1 files changed, 20 insertions, 72 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d9861e42b2bd..3147119a9a04 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -120,29 +120,6 @@ EXPORT_SYMBOL(laptop_mode);
 
 struct wb_domain global_wb_domain;
 
-/* consolidated parameters for balance_dirty_pages() and its subroutines */
-struct dirty_throttle_control {
-#ifdef CONFIG_CGROUP_WRITEBACK
-	struct wb_domain	*dom;
-	struct dirty_throttle_control *gdtc;	/* only set in memcg dtc's */
-#endif
-	struct bdi_writeback	*wb;
-	struct fprop_local_percpu *wb_completions;
-
-	unsigned long		avail;		/* dirtyable */
-	unsigned long		dirty;		/* file_dirty + write + nfs */
-	unsigned long		thresh;		/* dirty threshold */
-	unsigned long		bg_thresh;	/* dirty background threshold */
-
-	unsigned long		wb_dirty;	/* per-wb counterparts */
-	unsigned long		wb_thresh;
-	unsigned long		wb_bg_thresh;
-
-	unsigned long		pos_ratio;
-	bool			freerun;
-	bool			dirty_exceeded;
-};
-
 /*
  * Length of period for aging writeout fractions of bdis. This is an
  * arbitrarily chosen number. The longer the period, the slower fractions will
@@ -942,26 +919,25 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
 	wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);
 
 	wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
-	wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
-	if (wb_thresh > wb_max_thresh)
-		wb_thresh = wb_max_thresh;
 
 	/*
-	 * With strictlimit flag, the wb_thresh is treated as
-	 * a hard limit in balance_dirty_pages() and wb_position_ratio().
-	 * It's possible that wb_thresh is close to zero, not because
-	 * the device is slow, but because it has been inactive.
-	 * To prevent occasional writes from being blocked, we raise wb_thresh.
+	 * It's very possible that wb_thresh is close to 0 not because the
+	 * device is slow, but that it has remained inactive for long time.
+	 * Honour such devices a reasonable good (hopefully IO efficient)
+	 * threshold, so that the occasional writes won't be blocked and active
+	 * writes can rampup the threshold quickly.
 	 */
-	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
-		unsigned long limit = hard_dirty_limit(dom, dtc->thresh);
-		u64 wb_scale_thresh = 0;
-
-		if (limit > dtc->dirty)
-			wb_scale_thresh = (limit - dtc->dirty) / 100;
-		wb_thresh = max(wb_thresh, min(wb_scale_thresh, wb_max_thresh / 4));
+	if (thresh > dtc->dirty) {
+		if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT))
+			wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 100);
+		else
+			wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 8);
 	}
 
+	wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
+	if (wb_thresh > wb_max_thresh)
+		wb_thresh = wb_max_thresh;
+
 	return wb_thresh;
 }
 
@@ -969,6 +945,7 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
 {
 	struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
 
+	domain_dirty_avail(&gdtc, true);
 	return __wb_calc_thresh(&gdtc, thresh);
 }
 
@@ -1095,7 +1072,7 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc)
 	struct bdi_writeback *wb = dtc->wb;
 	unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
 	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
-	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
+	unsigned long limit = dtc->limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
 	unsigned long wb_thresh = dtc->wb_thresh;
 	unsigned long x_intercept;
 	unsigned long setpoint;		/* dirty pages' target balance point */
@@ -1145,12 +1122,6 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc)
 	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
 		long long wb_pos_ratio;
 
-		if (dtc->wb_dirty < 8) {
-			dtc->pos_ratio = min_t(long long, pos_ratio * 2,
-					   2 << RATELIMIT_CALC_SHIFT);
-			return;
-		}
-
 		if (dtc->wb_dirty >= wb_thresh)
 			return;
 
@@ -1222,14 +1193,6 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc)
 	if (unlikely(wb_thresh > dtc->thresh))
 		wb_thresh = dtc->thresh;
 	/*
-	 * It's very possible that wb_thresh is close to 0 not because the
-	 * device is slow, but that it has remained inactive for long time.
-	 * Honour such devices a reasonable good (hopefully IO efficient)
-	 * threshold, so that the occasional writes won't be blocked and active
-	 * writes can rampup the threshold quickly.
-	 */
-	wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
-	/*
 	 * scale global setpoint to wb's:
 	 *	wb_setpoint = setpoint * wb_thresh / thresh
 	 */
@@ -1484,17 +1447,10 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
 	 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
 	 * Hence, to calculate "step" properly, we have to use wb_dirty as
 	 * "dirty" and wb_setpoint as "setpoint".
-	 *
-	 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
-	 * it's possible that wb_thresh is close to zero due to inactivity
-	 * of backing device.
 	 */
 	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
 		dirty = dtc->wb_dirty;
-		if (dtc->wb_dirty < 8)
-			setpoint = dtc->wb_dirty + 1;
-		else
-			setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
+		setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
 	}
 
 	if (dirty < setpoint) {
@@ -1983,11 +1939,7 @@ free_running:
 		 */
 		if (pause < min_pause) {
 			trace_balance_dirty_pages(wb,
-						  sdtc->thresh,
-						  sdtc->bg_thresh,
-						  sdtc->dirty,
-						  sdtc->wb_thresh,
-						  sdtc->wb_dirty,
+						  sdtc,
 						  dirty_ratelimit,
 						  task_ratelimit,
 						  pages_dirtied,
@@ -2012,11 +1964,7 @@ free_running:
 
 pause:
 		trace_balance_dirty_pages(wb,
-					  sdtc->thresh,
-					  sdtc->bg_thresh,
-					  sdtc->dirty,
-					  sdtc->wb_thresh,
-					  sdtc->wb_dirty,
+					  sdtc,
 					  dirty_ratelimit,
 					  task_ratelimit,
 					  pages_dirtied,
@@ -2319,7 +2267,7 @@ static int page_writeback_cpu_online(unsigned int cpu)
 /* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
 static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
 
-static struct ctl_table vm_page_writeback_sysctls[] = {
+static const struct ctl_table vm_page_writeback_sysctls[] = {
 	{
 		.procname   = "dirty_background_ratio",
 		.data       = &dirty_background_ratio,