Maximum value for MultiplierUpdate (paritytech#12282)

* Maximum value for MultiplierUpdate

* Update frame/transaction-payment/src/lib.rs

Co-authored-by: Stephen Shelton <steve@brewcraft.org>

* Update lib.rs

* return constant

* fix in runtime

* Update frame/transaction-payment/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update frame/transaction-payment/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* fixes

* remove unused import

* Update lib.rs

* more readable

* fix

* fix nits

Co-authored-by: Stephen Shelton <steve@brewcraft.org>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

bin/node/runtime/src/impls.rs

@@ -125,8 +125,8 @@ mod multiplier_tests {
 
 	use crate::{
 		constants::{currency::*, time::*},
-		AdjustmentVariable, MinimumMultiplier, Runtime, RuntimeBlockWeights as BlockWeights,
-		System, TargetBlockFullness, TransactionPayment,
+		AdjustmentVariable, MaximumMultiplier, MinimumMultiplier, Runtime,
+		RuntimeBlockWeights as BlockWeights, System, TargetBlockFullness, TransactionPayment,
 	};
 	use frame_support::weights::{DispatchClass, Weight, WeightToFee};
 
@@ -152,6 +152,7 @@ mod multiplier_tests {
 			TargetBlockFullness,
 			AdjustmentVariable,
 			MinimumMultiplier,
+			MaximumMultiplier,
 		>::convert(fm)
 	}
 

bin/node/runtime/src/lib.rs

@@ -64,7 +64,7 @@ use sp_runtime::{
 	curve::PiecewiseLinear,
 	generic, impl_opaque_keys,
 	traits::{
-		self, BlakeTwo256, Block as BlockT, ConvertInto, NumberFor, OpaqueKeys,
+		self, BlakeTwo256, Block as BlockT, Bounded, ConvertInto, NumberFor, OpaqueKeys,
 		SaturatedConversion, StaticLookup,
 	},
 	transaction_validity::{TransactionPriority, TransactionSource, TransactionValidity},
@@ -443,6 +443,7 @@ parameter_types! {
 	pub const TargetBlockFullness: Perquintill = Perquintill::from_percent(25);
 	pub AdjustmentVariable: Multiplier = Multiplier::saturating_from_rational(1, 100_000);
 	pub MinimumMultiplier: Multiplier = Multiplier::saturating_from_rational(1, 1_000_000_000u128);
+	pub MaximumMultiplier: Multiplier = Bounded::max_value();
 }
 
 impl pallet_transaction_payment::Config for Runtime {
@@ -451,8 +452,13 @@ impl pallet_transaction_payment::Config for Runtime {
 	type OperationalFeeMultiplier = OperationalFeeMultiplier;
 	type WeightToFee = IdentityFee<Balance>;
 	type LengthToFee = ConstantMultiplier<Balance, TransactionByteFee>;
-	type FeeMultiplierUpdate =
-		TargetedFeeAdjustment<Self, TargetBlockFullness, AdjustmentVariable, MinimumMultiplier>;
+	type FeeMultiplierUpdate = TargetedFeeAdjustment<
+		Self,
+		TargetBlockFullness,
+		AdjustmentVariable,
+		MinimumMultiplier,
+		MaximumMultiplier,
+	>;
 }
 
 impl pallet_asset_tx_payment::Config for Runtime {

frame/transaction-payment/src/lib.rs

@@ -127,12 +127,14 @@ type BalanceOf<T> = <<T as Config>::OnChargeTransaction as OnChargeTransaction<T
 ///
 /// More info can be found at:
 /// <https://research.web3.foundation/en/latest/polkadot/overview/2-token-economics.html>
-pub struct TargetedFeeAdjustment<T, S, V, M>(sp_std::marker::PhantomData<(T, S, V, M)>);
+pub struct TargetedFeeAdjustment<T, S, V, M, X>(sp_std::marker::PhantomData<(T, S, V, M, X)>);
 
 /// Something that can convert the current multiplier to the next one.
 pub trait MultiplierUpdate: Convert<Multiplier, Multiplier> {
-	/// Minimum multiplier
+	/// Minimum multiplier. Any outcome of the `convert` function should be at least this.
 	fn min() -> Multiplier;
+	/// Maximum multiplier. Any outcome of the `convert` function should be less or equal this.
+	fn max() -> Multiplier;
 	/// Target block saturation level
 	fn target() -> Perquintill;
 	/// Variability factor
@@ -143,6 +145,9 @@ impl MultiplierUpdate for () {
 	fn min() -> Multiplier {
 		Default::default()
 	}
+	fn max() -> Multiplier {
+		<Multiplier as sp_runtime::traits::Bounded>::max_value()
+	}
 	fn target() -> Perquintill {
 		Default::default()
 	}
@@ -151,16 +156,20 @@ impl MultiplierUpdate for () {
 	}
 }
 
-impl<T, S, V, M> MultiplierUpdate for TargetedFeeAdjustment<T, S, V, M>
+impl<T, S, V, M, X> MultiplierUpdate for TargetedFeeAdjustment<T, S, V, M, X>
 where
 	T: frame_system::Config,
 	S: Get<Perquintill>,
 	V: Get<Multiplier>,
 	M: Get<Multiplier>,
+	X: Get<Multiplier>,
 {
 	fn min() -> Multiplier {
 		M::get()
 	}
+	fn max() -> Multiplier {
+		X::get()
+	}
 	fn target() -> Perquintill {
 		S::get()
 	}
@@ -169,18 +178,20 @@ where
 	}
 }
 
-impl<T, S, V, M> Convert<Multiplier, Multiplier> for TargetedFeeAdjustment<T, S, V, M>
+impl<T, S, V, M, X> Convert<Multiplier, Multiplier> for TargetedFeeAdjustment<T, S, V, M, X>
 where
 	T: frame_system::Config,
 	S: Get<Perquintill>,
 	V: Get<Multiplier>,
 	M: Get<Multiplier>,
+	X: Get<Multiplier>,
 {
 	fn convert(previous: Multiplier) -> Multiplier {
 		// Defensive only. The multiplier in storage should always be at most positive. Nonetheless
 		// we recover here in case of errors, because any value below this would be stale and can
 		// never change.
 		let min_multiplier = M::get();
+		let max_multiplier = X::get();
 		let previous = previous.max(min_multiplier);
 
 		let weights = T::BlockWeights::get();
@@ -217,15 +228,42 @@ where
 
 		if positive {
 			let excess = first_term.saturating_add(second_term).saturating_mul(previous);
-			previous.saturating_add(excess).max(min_multiplier)
+			previous.saturating_add(excess).max(min_multiplier).min(max_multiplier)
 		} else {
 			// Defensive-only: first_term > second_term. Safe subtraction.
 			let negative = first_term.saturating_sub(second_term).saturating_mul(previous);
-			previous.saturating_sub(negative).max(min_multiplier)
+			previous.saturating_sub(negative).max(min_multiplier).min(max_multiplier)
 		}
 	}
 }
 
+/// A struct to make the fee multiplier a constant
+pub struct ConstFeeMultiplier<M: Get<Multiplier>>(sp_std::marker::PhantomData<M>);
+
+impl<M: Get<Multiplier>> MultiplierUpdate for ConstFeeMultiplier<M> {
+	fn min() -> Multiplier {
+		M::get()
+	}
+	fn max() -> Multiplier {
+		M::get()
+	}
+	fn target() -> Perquintill {
+		Default::default()
+	}
+	fn variability() -> Multiplier {
+		Default::default()
+	}
+}
+
+impl<M> Convert<Multiplier, Multiplier> for ConstFeeMultiplier<M>
+where
+	M: Get<Multiplier>,
+{
+	fn convert(_previous: Multiplier) -> Multiplier {
+		Self::min()
+	}
+}
+
 /// Storage releases of the pallet.
 #[derive(Encode, Decode, Clone, Copy, PartialEq, Eq, RuntimeDebug, TypeInfo, MaxEncodedLen)]
 enum Releases {