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
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#endif 
    argsman.AddArg("-whitebind=<[permissions@]addr>", "Bind to the given address and add permission flags to the peers connecting to it. "
        "Use [host]:port notation for IPv6. Allowed permissions: " + Join(NET_PERMISSIONS_DOC, ", ") + ". "
        "Specify multiple permissions separated by commas (default: download,noban,mempool,relay). Can be specified multiple times.", ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
    argsman.AddArg("-whitelist=<[permissions@]IP address or network>", "Add permission flags to the peers connecting from the given IP address (e.g. 1.2.3.4) or "
        "CIDR-notated network (e.g. 1.2.3.0/24). Uses the same permissions as "
        "-whitebind. Can be specified multiple times." , ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
    g_wallet_init_interface.AddWalletOptions(argsman);
#if ENABLE_ZMQ
    argsman.AddArg("-zmqpubhashblock=<address>", "Enable publish hash block in <address>", ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubhashtx=<address>", "Enable publish hash transaction in <address>", ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubrawblock=<address>", "Enable publish raw block in <address>", ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubrawtx=<address>", "Enable publish raw transaction in <address>", ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubsequence=<address>", "Enable publish hash block and tx sequence in <address>", ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubhashblockhwm=<n>", strprintf("Set publish hash block outbound message high water mark (default: %d)", CZMQAbstractNotifier::DEFAULT_ZMQ_SNDHWM), ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubhashtxhwm=<n>", strprintf("Set publish hash transaction outbound message high water mark (default: %d)", CZMQAbstractNotifier::DEFAULT_ZMQ_SNDHWM), ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubrawblockhwm=<n>", strprintf("Set publish raw block outbound message high water mark (default: %d)", CZMQAbstractNotifier::DEFAULT_ZMQ_SNDHWM), ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubrawtxhwm=<n>", strprintf("Set publish raw transaction outbound message high water mark (default: %d)", CZMQAbstractNotifier::DEFAULT_ZMQ_SNDHWM), ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
    argsman.AddArg("-zmqpubsequencehwm=<n>", strprintf("Set publish hash sequence message high water mark (default: %d)", CZMQAbstractNotifier::DEFAULT_ZMQ_SNDHWM), ArgsManager::ALLOW_ANY, OptionsCategory::ZMQ);
#else
    hidden_args.emplace_back("-zmqpubhashblock=<address>");
    hidden_args.emplace_back("-zmqpubhashtx=<address>");
    hidden_args.emplace_back("-zmqpubrawblock=<address>");
    hidden_args.emplace_back("-zmqpubrawtx=<address>");
    hidden_args.emplace_back("-zmqpubsequence=<n>");
    hidden_args.emplace_back("-zmqpubhashblockhwm=<n>");
    hidden_args.emplace_back("-zmqpubhashtxhwm=<n>");
    hidden_args.emplace_back("-zmqpubrawblockhwm=<n>");
    hidden_args.emplace_back("-zmqpubrawtxhwm=<n>");
    hidden_args.emplace_back("-zmqpubsequencehwm=<n>");