Btrfs: track dirty block groups on their own list

Currently any time we try to update the block groups on disk we will walk _all_
block groups and check for the ->dirty flag to see if it is set.  This function
can get called several times during a commit.  So if you have several terabytes
of data you will be a very sad panda as we will loop through _all_ of the block
groups several times, which makes the commit take a while which slows down the
rest of the file system operations.

This patch introduces a dirty list for the block groups that we get added to
when we dirty the block group for the first time.  Then we simply update any
block groups that have been dirtied since the last time we called
btrfs_write_dirty_block_groups.  This allows us to clean up how we write the
free space cache out so it is much cleaner.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index aa2219ebecc9..e0faf803513a 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -248,6 +248,8 @@ loop:
 	INIT_LIST_HEAD(&cur_trans->pending_chunks);
 	INIT_LIST_HEAD(&cur_trans->switch_commits);
 	INIT_LIST_HEAD(&cur_trans->pending_ordered);
+	INIT_LIST_HEAD(&cur_trans->dirty_bgs);
+	spin_lock_init(&cur_trans->dirty_bgs_lock);
 	list_add_tail(&cur_trans->list, &fs_info->trans_list);
 	extent_io_tree_init(&cur_trans->dirty_pages,
 			     fs_info->btree_inode->i_mapping);
@@ -1028,7 +1030,9 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
 	while (1) {
 		old_root_bytenr = btrfs_root_bytenr(&root->root_item);
 		if (old_root_bytenr == root->node->start &&
-		    old_root_used == btrfs_root_used(&root->root_item))
+		    old_root_used == btrfs_root_used(&root->root_item) &&
+		    (!extent_root ||
+		     list_empty(&trans->transaction->dirty_bgs)))
 			break;
 
 		btrfs_set_root_node(&root->root_item, root->node);
@@ -1047,6 +1051,9 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
 		ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
 		if (ret)
 			return ret;
+		ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
+		if (ret)
+			return ret;
 	}
 
 	return 0;
@@ -1067,10 +1074,6 @@ static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
 	struct extent_buffer *eb;
 	int ret;
 
-	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
-	if (ret)
-		return ret;
-
 	eb = btrfs_lock_root_node(fs_info->tree_root);
 	ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL,
 			      0, &eb);
@@ -1990,6 +1993,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	switch_commit_roots(cur_trans, root->fs_info);
 
 	assert_qgroups_uptodate(trans);
+	ASSERT(list_empty(&cur_trans->dirty_bgs));
 	update_super_roots(root);
 
 	btrfs_set_super_log_root(root->fs_info->super_copy, 0);