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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BlockValidationState &state,
        FlushStateMode mode,
        int nManualPruneHeight = 0);
    
    void ForceFlushStateToDisk();
    
    
    void PruneAndFlush();
    /**
     * Find the best known block, and make it the tip of the block chain. The
     * result is either failure or an activated best chain. pblock is either
     * nullptr or a pointer to a block that is already loaded (to avoid loading
     * it again from disk).
     *
     * ActivateBestChain is split into steps (see ActivateBestChainStep) so that
     * we avoid holding cs_main for an extended period of time; the length of this
     * call may be quite long during reindexing or a substantial reorg.
     *
     * May not be called with cs_main held. May not be called in a
     * validationinterface callback.
     *
     * @returns true unless a system error occurred
     */
    bool ActivateBestChain(
        BlockValidationState& state,
        const CChainParams& chainparams,
        std::shared_ptr<const CBlock> pblock = nullptr) LOCKS_EXCLUDED(cs_main);
    bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    
    DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view);