__wb_update_bandwidth() is called from two places -
fs/fs-writeback.c::balance_dirty_pages() and
mm/page-writeback.c::wb_writeback().  The latter updates only the
write bandwidth while the former also deals with the dirty ratelimit.
The two callsites are distinguished by whether @thresh parameter is
zero or not, which is cryptic.  In addition, the two files define
their own different versions of wb_update_bandwidth() on top of
__wb_update_bandwidth(), which is confusing to say the least.  This
patch cleans up [__]wb_update_bandwidth() in the following ways.

* __wb_update_bandwidth() now takes explicit @update_ratelimit
  parameter to gate dirty ratelimit handling.

* mm/page-writeback.c::wb_update_bandwidth() is flattened into its
  caller - balance_dirty_pages().

* fs/fs-writeback.c::wb_update_bandwidth() is moved to
  mm/page-writeback.c and __wb_update_bandwidth() is made static.

* While at it, add a lockdep assertion to __wb_update_bandwidth().

Except for the lockdep addition, this is pure reorganization and
doesn't introduce any behavioral changes.

Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Jens Axboe <ax...@kernel.dk>
Cc: Jan Kara <j...@suse.cz>
Cc: Wu Fengguang <fengguang...@intel.com>
Cc: Greg Thelen <gthe...@google.com>
---
 fs/fs-writeback.c         | 10 ----------
 include/linux/writeback.h |  9 +--------
 mm/page-writeback.c       | 45 ++++++++++++++++++++++-----------------------
 3 files changed, 23 insertions(+), 41 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 2b6df69..85daae2 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1069,16 +1069,6 @@ static bool over_bground_thresh(struct bdi_writeback *wb)
 }
 
 /*
- * Called under wb->list_lock. If there are multiple wb per bdi,
- * only the flusher working on the first wb should do it.
- */
-static void wb_update_bandwidth(struct bdi_writeback *wb,
-                               unsigned long start_time)
-{
-       __wb_update_bandwidth(wb, 0, 0, 0, 0, 0, start_time);
-}
-
-/*
  * Explicit flushing or periodic writeback of "old" data.
  *
  * Define "old": the first time one of an inode's pages is dirtied, we mark the
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 6f6b8c8..c280c1d 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -154,14 +154,7 @@ int dirty_writeback_centisecs_handler(struct ctl_table *, 
int,
 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);
 
-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);
-
+void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
 void page_writeback_init(void);
 void balance_dirty_pages_ratelimited(struct address_space *mapping);
 
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3401634..3064809 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1160,19 +1160,22 @@ static void wb_update_dirty_ratelimit(struct 
bdi_writeback *wb,
        trace_bdi_dirty_ratelimit(wb->bdi, dirty_rate, task_ratelimit);
 }
 
-void __wb_update_bandwidth(struct bdi_writeback *wb,
-                          unsigned long thresh,
-                          unsigned long bg_thresh,
-                          unsigned long dirty,
-                          unsigned long wb_thresh,
-                          unsigned long wb_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 wb_thresh,
+                                 unsigned long wb_dirty,
+                                 unsigned long start_time,
+                                 bool update_ratelimit)
 {
        unsigned long now = jiffies;
        unsigned long elapsed = now - wb->bw_time_stamp;
        unsigned long dirtied;
        unsigned long written;
 
+       lockdep_assert_held(&wb->list_lock);
+
        /*
         * rate-limit, only update once every 200ms.
         */
@@ -1189,7 +1192,7 @@ void __wb_update_bandwidth(struct bdi_writeback *wb,
        if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
                goto snapshot;
 
-       if (thresh) {
+       if (update_ratelimit) {
                global_update_bandwidth(thresh, dirty, now);
                wb_update_dirty_ratelimit(wb, thresh, bg_thresh, dirty,
                                          wb_thresh, wb_dirty,
@@ -1203,20 +1206,9 @@ snapshot:
        wb->bw_time_stamp = now;
 }
 
-static void wb_update_bandwidth(struct bdi_writeback *wb,
-                               unsigned long thresh,
-                               unsigned long bg_thresh,
-                               unsigned long dirty,
-                               unsigned long wb_thresh,
-                               unsigned long wb_dirty,
-                               unsigned long start_time)
+void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
 {
-       if (time_is_after_eq_jiffies(wb->bw_time_stamp + BANDWIDTH_INTERVAL))
-               return;
-       spin_lock(&wb->list_lock);
-       __wb_update_bandwidth(wb, thresh, bg_thresh, dirty,
-                             wb_thresh, wb_dirty, start_time);
-       spin_unlock(&wb->list_lock);
+       __wb_update_bandwidth(wb, 0, 0, 0, 0, 0, start_time, false);
 }
 
 /*
@@ -1467,8 +1459,15 @@ static void balance_dirty_pages(struct address_space 
*mapping,
                if (dirty_exceeded && !wb->dirty_exceeded)
                        wb->dirty_exceeded = 1;
 
-               wb_update_bandwidth(wb, dirty_thresh, background_thresh,
-                                   nr_dirty, wb_thresh, wb_dirty, start_time);
+               if (time_is_before_jiffies(wb->bw_time_stamp +
+                                          BANDWIDTH_INTERVAL)) {
+                       spin_lock(&wb->list_lock);
+                       __wb_update_bandwidth(wb, dirty_thresh,
+                                             background_thresh, nr_dirty,
+                                             wb_thresh, wb_dirty, start_time,
+                                             true);
+                       spin_unlock(&wb->list_lock);
+               }
 
                dirty_ratelimit = wb->dirty_ratelimit;
                pos_ratio = wb_position_ratio(wb, dirty_thresh,
-- 
2.1.0

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