page-writeback.c:(.text+0x6446): undefined reference to `____ilog2_NaN'

writeback-dirty-throttling-v7

$ git grep avg_write_bandwidth

fs/fs-writeback.c:      pages = min(bdi->avg_write_bandwidth / 2,
include/linux/backing-dev.h:    unsigned long avg_write_bandwidth;
include/trace/events/writeback.h:               __entry->avg_bw         = KBps(bdi->avg_write_bandwidth);
mm/backing-dev.c:       bdi->avg_write_bandwidth = INIT_BW;
mm/page-writeback.c:    return 2 + ilog2(default_backing_dev_info.avg_write_bandwidth);
mm/page-writeback.c:    origin = bdi->avg_write_bandwidth + 2 * MIN_WRITEBACK_PAGES;
mm/page-writeback.c:            (2 * bdi->avg_write_bandwidth) * bdi_thresh;
mm/page-writeback.c:    unsigned long avg = bdi->avg_write_bandwidth;
mm/page-writeback.c:    bdi->avg_write_bandwidth = avg;
mm/page-writeback.c:    pos_ratio *= bdi->avg_write_bandwidth;
mm/page-writeback.c:    ref_bw = min(ref_bw, bdi->avg_write_bandwidth);