  In multi-task learning (MTL), gradient balancing has recently attracted more
research interest than loss balancing since it often leads to better
performance. However, loss balancing is much more efficient than gradient
balancing, and thus it is still worth further exploration in MTL. Note that
prior studies typically ignore that there exist varying improvable gaps across
multiple tasks, where the improvable gap per task is defined as the distance
between the current training progress and desired final training progress.
Therefore, after loss balancing, the performance imbalance still arises in many
cases. In this paper, following the loss balancing framework, we propose two
novel improvable gap balancing (IGB) algorithms for MTL: one takes a simple
heuristic, and the other (for the first time) deploys deep reinforcement
learning for MTL. Particularly, instead of directly balancing the losses in
MTL, both algorithms choose to dynamically assign task weights for improvable
gap balancing. Moreover, we combine IGB and gradient balancing to show the
complementarity between the two types of algorithms. Extensive experiments on
two benchmark datasets demonstrate that our IGB algorithms lead to the best
results in MTL via loss balancing and achieve further improvements when
combined with gradient balancing. Code is available at
https://github.com/YanqiDai/IGB4MTL.
