core: make txpool free space calculation more accurate (ethereum#22933)

core/tx_pool.go

@@ -711,7 +711,7 @@ func (pool *TxPool) add(tx *types.Transaction, local bool) (replaced bool, err e
 		return pool.promoteSpecialTx(from, tx, isLocal)
 	}
 	// If the transaction pool is full, discard underpriced transactions
-	if uint64(pool.all.Count()) >= pool.config.GlobalSlots+pool.config.GlobalQueue {
+	if uint64(pool.all.Slots()+numSlots(tx)) > pool.config.GlobalSlots+pool.config.GlobalQueue {
 		log.Debug("Add transaction to pool full", "hash", hash, "nonce", tx.Nonce())
 		// If the new transaction is underpriced, don't accept it
 		if !isLocal && pool.priced.Underpriced(tx) {