refactor(core/txpool/legacypool): use uint256.Int instead of big.Int #28606

[gzliudan]

Proposed changes

Ref: ethereum#28606

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• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
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[Copilot]

Pull request overview

Refactors the legacy transaction pool to use holiman/uint256.Int for internal cost accounting and adjusts the txpool initialization API to accept a uint64 gas tip derived from config (PriceLimit).

Changes:

• Update txpool.New and SubPool.Init to accept gasTip uint64 (instead of *big.Int) and adapt call sites.
• Switch legacypool list cost tracking (costcap, totalcost) from *big.Int to *uint256.Int, adding overflow/underflow handling paths.
• Update and extend tests/benchmarks to use uint256 and cover very-large-cost transactions.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
eth/backend.go	Pass PriceLimit directly into txpool.New after signature change.
core/txpool/txpool.go	Change New signature to gasTip uint64 and forward it to subpools.
core/txpool/subpool.go	Update SubPool.Init interface to accept gasTip uint64.
core/txpool/legacypool/list.go	Convert list cost accounting to uint256.Int and update filter/subtraction logic.
core/txpool/legacypool/list_test.go	Add “very expensive cost” test and adjust benchmark to uint256.
core/txpool/legacypool/legacypool.go	Store gasTip as atomic.Pointer[uint256.Int] and adapt comparisons/conversions.
core/txpool/legacypool/legacypool_test.go	Update init calls and adapt assertions for uint256-based totals.
core/txpool/legacypool/legacypool2_test.go	Update init calls for new Init(gasTip uint64, ...) signature.

Comments suppressed due to low confidence (4)

core/txpool/legacypool/legacypool_test.go:238

• txs.totalcost is a uint256.Int and cannot be negative, so txs.totalcost.Sign() < 0 is dead code and won’t catch accounting regressions. Consider replacing this with a meaningful invariant (e.g., recompute the sum of tx.Cost() across txs.txs.items and compare to txs.totalcost, or at least assert it doesn’t underflow during removals).

		}
		if txs.totalcost.Sign() < 0 {
			return fmt.Errorf("totalcost went negative: %v", txs.totalcost)
		}

core/txpool/legacypool/list.go:386

• Filter converts costLimit to big.Int inside the per-tx predicate (costLimit.ToBig() / maximum.ToBig()), which likely allocates each iteration. Since Filter can run over large account lists, consider hoisting the ToBig() conversion(s) outside the closure (once per call) to avoid per-transaction allocations.

	// Filter out all the transactions above the account's funds
	removed := l.txs.Filter(func(tx *types.Transaction) bool {
		maximum := costLimit
		if tx.To() != nil {
			if feeCapacity, ok := trc21Issuers[*tx.To()]; ok {
				return tx.Gas() > gasLimit || new(big.Int).Add(costLimit.ToBig(), feeCapacity).Cmp(tx.TxCost(number)) < 0
			}
		}
		return tx.Gas() > gasLimit || tx.Cost().Cmp(maximum.ToBig()) > 0
	})

core/txpool/legacypool/legacypool.go:603

• Pending(enforceTips=true) converts the atomic uint256 gas tip to *big.Int inside the inner loop (pool.gasTip.Load().ToBig()), likely allocating once per tx. Cache the converted tip once per Pending call (or at least once per account) to avoid repeated allocations when building pending sets.

		// If the miner requests tip enforcement, cap the lists now
		if enforceTips && !pool.locals.contains(addr) {
			for i, tx := range txs {
				if !tx.IsSpecialTransaction() && tx.EffectiveGasTipIntCmp(pool.gasTip.Load().ToBig(), pool.priced.urgent.baseFee) < 0 {
					txs = txs[:i]
					break

core/txpool/legacypool/legacypool.go:663

• validateTxBasics now calls pool.gasTip.Load().ToBig() for every validation, which likely allocates. Since this runs for each incoming tx, consider caching a *big.Int view of the current tip (updated alongside the atomic) or otherwise avoid repeated conversions on the hot path.

			1<<types.DynamicFeeTxType |
			1<<types.SetCodeTxType,
		MaxSize: txMaxSize,
		MinTip:  pool.gasTip.Load().ToBig(),
		NotSigner: func(from common.Address) bool {

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[Copilot]

promoteSpecialTx updates list.costcap/gascap but never updates list.totalcost. With totalcost now a uint256.Int and subTotalCost using SubOverflow, removing a mined/forwarded special tx (or any later list maintenance that calls subTotalCost) can trigger an underflow and panic, and ExistingExpenditure will also undercount spent funds while the special tx is pending. Update this path to keep totalcost consistent (subtract any replaced tx’s cost and add the new tx’s cost) using the same overflow handling as list.Add.

[Copilot]

subTotalCost panics on underflow. Since this runs in normal pool maintenance paths (Forward/Filter/Cap/Ready/Remove), any accounting mismatch (e.g., a tx added without incrementing totalcost, or a cost conversion mismatch) will crash the node. Prefer making this non-fatal (e.g., recompute totalcost from l.txs when an underflow is detected, or clamp to zero and log) so internal inconsistencies don’t take down the process.