bcache: get rid of discard code from journal

In bcache journal there is discard functionality but almost useless in
reality. Because discard happens after a journal bucket is reclaimed,
and the reclaimed bucket is allocated for new journaling immediately.
There is no time for underlying SSD to use the discard hint for internal
data management.

The discard code in bcache journal doesn't bring any performance
optimization and wastes CPU cycles for issuing discard bios. Therefore
this patch gits rid of it from journal.c and journal.h.

Signed-off-by: Coly Li <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/md/bcache/journal.c

···
 			 * ja->cur_idx
 			 */
 			ja->cur_idx = i;
-			ja->last_idx = ja->discard_idx = (i + 1) %
-				ca->sb.njournal_buckets;
+			ja->last_idx = (i + 1) % ca->sb.njournal_buckets;
 
 		}
 
···
 	}
 }
 
-static bool is_discard_enabled(struct cache_set *s)
-{
-	struct cache *ca = s->cache;
-
-	if (ca->discard)
-		return true;
-
-	return false;
-}
-
 int bch_journal_replay(struct cache_set *s, struct list_head *list)
 {
 	int ret = 0, keys = 0, entries = 0;
···
 		BUG_ON(i->pin && atomic_read(i->pin) != 1);
 
 		if (n != i->j.seq) {
-			if (n == start && is_discard_enabled(s))
-				pr_info("journal entries %llu-%llu may be discarded! (replaying %llu-%llu)\n",
-					n, i->j.seq - 1, start, end);
-			else {
-				pr_err("journal entries %llu-%llu missing! (replaying %llu-%llu)\n",
-					n, i->j.seq - 1, start, end);
-				ret = -EIO;
-				goto err;
-			}
+			pr_err("journal entries %llu-%llu missing! (replaying %llu-%llu)\n",
+				n, i->j.seq - 1, start, end);
+			ret = -EIO;
+			goto err;
 		}
 
 		for (k = i->j.start;
···
 
 #define last_seq(j)	((j)->seq - fifo_used(&(j)->pin) + 1)
 
-static void journal_discard_endio(struct bio *bio)
-{
-	struct journal_device *ja =
-		container_of(bio, struct journal_device, discard_bio);
-	struct cache *ca = container_of(ja, struct cache, journal);
-
-	atomic_set(&ja->discard_in_flight, DISCARD_DONE);
-
-	closure_wake_up(&ca->set->journal.wait);
-	closure_put(&ca->set->cl);
-}
-
-static void journal_discard_work(struct work_struct *work)
-{
-	struct journal_device *ja =
-		container_of(work, struct journal_device, discard_work);
-
-	submit_bio(&ja->discard_bio);
-}
-
-static void do_journal_discard(struct cache *ca)
-{
-	struct journal_device *ja = &ca->journal;
-	struct bio *bio = &ja->discard_bio;
-
-	if (!ca->discard) {
-		ja->discard_idx = ja->last_idx;
-		return;
-	}
-
-	switch (atomic_read(&ja->discard_in_flight)) {
-	case DISCARD_IN_FLIGHT:
-		return;
-
-	case DISCARD_DONE:
-		ja->discard_idx = (ja->discard_idx + 1) %
-			ca->sb.njournal_buckets;
-
-		atomic_set(&ja->discard_in_flight, DISCARD_READY);
-		fallthrough;
-
-	case DISCARD_READY:
-		if (ja->discard_idx == ja->last_idx)
-			return;
-
-		atomic_set(&ja->discard_in_flight, DISCARD_IN_FLIGHT);
-
-		bio_init_inline(bio, ca->bdev, 1, REQ_OP_DISCARD);
-		bio->bi_iter.bi_sector	= bucket_to_sector(ca->set,
-						ca->sb.d[ja->discard_idx]);
-		bio->bi_iter.bi_size	= bucket_bytes(ca);
-		bio->bi_end_io		= journal_discard_endio;
-
-		closure_get(&ca->set->cl);
-		INIT_WORK(&ja->discard_work, journal_discard_work);
-		queue_work(bch_journal_wq, &ja->discard_work);
-	}
-}
-
 static unsigned int free_journal_buckets(struct cache_set *c)
 {
 	struct journal *j = &c->journal;
···
 	unsigned int n;
 
 	/* In case njournal_buckets is not power of 2 */
-	if (ja->cur_idx >= ja->discard_idx)
-		n = ca->sb.njournal_buckets +  ja->discard_idx - ja->cur_idx;
+	if (ja->cur_idx >= ja->last_idx)
+		n = ca->sb.njournal_buckets + ja->last_idx - ja->cur_idx;
 	else
-		n = ja->discard_idx - ja->cur_idx;
+		n = ja->last_idx - ja->cur_idx;
 
 	if (n > (1 + j->do_reserve))
 		return n - (1 + j->do_reserve);
···
 	       ja->seq[ja->last_idx] < last_seq)
 		ja->last_idx = (ja->last_idx + 1) %
 			ca->sb.njournal_buckets;
-
-	do_journal_discard(ca);
 
 	if (c->journal.blocks_free)
 		goto out;

drivers/md/bcache/journal.h

···
 	/* Last journal bucket that still contains an open journal entry */
 	unsigned int		last_idx;
 
-	/* Next journal bucket to be discarded */
-	unsigned int		discard_idx;
-
-#define DISCARD_READY		0
-#define DISCARD_IN_FLIGHT	1
-#define DISCARD_DONE		2
-	/* 1 - discard in flight, -1 - discard completed */
-	atomic_t		discard_in_flight;
-
-	struct work_struct	discard_work;
-	struct bio		discard_bio;
-	struct bio_vec		discard_bv;
-
 	/* Bio for journal reads/writes to this device */
 	struct bio		bio;
 	struct bio_vec		bv[8];