bcachefs: Don't use in-memory bucket array for alloc updates

More prep work for getting rid of the in-memory bucket array: now that
we have BTREE_ITER_WITH_JOURNAL, the allocator code can do ntree lookups
before journal replay is finished, and there's no longer any need for it
to get allocation information from the in-memory bucket array.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/alloc_background.c

@@ -464,19 +464,20 @@ int bch2_bucket_io_time_reset(struct btree_trans *trans, unsigned dev,
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter iter;
+	struct bkey_s_c k;
 	struct bkey_alloc_unpacked u;
 	u64 *time, now;
 	int ret = 0;
 
 	bch2_trans_iter_init(trans, &iter, BTREE_ID_alloc, POS(dev, bucket_nr),
 			     BTREE_ITER_CACHED|
-			     BTREE_ITER_CACHED_NOFILL|
 			     BTREE_ITER_INTENT);
-	ret = bch2_btree_iter_traverse(&iter);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
 	if (ret)
 		goto out;
 
-	u = alloc_mem_to_key(c, &iter);
+	u = bch2_alloc_unpack(k);
 
 	time = rw == READ ? &u.read_time : &u.write_time;
 	now = atomic64_read(&c->io_clock[rw].now);
@@ -673,20 +674,20 @@ static int bucket_invalidate_btree(struct btree_trans *trans,
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter iter;
+	struct bkey_s_c k;
 	int ret;
 
 	bch2_trans_iter_init(trans, &iter, BTREE_ID_alloc,
 			     POS(ca->dev_idx, b),
 			     BTREE_ITER_CACHED|
-			     BTREE_ITER_CACHED_NOFILL|
 			     BTREE_ITER_INTENT);
 
-	ret = bch2_btree_iter_traverse(&iter);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
 	if (ret)
 		goto err;
 
-	*u = alloc_mem_to_key(c, &iter);
-
+	*u = bch2_alloc_unpack(k);
 	u->gen++;
 	u->data_type		= 0;
 	u->dirty_sectors	= 0;

fs/bcachefs/btree_iter.c

@@ -2183,6 +2183,7 @@ inline bool bch2_btree_iter_rewind(struct btree_iter *iter)
 	return ret;
 }
 
+static noinline
 struct bkey_i *__bch2_btree_trans_peek_updates(struct btree_iter *iter)
 {
 	struct btree_insert_entry *i;
@@ -2202,6 +2203,13 @@ struct bkey_i *__bch2_btree_trans_peek_updates(struct btree_iter *iter)
 	return ret;
 }
 
+static inline struct bkey_i *btree_trans_peek_updates(struct btree_iter *iter)
+{
+	return iter->flags & BTREE_ITER_WITH_UPDATES
+		? __bch2_btree_trans_peek_updates(iter)
+		: NULL;
+}
+
 static struct bkey_i *__btree_trans_peek_journal(struct btree_trans *trans,
 						 struct btree_path *path)
 {

fs/bcachefs/btree_update.h

@@ -141,13 +141,4 @@ static inline int bch2_trans_commit(struct btree_trans *trans,
 	     (_i) < (_trans)->updates + (_trans)->nr_updates;		\
 	     (_i)++)
 
-struct bkey_i *__bch2_btree_trans_peek_updates(struct btree_iter *);
-
-static inline struct bkey_i *btree_trans_peek_updates(struct btree_iter *iter)
-{
-	return iter->flags & BTREE_ITER_WITH_UPDATES
-		? __bch2_btree_trans_peek_updates(iter)
-		: NULL;
-}
-
 #endif /* _BCACHEFS_BTREE_UPDATE_H */

fs/bcachefs/buckets.c

@@ -1429,25 +1429,22 @@ static int bch2_trans_start_alloc_update(struct btree_trans *trans, struct btree
 {
 	struct bch_fs *c = trans->c;
 	struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
-	struct bpos pos = POS(ptr->dev, PTR_BUCKET_NR(ca, ptr));
-	struct bkey_i *update;
+	struct bkey_s_c k;
 	int ret;
 
-	bch2_trans_iter_init(trans, iter, BTREE_ID_alloc, pos,
+	bch2_trans_iter_init(trans, iter, BTREE_ID_alloc,
+			     POS(ptr->dev, PTR_BUCKET_NR(ca, ptr)),
+			     BTREE_ITER_WITH_UPDATES|
 			     BTREE_ITER_CACHED|
-			     BTREE_ITER_CACHED_NOFILL|
 			     BTREE_ITER_INTENT);
-	ret = bch2_btree_iter_traverse(iter);
+	k = bch2_btree_iter_peek_slot(iter);
+	ret = bkey_err(k);
 	if (ret) {
 		bch2_trans_iter_exit(trans, iter);
 		return ret;
 	}
 
-	update = __bch2_btree_trans_peek_updates(iter);
-	*u = update && !bpos_cmp(update->k.p, pos)
-		? bch2_alloc_unpack(bkey_i_to_s_c(update))
-		: alloc_mem_to_key(c, iter);
-
+	*u = bch2_alloc_unpack(k);
 	return 0;
 }