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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const GenTxid gtxid{false, parent_txid};
                    pfrom.AddKnownTx(parent_txid);
                    if (!AlreadyHaveTx(gtxid)) AddTxAnnouncement(pfrom, gtxid, current_time);
                }
                if (m_orphanage.AddTx(ptx, pfrom.GetId())) {
                    AddToCompactExtraTransactions(ptx);
                }
                
                m_txrequest.ForgetTxHash(tx.GetHash());
                m_txrequest.ForgetTxHash(tx.GetWitnessHash());
                
                unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, gArgs.GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
                unsigned int nEvicted = m_orphanage.LimitOrphans(nMaxOrphanTx);
                if (nEvicted > 0) {
                    LogPrint(BCLog::MEMPOOL, "orphanage overflow, removed %u tx\n", nEvicted);
                }
            } else {
                LogPrint(BCLog::MEMPOOL, "not keeping orphan with rejected parents %s\n",tx.GetHash().ToString());
                
                
                
                
                
                
                recentRejects->insert(tx.GetHash());