blk-throttle: don't take carryover for prioritized processing of metadata

Commit 29390bb ("blk-throttle: support prioritized processing of metadata")
takes bytes/ios carryover for prioritized processing of metadata. Turns out
we can support it by charging it directly without trimming slice, and the
result is same with carryover.

Cc: Tejun Heo <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Yu Kuai <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Ming Lei

block/blk-throttle.c

@@ -1620,13 +1620,6 @@ static bool tg_within_limit(struct throtl_grp *tg, struct bio *bio, bool rw)
 	return tg_may_dispatch(tg, bio, NULL);
 }
 
-static void tg_dispatch_in_debt(struct throtl_grp *tg, struct bio *bio, bool rw)
-{
-	if (!bio_flagged(bio, BIO_BPS_THROTTLED))
-		tg->carryover_bytes[rw] -= throtl_bio_data_size(bio);
-	tg->carryover_ios[rw]--;
-}
-
 bool __blk_throtl_bio(struct bio *bio)
 {
 	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
@@ -1663,10 +1656,12 @@ bool __blk_throtl_bio(struct bio *bio)
 			/*
 			 * IOs which may cause priority inversions are
 			 * dispatched directly, even if they're over limit.
-			 * Debts are handled by carryover_bytes/ios while
-			 * calculating wait time.
+			 *
+			 * Charge and dispatch directly, and our throttle
+			 * control algorithm is adaptive, and extra IO bytes
+			 * will be throttled for paying the debt
 			 */
-			tg_dispatch_in_debt(tg, bio, rw);
+			throtl_charge_bio(tg, bio);
 		} else {
 			/* if above limits, break to queue */
 			break;