bcachefs: trans->nr_paths

Start to plumb through dynamically growable btree_paths; this patch
replaces most BTREE_ITER_MAX references with trans->nr_paths.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -1475,7 +1475,7 @@ static void bch2_trans_update_max_paths(struct btree_trans *trans)
 {
 	struct btree_transaction_stats *s = btree_trans_stats(trans);
 	struct printbuf buf = PRINTBUF;
-	size_t nr = bitmap_weight(trans->paths_allocated, BTREE_ITER_MAX);
+	size_t nr = bitmap_weight(trans->paths_allocated, trans->nr_paths);
 
 	if (!s)
 		return;
@@ -1521,9 +1521,9 @@ static noinline void btree_path_overflow(struct btree_trans *trans)
 static inline btree_path_idx_t btree_path_alloc(struct btree_trans *trans,
 						btree_path_idx_t pos)
 {
-	btree_path_idx_t idx = find_first_zero_bit(trans->paths_allocated, BTREE_ITER_MAX);
+	btree_path_idx_t idx = find_first_zero_bit(trans->paths_allocated, trans->nr_paths);
 
-	if (unlikely(idx == BTREE_ITER_MAX))
+	if (unlikely(idx == trans->nr_paths))
 		btree_path_overflow(trans);
 
 	/*
@@ -2527,7 +2527,7 @@ static void btree_trans_verify_sorted_refs(struct btree_trans *trans)
 	struct btree_path *path;
 	unsigned i;
 
-	BUG_ON(trans->nr_sorted != bitmap_weight(trans->paths_allocated, BTREE_ITER_MAX) - 1);
+	BUG_ON(trans->nr_sorted != bitmap_weight(trans->paths_allocated, trans->nr_paths) - 1);
 
 	trans_for_each_path(trans, path, i) {
 		BUG_ON(path->sorted_idx >= trans->nr_sorted);
@@ -2933,6 +2933,7 @@ struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx)
 	trans->journal_replay_not_finished =
 		unlikely(!test_bit(JOURNAL_REPLAY_DONE, &c->journal.flags)) &&
 		atomic_inc_not_zero(&c->journal_keys.ref);
+	trans->nr_paths		= ARRAY_SIZE(trans->_paths);
 	trans->paths_allocated	= trans->_paths_allocated;
 	trans->sorted		= trans->_sorted;
 	trans->paths		= trans->_paths;

fs/bcachefs/btree_iter.h

@@ -82,9 +82,25 @@ static inline unsigned long *trans_paths_allocated(struct btree_path *paths)
 static inline struct btree_path *
 __trans_next_path(struct btree_trans *trans, unsigned *idx)
 {
-	*idx = find_next_bit(trans->paths_allocated, BTREE_ITER_MAX, *idx);
+	unsigned long *w = trans->paths_allocated + *idx / BITS_PER_LONG;
+	/*
+	 * Open coded find_next_bit(), because
+	 *  - this is fast path, we can't afford the function call
+	 *  - and we know that nr_paths is a multiple of BITS_PER_LONG,
+	 */
+	while (*idx < trans->nr_paths) {
+		unsigned long v = *w >> (*idx & (BITS_PER_LONG - 1));
+		if (v) {
+			*idx += __ffs(v);
+			return trans->paths + *idx;
+		}
+
+		*idx += BITS_PER_LONG;
+		*idx &= ~(BITS_PER_LONG - 1);
+		w++;
+	}
 
-	return *idx < BTREE_ITER_MAX ? &trans->paths[*idx] : NULL;
+	return NULL;
 }
 
 /*
@@ -626,7 +642,7 @@ int __bch2_btree_trans_too_many_iters(struct btree_trans *);
 
 static inline int btree_trans_too_many_iters(struct btree_trans *trans)
 {
-	if (bitmap_weight(trans->paths_allocated, BTREE_ITER_MAX) > BTREE_ITER_MAX - 8)
+	if (bitmap_weight(trans->paths_allocated, trans->nr_paths) > BTREE_ITER_MAX - 8)
 		return __bch2_btree_trans_too_many_iters(trans);
 
 	return 0;

fs/bcachefs/btree_types.h

@@ -390,6 +390,7 @@ struct btree_trans {
 	unsigned		mem_bytes;
 
 	btree_path_idx_t	nr_sorted;
+	btree_path_idx_t	nr_paths;
 	btree_path_idx_t	nr_paths_max;
 	u8			fn_idx;
 	u8			nr_updates;

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 >= BTREE_ITER_MAX);
+	EBUG_ON(trans->nr_updates >= trans->nr_paths);
 	EBUG_ON(!bpos_eq(k->k.p, path->pos));
 
 	n = (struct btree_insert_entry) {