There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

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* Bitcoin protocol messages
* Bitcoin Core P2P design
* Running our unit and functional tests

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class CConnman;
class CScriptCheck;
class CTxMemPool;
class ChainstateManager;
struct ChainTxData;
struct DisconnectedBlockTransactions;
struct PrecomputedTransactionData;
struct LockPoints;
struct AssumeutxoData;
static const unsigned int DEFAULT_MIN_RELAY_TX_FEE = 1000;
static const unsigned int DEFAULT_ANCESTOR_LIMIT = 25;
static const unsigned int DEFAULT_ANCESTOR_SIZE_LIMIT = 101;
static const unsigned int DEFAULT_DESCENDANT_LIMIT = 25;
static const unsigned int DEFAULT_DESCENDANT_SIZE_LIMIT = 101;
static const unsigned int DEFAULT_MEMPOOL_EXPIRY = 336;
static const int MAX_SCRIPTCHECK_THREADS = 15;
static const int DEFAULT_SCRIPTCHECK_THREADS = 0;
static const int64_t DEFAULT_MAX_TIP_AGE = 24 * 60 * 60;
static const bool DEFAULT_CHECKPOINTS_ENABLED = true;
static const bool DEFAULT_TXINDEX = false;
static constexpr bool DEFAULT_COINSTATSINDEX{false};
static const char* const DEFAULT_BLOCKFILTERINDEX = "0";
static const bool DEFAULT_PERSIST_MEMPOOL = true;
static const bool DEFAULT_FEEFILTER = true;
static const int DEFAULT_STOPATHEIGHT = 0;
static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
static const signed int DEFAULT_CHECKBLOCKS = 6;
static const unsigned int DEFAULT_CHECKLEVEL = 3;
static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
enum class SynchronizationState {