[PATCH v2 1/8] writeback: factor out wb_bg_dirty_limits to remove repeated code

[Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>]

Similar to wb_dirty_limits which calculates dirty and thresh of wb,
wb_bg_dirty_limits calculates background dirty and background thresh of
wb. With wb_bg_dirty_limits, we could remove repeated code in
wb_over_bg_thresh.

Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
---
 mm/page-writeback.c | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 692c0da04cbd..e1f73643aca1 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2087,6 +2087,21 @@ void balance_dirty_pages_ratelimited(struct address_space *mapping)
 }
 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
 
+/*
+ * Similar to wb_dirty_limits, wb_bg_dirty_limits also calculates dirty
+ * and thresh, but it's for background writeback.
+ */
+static void wb_bg_dirty_limits(struct dirty_throttle_control *dtc)
+{
+	struct bdi_writeback *wb = dtc->wb;
+
+	dtc->wb_bg_thresh = __wb_calc_thresh(dtc, dtc->bg_thresh);
+	if (dtc->wb_bg_thresh < 2 * wb_stat_error())
+		dtc->wb_dirty = wb_stat_sum(wb, WB_RECLAIMABLE);
+	else
+		dtc->wb_dirty = wb_stat(wb, WB_RECLAIMABLE);
+}
+
 /**
  * wb_over_bg_thresh - does @wb need to be written back?
  * @wb: bdi_writeback of interest
@@ -2103,8 +2118,6 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb)
 	struct dirty_throttle_control * const gdtc = &gdtc_stor;
 	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
 						     &mdtc_stor : NULL;
-	unsigned long reclaimable;
-	unsigned long thresh;
 
 	/*
 	 * Similar to balance_dirty_pages() but ignores pages being written
@@ -2117,13 +2130,8 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb)
 	if (gdtc->dirty > gdtc->bg_thresh)
 		return true;
 
-	thresh = __wb_calc_thresh(gdtc, gdtc->bg_thresh);
-	if (thresh < 2 * wb_stat_error())
-		reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
-	else
-		reclaimable = wb_stat(wb, WB_RECLAIMABLE);
-
-	if (reclaimable > thresh)
+	wb_bg_dirty_limits(gdtc);
+	if (gdtc->wb_dirty > gdtc->wb_bg_thresh)
 		return true;
 
 	if (mdtc) {
@@ -2137,13 +2145,8 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb)
 		if (mdtc->dirty > mdtc->bg_thresh)
 			return true;
 
-		thresh = __wb_calc_thresh(mdtc, mdtc->bg_thresh);
-		if (thresh < 2 * wb_stat_error())
-			reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
-		else
-			reclaimable = wb_stat(wb, WB_RECLAIMABLE);
-
-		if (reclaimable > thresh)
+		wb_bg_dirty_limits(mdtc);
+		if (mdtc->wb_dirty > mdtc->wb_bg_thresh)
 			return true;
 	}
 
-- 
2.30.0