https://github.com/darwinia-network/darwinia/blob/368a8d3b1352e059bb7cf5877e776e25843fb1ca/srml/staking/src/lib.rs#L1556 Since `total_payout` may be larger than 10,000,000,000, should we consider replace Perbill with Perquintil?