writeback: make __wb_calc_thresh() take dirty_throttle_control

wb_calc_thresh() calculates wb_thresh by scaling thresh according to
the wb's portion in the system-wide write bandwidth.  cgroup writeback
support would need to calculate wb_thresh against memcg domain too.
This patch renames wb_calc_thresh() to __wb_calc_thresh() and makes it
take dirty_throttle_control so that the function can later be updated
to calculate against different domains according to
dirty_throttle_control.

wb_calc_thresh() is now a thin wrapper around __wb_calc_thresh().

v2: The original version was incorrectly scaling dtc->dirty instead of
    dtc->thresh.  This was due to the extremely confusing function and
    variable names.  Added a rename patch and fixed this one.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3ec922309178..2352c69bff12 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -557,9 +557,8 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
 }
 
 /**
- * wb_calc_thresh - @wb's share of dirty throttling threshold
- * @wb: bdi_writeback to query
- * @dirty: global dirty limit in pages
+ * __wb_calc_thresh - @wb's share of dirty throttling threshold
+ * @dtc: dirty_throttle_context of interest
  *
  * 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.
@@ -578,9 +577,10 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
  * 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 wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
+static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
 {
         struct wb_domain *dom = &global_wb_domain;
+        unsigned long thresh = dtc->thresh;
         u64 wb_thresh;
         long numerator, denominator;
         unsigned long wb_min_ratio, wb_max_ratio;
@@ -588,14 +588,14 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
         /*
          * Calculate this BDI's share of the thresh ratio.
          */
-        fprop_fraction_percpu(&dom->completions, &wb->completions,
+        fprop_fraction_percpu(&dom->completions, &dtc->wb->completions,
                               &numerator, &denominator);
 
         wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
         wb_thresh *= numerator;
         do_div(wb_thresh, denominator);
 
-        wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);
+        wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
 
         wb_thresh += (thresh * wb_min_ratio) / 100;
         if (wb_thresh > (thresh * wb_max_ratio) / 100)
@@ -604,6 +604,13 @@ unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
         return wb_thresh;
 }
 
+unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
+{
+        struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
+                                               .thresh = thresh };
+        return __wb_calc_thresh(&gdtc);
+}
+
 /*
  *                           setpoint - dirty 3
  *        f(dirty) := 1.0 + (----------------)
@@ -1323,7 +1330,7 @@ static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
          *   wb_position_ratio() will let the dirtier task progress
          *   at some rate <= (write_bw / 2) for bringing down wb_dirty.
          */
-        dtc->wb_thresh = wb_calc_thresh(dtc->wb, dtc->thresh);
+        dtc->wb_thresh = __wb_calc_thresh(dtc);
         dtc->wb_bg_thresh = dtc->thresh ?
                 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;