Merge git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable

* git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
Btrfs: be more polite in the async caching threads
Btrfs: preserve commit_root for async caching

fs/btrfs/ctree.h

···
 	struct mutex drop_mutex;
 	struct mutex volume_mutex;
 	struct mutex tree_reloc_mutex;
+	struct rw_semaphore extent_commit_sem;
 
 	/*
 	 * this protects the ordered operations list only while we are
···
 
 	/* the node lock is held while changing the node pointer */
 	spinlock_t node_lock;
-
-	/* taken when updating the commit root */
-	struct rw_semaphore commit_root_sem;
 
 	struct extent_buffer *commit_root;
 	struct btrfs_root *log_root;

fs/btrfs/disk-io.c

···
 	spin_lock_init(&root->inode_lock);
 	mutex_init(&root->objectid_mutex);
 	mutex_init(&root->log_mutex);
-	init_rwsem(&root->commit_root_sem);
 	init_waitqueue_head(&root->log_writer_wait);
 	init_waitqueue_head(&root->log_commit_wait[0]);
 	init_waitqueue_head(&root->log_commit_wait[1]);
···
 	mutex_init(&fs_info->cleaner_mutex);
 	mutex_init(&fs_info->volume_mutex);
 	mutex_init(&fs_info->tree_reloc_mutex);
+	init_rwsem(&fs_info->extent_commit_sem);
 
 	btrfs_init_free_cluster(&fs_info->meta_alloc_cluster);
 	btrfs_init_free_cluster(&fs_info->data_alloc_cluster);

fs/btrfs/extent-tree.c

···
 	last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);
 again:
 	/* need to make sure the commit_root doesn't disappear */
-	down_read(&fs_info->extent_root->commit_root_sem);
+	down_read(&fs_info->extent_commit_sem);
 
 	/*
 	 * We don't want to deadlock with somebody trying to allocate a new
···
 			else if (ret)
 				break;
 
-			if (need_resched()) {
+			if (need_resched() ||
+			    btrfs_transaction_in_commit(fs_info)) {
 				btrfs_release_path(fs_info->extent_root, path);
-				up_read(&fs_info->extent_root->commit_root_sem);
-				cond_resched();
+				up_read(&fs_info->extent_commit_sem);
+				schedule_timeout(1);
 				goto again;
 			}
 
···
 
 err:
 	btrfs_free_path(path);
-	up_read(&fs_info->extent_root->commit_root_sem);
+	up_read(&fs_info->extent_commit_sem);
 	atomic_dec(&block_group->space_info->caching_threads);
 	wake_up(&block_group->caching_q);
 

fs/btrfs/transaction.c

···
 
 static noinline void switch_commit_root(struct btrfs_root *root)
 {
-	down_write(&root->commit_root_sem);
 	free_extent_buffer(root->commit_root);
 	root->commit_root = btrfs_root_node(root);
-	up_write(&root->commit_root_sem);
 }
 
 /*
···
 		ret = btrfs_write_dirty_block_groups(trans, root);
 		BUG_ON(ret);
 	}
-	switch_commit_root(root);
+
+	if (root != root->fs_info->extent_root)
+		switch_commit_root(root);
+
 	return 0;
 }
 
···
 
 		update_cowonly_root(trans, root);
 	}
+
+	down_write(&fs_info->extent_commit_sem);
+	switch_commit_root(fs_info->extent_root);
+	up_write(&fs_info->extent_commit_sem);
+
 	return 0;
 }
 
···
 	super->root = root_item->bytenr;
 	super->generation = root_item->generation;
 	super->root_level = root_item->level;
+}
+
+int btrfs_transaction_in_commit(struct btrfs_fs_info *info)
+{
+	int ret = 0;
+	spin_lock(&info->new_trans_lock);
+	if (info->running_transaction)
+		ret = info->running_transaction->in_commit;
+	spin_unlock(&info->new_trans_lock);
+	return ret;
 }
 
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,

fs/btrfs/transaction.h

···
 				struct btrfs_root *root);
 int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,
 					struct extent_io_tree *dirty_pages);
+int btrfs_transaction_in_commit(struct btrfs_fs_info *info);
 #endif