Btrfs: fix tree logs parallel sync

To improve performance, btrfs_sync_log merges tree log sync
requests. But it wrongly merges sync requests for different
tree logs. If multiple tree logs are synced at the same time,
only one of them actually gets synced.

This patch has following changes to fix the bug:

Move most tree log related fields in btrfs_fs_info to
btrfs_root. This allows merging sync requests separately
for each tree log.

Don't insert root item into the log root tree immediately
after log tree is allocated. Root item for log tree is
inserted when log tree get synced for the first time. This
allows syncing the log root tree without first syncing all
log trees.

At tree-log sync, btrfs_sync_log first sync the log tree;
then updates corresponding root item in the log root tree;
sync the log root tree; then update the super block.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

6 files changed, 248 insertions, 210 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e1fec636f37..de103a8a815 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -695,9 +695,7 @@ struct btrfs_fs_info {
 	struct btrfs_transaction *running_transaction;
 	wait_queue_head_t transaction_throttle;
 	wait_queue_head_t transaction_wait;
-
 	wait_queue_head_t async_submit_wait;
-	wait_queue_head_t tree_log_wait;
 
 	struct btrfs_super_block super_copy;
 	struct btrfs_super_block super_for_commit;
@@ -724,10 +722,6 @@ struct btrfs_fs_info {
 	atomic_t async_submit_draining;
 	atomic_t nr_async_bios;
 	atomic_t async_delalloc_pages;
-	atomic_t tree_log_writers;
-	atomic_t tree_log_commit;
-	unsigned long tree_log_batch;
-	u64 tree_log_transid;
 
 	/*
 	 * this is used by the balancing code to wait for all the pending
@@ -827,7 +821,14 @@ struct btrfs_root {
 	struct kobject root_kobj;
 	struct completion kobj_unregister;
 	struct mutex objectid_mutex;
+
 	struct mutex log_mutex;
+	wait_queue_head_t log_writer_wait;
+	wait_queue_head_t log_commit_wait[2];
+	atomic_t log_writers;
+	atomic_t log_commit[2];
+	unsigned long log_transid;
+	unsigned long log_batch;
 
 	u64 objectid;
 	u64 last_trans;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3cf17257f89..7feac5a475e 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -849,6 +849,14 @@ static int __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
 	spin_lock_init(&root->list_lock);
 	mutex_init(&root->objectid_mutex);
 	mutex_init(&root->log_mutex);
+	init_waitqueue_head(&root->log_writer_wait);
+	init_waitqueue_head(&root->log_commit_wait[0]);
+	init_waitqueue_head(&root->log_commit_wait[1]);
+	atomic_set(&root->log_commit[0], 0);
+	atomic_set(&root->log_commit[1], 0);
+	atomic_set(&root->log_writers, 0);
+	root->log_batch = 0;
+	root->log_transid = 0;
 	extent_io_tree_init(&root->dirty_log_pages,
 			     fs_info->btree_inode->i_mapping, GFP_NOFS);
 
@@ -933,15 +941,16 @@ int btrfs_free_log_root_tree(struct btrfs_trans_handle *trans,
 	return 0;
 }
 
-int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
-			     struct btrfs_fs_info *fs_info)
+static struct btrfs_root *alloc_log_tree(struct btrfs_trans_handle *trans,
+					 struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_root *root;
 	struct btrfs_root *tree_root = fs_info->tree_root;
+	struct extent_buffer *leaf;
 
 	root = kzalloc(sizeof(*root), GFP_NOFS);
 	if (!root)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	__setup_root(tree_root->nodesize, tree_root->leafsize,
 		     tree_root->sectorsize, tree_root->stripesize,
@@ -950,12 +959,23 @@ int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
 	root->root_key.objectid = BTRFS_TREE_LOG_OBJECTID;
 	root->root_key.type = BTRFS_ROOT_ITEM_KEY;
 	root->root_key.offset = BTRFS_TREE_LOG_OBJECTID;
+	/*
+	 * log trees do not get reference counted because they go away
+	 * before a real commit is actually done.  They do store pointers
+	 * to file data extents, and those reference counts still get
+	 * updated (along with back refs to the log tree).
+	 */
 	root->ref_cows = 0;
 
-	root->node = btrfs_alloc_free_block(trans, root, root->leafsize,
-					    0, BTRFS_TREE_LOG_OBJECTID,
-					    trans->transid, 0, 0, 0);
+	leaf = btrfs_alloc_free_block(trans, root, root->leafsize,
+				      0, BTRFS_TREE_LOG_OBJECTID,
+				      trans->transid, 0, 0, 0);
+	if (IS_ERR(leaf)) {
+		kfree(root);
+		return ERR_CAST(leaf);
+	}
 
+	root->node = leaf;
 	btrfs_set_header_nritems(root->node, 0);
 	btrfs_set_header_level(root->node, 0);
 	btrfs_set_header_bytenr(root->node, root->node->start);
@@ -967,7 +987,48 @@ int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
 			    BTRFS_FSID_SIZE);
 	btrfs_mark_buffer_dirty(root->node);
 	btrfs_tree_unlock(root->node);
-	fs_info->log_root_tree = root;
+	return root;
+}
+
+int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
+			     struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *log_root;
+
+	log_root = alloc_log_tree(trans, fs_info);
+	if (IS_ERR(log_root))
+		return PTR_ERR(log_root);
+	WARN_ON(fs_info->log_root_tree);
+	fs_info->log_root_tree = log_root;
+	return 0;
+}
+
+int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
+		       struct btrfs_root *root)
+{
+	struct btrfs_root *log_root;
+	struct btrfs_inode_item *inode_item;
+
+	log_root = alloc_log_tree(trans, root->fs_info);
+	if (IS_ERR(log_root))
+		return PTR_ERR(log_root);
+
+	log_root->last_trans = trans->transid;
+	log_root->root_key.offset = root->root_key.objectid;
+
+	inode_item = &log_root->root_item.inode;
+	inode_item->generation = cpu_to_le64(1);
+	inode_item->size = cpu_to_le64(3);
+	inode_item->nlink = cpu_to_le32(1);
+	inode_item->nbytes = cpu_to_le64(root->leafsize);
+	inode_item->mode = cpu_to_le32(S_IFDIR | 0755);
+
+	btrfs_set_root_bytenr(&log_root->root_item, log_root->node->start);
+	btrfs_set_root_generation(&log_root->root_item, trans->transid);
+
+	WARN_ON(root->log_root);
+	root->log_root = log_root;
+	root->log_transid = 0;
 	return 0;
 }
 
@@ -1530,10 +1591,6 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	init_waitqueue_head(&fs_info->transaction_throttle);
 	init_waitqueue_head(&fs_info->transaction_wait);
 	init_waitqueue_head(&fs_info->async_submit_wait);
-	init_waitqueue_head(&fs_info->tree_log_wait);
-	atomic_set(&fs_info->tree_log_commit, 0);
-	atomic_set(&fs_info->tree_log_writers, 0);
-	fs_info->tree_log_transid = 0;
 
 	__setup_root(4096, 4096, 4096, 4096, tree_root,
 		     fs_info, BTRFS_ROOT_TREE_OBJECTID);
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index c0ff404c31b..494a56eb298 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -98,5 +98,7 @@ int btrfs_free_log_root_tree(struct btrfs_trans_handle *trans,
 			     struct btrfs_fs_info *fs_info);
 int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
 			     struct btrfs_fs_info *fs_info);
+int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
+		       struct btrfs_root *root);
 int btree_lock_page_hook(struct page *page);
 #endif
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 1d7f043152b..3b26f098094 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2698,13 +2698,9 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 	/* if metadata always pin */
 	if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID) {
 		if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
-			struct btrfs_block_group_cache *cache;
-
-			/* btrfs_free_reserved_extent */
-			cache = btrfs_lookup_block_group(root->fs_info, bytenr);
-			BUG_ON(!cache);
-			btrfs_add_free_space(cache, bytenr, num_bytes);
-			put_block_group(cache);
+			mutex_lock(&root->fs_info->pinned_mutex);
+			btrfs_update_pinned_extents(root, bytenr, num_bytes, 1);
+			mutex_unlock(&root->fs_info->pinned_mutex);
 			update_reserved_extents(root, bytenr, num_bytes, 0);
 			return 0;
 		}
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index fbcbf43f511..3e8023efaff 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1214,10 +1214,10 @@ int btrfs_sync_file(struct file *file, struct dentry *dentry, int datasync)
 	}
 	mutex_unlock(&root->fs_info->trans_mutex);
 
-	root->fs_info->tree_log_batch++;
+	root->log_batch++;
 	filemap_fdatawrite(inode->i_mapping);
 	btrfs_wait_ordered_range(inode, 0, (u64)-1);
-	root->fs_info->tree_log_batch++;
+	root->log_batch++;
 
 	/*
 	 * ok we haven't committed the transaction yet, lets do a commit
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index d81cda2e077..4f26f3ed0c8 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -78,104 +78,6 @@ static int link_to_fixup_dir(struct btrfs_trans_handle *trans,
  */
 
 /*
- * btrfs_add_log_tree adds a new per-subvolume log tree into the
- * tree of log tree roots.  This must be called with a tree log transaction
- * running (see start_log_trans).
- */
-static int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
-		      struct btrfs_root *root)
-{
-	struct btrfs_key key;
-	struct btrfs_root_item root_item;
-	struct btrfs_inode_item *inode_item;
-	struct extent_buffer *leaf;
-	struct btrfs_root *new_root = root;
-	int ret;
-	u64 objectid = root->root_key.objectid;
-
-	leaf = btrfs_alloc_free_block(trans, root, root->leafsize, 0,
-				      BTRFS_TREE_LOG_OBJECTID,
-				      trans->transid, 0, 0, 0);
-	if (IS_ERR(leaf)) {
-		ret = PTR_ERR(leaf);
-		return ret;
-	}
-
-	btrfs_set_header_nritems(leaf, 0);
-	btrfs_set_header_level(leaf, 0);
-	btrfs_set_header_bytenr(leaf, leaf->start);
-	btrfs_set_header_generation(leaf, trans->transid);
-	btrfs_set_header_owner(leaf, BTRFS_TREE_LOG_OBJECTID);
-
-	write_extent_buffer(leaf, root->fs_info->fsid,
-			    (unsigned long)btrfs_header_fsid(leaf),
-			    BTRFS_FSID_SIZE);
-	btrfs_mark_buffer_dirty(leaf);
-
-	inode_item = &root_item.inode;
-	memset(inode_item, 0, sizeof(*inode_item));
-	inode_item->generation = cpu_to_le64(1);
-	inode_item->size = cpu_to_le64(3);
-	inode_item->nlink = cpu_to_le32(1);
-	inode_item->nbytes = cpu_to_le64(root->leafsize);
-	inode_item->mode = cpu_to_le32(S_IFDIR | 0755);
-
-	btrfs_set_root_bytenr(&root_item, leaf->start);
-	btrfs_set_root_generation(&root_item, trans->transid);
-	btrfs_set_root_level(&root_item, 0);
-	btrfs_set_root_refs(&root_item, 0);
-	btrfs_set_root_used(&root_item, 0);
-
-	memset(&root_item.drop_progress, 0, sizeof(root_item.drop_progress));
-	root_item.drop_level = 0;
-
-	btrfs_tree_unlock(leaf);
-	free_extent_buffer(leaf);
-	leaf = NULL;
-
-	btrfs_set_root_dirid(&root_item, 0);
-
-	key.objectid = BTRFS_TREE_LOG_OBJECTID;
-	key.offset = objectid;
-	btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
-	ret = btrfs_insert_root(trans, root->fs_info->log_root_tree, &key,
-				&root_item);
-	if (ret)
-		goto fail;
-
-	new_root = btrfs_read_fs_root_no_radix(root->fs_info->log_root_tree,
-					       &key);
-	BUG_ON(!new_root);
-
-	WARN_ON(root->log_root);
-	root->log_root = new_root;
-
-	/*
-	 * log trees do not get reference counted because they go away
-	 * before a real commit is actually done.  They do store pointers
-	 * to file data extents, and those reference counts still get
-	 * updated (along with back refs to the log tree).
-	 */
-	new_root->ref_cows = 0;
-	new_root->last_trans = trans->transid;
-
-	/*
-	 * we need to make sure the root block for this new tree
-	 * is marked as dirty in the dirty_log_pages tree.  This
-	 * is how it gets flushed down to disk at tree log commit time.
-	 *
-	 * the tree logging mutex keeps others from coming in and changing
-	 * the new_root->node, so we can safely access it here
-	 */
-	set_extent_dirty(&new_root->dirty_log_pages, new_root->node->start,
-			 new_root->node->start + new_root->node->len - 1,
-			 GFP_NOFS);
-
-fail:
-	return ret;
-}
-
-/*
  * start a sub transaction and setup the log tree
  * this increments the log tree writer count to make the people
  * syncing the tree wait for us to finish
@@ -184,6 +86,14 @@ static int start_log_trans(struct btrfs_trans_handle *trans,
 			   struct btrfs_root *root)
 {
 	int ret;
+
+	mutex_lock(&root->log_mutex);
+	if (root->log_root) {
+		root->log_batch++;
+		atomic_inc(&root->log_writers);
+		mutex_unlock(&root->log_mutex);
+		return 0;
+	}
 	mutex_lock(&root->fs_info->tree_log_mutex);
 	if (!root->fs_info->log_root_tree) {
 		ret = btrfs_init_log_root_tree(trans, root->fs_info);
@@ -193,9 +103,10 @@ static int start_log_trans(struct btrfs_trans_handle *trans,
 		ret = btrfs_add_log_tree(trans, root);
 		BUG_ON(ret);
 	}
-	atomic_inc(&root->fs_info->tree_log_writers);
-	root->fs_info->tree_log_batch++;
 	mutex_unlock(&root->fs_info->tree_log_mutex);
+	root->log_batch++;
+	atomic_inc(&root->log_writers);
+	mutex_unlock(&root->log_mutex);
 	return 0;
 }
 
@@ -212,13 +123,12 @@ static int join_running_log_trans(struct btrfs_root *root)
 	if (!root->log_root)
 		return -ENOENT;
 
-	mutex_lock(&root->fs_info->tree_log_mutex);
+	mutex_lock(&root->log_mutex);
 	if (root->log_root) {
 		ret = 0;
-		atomic_inc(&root->fs_info->tree_log_writers);
-		root->fs_info->tree_log_batch++;
+		atomic_inc(&root->log_writers);
 	}
-	mutex_unlock(&root->fs_info->tree_log_mutex);
+	mutex_unlock(&root->log_mutex);
 	return ret;
 }
 
@@ -228,10 +138,11 @@ static int join_running_log_trans(struct btrfs_root *root)
  */
 static int end_log_trans(struct btrfs_root *root)
 {
-	atomic_dec(&root->fs_info->tree_log_writers);
-	smp_mb();
-	if (waitqueue_active(&root->fs_info->tree_log_wait))
-		wake_up(&root->fs_info->tree_log_wait);
+	if (atomic_dec_and_test(&root->log_writers)) {
+		smp_mb();
+		if (waitqueue_active(&root->log_writer_wait))
+			wake_up(&root->log_writer_wait);
+	}
 	return 0;
 }
 
@@ -1902,26 +1813,65 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
 		}
 	}
 	btrfs_free_path(path);
-	if (wc->free)
-		free_extent_buffer(log->node);
 	return ret;
 }
 
-static int wait_log_commit(struct btrfs_root *log)
+/*
+ * helper function to update the item for a given subvolumes log root
+ * in the tree of log roots
+ */
+static int update_log_root(struct btrfs_trans_handle *trans,
+			   struct btrfs_root *log)
+{
+	int ret;
+
+	if (log->log_transid == 1) {
+		/* insert root item on the first sync */
+		ret = btrfs_insert_root(trans, log->fs_info->log_root_tree,
+				&log->root_key, &log->root_item);
+	} else {
+		ret = btrfs_update_root(trans, log->fs_info->log_root_tree,
+				&log->root_key, &log->root_item);
+	}
+	return ret;
+}
+
+static int wait_log_commit(struct btrfs_root *root, unsigned long transid)
 {
 	DEFINE_WAIT(wait);
-	u64 transid = log->fs_info->tree_log_transid;
+	int index = transid % 2;
 
+	/*
+	 * we only allow two pending log transactions at a time,
+	 * so we know that if ours is more than 2 older than the
+	 * current transaction, we're done
+	 */
 	do {
-		prepare_to_wait(&log->fs_info->tree_log_wait, &wait,
-				TASK_UNINTERRUPTIBLE);
-		mutex_unlock(&log->fs_info->tree_log_mutex);
-		if (atomic_read(&log->fs_info->tree_log_commit))
+		prepare_to_wait(&root->log_commit_wait[index],
+				&wait, TASK_UNINTERRUPTIBLE);
+		mutex_unlock(&root->log_mutex);
+		if (root->log_transid < transid + 2 &&
+		    atomic_read(&root->log_commit[index]))
 			schedule();
-		finish_wait(&log->fs_info->tree_log_wait, &wait);
-		mutex_lock(&log->fs_info->tree_log_mutex);
-	} while (transid == log->fs_info->tree_log_transid &&
-		atomic_read(&log->fs_info->tree_log_commit));
+		finish_wait(&root->log_commit_wait[index], &wait);
+		mutex_lock(&root->log_mutex);
+	} while (root->log_transid < transid + 2 &&
+		 atomic_read(&root->log_commit[index]));
+	return 0;
+}
+
+static int wait_for_writer(struct btrfs_root *root)
+{
+	DEFINE_WAIT(wait);
+	while (atomic_read(&root->log_writers)) {
+		prepare_to_wait(&root->log_writer_wait,
+				&wait, TASK_UNINTERRUPTIBLE);
+		mutex_unlock(&root->log_mutex);
+		if (atomic_read(&root->log_writers))
+			schedule();
+		mutex_lock(&root->log_mutex);
+		finish_wait(&root->log_writer_wait, &wait);
+	}
 	return 0;
 }
 
@@ -1933,57 +1883,114 @@ static int wait_log_commit(struct btrfs_root *log)
 int btrfs_sync_log(struct btrfs_trans_handle *trans,
 		   struct btrfs_root *root)
 {
+	int index1;
+	int index2;
 	int ret;
-	unsigned long batch;
 	struct btrfs_root *log = root->log_root;
+	struct btrfs_root *log_root_tree = root->fs_info->log_root_tree;
 
-	mutex_lock(&log->fs_info->tree_log_mutex);
-	if (atomic_read(&log->fs_info->tree_log_commit)) {
-		wait_log_commit(log);
-		goto out;
+	mutex_lock(&root->log_mutex);
+	index1 = root->log_transid % 2;
+	if (atomic_read(&root->log_commit[index1])) {
+		wait_log_commit(root, root->log_transid);
+		mutex_unlock(&root->log_mutex);
+		return 0;
 	}
-	atomic_set(&log->fs_info->tree_log_commit, 1);
+	atomic_set(&root->log_commit[index1], 1);
+
+	/* wait for previous tree log sync to complete */
+	if (atomic_read(&root->log_commit[(index1 + 1) % 2]))
+		wait_log_commit(root, root->log_transid - 1);
 
 	while (1) {
-		batch = log->fs_info->tree_log_batch;
-		mutex_unlock(&log->fs_info->tree_log_mutex);
+		unsigned long batch = root->log_batch;
+		mutex_unlock(&root->log_mutex);
 		schedule_timeout_uninterruptible(1);
-		mutex_lock(&log->fs_info->tree_log_mutex);
-
-		while (atomic_read(&log->fs_info->tree_log_writers)) {
-			DEFINE_WAIT(wait);
-			prepare_to_wait(&log->fs_info->tree_log_wait, &wait,
-					TASK_UNINTERRUPTIBLE);
-			mutex_unlock(&log->fs_info->tree_log_mutex);
-			if (atomic_read(&log->fs_info->tree_log_writers))
-				schedule();
-			mutex_lock(&log->fs_info->tree_log_mutex);
-			finish_wait(&log->fs_info->tree_log_wait, &wait);
-		}
-		if (batch == log->fs_info->tree_log_batch)
+		mutex_lock(&root->log_mutex);
+		wait_for_writer(root);
+		if (batch == root->log_batch)
 			break;
 	}
 
 	ret = btrfs_write_and_wait_marked_extents(log, &log->dirty_log_pages);
 	BUG_ON(ret);
-	ret = btrfs_write_and_wait_marked_extents(root->fs_info->log_root_tree,
-			       &root->fs_info->log_root_tree->dirty_log_pages);
+
+	btrfs_set_root_bytenr(&log->root_item, log->node->start);
+	btrfs_set_root_generation(&log->root_item, trans->transid);
+	btrfs_set_root_level(&log->root_item, btrfs_header_level(log->node));
+
+	root->log_batch = 0;
+	root->log_transid++;
+	log->log_transid = root->log_transid;
+	smp_mb();
+	/*
+	 * log tree has been flushed to disk, new modifications of
+	 * the log will be written to new positions. so it's safe to
+	 * allow log writers to go in.
+	 */
+	mutex_unlock(&root->log_mutex);
+
+	mutex_lock(&log_root_tree->log_mutex);
+	log_root_tree->log_batch++;
+	atomic_inc(&log_root_tree->log_writers);
+	mutex_unlock(&log_root_tree->log_mutex);
+
+	ret = update_log_root(trans, log);
+	BUG_ON(ret);
+
+	mutex_lock(&log_root_tree->log_mutex);
+	if (atomic_dec_and_test(&log_root_tree->log_writers)) {
+		smp_mb();
+		if (waitqueue_active(&log_root_tree->log_writer_wait))
+			wake_up(&log_root_tree->log_writer_wait);
+	}
+
+	index2 = log_root_tree->log_transid % 2;
+	if (atomic_read(&log_root_tree->log_commit[index2])) {
+		wait_log_commit(log_root_tree, log_root_tree->log_transid);
+		mutex_unlock(&log_root_tree->log_mutex);
+		goto out;
+	}
+	atomic_set(&log_root_tree->log_commit[index2], 1);
+
+	if (atomic_read(&log_root_tree->log_commit[(index2 + 1) % 2]))
+		wait_log_commit(log_root_tree, log_root_tree->log_transid - 1);
+
+	wait_for_writer(log_root_tree);
+
+	ret = btrfs_write_and_wait_marked_extents(log_root_tree,
+				&log_root_tree->dirty_log_pages);
 	BUG_ON(ret);
 
 	btrfs_set_super_log_root(&root->fs_info->super_for_commit,
-				 log->fs_info->log_root_tree->node->start);
+				log_root_tree->node->start);
 	btrfs_set_super_log_root_level(&root->fs_info->super_for_commit,
-		       btrfs_header_level(log->fs_info->log_root_tree->node));
+				btrfs_header_level(log_root_tree->node));
+
+	log_root_tree->log_batch = 0;
+	log_root_tree->log_transid++;
+	smp_mb();
+
+	mutex_unlock(&log_root_tree->log_mutex);
+
+	/*
+	 * nobody else is going to jump in and write the the ctree
+	 * super here because the log_commit atomic below is protecting
+	 * us.  We must be called with a transaction handle pinning
+	 * the running transaction open, so a full commit can't hop
+	 * in and cause problems either.
+	 */
+	write_ctree_super(trans, root->fs_info->tree_root, 2);
 
-	write_ctree_super(trans, log->fs_info->tree_root, 2);
-	log->fs_info->tree_log_transid++;
-	log->fs_info->tree_log_batch = 0;
-	atomic_set(&log->fs_info->tree_log_commit, 0);
+	atomic_set(&log_root_tree->log_commit[index2], 0);
 	smp_mb();
-	if (waitqueue_active(&log->fs_info->tree_log_wait))
-		wake_up(&log->fs_info->tree_log_wait);
+	if (waitqueue_active(&log_root_tree->log_commit_wait[index2]))
+		wake_up(&log_root_tree->log_commit_wait[index2]);
 out:
-	mutex_unlock(&log->fs_info->tree_log_mutex);
+	atomic_set(&root->log_commit[index1], 0);
+	smp_mb();
+	if (waitqueue_active(&root->log_commit_wait[index1]))
+		wake_up(&root->log_commit_wait[index1]);
 	return 0;
 }
 
@@ -2019,38 +2026,18 @@ int btrfs_free_log(struct btrfs_trans_handle *trans, struct btrfs_root *root)
 				   start, end, GFP_NOFS);
 	}
 
-	log = root->log_root;
-	ret = btrfs_del_root(trans, root->fs_info->log_root_tree,
-			     &log->root_key);
-	BUG_ON(ret);
+	if (log->log_transid > 0) {
+		ret = btrfs_del_root(trans, root->fs_info->log_root_tree,
+				     &log->root_key);
+		BUG_ON(ret);
+	}
 	root->log_root = NULL;
-	kfree(root->log_root);
+	free_extent_buffer(log->node);
+	kfree(log);
 	return 0;
 }
 
 /*
- * helper function to update the item for a given subvolumes log root
- * in the tree of log roots
- */
-static int update_log_root(struct btrfs_trans_handle *trans,
-			   struct btrfs_root *log)
-{
-	u64 bytenr = btrfs_root_bytenr(&log->root_item);
-	int ret;
-
-	if (log->node->start == bytenr)
-		return 0;
-
-	btrfs_set_root_bytenr(&log->root_item, log->node->start);
-	btrfs_set_root_generation(&log->root_item, trans->transid);
-	btrfs_set_root_level(&log->root_item, btrfs_header_level(log->node));
-	ret = btrfs_update_root(trans, log->fs_info->log_root_tree,
-				&log->root_key, &log->root_item);
-	BUG_ON(ret);
-	return ret;
-}
-
-/*
  * If both a file and directory are logged, and unlinks or renames are
  * mixed in, we have a few interesting corners:
  *
@@ -2711,11 +2698,6 @@ next_slot:
 
 	btrfs_free_path(path);
 	btrfs_free_path(dst_path);
-
-	mutex_lock(&root->fs_info->tree_log_mutex);
-	ret = update_log_root(trans, log);
-	BUG_ON(ret);
-	mutex_unlock(&root->fs_info->tree_log_mutex);
 out:
 	return 0;
 }