block, bfq: save & resume weight on a queue merge/split

bfq saves the state of a queue each time a merge occurs, to be
able to resume such a state when the queue is associated again
with its original process, on a split.

Unfortunately bfq does not save & restore also the weight of the
queue. If the weight is not correctly resumed when the queue is
recycled, then the weight of the recycled queue could differ
from the weight of the original queue.

This commit adds the missing save & resume of the weight.

Tested-by: Holger Hoffstätte <[e-mail]>
Tested-by: Oleksandr Natalenko <[e-mail]>
Signed-off-by: Francesco Pollicino <[e-mail]>
Signed-off-by: Paolo Valente <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

block/bfq-iosched.c

···
 	else
 		bfq_clear_bfqq_IO_bound(bfqq);
 
+	bfqq->entity.new_weight = bic->saved_weight;
 	bfqq->ttime = bic->saved_ttime;
 	bfqq->wr_coeff = bic->saved_wr_coeff;
 	bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
···
 	if (!bic)
 		return;
 
+	bic->saved_weight = bfqq->entity.orig_weight;
 	bic->saved_ttime = bfqq->ttime;
 	bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
 	bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);

block/bfq-iosched.h

···
 	bool was_in_burst_list;
 
 	/*
+	 * Save the weight when a merge occurs, to be able
+	 * to restore it in case of split. If the weight is not
+	 * correctly resumed when the queue is recycled,
+	 * then the weight of the recycled queue could differ
+	 * from the weight of the original queue.
+	 */
+	unsigned int saved_weight;
+
+	/*
 	 * Similar to previous fields: save wr information.
 	 */
 	unsigned long saved_wr_coeff;