3 files changed, 53 insertions, 3 deletions

diff --git a/mm/swap.c b/mm/swap.c
index e3045040dc3e..88a394872677 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -428,6 +428,30 @@ void pagevec_strip(struct pagevec *pvec)
 }
 
 /**
+ * pagevec_swap_free - try to free swap space from the pages in a pagevec
+ * @pvec: pagevec with swapcache pages to free the swap space of
+ *
+ * The caller needs to hold an extra reference to each page and
+ * not hold the page lock on the pages.  This function uses a
+ * trylock on the page lock so it may not always free the swap
+ * space associated with a page.
+ */
+void pagevec_swap_free(struct pagevec *pvec)
+{
+        int i;
+
+        for (i = 0; i < pagevec_count(pvec); i++) {
+                struct page *page = pvec->pages[i];
+
+                if (PageSwapCache(page) && trylock_page(page)) {
+                        if (PageSwapCache(page))
+                                remove_exclusive_swap_page_ref(page);
+                        unlock_page(page);
+                }
+        }
+}
+
+/**
  * pagevec_lookup - gang pagecache lookup
  * @pvec:       Where the resulting pages are placed
  * @mapping:    The address_space to search
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1e330f2998fa..2a97fafa3d89 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -344,7 +344,7 @@ int can_share_swap_page(struct page *page)
  * Work out if there are any other processes sharing this
  * swap cache page. Free it if you can. Return success.
  */
-int remove_exclusive_swap_page(struct page *page)
+static int remove_exclusive_swap_page_count(struct page *page, int count)
 {
         int retval;
         struct swap_info_struct * p;
@@ -357,7 +357,7 @@ int remove_exclusive_swap_page(struct page *page)
                 return 0;
         if (PageWriteback(page))
                 return 0;
-        if (page_count(page) != 2) /* 2: us + cache */
+        if (page_count(page) != count) /* us + cache + ptes */
                 return 0;
 
         entry.val = page_private(page);
@@ -370,7 +370,7 @@ int remove_exclusive_swap_page(struct page *page)
         if (p->swap_map[swp_offset(entry)] == 1) {
                 /* Recheck the page count with the swapcache lock held.. */
                 spin_lock_irq(&swapper_space.tree_lock);
-                if ((page_count(page) == 2) && !PageWriteback(page)) {
+                if ((page_count(page) == count) && !PageWriteback(page)) {
                         __delete_from_swap_cache(page);
                         SetPageDirty(page);
                         retval = 1;
@@ -388,6 +388,25 @@ int remove_exclusive_swap_page(struct page *page)
 }
 
 /*
+ * Most of the time the page should have two references: one for the
+ * process and one for the swap cache.
+ */
+int remove_exclusive_swap_page(struct page *page)
+{
+        return remove_exclusive_swap_page_count(page, 2);
+}
+
+/*
+ * The pageout code holds an extra reference to the page.  That raises
+ * the reference count to test for to 2 for a page that is only in the
+ * swap cache plus 1 for each process that maps the page.
+ */
+int remove_exclusive_swap_page_ref(struct page *page)
+{
+        return remove_exclusive_swap_page_count(page, 2 + page_mapcount(page));
+}
+
+/*
  * Free the swap entry like above, but also try to
  * free the page cache entry if it is the last user.
  */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 46fdaa546b8d..e656035d3406 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -647,6 +647,9 @@ free_it:
                 continue;
 
 activate_locked:
+                /* Not a candidate for swapping, so reclaim swap space. */
+                if (PageSwapCache(page) && vm_swap_full())
+                        remove_exclusive_swap_page_ref(page);
                 SetPageActive(page);
                 pgactivate++;
 keep_locked:
@@ -1228,6 +1231,8 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
                         __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
                         pgmoved = 0;
                         spin_unlock_irq(&zone->lru_lock);
+                        if (vm_swap_full())
+                                pagevec_swap_free(&pvec);
                         __pagevec_release(&pvec);
                         spin_lock_irq(&zone->lru_lock);
                 }
@@ -1237,6 +1242,8 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
         __count_zone_vm_events(PGREFILL, zone, pgscanned);
         __count_vm_events(PGDEACTIVATE, pgdeactivate);
         spin_unlock_irq(&zone->lru_lock);
+        if (vm_swap_full())
+                pagevec_swap_free(&pvec);
 
         pagevec_release(&pvec);
 }