1 files changed, 40 insertions, 10 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index a794945fd194..029dfad5a235 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -119,6 +119,44 @@ static void background_writeout(unsigned long _min_pages);
  * We make sure that the background writeout level is below the adjusted
  * clamping level.
  */
+
+static unsigned long highmem_dirtyable_memory(unsigned long total)
+{
+#ifdef CONFIG_HIGHMEM
+        int node;
+        unsigned long x = 0;
+
+        for_each_online_node(node) {
+                struct zone *z =
+                        &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
+
+                x += zone_page_state(z, NR_FREE_PAGES)
+                        + zone_page_state(z, NR_INACTIVE)
+                        + zone_page_state(z, NR_ACTIVE);
+        }
+        /*
+         * Make sure that the number of highmem pages is never larger
+         * than the number of the total dirtyable memory. This can only
+         * occur in very strange VM situations but we want to make sure
+         * that this does not occur.
+         */
+        return min(x, total);
+#else
+        return 0;
+#endif
+}
+
+static unsigned long determine_dirtyable_memory(void)
+{
+        unsigned long x;
+
+        x = global_page_state(NR_FREE_PAGES)
+                + global_page_state(NR_INACTIVE)
+                + global_page_state(NR_ACTIVE);
+        x -= highmem_dirtyable_memory(x);
+        return x + 1;   /* Ensure that we never return 0 */
+}
+
 static void
 get_dirty_limits(long *pbackground, long *pdirty,
                                         struct address_space *mapping)
@@ -128,20 +166,12 @@ get_dirty_limits(long *pbackground, long *pdirty,
         int unmapped_ratio;
         long background;
         long dirty;
-        unsigned long available_memory = vm_total_pages;
+        unsigned long available_memory = determine_dirtyable_memory();
         struct task_struct *tsk;
 
-#ifdef CONFIG_HIGHMEM
-        /*
-         * We always exclude high memory from our count.
-         */
-        available_memory -= totalhigh_pages;
-#endif
-
-
         unmapped_ratio = 100 - ((global_page_state(NR_FILE_MAPPED) +
                                 global_page_state(NR_ANON_PAGES)) * 100) /
-                                        vm_total_pages;
+                                        available_memory;
 
         dirty_ratio = vm_dirty_ratio;
         if (dirty_ratio > unmapped_ratio / 2)