bcache: allow quick writeback when backing idle

If the control system would wait for at least half a second, and there's
been no reqs hitting the backing disk for awhile: use an alternate mode
where we have at most one contiguous set of writebacks in flight at a
time. (But don't otherwise delay).  If front-end IO appears, it will
still be quick, as it will only have to contend with one real operation
in flight.  But otherwise, we'll be sending data to the backing disk as
quickly as it can accept it (with one op at a time).

Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reviewed-by: Tang Junhui <tang.junhui@zte.com.cn>
Acked-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 52b4ce24f9e2..ddd941056f3c 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -996,6 +996,7 @@ static blk_qc_t cached_dev_make_request(struct request_queue *q,
 	struct cached_dev *dc = container_of(d, struct cached_dev, disk);
 	int rw = bio_data_dir(bio);
 
+	atomic_set(&dc->backing_idle, 0);
 	generic_start_io_acct(q, rw, bio_sectors(bio), &d->disk->part0);
 
 	bio_set_dev(bio, dc->bdev);