btrfs: make tree iteration in extent_io_tree_release() more efficient

Currently extent_io_tree_release() is a loop that keeps getting the first
node in the io tree, using rb_first() which is a loop that gets to the
leftmost node of the rbtree, and then for each node it calls rb_erase(),
which often requires rebalancing the rbtree.

We can make this more efficient by using
rbtree_postorder_for_each_entry_safe() to free each node without having
to delete it from the rbtree and without looping to get the first node.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-io-tree.c b/fs/btrfs/extent-io-tree.c
index 9fb4f38347fe81be8ab2f3e3fbad463cdbb01404..f9f7cf028ffbd0e86d7ecc60e9ab7eb9b929a8d1 100644 (file)
--- a/fs/btrfs/extent-io-tree.c
+++ b/fs/btrfs/extent-io-tree.c
@@ -114,14 +114,15 @@ void extent_io_tree_init(struct btrfs_fs_info *fs_info,
  */
 void extent_io_tree_release(struct extent_io_tree *tree)
 {
-       spin_lock(&tree->lock);
-       while (!RB_EMPTY_ROOT(&tree->state)) {
-               struct rb_node *node;
-               struct extent_state *state;
+       struct rb_root root;
+       struct extent_state *state;
+       struct extent_state *tmp;
 
-               node = rb_first(&tree->state);
-               state = rb_entry(node, struct extent_state, rb_node);
-               rb_erase(&state->rb_node, &tree->state);
+       spin_lock(&tree->lock);
+       root = tree->state;
+       tree->state = RB_ROOT;
+       rbtree_postorder_for_each_entry_safe(state, tmp, &root, rb_node) {
+               /* Clear node to keep free_extent_state() happy. */
                RB_CLEAR_NODE(&state->rb_node);
                ASSERT(!(state->state & EXTENT_LOCKED));
                /*
@@ -131,9 +132,13 @@ void extent_io_tree_release(struct extent_io_tree *tree)
                 */
                ASSERT(!waitqueue_active(&state->wq));
                free_extent_state(state);
-
                cond_resched_lock(&tree->lock);
        }
+       /*
+        * Should still be empty even after a reschedule, no other task should
+        * be accessing the tree anymore.
+        */
+       ASSERT(RB_EMPTY_ROOT(&tree->state));
        spin_unlock(&tree->lock);
 }