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

8 files changed, 448 insertions, 50 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8f660dd6137a..50d0b78130a1 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -628,8 +628,8 @@ static long writeback_sb_inodes(struct super_block *sb,
                 }
 
                 /*
-                 * Don't bother with new inodes or inodes beeing freed, first
-                 * kind does not need peridic writeout yet, and for the latter
+                 * Don't bother with new inodes or inodes being freed, first
+                 * kind does not need periodic writeout yet, and for the latter
                  * kind writeout is handled by the freer.
                  */
                 spin_lock(&inode->i_lock);
diff --git a/fs/super.c b/fs/super.c
index c743fb3be4b8..4c5d82f56ec4 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -320,7 +320,7 @@ static int grab_super(struct super_block *s) __releases(sb_lock)
 
 /*
  *      grab_super_passive - acquire a passive reference
- *      @s: reference we are trying to grab
+ *      @sb: reference we are trying to grab
  *
  *      Tries to acquire a passive reference. This is used in places where we
  *      cannot take an active reference but we need to ensure that the
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index b1038bd686ac..489de625cd25 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -10,7 +10,7 @@
 
 #include <linux/percpu_counter.h>
 #include <linux/log2.h>
-#include <linux/proportions.h>
+#include <linux/flex_proportions.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/sched.h>
@@ -89,7 +89,7 @@ struct backing_dev_info {
         unsigned long dirty_ratelimit;
         unsigned long balanced_dirty_ratelimit;
 
-        struct prop_local_percpu completions;
+        struct fprop_local_percpu completions;
         int dirty_exceeded;
 
         unsigned int min_ratio;
diff --git a/include/linux/flex_proportions.h b/include/linux/flex_proportions.h
new file mode 100644
index 000000000000..4ebc49fae391
--- /dev/null
+++ b/include/linux/flex_proportions.h
@@ -0,0 +1,101 @@
+/*
+ * Floating proportions with flexible aging period
+ *
+ *  Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
+ */
+
+#ifndef _LINUX_FLEX_PROPORTIONS_H
+#define _LINUX_FLEX_PROPORTIONS_H
+
+#include <linux/percpu_counter.h>
+#include <linux/spinlock.h>
+#include <linux/seqlock.h>
+
+/*
+ * When maximum proportion of some event type is specified, this is the
+ * precision with which we allow limitting. Note that this creates an upper
+ * bound on the number of events per period like
+ *   ULLONG_MAX >> FPROP_FRAC_SHIFT.
+ */
+#define FPROP_FRAC_SHIFT 10
+#define FPROP_FRAC_BASE (1UL << FPROP_FRAC_SHIFT)
+
+/*
+ * ---- Global proportion definitions ----
+ */
+struct fprop_global {
+        /* Number of events in the current period */
+        struct percpu_counter events;
+        /* Current period */
+        unsigned int period;
+        /* Synchronization with period transitions */
+        seqcount_t sequence;
+};
+
+int fprop_global_init(struct fprop_global *p);
+void fprop_global_destroy(struct fprop_global *p);
+bool fprop_new_period(struct fprop_global *p, int periods);
+
+/*
+ *  ---- SINGLE ----
+ */
+struct fprop_local_single {
+        /* the local events counter */
+        unsigned long events;
+        /* Period in which we last updated events */
+        unsigned int period;
+        raw_spinlock_t lock;    /* Protect period and numerator */
+};
+
+#define INIT_FPROP_LOCAL_SINGLE(name)                   \
+{       .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock),    \
+}
+
+int fprop_local_init_single(struct fprop_local_single *pl);
+void fprop_local_destroy_single(struct fprop_local_single *pl);
+void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl);
+void fprop_fraction_single(struct fprop_global *p,
+        struct fprop_local_single *pl, unsigned long *numerator,
+        unsigned long *denominator);
+
+static inline
+void fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        __fprop_inc_single(p, pl);
+        local_irq_restore(flags);
+}
+
+/*
+ * ---- PERCPU ----
+ */
+struct fprop_local_percpu {
+        /* the local events counter */
+        struct percpu_counter events;
+        /* Period in which we last updated events */
+        unsigned int period;
+        raw_spinlock_t lock;    /* Protect period and numerator */
+};
+
+int fprop_local_init_percpu(struct fprop_local_percpu *pl);
+void fprop_local_destroy_percpu(struct fprop_local_percpu *pl);
+void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl);
+void __fprop_inc_percpu_max(struct fprop_global *p, struct fprop_local_percpu *pl,
+                            int max_frac);
+void fprop_fraction_percpu(struct fprop_global *p,
+        struct fprop_local_percpu *pl, unsigned long *numerator,
+        unsigned long *denominator);
+
+static inline
+void fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        __fprop_inc_percpu(p, pl);
+        local_irq_restore(flags);
+}
+
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index 9cb4104f47d9..42d283edc4d3 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -11,7 +11,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
          rbtree.o radix-tree.o dump_stack.o timerqueue.o\
          idr.o int_sqrt.o extable.o prio_tree.o \
          sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \
-         proportions.o prio_heap.o ratelimit.o show_mem.o \
+         proportions.o flex_proportions.o prio_heap.o ratelimit.o show_mem.o \
          is_single_threaded.o plist.o decompress.o
 
 lib-$(CONFIG_MMU) += ioremap.o
diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
new file mode 100644
index 000000000000..c785554f9523
--- /dev/null
+++ b/lib/flex_proportions.c
@@ -0,0 +1,272 @@
+/*
+ *  Floating proportions with flexible aging period
+ *
+ *   Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
+ *
+ * The goal of this code is: Given different types of event, measure proportion
+ * of each type of event over time. The proportions are measured with
+ * exponentially decaying history to give smooth transitions. A formula
+ * expressing proportion of event of type 'j' is:
+ *
+ *   p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
+ *
+ * Where x_{i,j} is j's number of events in i-th last time period and x_i is
+ * total number of events in i-th last time period.
+ *
+ * Note that p_{j}'s are normalised, i.e.
+ *
+ *   \Sum_{j} p_{j} = 1,
+ *
+ * This formula can be straightforwardly computed by maintaing denominator
+ * (let's call it 'd') and for each event type its numerator (let's call it
+ * 'n_j'). When an event of type 'j' happens, we simply need to do:
+ *   n_j++; d++;
+ *
+ * When a new period is declared, we could do:
+ *   d /= 2
+ *   for each j
+ *     n_j /= 2
+ *
+ * To avoid iteration over all event types, we instead shift numerator of event
+ * j lazily when someone asks for a proportion of event j or when event j
+ * occurs. This can bit trivially implemented by remembering last period in
+ * which something happened with proportion of type j.
+ */
+#include <linux/flex_proportions.h>
+
+int fprop_global_init(struct fprop_global *p)
+{
+        int err;
+
+        p->period = 0;
+        /* Use 1 to avoid dealing with periods with 0 events... */
+        err = percpu_counter_init(&p->events, 1);
+        if (err)
+                return err;
+        seqcount_init(&p->sequence);
+        return 0;
+}
+
+void fprop_global_destroy(struct fprop_global *p)
+{
+        percpu_counter_destroy(&p->events);
+}
+
+/*
+ * Declare @periods new periods. It is upto the caller to make sure period
+ * transitions cannot happen in parallel.
+ *
+ * The function returns true if the proportions are still defined and false
+ * if aging zeroed out all events. This can be used to detect whether declaring
+ * further periods has any effect.
+ */
+bool fprop_new_period(struct fprop_global *p, int periods)
+{
+        u64 events;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        events = percpu_counter_sum(&p->events);
+        /*
+         * Don't do anything if there are no events.
+         */
+        if (events <= 1) {
+                local_irq_restore(flags);
+                return false;
+        }
+        write_seqcount_begin(&p->sequence);
+        if (periods < 64)
+                events -= events >> periods;
+        /* Use addition to avoid losing events happening between sum and set */
+        percpu_counter_add(&p->events, -events);
+        p->period += periods;
+        write_seqcount_end(&p->sequence);
+        local_irq_restore(flags);
+
+        return true;
+}
+
+/*
+ * ---- SINGLE ----
+ */
+
+int fprop_local_init_single(struct fprop_local_single *pl)
+{
+        pl->events = 0;
+        pl->period = 0;
+        raw_spin_lock_init(&pl->lock);
+        return 0;
+}
+
+void fprop_local_destroy_single(struct fprop_local_single *pl)
+{
+}
+
+static void fprop_reflect_period_single(struct fprop_global *p,
+                                        struct fprop_local_single *pl)
+{
+        unsigned int period = p->period;
+        unsigned long flags;
+
+        /* Fast path - period didn't change */
+        if (pl->period == period)
+                return;
+        raw_spin_lock_irqsave(&pl->lock, flags);
+        /* Someone updated pl->period while we were spinning? */
+        if (pl->period >= period) {
+                raw_spin_unlock_irqrestore(&pl->lock, flags);
+                return;
+        }
+        /* Aging zeroed our fraction? */
+        if (period - pl->period < BITS_PER_LONG)
+                pl->events >>= period - pl->period;
+        else
+                pl->events = 0;
+        pl->period = period;
+        raw_spin_unlock_irqrestore(&pl->lock, flags);
+}
+
+/* Event of type pl happened */
+void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
+{
+        fprop_reflect_period_single(p, pl);
+        pl->events++;
+        percpu_counter_add(&p->events, 1);
+}
+
+/* Return fraction of events of type pl */
+void fprop_fraction_single(struct fprop_global *p,
+                           struct fprop_local_single *pl,
+                           unsigned long *numerator, unsigned long *denominator)
+{
+        unsigned int seq;
+        s64 num, den;
+
+        do {
+                seq = read_seqcount_begin(&p->sequence);
+                fprop_reflect_period_single(p, pl);
+                num = pl->events;
+                den = percpu_counter_read_positive(&p->events);
+        } while (read_seqcount_retry(&p->sequence, seq));
+
+        /*
+         * Make fraction <= 1 and denominator > 0 even in presence of percpu
+         * counter errors
+         */
+        if (den <= num) {
+                if (num)
+                        den = num;
+                else
+                        den = 1;
+        }
+        *denominator = den;
+        *numerator = num;
+}
+
+/*
+ * ---- PERCPU ----
+ */
+#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
+
+int fprop_local_init_percpu(struct fprop_local_percpu *pl)
+{
+        int err;
+
+        err = percpu_counter_init(&pl->events, 0);
+        if (err)
+                return err;
+        pl->period = 0;
+        raw_spin_lock_init(&pl->lock);
+        return 0;
+}
+
+void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
+{
+        percpu_counter_destroy(&pl->events);
+}
+
+static void fprop_reflect_period_percpu(struct fprop_global *p,
+                                        struct fprop_local_percpu *pl)
+{
+        unsigned int period = p->period;
+        unsigned long flags;
+
+        /* Fast path - period didn't change */
+        if (pl->period == period)
+                return;
+        raw_spin_lock_irqsave(&pl->lock, flags);
+        /* Someone updated pl->period while we were spinning? */
+        if (pl->period >= period) {
+                raw_spin_unlock_irqrestore(&pl->lock, flags);
+                return;
+        }
+        /* Aging zeroed our fraction? */
+        if (period - pl->period < BITS_PER_LONG) {
+                s64 val = percpu_counter_read(&pl->events);
+
+                if (val < (nr_cpu_ids * PROP_BATCH))
+                        val = percpu_counter_sum(&pl->events);
+
+                __percpu_counter_add(&pl->events,
+                        -val + (val >> (period-pl->period)), PROP_BATCH);
+        } else
+                percpu_counter_set(&pl->events, 0);
+        pl->period = period;
+        raw_spin_unlock_irqrestore(&pl->lock, flags);
+}
+
+/* Event of type pl happened */
+void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
+{
+        fprop_reflect_period_percpu(p, pl);
+        __percpu_counter_add(&pl->events, 1, PROP_BATCH);
+        percpu_counter_add(&p->events, 1);
+}
+
+void fprop_fraction_percpu(struct fprop_global *p,
+                           struct fprop_local_percpu *pl,
+                           unsigned long *numerator, unsigned long *denominator)
+{
+        unsigned int seq;
+        s64 num, den;
+
+        do {
+                seq = read_seqcount_begin(&p->sequence);
+                fprop_reflect_period_percpu(p, pl);
+                num = percpu_counter_read_positive(&pl->events);
+                den = percpu_counter_read_positive(&p->events);
+        } while (read_seqcount_retry(&p->sequence, seq));
+
+        /*
+         * Make fraction <= 1 and denominator > 0 even in presence of percpu
+         * counter errors
+         */
+        if (den <= num) {
+                if (num)
+                        den = num;
+                else
+                        den = 1;
+        }
+        *denominator = den;
+        *numerator = num;
+}
+
+/*
+ * Like __fprop_inc_percpu() except that event is counted only if the given
+ * type has fraction smaller than @max_frac/FPROP_FRAC_BASE
+ */
+void __fprop_inc_percpu_max(struct fprop_global *p,
+                            struct fprop_local_percpu *pl, int max_frac)
+{
+        if (unlikely(max_frac < FPROP_FRAC_BASE)) {
+                unsigned long numerator, denominator;
+
+                fprop_fraction_percpu(p, pl, &numerator, &denominator);
+                if (numerator >
+                    (((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
+                        return;
+        } else
+                fprop_reflect_period_percpu(p, pl);
+        __percpu_counter_add(&pl->events, 1, PROP_BATCH);
+        percpu_counter_add(&p->events, 1);
+}
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);
 }
 
 /**