writeback: factor out balance_domain_limits to remove repeated code

Factor out balance_domain_limits to remove repeated code.

Link: https://lkml.kernel.org/r/20240514125254.142203-7-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page-writeback.c

@@ -1746,6 +1746,14 @@ static void domain_dirty_freerun(struct dirty_throttle_control *dtc,
 	dtc->freerun = dirty <= dirty_freerun_ceiling(thresh, bg_thresh);
 }
 
+static void balance_domain_limits(struct dirty_throttle_control *dtc,
+				  bool strictlimit)
+{
+	domain_dirty_avail(dtc, true);
+	domain_dirty_limits(dtc);
+	domain_dirty_freerun(dtc, strictlimit);
+}
+
 static void wb_dirty_freerun(struct dirty_throttle_control *dtc,
 			     bool strictlimit)
 {
@@ -1802,18 +1810,13 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
 
 		nr_dirty = global_node_page_state(NR_FILE_DIRTY);
 
-		domain_dirty_avail(gdtc, true);
-		domain_dirty_limits(gdtc);
-		domain_dirty_freerun(gdtc, strictlimit);
-
+		balance_domain_limits(gdtc, strictlimit);
 		if (mdtc) {
 			/*
 			 * If @wb belongs to !root memcg, repeat the same
 			 * basic calculations for the memcg domain.
 			 */
-			domain_dirty_avail(mdtc, true);
-			domain_dirty_limits(mdtc);
-			domain_dirty_freerun(mdtc, strictlimit);
+			balance_domain_limits(mdtc, strictlimit);
 		}
 
 		/*