bcachefs: trans->updates will also be resizable

the reflink triggers are also bumping up against the maximum number of
paths in a transaction - and generating proportional numbers of updates.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -2888,7 +2888,7 @@ struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx)
 	if (IS_ENABLED(__KERNEL__)) {
 		trans = this_cpu_xchg(c->btree_trans_bufs->trans, NULL);
 		if (trans) {
-			memset(trans, 0, offsetof(struct btree_trans, updates));
+			memset(trans, 0, offsetof(struct btree_trans, list));
 			goto got_trans;
 		}
 	}
@@ -2936,6 +2936,7 @@ struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx)
 	trans->paths_allocated	= trans->_paths_allocated;
 	trans->sorted		= trans->_sorted;
 	trans->paths		= trans->_paths;
+	trans->updates		= trans->_updates;
 
 	*trans_paths_nr(trans->paths) = BTREE_ITER_MAX;
 

fs/bcachefs/btree_types.h

@@ -383,6 +383,7 @@ struct btree_trans {
 	unsigned long		*paths_allocated;
 	struct btree_path	*paths;
 	u8			*sorted;
+	struct btree_insert_entry *updates;
 
 	void			*mem;
 	unsigned		mem_top;
@@ -433,8 +434,6 @@ struct btree_trans {
 
 	/* Entries before this are zeroed out on every bch2_trans_get() call */
 
-	struct btree_insert_entry updates[BTREE_ITER_MAX];
-
 	struct list_head	list;
 	struct closure		ref;
 
@@ -442,6 +441,7 @@ struct btree_trans {
 	struct btree_trans_paths trans_paths;
 	struct btree_path	_paths[BTREE_ITER_MAX];
 	u8			_sorted[BTREE_ITER_MAX + 8];
+	struct btree_insert_entry _updates[BTREE_ITER_MAX];
 };
 
 static inline struct btree_path *btree_iter_path(struct btree_trans *trans, struct btree_iter *iter)

fs/bcachefs/btree_update.c

@@ -386,7 +386,7 @@ bch2_trans_update_by_path(struct btree_trans *trans, btree_path_idx_t path_idx,
 
 	struct btree_path *path = trans->paths + path_idx;
 	EBUG_ON(!path->should_be_locked);
-	EBUG_ON(trans->nr_updates >= ARRAY_SIZE(trans->updates));
+	EBUG_ON(trans->nr_updates >= BTREE_ITER_MAX);
 	EBUG_ON(!bpos_eq(k->k.p, path->pos));
 
 	n = (struct btree_insert_entry) {