Merge tag 'writeback-proportions' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux

Pull writeback updates from Wu Fengguang:
 "Use time based periods to age the writeback proportions, which can
  adapt equally well to fast/slow devices."

Fix up trivial conflict in comment in fs/sync.c

* tag 'writeback-proportions' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
  writeback: Fix some comment errors
  block: Convert BDI proportion calculations to flexible proportions
  lib: Fix possible deadlock in flexible proportion code
  lib: Proportions with flexible period

2 files changed, 69 insertions, 44 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index dd8e2aafb07e..3387aea11209 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -677,7 +677,7 @@ int bdi_init(struct backing_dev_info *bdi)
 
 	bdi->min_ratio = 0;
 	bdi->max_ratio = 100;
-	bdi->max_prop_frac = PROP_FRAC_BASE;
+	bdi->max_prop_frac = FPROP_FRAC_BASE;
 	spin_lock_init(&bdi->wb_lock);
 	INIT_LIST_HEAD(&bdi->bdi_list);
 	INIT_LIST_HEAD(&bdi->work_list);
@@ -700,7 +700,7 @@ int bdi_init(struct backing_dev_info *bdi)
 	bdi->write_bandwidth = INIT_BW;
 	bdi->avg_write_bandwidth = INIT_BW;
 
-	err = prop_local_init_percpu(&bdi->completions);
+	err = fprop_local_init_percpu(&bdi->completions);
 
 	if (err) {
 err:
@@ -744,7 +744,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 		percpu_counter_destroy(&bdi->bdi_stat[i]);
 
-	prop_local_destroy_percpu(&bdi->completions);
+	fprop_local_destroy_percpu(&bdi->completions);
 }
 EXPORT_SYMBOL(bdi_destroy);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 93d8d2f7108c..e5363f34e025 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -34,6 +34,7 @@
 #include <linux/syscalls.h>
 #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
 #include <linux/pagevec.h>
+#include <linux/timer.h>
 #include <trace/events/writeback.h>
 
 /*
@@ -135,7 +136,20 @@ unsigned long global_dirty_limit;
  * measured in page writeback completions.
  *
  */
-static struct prop_descriptor vm_completions;
+static struct fprop_global writeout_completions;
+
+static void writeout_period(unsigned long t);
+/* Timer for aging of writeout_completions */
+static struct timer_list writeout_period_timer =
+		TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0);
+static unsigned long writeout_period_time = 0;
+
+/*
+ * Length of period for aging writeout fractions of bdis. This is an
+ * arbitrarily chosen number. The longer the period, the slower fractions will
+ * reflect changes in current writeout rate.
+ */
+#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
 
 /*
  * Work out the current dirty-memory clamping and background writeout
@@ -322,34 +336,6 @@ bool zone_dirty_ok(struct zone *zone)
 	       zone_page_state(zone, NR_WRITEBACK) <= limit;
 }
 
-/*
- * couple the period to the dirty_ratio:
- *
- *   period/2 ~ roundup_pow_of_two(dirty limit)
- */
-static int calc_period_shift(void)
-{
-	unsigned long dirty_total;
-
-	if (vm_dirty_bytes)
-		dirty_total = vm_dirty_bytes / PAGE_SIZE;
-	else
-		dirty_total = (vm_dirty_ratio * global_dirtyable_memory()) /
-				100;
-	return 2 + ilog2(dirty_total - 1);
-}
-
-/*
- * update the period when the dirty threshold changes.
- */
-static void update_completion_period(void)
-{
-	int shift = calc_period_shift();
-	prop_change_shift(&vm_completions, shift);
-
-	writeback_set_ratelimit();
-}
-
 int dirty_background_ratio_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos)
@@ -383,7 +369,7 @@ int dirty_ratio_handler(struct ctl_table *table, int write,
 
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
-		update_completion_period();
+		writeback_set_ratelimit();
 		vm_dirty_bytes = 0;
 	}
 	return ret;
@@ -398,12 +384,21 @@ int dirty_bytes_handler(struct ctl_table *table, int write,
 
 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 	if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
-		update_completion_period();
+		writeback_set_ratelimit();
 		vm_dirty_ratio = 0;
 	}
 	return ret;
 }
 
+static unsigned long wp_next_time(unsigned long cur_time)
+{
+	cur_time += VM_COMPLETIONS_PERIOD_LEN;
+	/* 0 has a special meaning... */
+	if (!cur_time)
+		return 1;
+	return cur_time;
+}
+
 /*
  * Increment the BDI's writeout completion count and the global writeout
  * completion count. Called from test_clear_page_writeback().
@@ -411,8 +406,19 @@ int dirty_bytes_handler(struct ctl_table *table, int write,
 static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
 {
 	__inc_bdi_stat(bdi, BDI_WRITTEN);
-	__prop_inc_percpu_max(&vm_completions, &bdi->completions,
-			      bdi->max_prop_frac);
+	__fprop_inc_percpu_max(&writeout_completions, &bdi->completions,
+			       bdi->max_prop_frac);
+	/* First event after period switching was turned off? */
+	if (!unlikely(writeout_period_time)) {
+		/*
+		 * We can race with other __bdi_writeout_inc calls here but
+		 * it does not cause any harm since the resulting time when
+		 * timer will fire and what is in writeout_period_time will be
+		 * roughly the same.
+		 */
+		writeout_period_time = wp_next_time(jiffies);
+		mod_timer(&writeout_period_timer, writeout_period_time);
+	}
 }
 
 void bdi_writeout_inc(struct backing_dev_info *bdi)
@@ -431,11 +437,33 @@ EXPORT_SYMBOL_GPL(bdi_writeout_inc);
 static void bdi_writeout_fraction(struct backing_dev_info *bdi,
 		long *numerator, long *denominator)
 {
-	prop_fraction_percpu(&vm_completions, &bdi->completions,
+	fprop_fraction_percpu(&writeout_completions, &bdi->completions,
 				numerator, denominator);
 }
 
 /*
+ * On idle system, we can be called long after we scheduled because we use
+ * deferred timers so count with missed periods.
+ */
+static void writeout_period(unsigned long t)
+{
+	int miss_periods = (jiffies - writeout_period_time) /
+						 VM_COMPLETIONS_PERIOD_LEN;
+
+	if (fprop_new_period(&writeout_completions, miss_periods + 1)) {
+		writeout_period_time = wp_next_time(writeout_period_time +
+				miss_periods * VM_COMPLETIONS_PERIOD_LEN);
+		mod_timer(&writeout_period_timer, writeout_period_time);
+	} else {
+		/*
+		 * Aging has zeroed all fractions. Stop wasting CPU on period
+		 * updates.
+		 */
+		writeout_period_time = 0;
+	}
+}
+
+/*
  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
  * registered backing devices, which, for obvious reasons, can not
  * exceed 100%.
@@ -475,7 +503,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 		ret = -EINVAL;
 	} else {
 		bdi->max_ratio = max_ratio;
-		bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
+		bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
 	}
 	spin_unlock_bh(&bdi_lock);
 
@@ -918,7 +946,7 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
 	 *	bdi->dirty_ratelimit = balanced_dirty_ratelimit;
 	 *
 	 * However to get a more stable dirty_ratelimit, the below elaborated
-	 * code makes use of task_ratelimit to filter out sigular points and
+	 * code makes use of task_ratelimit to filter out singular points and
 	 * limit the step size.
 	 *
 	 * The below code essentially only uses the relative value of
@@ -941,7 +969,7 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
 	 * feel and care are stable dirty rate and small position error.
 	 *
 	 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
-	 * and filter out the sigular points of balanced_dirty_ratelimit. Which
+	 * and filter out the singular points of balanced_dirty_ratelimit. Which
 	 * keeps jumping around randomly and can even leap far away at times
 	 * due to the small 200ms estimation period of dirty_rate (we want to
 	 * keep that period small to reduce time lags).
@@ -1606,13 +1634,10 @@ static struct notifier_block __cpuinitdata ratelimit_nb = {
  */
 void __init page_writeback_init(void)
 {
-	int shift;
-
 	writeback_set_ratelimit();
 	register_cpu_notifier(&ratelimit_nb);
 
-	shift = calc_period_shift();
-	prop_descriptor_init(&vm_completions, shift);
+	fprop_global_init(&writeout_completions);
 }
 
 /**