1 files changed, 49 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 94ce79f76e5f..b13f1fbc3733 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -34,6 +34,8 @@
 #include "locking.h"
 #include "free-space-cache.h"
 
+#undef SCRAMBLE_DELAYED_REFS
+
 /*
  * control flags for do_chunk_alloc's force field
  * CHUNK_ALLOC_NO_FORCE means to only allocate a chunk
@@ -2364,6 +2366,49 @@ static void wait_for_more_refs(struct btrfs_fs_info *fs_info,
         spin_lock(&delayed_refs->lock);
 }
 
+#ifdef SCRAMBLE_DELAYED_REFS
+/*
+ * Normally delayed refs get processed in ascending bytenr order. This
+ * correlates in most cases to the order added. To expose dependencies on this
+ * order, we start to process the tree in the middle instead of the beginning
+ */
+static u64 find_middle(struct rb_root *root)
+{
+        struct rb_node *n = root->rb_node;
+        struct btrfs_delayed_ref_node *entry;
+        int alt = 1;
+        u64 middle;
+        u64 first = 0, last = 0;
+
+        n = rb_first(root);
+        if (n) {
+                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
+                first = entry->bytenr;
+        }
+        n = rb_last(root);
+        if (n) {
+                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
+                last = entry->bytenr;
+        }
+        n = root->rb_node;
+
+        while (n) {
+                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
+                WARN_ON(!entry->in_tree);
+
+                middle = entry->bytenr;
+
+                if (alt)
+                        n = n->rb_left;
+                else
+                        n = n->rb_right;
+
+                alt = 1 - alt;
+        }
+        return middle;
+}
+#endif
+
 /*
  * this starts processing the delayed reference count updates and
  * extent insertions we have queued up so far.  count can be
@@ -2406,6 +2451,10 @@ again:
         consider_waiting = 0;
         spin_lock(&delayed_refs->lock);
 
+#ifdef SCRAMBLE_DELAYED_REFS
+        delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
+#endif
+
         if (count == 0) {
                 count = delayed_refs->num_entries * 2;
                 run_most = 1;