bool                    BgBufferSync(void)                    {                        ……                                        /*                     * Information saved between calls so we can determine the strategy                     * point's advance rate and avoid scanning already-cleaned buffers.                     */                    static           bool       saved_info_valid = false;                    static           int        prev_strategy_buf_id;            static          uint32         prev_strategy_passes;            static          int        next_to_clean;            static     uint32     next_passes;                                                    /* Moving averages of allocation rate and clean-buffer density */                    static     float     smoothed_alloc = 0;            static     float     smoothed_density = 10.0;                                ……                                        /*                     * If we're not running the LRU scan, just stop after doing the stats                     * stuff.  We mark the saved state invalid so that we can recover sanely                     * if LRU scan is turned back on later.                     */                    if (bgwriter_lru_maxpages <= 0)                    {                        saved_info_valid = false;                    return true;                }                                        if (saved_info_valid)                    {                        ……                }                    else                    {                        ……                }                                        /* Update saved info for next time */                    prev_strategy_buf_id = strategy_buf_id;                    prev_strategy_passes = strategy_passes;                    saved_info_valid = true;                                        ……                    /* Return true if OK to hibernate */                    return (bufs_to_lap == 0 && recent_alloc == 0);                }