse(type, true, pages_to_unuse);
         return;
 }