Btrfs: space leak tracepoints

This in addition to a script in my btrfs-tracing tree will help track down space
leaks when we're getting space left over in block groups on umount.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index d5f987b..287a672 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -326,6 +326,8 @@
 	}
 
 	if (num_bytes) {
+		trace_btrfs_space_reservation(root->fs_info, "transaction",
+					      (u64)h, num_bytes, 1);
 		h->block_rsv = &root->fs_info->trans_block_rsv;
 		h->bytes_reserved = num_bytes;
 	}