writeback: move bandwidth related fields from backing_dev_info into bdi_writeback

Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
and the role of the separation is unclear.  For cgroup support for
writeback IOs, a bdi will be updated to host multiple wb's where each
wb serves writeback IOs of a different cgroup on the bdi.  To achieve
that, a wb should carry all states necessary for servicing writeback
IOs for a cgroup independently.

This patch moves bandwidth related fields from backing_dev_info into
bdi_writeback.

* The moved fields are: bw_time_stamp, dirtied_stamp, written_stamp,
  write_bandwidth, avg_write_bandwidth, dirty_ratelimit,
  balanced_dirty_ratelimit, completions and dirty_exceeded.

* writeback_chunk_size() and over_bground_thresh() now take @wb
  instead of @bdi.

* bdi_writeout_fraction(bdi, ...)	-> wb_writeout_fraction(wb, ...)
  bdi_dirty_limit(bdi, ...)		-> wb_dirty_limit(wb, ...)
  bdi_position_ration(bdi, ...)		-> wb_position_ratio(wb, ...)
  bdi_update_writebandwidth(bdi, ...)	-> wb_update_write_bandwidth(wb, ...)
  [__]bdi_update_bandwidth(bdi, ...)	-> [__]wb_update_bandwidth(wb, ...)
  bdi_{max|min}_pause(bdi, ...)		-> wb_{max|min}_pause(wb, ...)
  bdi_dirty_limits(bdi, ...)		-> wb_dirty_limits(wb, ...)

* Init/exits of the relocated fields are moved to bdi_wb_init/exit()
  respectively.  Note that explicit zeroing is dropped in the process
  as wb's are cleared in entirety anyway.

* As there's still only one bdi_writeback per backing_dev_info, all
  uses of bdi->stat[] are mechanically replaced with bdi->wb.stat[]
  introducing no behavior changes.

v2: Typo in description fixed as suggested by Jan.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 132 insertions, 130 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index dc673a035413..cd39ee91b7bb 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -399,7 +399,7 @@ static unsigned long wp_next_time(unsigned long cur_time)
 static inline void __wb_writeout_inc(struct bdi_writeback *wb)
 {
         __inc_wb_stat(wb, WB_WRITTEN);
-        __fprop_inc_percpu_max(&writeout_completions, &wb->bdi->completions,
+        __fprop_inc_percpu_max(&writeout_completions, &wb->completions,
                                wb->bdi->max_prop_frac);
         /* First event after period switching was turned off? */
         if (!unlikely(writeout_period_time)) {
@@ -427,10 +427,10 @@ EXPORT_SYMBOL_GPL(wb_writeout_inc);
 /*
  * Obtain an accurate fraction of the BDI's portion.
  */
-static void bdi_writeout_fraction(struct backing_dev_info *bdi,
-                long *numerator, long *denominator)
+static void wb_writeout_fraction(struct bdi_writeback *wb,
+                                 long *numerator, long *denominator)
 {
-        fprop_fraction_percpu(&writeout_completions, &bdi->completions,
+        fprop_fraction_percpu(&writeout_completions, &wb->completions,
                                 numerator, denominator);
 }
 
@@ -516,11 +516,11 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
 }
 
 /**
- * bdi_dirty_limit - @bdi's share of dirty throttling threshold
- * @bdi: the backing_dev_info to query
+ * wb_dirty_limit - @wb's share of dirty throttling threshold
+ * @wb: bdi_writeback to query
  * @dirty: global dirty limit in pages
  *
- * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
+ * Returns @wb's dirty limit in pages. The term "dirty" in the context of
  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
  *
  * Note that balance_dirty_pages() will only seriously take it as a hard limit
@@ -528,34 +528,35 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
  * control. For example, when the device is completely stalled due to some error
  * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
  * In the other normal situations, it acts more gently by throttling the tasks
- * more (rather than completely block them) when the bdi dirty pages go high.
+ * more (rather than completely block them) when the wb dirty pages go high.
  *
  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
  * - starving fast devices
  * - piling up dirty pages (that will take long time to sync) on slow devices
  *
- * The bdi's share of dirty limit will be adapting to its throughput and
+ * The wb's share of dirty limit will be adapting to its throughput and
  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
  */
-unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
+unsigned long wb_dirty_limit(struct bdi_writeback *wb, unsigned long dirty)
 {
-        u64 bdi_dirty;
+        struct backing_dev_info *bdi = wb->bdi;
+        u64 wb_dirty;
         long numerator, denominator;
 
         /*
          * Calculate this BDI's share of the dirty ratio.
          */
-        bdi_writeout_fraction(bdi, &numerator, &denominator);
+        wb_writeout_fraction(wb, &numerator, &denominator);
 
-        bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
-        bdi_dirty *= numerator;
-        do_div(bdi_dirty, denominator);
+        wb_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
+        wb_dirty *= numerator;
+        do_div(wb_dirty, denominator);
 
-        bdi_dirty += (dirty * bdi->min_ratio) / 100;
-        if (bdi_dirty > (dirty * bdi->max_ratio) / 100)
-                bdi_dirty = dirty * bdi->max_ratio / 100;
+        wb_dirty += (dirty * bdi->min_ratio) / 100;
+        if (wb_dirty > (dirty * bdi->max_ratio) / 100)
+                wb_dirty = dirty * bdi->max_ratio / 100;
 
-        return bdi_dirty;
+        return wb_dirty;
 }
 
 /*
@@ -664,14 +665,14 @@ static long long pos_ratio_polynom(unsigned long setpoint,
  *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
  * - the bdi dirty thresh drops quickly due to change of JBOD workload
  */
-static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
-                                        unsigned long thresh,
-                                        unsigned long bg_thresh,
-                                        unsigned long dirty,
-                                        unsigned long bdi_thresh,
-                                        unsigned long bdi_dirty)
+static unsigned long wb_position_ratio(struct bdi_writeback *wb,
+                                       unsigned long thresh,
+                                       unsigned long bg_thresh,
+                                       unsigned long dirty,
+                                       unsigned long bdi_thresh,
+                                       unsigned long bdi_dirty)
 {
-        unsigned long write_bw = bdi->avg_write_bandwidth;
+        unsigned long write_bw = wb->avg_write_bandwidth;
         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
         unsigned long limit = hard_dirty_limit(thresh);
         unsigned long x_intercept;
@@ -702,12 +703,12 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
          * consume arbitrary amount of RAM because it is accounted in
          * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
          *
-         * Here, in bdi_position_ratio(), we calculate pos_ratio based on
+         * Here, in wb_position_ratio(), we calculate pos_ratio based on
          * two values: bdi_dirty and bdi_thresh. Let's consider an example:
          * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
          * limits are set by default to 10% and 20% (background and throttle).
          * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
-         * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
+         * wb_dirty_limit(wb, bg_thresh) is about ~4K pages. bdi_setpoint is
          * about ~6K pages (as the average of background and throttle bdi
          * limits). The 3rd order polynomial will provide positive feedback if
          * bdi_dirty is under bdi_setpoint and vice versa.
@@ -717,7 +718,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
          * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
          * in the example above).
          */
-        if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
+        if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
                 long long bdi_pos_ratio;
                 unsigned long bdi_bg_thresh;
 
@@ -842,13 +843,13 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
         return pos_ratio;
 }
 
-static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
-                                       unsigned long elapsed,
-                                       unsigned long written)
+static void wb_update_write_bandwidth(struct bdi_writeback *wb,
+                                      unsigned long elapsed,
+                                      unsigned long written)
 {
         const unsigned long period = roundup_pow_of_two(3 * HZ);
-        unsigned long avg = bdi->avg_write_bandwidth;
-        unsigned long old = bdi->write_bandwidth;
+        unsigned long avg = wb->avg_write_bandwidth;
+        unsigned long old = wb->write_bandwidth;
         u64 bw;
 
         /*
@@ -861,14 +862,14 @@ static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
          * @written may have decreased due to account_page_redirty().
          * Avoid underflowing @bw calculation.
          */
-        bw = written - min(written, bdi->written_stamp);
+        bw = written - min(written, wb->written_stamp);
         bw *= HZ;
         if (unlikely(elapsed > period)) {
                 do_div(bw, elapsed);
                 avg = bw;
                 goto out;
         }
-        bw += (u64)bdi->write_bandwidth * (period - elapsed);
+        bw += (u64)wb->write_bandwidth * (period - elapsed);
         bw >>= ilog2(period);
 
         /*
@@ -881,8 +882,8 @@ static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
                 avg += (old - avg) >> 3;
 
 out:
-        bdi->write_bandwidth = bw;
-        bdi->avg_write_bandwidth = avg;
+        wb->write_bandwidth = bw;
+        wb->avg_write_bandwidth = avg;
 }
 
 /*
@@ -947,20 +948,20 @@ static void global_update_bandwidth(unsigned long thresh,
  * Normal bdi tasks will be curbed at or below it in long term.
  * Obviously it should be around (write_bw / N) when there are N dd tasks.
  */
-static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
-                                       unsigned long thresh,
-                                       unsigned long bg_thresh,
-                                       unsigned long dirty,
-                                       unsigned long bdi_thresh,
-                                       unsigned long bdi_dirty,
-                                       unsigned long dirtied,
-                                       unsigned long elapsed)
+static void wb_update_dirty_ratelimit(struct bdi_writeback *wb,
+                                      unsigned long thresh,
+                                      unsigned long bg_thresh,
+                                      unsigned long dirty,
+                                      unsigned long bdi_thresh,
+                                      unsigned long bdi_dirty,
+                                      unsigned long dirtied,
+                                      unsigned long elapsed)
 {
         unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
         unsigned long limit = hard_dirty_limit(thresh);
         unsigned long setpoint = (freerun + limit) / 2;
-        unsigned long write_bw = bdi->avg_write_bandwidth;
-        unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
+        unsigned long write_bw = wb->avg_write_bandwidth;
+        unsigned long dirty_ratelimit = wb->dirty_ratelimit;
         unsigned long dirty_rate;
         unsigned long task_ratelimit;
         unsigned long balanced_dirty_ratelimit;
@@ -972,10 +973,10 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
          * The dirty rate will match the writeout rate in long term, except
          * when dirty pages are truncated by userspace or re-dirtied by FS.
          */
-        dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
+        dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
 
-        pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
-                                       bdi_thresh, bdi_dirty);
+        pos_ratio = wb_position_ratio(wb, thresh, bg_thresh, dirty,
+                                      bdi_thresh, bdi_dirty);
         /*
          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
          */
@@ -1059,31 +1060,31 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
 
         /*
          * For strictlimit case, calculations above were based on bdi counters
-         * and limits (starting from pos_ratio = bdi_position_ratio() and up to
+         * and limits (starting from pos_ratio = wb_position_ratio() and up to
          * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
          * Hence, to calculate "step" properly, we have to use bdi_dirty as
          * "dirty" and bdi_setpoint as "setpoint".
          *
          * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
          * it's possible that bdi_thresh is close to zero due to inactivity
-         * of backing device (see the implementation of bdi_dirty_limit()).
+         * of backing device (see the implementation of wb_dirty_limit()).
          */
-        if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
+        if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
                 dirty = bdi_dirty;
                 if (bdi_dirty < 8)
                         setpoint = bdi_dirty + 1;
                 else
                         setpoint = (bdi_thresh +
-                                    bdi_dirty_limit(bdi, bg_thresh)) / 2;
+                                    wb_dirty_limit(wb, bg_thresh)) / 2;
         }
 
         if (dirty < setpoint) {
-                x = min3(bdi->balanced_dirty_ratelimit,
+                x = min3(wb->balanced_dirty_ratelimit,
                          balanced_dirty_ratelimit, task_ratelimit);
                 if (dirty_ratelimit < x)
                         step = x - dirty_ratelimit;
         } else {
-                x = max3(bdi->balanced_dirty_ratelimit,
+                x = max3(wb->balanced_dirty_ratelimit,
                          balanced_dirty_ratelimit, task_ratelimit);
                 if (dirty_ratelimit > x)
                         step = dirty_ratelimit - x;
@@ -1105,22 +1106,22 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
         else
                 dirty_ratelimit -= step;
 
-        bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
-        bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
+        wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
+        wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
 
-        trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
+        trace_bdi_dirty_ratelimit(wb->bdi, dirty_rate, task_ratelimit);
 }
 
-void __bdi_update_bandwidth(struct backing_dev_info *bdi,
-                            unsigned long thresh,
-                            unsigned long bg_thresh,
-                            unsigned long dirty,
-                            unsigned long bdi_thresh,
-                            unsigned long bdi_dirty,
-                            unsigned long start_time)
+void __wb_update_bandwidth(struct bdi_writeback *wb,
+                           unsigned long thresh,
+                           unsigned long bg_thresh,
+                           unsigned long dirty,
+                           unsigned long bdi_thresh,
+                           unsigned long bdi_dirty,
+                           unsigned long start_time)
 {
         unsigned long now = jiffies;
-        unsigned long elapsed = now - bdi->bw_time_stamp;
+        unsigned long elapsed = now - wb->bw_time_stamp;
         unsigned long dirtied;
         unsigned long written;
 
@@ -1130,44 +1131,44 @@ void __bdi_update_bandwidth(struct backing_dev_info *bdi,
         if (elapsed < BANDWIDTH_INTERVAL)
                 return;
 
-        dirtied = percpu_counter_read(&bdi->wb.stat[WB_DIRTIED]);
-        written = percpu_counter_read(&bdi->wb.stat[WB_WRITTEN]);
+        dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
+        written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
 
         /*
          * Skip quiet periods when disk bandwidth is under-utilized.
          * (at least 1s idle time between two flusher runs)
          */
-        if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
+        if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
                 goto snapshot;
 
         if (thresh) {
                 global_update_bandwidth(thresh, dirty, now);
-                bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
-                                           bdi_thresh, bdi_dirty,
-                                           dirtied, elapsed);
+                wb_update_dirty_ratelimit(wb, thresh, bg_thresh, dirty,
+                                          bdi_thresh, bdi_dirty,
+                                          dirtied, elapsed);
         }
-        bdi_update_write_bandwidth(bdi, elapsed, written);
+        wb_update_write_bandwidth(wb, elapsed, written);
 
 snapshot:
-        bdi->dirtied_stamp = dirtied;
-        bdi->written_stamp = written;
-        bdi->bw_time_stamp = now;
+        wb->dirtied_stamp = dirtied;
+        wb->written_stamp = written;
+        wb->bw_time_stamp = now;
 }
 
-static void bdi_update_bandwidth(struct backing_dev_info *bdi,
-                                 unsigned long thresh,
-                                 unsigned long bg_thresh,
-                                 unsigned long dirty,
-                                 unsigned long bdi_thresh,
-                                 unsigned long bdi_dirty,
-                                 unsigned long start_time)
+static void wb_update_bandwidth(struct bdi_writeback *wb,
+                                unsigned long thresh,
+                                unsigned long bg_thresh,
+                                unsigned long dirty,
+                                unsigned long bdi_thresh,
+                                unsigned long bdi_dirty,
+                                unsigned long start_time)
 {
-        if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
+        if (time_is_after_eq_jiffies(wb->bw_time_stamp + BANDWIDTH_INTERVAL))
                 return;
-        spin_lock(&bdi->wb.list_lock);
-        __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
-                               bdi_thresh, bdi_dirty, start_time);
-        spin_unlock(&bdi->wb.list_lock);
+        spin_lock(&wb->list_lock);
+        __wb_update_bandwidth(wb, thresh, bg_thresh, dirty,
+                              bdi_thresh, bdi_dirty, start_time);
+        spin_unlock(&wb->list_lock);
 }
 
 /*
@@ -1187,10 +1188,10 @@ static unsigned long dirty_poll_interval(unsigned long dirty,
         return 1;
 }
 
-static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
-                                   unsigned long bdi_dirty)
+static unsigned long wb_max_pause(struct bdi_writeback *wb,
+                                      unsigned long bdi_dirty)
 {
-        unsigned long bw = bdi->avg_write_bandwidth;
+        unsigned long bw = wb->avg_write_bandwidth;
         unsigned long t;
 
         /*
@@ -1206,14 +1207,14 @@ static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
         return min_t(unsigned long, t, MAX_PAUSE);
 }
 
-static long bdi_min_pause(struct backing_dev_info *bdi,
-                          long max_pause,
-                          unsigned long task_ratelimit,
-                          unsigned long dirty_ratelimit,
-                          int *nr_dirtied_pause)
+static long wb_min_pause(struct bdi_writeback *wb,
+                         long max_pause,
+                         unsigned long task_ratelimit,
+                         unsigned long dirty_ratelimit,
+                         int *nr_dirtied_pause)
 {
-        long hi = ilog2(bdi->avg_write_bandwidth);
-        long lo = ilog2(bdi->dirty_ratelimit);
+        long hi = ilog2(wb->avg_write_bandwidth);
+        long lo = ilog2(wb->dirty_ratelimit);
         long t;         /* target pause */
         long pause;     /* estimated next pause */
         int pages;      /* target nr_dirtied_pause */
@@ -1281,14 +1282,13 @@ static long bdi_min_pause(struct backing_dev_info *bdi,
         return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
 }
 
-static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
-                                    unsigned long dirty_thresh,
-                                    unsigned long background_thresh,
-                                    unsigned long *bdi_dirty,
-                                    unsigned long *bdi_thresh,
-                                    unsigned long *bdi_bg_thresh)
+static inline void wb_dirty_limits(struct bdi_writeback *wb,
+                                   unsigned long dirty_thresh,
+                                   unsigned long background_thresh,
+                                   unsigned long *bdi_dirty,
+                                   unsigned long *bdi_thresh,
+                                   unsigned long *bdi_bg_thresh)
 {
-        struct bdi_writeback *wb = &bdi->wb;
         unsigned long wb_reclaimable;
 
         /*
@@ -1301,10 +1301,10 @@ static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
          *   In this case we don't want to hard throttle the USB key
          *   dirtiers for 100 seconds until bdi_dirty drops under
          *   bdi_thresh. Instead the auxiliary bdi control line in
-         *   bdi_position_ratio() will let the dirtier task progress
+         *   wb_position_ratio() will let the dirtier task progress
          *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
          */
-        *bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
+        *bdi_thresh = wb_dirty_limit(wb, dirty_thresh);
 
         if (bdi_bg_thresh)
                 *bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh *
@@ -1354,6 +1354,7 @@ static void balance_dirty_pages(struct address_space *mapping,
         unsigned long dirty_ratelimit;
         unsigned long pos_ratio;
         struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+        struct bdi_writeback *wb = &bdi->wb;
         bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
         unsigned long start_time = jiffies;
 
@@ -1378,8 +1379,8 @@ static void balance_dirty_pages(struct address_space *mapping,
                 global_dirty_limits(&background_thresh, &dirty_thresh);
 
                 if (unlikely(strictlimit)) {
-                        bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
-                                         &bdi_dirty, &bdi_thresh, &bg_thresh);
+                        wb_dirty_limits(wb, dirty_thresh, background_thresh,
+                                        &bdi_dirty, &bdi_thresh, &bg_thresh);
 
                         dirty = bdi_dirty;
                         thresh = bdi_thresh;
@@ -1410,28 +1411,28 @@ static void balance_dirty_pages(struct address_space *mapping,
                         bdi_start_background_writeback(bdi);
 
                 if (!strictlimit)
-                        bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
-                                         &bdi_dirty, &bdi_thresh, NULL);
+                        wb_dirty_limits(wb, dirty_thresh, background_thresh,
+                                        &bdi_dirty, &bdi_thresh, NULL);
 
                 dirty_exceeded = (bdi_dirty > bdi_thresh) &&
                                  ((nr_dirty > dirty_thresh) || strictlimit);
-                if (dirty_exceeded && !bdi->dirty_exceeded)
-                        bdi->dirty_exceeded = 1;
+                if (dirty_exceeded && !wb->dirty_exceeded)
+                        wb->dirty_exceeded = 1;
 
-                bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
-                                     nr_dirty, bdi_thresh, bdi_dirty,
-                                     start_time);
+                wb_update_bandwidth(wb, dirty_thresh, background_thresh,
+                                    nr_dirty, bdi_thresh, bdi_dirty,
+                                    start_time);
 
-                dirty_ratelimit = bdi->dirty_ratelimit;
-                pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
-                                               background_thresh, nr_dirty,
-                                               bdi_thresh, bdi_dirty);
+                dirty_ratelimit = wb->dirty_ratelimit;
+                pos_ratio = wb_position_ratio(wb, dirty_thresh,
+                                              background_thresh, nr_dirty,
+                                              bdi_thresh, bdi_dirty);
                 task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
                                                         RATELIMIT_CALC_SHIFT;
-                max_pause = bdi_max_pause(bdi, bdi_dirty);
-                min_pause = bdi_min_pause(bdi, max_pause,
-                                          task_ratelimit, dirty_ratelimit,
-                                          &nr_dirtied_pause);
+                max_pause = wb_max_pause(wb, bdi_dirty);
+                min_pause = wb_min_pause(wb, max_pause,
+                                         task_ratelimit, dirty_ratelimit,
+                                         &nr_dirtied_pause);
 
                 if (unlikely(task_ratelimit == 0)) {
                         period = max_pause;
@@ -1515,15 +1516,15 @@ pause:
                  * more page. However bdi_dirty has accounting errors.  So use
                  * the larger and more IO friendly wb_stat_error.
                  */
-                if (bdi_dirty <= wb_stat_error(&bdi->wb))
+                if (bdi_dirty <= wb_stat_error(wb))
                         break;
 
                 if (fatal_signal_pending(current))
                         break;
         }
 
-        if (!dirty_exceeded && bdi->dirty_exceeded)
-                bdi->dirty_exceeded = 0;
+        if (!dirty_exceeded && wb->dirty_exceeded)
+                wb->dirty_exceeded = 0;
 
         if (writeback_in_progress(bdi))
                 return;
@@ -1577,6 +1578,7 @@ DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
 void balance_dirty_pages_ratelimited(struct address_space *mapping)
 {
         struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+        struct bdi_writeback *wb = &bdi->wb;
         int ratelimit;
         int *p;
 
@@ -1584,7 +1586,7 @@ void balance_dirty_pages_ratelimited(struct address_space *mapping)
                 return;
 
         ratelimit = current->nr_dirtied_pause;
-        if (bdi->dirty_exceeded)
+        if (wb->dirty_exceeded)
                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
 
         preempt_disable();