bcachefs: Keep a sorted list of btree iterators

This will be used to make other operations on btree iterators within a
transaction more efficient, and enable some other improvements to how we
manage btree iterators.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.h

@@ -71,6 +71,36 @@ __trans_next_iter(struct btree_trans *trans, unsigned idx)
 	     (_iter);							\
 	     _iter = __trans_next_iter((_trans), (_iter)->idx + 1))
 
+static inline struct btree_iter *next_btree_iter(struct btree_trans *trans, struct btree_iter *iter)
+{
+	unsigned idx = iter ? iter->sorted_idx + 1 : 0;
+
+	EBUG_ON(idx > trans->nr_sorted);
+
+	return idx < trans->nr_sorted
+		? trans->iters + trans->sorted[idx]
+		: NULL;
+}
+
+static inline struct btree_iter *prev_btree_iter(struct btree_trans *trans, struct btree_iter *iter)
+{
+	unsigned idx = iter ? iter->sorted_idx : trans->nr_sorted;
+
+	return idx
+		? trans->iters + trans->sorted[idx - 1]
+		: NULL;
+}
+
+#define trans_for_each_iter_inorder(_trans, _iter, _i)			\
+	for (_i = 0;							\
+	     ((_iter) = (_trans)->iters + trans->sorted[_i]), (_i) < (_trans)->nr_sorted;\
+	     _i++)
+
+#define trans_for_each_iter_inorder_reverse(_trans, _iter, _i)		\
+	for (_i = trans->nr_sorted - 1;					\
+	     ((_iter) = (_trans)->iters + trans->sorted[_i]), (_i) >= 0;\
+	     --_i)
+
 static inline bool __iter_has_node(const struct btree_iter *iter,
 				   const struct btree *b)
 {
@@ -191,19 +221,14 @@ static inline void bch2_btree_iter_set_pos_to_extent_start(struct btree_iter *it
 	iter->pos = bkey_start_pos(&iter->k);
 }
 
-static inline struct btree_iter *btree_iter_child(struct btree_iter *iter)
+static inline struct btree_iter *idx_to_btree_iter(struct btree_trans *trans, unsigned idx)
 {
-	return iter->child_idx == U8_MAX ? NULL
-		: iter->trans->iters + iter->child_idx;
+	return idx != U8_MAX ? trans->iters + idx : NULL;
 }
 
-/* Sort order for locking btree iterators: */
-static inline int btree_iter_lock_cmp(const struct btree_iter *l,
-				      const struct btree_iter *r)
+static inline struct btree_iter *btree_iter_child(struct btree_iter *iter)
 {
-	return   cmp_int(l->btree_id, r->btree_id) ?:
-		-cmp_int(btree_iter_is_cached(l), btree_iter_is_cached(r)) ?:
-		 bkey_cmp(l->real_pos, r->real_pos);
+	return idx_to_btree_iter(iter->trans, iter->child_idx);
 }
 
 /*

fs/bcachefs/btree_types.h

@@ -246,6 +246,7 @@ struct btree_iter {
 
 	u8			idx;
 	u8			child_idx;
+	u8			sorted_idx;
 
 	/* btree_iter_copy starts here: */
 	u16			flags;
@@ -379,11 +380,13 @@ struct btree_trans {
 	unsigned long		ip;
 	int			srcu_idx;
 
+	u8			nr_sorted;
 	u8			nr_updates;
 	bool			used_mempool:1;
 	bool			error:1;
 	bool			in_traverse_all:1;
 	bool			restarted:1;
+	bool			iters_sorted:1;
 	/*
 	 * For when bch2_trans_update notices we'll be splitting a compressed
 	 * extent:
@@ -398,6 +401,7 @@ struct btree_trans {
 	unsigned		mem_bytes;
 	void			*mem;
 
+	u8			sorted[BTREE_ITER_MAX + 8];
 	struct btree_iter	*iters;
 	struct btree_insert_entry *updates;
 

fs/bcachefs/util.h

@@ -593,6 +593,20 @@ static inline void memmove_u64s_down(void *dst, const void *src,
 	__memmove_u64s_down(dst, src, u64s);
 }
 
+static inline void __memmove_u64s_down_small(void *dst, const void *src,
+				       unsigned u64s)
+{
+	memcpy_u64s_small(dst, src, u64s);
+}
+
+static inline void memmove_u64s_down_small(void *dst, const void *src,
+				     unsigned u64s)
+{
+	EBUG_ON(dst > src);
+
+	__memmove_u64s_down_small(dst, src, u64s);
+}
+
 static inline void __memmove_u64s_up_small(void *_dst, const void *_src,
 					   unsigned u64s)
 {