...

--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h

@@ -33,6 +33,8 @@ enum bdi_state {
 	BDI_sync_congested,	/* The sync queue is getting full */
 	BDI_registered,		/* bdi_register() was done */
 	BDI_writeback_running,	/* Writeback is in progress */
+	BDI_idle,		/* No pages under writeback at the moment of
+				 * last update of write bw */

 	BDI_unused,		/* Available bits start here */
 };
 

@@ -43,6 +45,7 @@ enum bdi_stat_item {
 	BDI_WRITEBACK,
 	BDI_DIRTIED,
 	BDI_WRITTEN,
+	BDI_WRITTEN_BACK,
 	NR_BDI_STAT_ITEMS
 };
 

@@ -76,6 +79,8 @@ struct backing_dev_info {
 	unsigned long bw_time_stamp;	/* last time write bw is updated */
 	unsigned long dirtied_stamp;
 	unsigned long written_stamp;	/* pages written at bw_time_stamp */
+	unsigned long writeback_stamp;	/* pages sent to writeback at
+					 * bw_time_stamp */

 	unsigned long write_bandwidth;	/* the estimated write bandwidth */
 	unsigned long avg_write_bandwidth; /* further smoothed write bw */
 

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e3dea75..baac702 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h

@@ -25,6 +25,7 @@ enum mapping_flags {
 	AS_MM_ALL_LOCKS	= __GFP_BITS_SHIFT + 2,	/* under mm_take_all_locks() */
 	AS_UNEVICTABLE	= __GFP_BITS_SHIFT + 3,	/* e.g., ramdisk, SHM_LOCK */
 	AS_BALLOON_MAP  = __GFP_BITS_SHIFT + 4, /* balloon page special map */
+	AS_STRICTLIMIT	= __GFP_BITS_SHIFT + 5, /* strict dirty limit */

...

--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c

@@ -94,6 +94,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
 		   "BackgroundThresh:   %10lu kB\n"
 		   "BdiDirtied:         %10lu kB\n"
 		   "BdiWritten:         %10lu kB\n"
+		   "BdiWrittenBack:     %10lu kB\n"
 		   "BdiWriteBandwidth:  %10lu kBps\n"
 		   "b_dirty:            %10lu\n"
 		   "b_io:               %10lu\n"

...

@@ -679,29 +711,31 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
 	if (unlikely(dirty >= limit))
 		return 0;
 
+	if (unlikely(strictlimit)) {
+		if (bdi_dirty < 8)
+			return 2 << RATELIMIT_CALC_SHIFT;
+
+		if (bdi_dirty >= bdi_thresh)
+			return 0;
+
+		bdi_setpoint = bdi_thresh + bdi_dirty_limit(bdi, bg_thresh);
+		bdi_setpoint /= 2;
+
+		if (bdi_setpoint == 0 || bdi_setpoint == bdi_thresh)
+			return 0;
+
+		pos_ratio = pos_ratio_polynom(bdi_setpoint, bdi_dirty,
+					      bdi_thresh);
+		return min_t(long long, pos_ratio, 2 << RATELIMIT_CALC_SHIFT);
+	}

...

@@ -994,6 +1029,16 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
 	 * keep that period small to reduce time lags).
 	 */
 	step = 0;
+
+	if (unlikely(strictlimit)) {
+		dirty = bdi_dirty;
+		if (bdi_dirty < 8)
+			setpoint = bdi_dirty + 1;
+		else
+			setpoint = (bdi_thresh +
+				    bdi_dirty_limit(bdi, bg_thresh)) / 2;
+	}