linux/mm/page-writeback.c

905 	u64 wb_thresh;
916 	wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
917 	wb_thresh *= numerator;
918 	wb_thresh = div64_ul(wb_thresh, denominator);
922 	wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
925 	 * It's very possible that wb_thresh is close to 0 not because the
933 			wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 100);
935 			wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 8);
939 	if (wb_thresh > wb_max_thresh)
940 		wb_thresh = wb_max_thresh;
942 	return wb_thresh;
1077 	unsigned long wb_thresh = dtc->wb_thresh;
1107 	 * two values: wb_dirty and wb_thresh. Let's consider an example:
1110 	 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
1124 		if (dtc->wb_dirty >= wb_thresh)
1127 		wb_setpoint = dirty_freerun_ceiling(wb_thresh,
1130 		if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
1134 						 wb_thresh);
1188 	 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1190 	 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1192 	if (unlikely(wb_thresh > dtc->thresh))
1193 		wb_thresh = dtc->thresh;
1196 	 *	wb_setpoint = setpoint * wb_thresh / thresh
1198 	x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1202 	 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1204 	 *        wb_thresh                    thresh - wb_thresh
1205 	 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1208 	span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1222 	x_intercept = wb_thresh / 2;
1452 		setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1674 	 * wb_thresh is not treated as some limiting factor as
1676 	 * - in JBOD setup, wb_thresh can fluctuate a lot
1678 	 *   go into state (wb_dirty >> wb_thresh) either because
1679 	 *   wb_dirty starts high, or because wb_thresh drops low.
1682 	 *   wb_thresh. Instead the auxiliary wb control line in
1686 	dtc->wb_thresh = __wb_calc_thresh(dtc, dtc->thresh);
1688 		div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1700 	if (dtc->wb_thresh < 2 * wb_stat_error()) {
1716 		thresh = dtc->wb_thresh;
1742 		thresh = dtc->wb_thresh;
1778 		       dirty_freerun_ceiling(dtc->wb_thresh, dtc->wb_bg_thresh);
1784 	dtc->dirty_exceeded = (dtc->wb_dirty > dtc->wb_thresh) &&