mm: backing-dev: use group allocation/free of per-cpu counters API

Use group allocation/free of per-cpu counters api to accelerate
wb_init/exit() and simplify code.

Link: https://lkml.kernel.org/r/20240325035635.49342-1-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Dennis Zhou <dennis@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/backing-dev.c

@@ -388,7 +388,7 @@ static void wb_update_bandwidth_workfn(struct work_struct *work)
 static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 		   gfp_t gfp)
 {
-	int i, err;
+	int err;
 
 	memset(wb, 0, sizeof(*wb));
 
@@ -416,18 +416,10 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 	if (err)
 		return err;
 
-	for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
-		err = percpu_counter_init(&wb->stat[i], 0, gfp);
-		if (err)
-			goto out_destroy_stat;
-	}
-
-	return 0;
+	err = percpu_counter_init_many(wb->stat, 0, gfp, NR_WB_STAT_ITEMS);
+	if (err)
+		fprop_local_destroy_percpu(&wb->completions);
 
-out_destroy_stat:
-	while (i--)
-		percpu_counter_destroy(&wb->stat[i]);
-	fprop_local_destroy_percpu(&wb->completions);
 	return err;
 }
 
@@ -460,13 +452,8 @@ static void wb_shutdown(struct bdi_writeback *wb)
 
 static void wb_exit(struct bdi_writeback *wb)
 {
-	int i;
-
 	WARN_ON(delayed_work_pending(&wb->dwork));
-
-	for (i = 0; i < NR_WB_STAT_ITEMS; i++)
-		percpu_counter_destroy(&wb->stat[i]);
-
+	percpu_counter_destroy_many(wb->stat, NR_WB_STAT_ITEMS);
 	fprop_local_destroy_percpu(&wb->completions);
 }