Only maintain at most 1 UnlockChunk per era

frame/staking/src/benchmarking.rs

@@ -618,7 +618,7 @@ benchmarks! {
 	}
 
 	rebond {
-		let l in 1 .. MAX_UNLOCKING_CHUNKS as u32;
+		let l in 1 .. MaxUnlockingChunks::get() as u32;
 
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
@@ -652,7 +652,7 @@ benchmarks! {
 		let mut staking_ledger = Ledger::<T>::get(controller.clone()).unwrap();
 
 		for _ in 0 .. l {
-			staking_ledger.unlocking.push(unlock_chunk.clone())
+			staking_ledger.unlocking.try_push(unlock_chunk.clone()).unwrap()
 		}
 		Ledger::<T>::insert(controller.clone(), staking_ledger.clone());
 		let original_bonded: BalanceOf<T> = staking_ledger.active;
@@ -702,7 +702,7 @@ benchmarks! {
 			stash: stash.clone(),
 			active: T::Currency::minimum_balance() - One::one(),
 			total: T::Currency::minimum_balance() - One::one(),
-			unlocking: vec![],
+			unlocking: Default::default(),
 			claimed_rewards: vec![],
 		};
 		Ledger::<T>::insert(&controller, l);
@@ -788,15 +788,15 @@ benchmarks! {
 
 	#[extra]
 	do_slash {
-		let l in 1 .. MAX_UNLOCKING_CHUNKS as u32;
+		let l in 1 .. MaxUnlockingChunks::get() as u32;
 		let (stash, controller) = create_stash_controller::<T>(0, 100, Default::default())?;
 		let mut staking_ledger = Ledger::<T>::get(controller.clone()).unwrap();
 		let unlock_chunk = UnlockChunk::<BalanceOf<T>> {
 			value: 1u32.into(),
 			era: EraIndex::zero(),
 		};
 		for _ in 0 .. l {
-			staking_ledger.unlocking.push(unlock_chunk.clone())
+			staking_ledger.unlocking.try_push(unlock_chunk.clone()).unwrap();
 		}
 		Ledger::<T>::insert(controller, staking_ledger);
 		let slash_amount = T::Currency::minimum_balance() * 10u32.into();

frame/staking/src/lib.rs

@@ -301,6 +301,7 @@ mod pallet;
 
 use codec::{Decode, Encode, HasCompact};
 use frame_support::{
+	parameter_types,
 	traits::{ConstU32, Currency, Get},
 	weights::Weight,
 	BoundedVec, EqNoBound, PartialEqNoBound, RuntimeDebugNoBound,
@@ -347,6 +348,10 @@ type NegativeImbalanceOf<T> = <<T as Config>::Currency as Currency<
 	<T as frame_system::Config>::AccountId,
 >>::NegativeImbalance;
 
+parameter_types! {
+	pub MaxUnlockingChunks: u32 = 32;
+}
+
 /// Information regarding the active era (era in used in session).
 #[derive(Encode, Decode, RuntimeDebug, TypeInfo)]
 pub struct ActiveEraInfo {
@@ -446,9 +451,10 @@ pub struct StakingLedger<AccountId, Balance: HasCompact> {
 	/// rounds.
 	#[codec(compact)]
 	pub active: Balance,
-	/// Any balance that is becoming free, which may eventually be transferred out
-	/// of the stash (assuming it doesn't get slashed first).
-	pub unlocking: Vec<UnlockChunk<Balance>>,
+	/// Any balance that is becoming free, which may eventually be transferred out of the stash
+	/// (assuming it doesn't get slashed first). It is assumed that this will be treated as a first
+	/// in, first out queue where the new (higher value) eras get pushing on the back.
+	pub unlocking: BoundedVec<UnlockChunk<Balance>, MaxUnlockingChunks>,
 	/// List of eras for which the stakers behind a validator have claimed rewards. Only updated
 	/// for validators.
 	pub claimed_rewards: Vec<EraIndex>,
@@ -463,7 +469,7 @@ impl<AccountId, Balance: HasCompact + Copy + Saturating + AtLeast32BitUnsigned +
 			stash,
 			total: Zero::zero(),
 			active: Zero::zero(),
-			unlocking: vec![],
+			unlocking: Default::default(),
 			claimed_rewards: vec![],
 		}
 	}
@@ -472,7 +478,7 @@ impl<AccountId, Balance: HasCompact + Copy + Saturating + AtLeast32BitUnsigned +
 	/// total by the sum of their balances.
 	fn consolidate_unlocked(self, current_era: EraIndex) -> Self {
 		let mut total = self.total;
-		let unlocking = self
+		let unlocking: BoundedVec<_, _> = self
 			.unlocking
 			.into_iter()
 			.filter(|chunk| {
@@ -483,7 +489,11 @@ impl<AccountId, Balance: HasCompact + Copy + Saturating + AtLeast32BitUnsigned +
 					false
 				}
 			})
-			.collect();
+			.collect::<Vec<_>>()
+			.try_into()
+			.expect(
+				"filtering items from a bounded vec always leaves length less than bounds. qed",
+			);
 
 		Self {
 			stash: self.stash,

frame/staking/src/pallet/impls.rs

@@ -928,7 +928,7 @@ impl<T: Config> ElectionDataProvider for Pallet<T> {
 				stash: voter.clone(),
 				active: stake,
 				total: stake,
-				unlocking: vec![],
+				unlocking: Default::default(),
 				claimed_rewards: vec![],
 			},
 		);
@@ -946,7 +946,7 @@ impl<T: Config> ElectionDataProvider for Pallet<T> {
 				stash: target.clone(),
 				active: stake,
 				total: stake,
-				unlocking: vec![],
+				unlocking: Default::default(),
 				claimed_rewards: vec![],
 			},
 		);
@@ -983,7 +983,7 @@ impl<T: Config> ElectionDataProvider for Pallet<T> {
 					stash: v.clone(),
 					active: stake,
 					total: stake,
-					unlocking: vec![],
+					unlocking: Default::default(),
 					claimed_rewards: vec![],
 				},
 			);
@@ -1004,7 +1004,7 @@ impl<T: Config> ElectionDataProvider for Pallet<T> {
 					stash: v.clone(),
 					active: stake,
 					total: stake,
-					unlocking: vec![],
+					unlocking: Default::default(),
 					claimed_rewards: vec![],
 				},
 			);

frame/staking/src/pallet/mod.rs

@@ -28,7 +28,7 @@ use frame_support::{
 };
 use frame_system::{ensure_root, ensure_signed, offchain::SendTransactionTypes, pallet_prelude::*};
 use sp_runtime::{
-	traits::{CheckedSub, SaturatedConversion, StaticLookup, Zero},
+	traits::{CheckedSub, SaturatedConversion, Saturating, StaticLookup, Zero},
 	DispatchError, Perbill, Percent,
 };
 use sp_staking::{EraIndex, SessionIndex};
@@ -40,12 +40,11 @@ pub use impls::*;
 
 use crate::{
 	log, slashing, weights::WeightInfo, ActiveEraInfo, BalanceOf, EraPayout, EraRewardPoints,
-	Exposure, Forcing, NegativeImbalanceOf, Nominations, PositiveImbalanceOf, Releases,
-	RewardDestination, SessionInterface, StakingLedger, UnappliedSlash, UnlockChunk,
+	Exposure, Forcing, MaxUnlockingChunks, NegativeImbalanceOf, Nominations, PositiveImbalanceOf,
+	Releases, RewardDestination, SessionInterface, StakingLedger, UnappliedSlash, UnlockChunk,
 	ValidatorPrefs,
 };
 
-pub const MAX_UNLOCKING_CHUNKS: usize = 32;
 const STAKING_ID: LockIdentifier = *b"staking ";
 
 #[frame_support::pallet]
@@ -771,7 +770,7 @@ pub mod pallet {
 				stash,
 				total: value,
 				active: value,
-				unlocking: vec![],
+				unlocking: Default::default(),
 				claimed_rewards: (last_reward_era..current_era).collect(),
 			};
 			Self::update_ledger(&controller, &item);
@@ -836,7 +835,7 @@ pub mod pallet {
 		/// Once the unlock period is done, you can call `withdraw_unbonded` to actually move
 		/// the funds out of management ready for transfer.
 		///
-		/// No more than a limited number of unlocking chunks (see `MAX_UNLOCKING_CHUNKS`)
+		/// No more than a limited number of unlocking chunks (see `MaxUnlockingChunks`)
 		/// can co-exists at the same time. In that case, [`Call::withdraw_unbonded`] need
 		/// to be called first to remove some of the chunks (if possible).
 		///
@@ -853,7 +852,10 @@ pub mod pallet {
 		) -> DispatchResult {
 			let controller = ensure_signed(origin)?;
 			let mut ledger = Self::ledger(&controller).ok_or(Error::<T>::NotController)?;
-			ensure!(ledger.unlocking.len() < MAX_UNLOCKING_CHUNKS, Error::<T>::NoMoreChunks,);
+			ensure!(
+				ledger.unlocking.len() < MaxUnlockingChunks::get() as usize,
+				Error::<T>::NoMoreChunks,
+			);
 
 			let mut value = value.min(ledger.active);
 
@@ -880,7 +882,19 @@ pub mod pallet {
 
 				// Note: in case there is no current era it is fine to bond one era more.
 				let era = Self::current_era().unwrap_or(0) + T::BondingDuration::get();
-				ledger.unlocking.push(UnlockChunk { value, era });
+				if let Some(mut chunk) =
+					ledger.unlocking.last_mut().filter(|chunk| chunk.era == era)
+				{
+					// To keep the chunk count down, we only keep one chunk per era. Since
+					// `unlocking` is a FiFo queue, if a chunk exists for `era` we know that it will
+					// be the last one.
+					chunk.value = chunk.value.saturating_add(value)
+				} else {
+					ledger
+						.unlocking
+						.try_push(UnlockChunk { value, era })
+						.map_err(|_| Error::<T>::NoMoreChunks)?;
+				};
 				// NOTE: ledger must be updated prior to calling `Self::weight_of`.
 				Self::update_ledger(&controller, &ledger);
 
@@ -1347,10 +1361,10 @@ pub mod pallet {
 		///
 		/// # <weight>
 		/// - Time complexity: O(L), where L is unlocking chunks
-		/// - Bounded by `MAX_UNLOCKING_CHUNKS`.
+		/// - Bounded by `MaxUnlockingChunks`.
 		/// - Storage changes: Can't increase storage, only decrease it.
 		/// # </weight>
-		#[pallet::weight(T::WeightInfo::rebond(MAX_UNLOCKING_CHUNKS as u32))]
+		#[pallet::weight(T::WeightInfo::rebond(MaxUnlockingChunks::get() as u32))]
 		pub fn rebond(
 			origin: OriginFor<T>,
 			#[pallet::compact] value: BalanceOf<T>,