Merging upstream version 6.8.9.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 477 insertions, 470 deletions

diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index 816ecc3375..3ef338df82 100644
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -13,6 +13,7 @@
 #include "error.h"
 #include "extents.h"
 #include "journal.h"
+#include "journal_io.h"
 #include "replicas.h"
 #include "snapshot.h"
 #include "trace.h"
@@ -21,8 +22,8 @@
 #include <linux/prefetch.h>
 
 static inline void btree_path_list_remove(struct btree_trans *, struct btree_path *);
-static inline void btree_path_list_add(struct btree_trans *, struct btree_path *,
-				       struct btree_path *);
+static inline void btree_path_list_add(struct btree_trans *,
+			btree_path_idx_t, btree_path_idx_t);
 
 static inline unsigned long btree_iter_ip_allocated(struct btree_iter *iter)
 {
@@ -33,7 +34,8 @@ static inline unsigned long btree_iter_ip_allocated(struct btree_iter *iter)
 #endif
 }
 
-static struct btree_path *btree_path_alloc(struct btree_trans *, struct btree_path *);
+static btree_path_idx_t btree_path_alloc(struct btree_trans *, btree_path_idx_t);
+static void bch2_trans_srcu_lock(struct btree_trans *);
 
 static inline int __btree_path_cmp(const struct btree_path *l,
 				   enum btree_id	r_btree_id,
@@ -239,8 +241,9 @@ static void bch2_btree_path_verify(struct btree_trans *trans,
 void bch2_trans_verify_paths(struct btree_trans *trans)
 {
 	struct btree_path *path;
+	unsigned iter;
 
-	trans_for_each_path(trans, path)
+	trans_for_each_path(trans, path, iter)
 		bch2_btree_path_verify(trans, path);
 }
 
@@ -250,7 +253,7 @@ static void bch2_btree_iter_verify(struct btree_iter *iter)
 
 	BUG_ON(iter->btree_id >= BTREE_ID_NR);
 
-	BUG_ON(!!(iter->flags & BTREE_ITER_CACHED) != iter->path->cached);
+	BUG_ON(!!(iter->flags & BTREE_ITER_CACHED) != btree_iter_path(trans, iter)->cached);
 
 	BUG_ON((iter->flags & BTREE_ITER_IS_EXTENTS) &&
 	       (iter->flags & BTREE_ITER_ALL_SNAPSHOTS));
@@ -260,8 +263,8 @@ static void bch2_btree_iter_verify(struct btree_iter *iter)
 	       !btree_type_has_snapshot_field(iter->btree_id));
 
 	if (iter->update_path)
-		bch2_btree_path_verify(trans, iter->update_path);
-	bch2_btree_path_verify(trans, iter->path);
+		bch2_btree_path_verify(trans, &trans->paths[iter->update_path]);
+	bch2_btree_path_verify(trans, btree_iter_path(trans, iter));
 }
 
 static void bch2_btree_iter_verify_entry_exit(struct btree_iter *iter)
@@ -330,12 +333,12 @@ void bch2_assert_pos_locked(struct btree_trans *trans, enum btree_id id,
 			    struct bpos pos, bool key_cache)
 {
 	struct btree_path *path;
-	unsigned idx;
+	struct trans_for_each_path_inorder_iter iter;
 	struct printbuf buf = PRINTBUF;
 
 	btree_trans_sort_paths(trans);
 
-	trans_for_each_path_inorder(trans, path, idx) {
+	trans_for_each_path_inorder(trans, path, iter) {
 		int cmp = cmp_int(path->btree_id, id) ?:
 			cmp_int(path->cached, key_cache);
 
@@ -415,8 +418,9 @@ void bch2_btree_path_fix_key_modified(struct btree_trans *trans,
 				      struct bkey_packed *where)
 {
 	struct btree_path *path;
+	unsigned i;
 
-	trans_for_each_path_with_node(trans, b, path) {
+	trans_for_each_path_with_node(trans, b, path, i) {
 		__bch2_btree_path_fix_key_modified(path, b, where);
 		bch2_btree_path_verify_level(trans, path, b->c.level);
 	}
@@ -523,6 +527,7 @@ void bch2_btree_node_iter_fix(struct btree_trans *trans,
 {
 	struct bset_tree *t = bch2_bkey_to_bset_inlined(b, where);
 	struct btree_path *linked;
+	unsigned i;
 
 	if (node_iter != &path->l[b->c.level].iter) {
 		__bch2_btree_node_iter_fix(path, b, node_iter, t,
@@ -532,7 +537,7 @@ void bch2_btree_node_iter_fix(struct btree_trans *trans,
 			bch2_btree_node_iter_verify(node_iter, b);
 	}
 
-	trans_for_each_path_with_node(trans, b, linked) {
+	trans_for_each_path_with_node(trans, b, linked, i) {
 		__bch2_btree_node_iter_fix(linked, b,
 					   &linked->l[b->c.level].iter, t,
 					   where, clobber_u64s, new_u64s);
@@ -647,7 +652,6 @@ void bch2_btree_path_level_init(struct btree_trans *trans,
 static void bch2_trans_revalidate_updates_in_node(struct btree_trans *trans, struct btree *b)
 {
 	struct bch_fs *c = trans->c;
-	struct btree_insert_entry *i;
 
 	trans_for_each_update(trans, i)
 		if (!i->cached &&
@@ -655,7 +659,7 @@ static void bch2_trans_revalidate_updates_in_node(struct btree_trans *trans, str
 		    i->btree_id	== b->c.btree_id &&
 		    bpos_cmp(i->k->k.p, b->data->min_key) >= 0 &&
 		    bpos_cmp(i->k->k.p, b->data->max_key) <= 0) {
-			i->old_v = bch2_btree_path_peek_slot(i->path, &i->old_k).v;
+			i->old_v = bch2_btree_path_peek_slot(trans->paths + i->path, &i->old_k).v;
 
 			if (unlikely(trans->journal_replay_not_finished)) {
 				struct bkey_i *j_k =
@@ -674,14 +678,22 @@ static void bch2_trans_revalidate_updates_in_node(struct btree_trans *trans, str
  * A btree node is being replaced - update the iterator to point to the new
  * node:
  */
-void bch2_trans_node_add(struct btree_trans *trans, struct btree *b)
+void bch2_trans_node_add(struct btree_trans *trans,
+			 struct btree_path *path,
+			 struct btree *b)
 {
-	struct btree_path *path;
+	struct btree_path *prev;
+
+	BUG_ON(!btree_path_pos_in_node(path, b));
+
+	while ((prev = prev_btree_path(trans, path)) &&
+	       btree_path_pos_in_node(prev, b))
+		path = prev;
 
-	trans_for_each_path(trans, path)
-		if (path->uptodate == BTREE_ITER_UPTODATE &&
-		    !path->cached &&
-		    btree_path_pos_in_node(path, b)) {
+	for (;
+	     path && btree_path_pos_in_node(path, b);
+	     path = next_btree_path(trans, path))
+		if (path->uptodate == BTREE_ITER_UPTODATE && !path->cached) {
 			enum btree_node_locked_type t =
 				btree_lock_want(path, b->c.level);
 
@@ -704,8 +716,9 @@ void bch2_trans_node_add(struct btree_trans *trans, struct btree *b)
 void bch2_trans_node_reinit_iter(struct btree_trans *trans, struct btree *b)
 {
 	struct btree_path *path;
+	unsigned i;
 
-	trans_for_each_path_with_node(trans, b, path)
+	trans_for_each_path_with_node(trans, b, path, i)
 		__btree_path_level_init(path, b->c.level);
 
 	bch2_trans_revalidate_updates_in_node(trans, b);
@@ -781,7 +794,7 @@ static int btree_path_prefetch(struct btree_trans *trans, struct btree_path *pat
 	struct btree_node_iter node_iter = l->iter;
 	struct bkey_packed *k;
 	struct bkey_buf tmp;
-	unsigned nr = test_bit(BCH_FS_STARTED, &c->flags)
+	unsigned nr = test_bit(BCH_FS_started, &c->flags)
 		? (path->level > 1 ? 0 :  2)
 		: (path->level > 1 ? 1 : 16);
 	bool was_locked = btree_node_locked(path, path->level);
@@ -816,7 +829,7 @@ static int btree_path_prefetch_j(struct btree_trans *trans, struct btree_path *p
 	struct bch_fs *c = trans->c;
 	struct bkey_s_c k;
 	struct bkey_buf tmp;
-	unsigned nr = test_bit(BCH_FS_STARTED, &c->flags)
+	unsigned nr = test_bit(BCH_FS_started, &c->flags)
 		? (path->level > 1 ? 0 :  2)
 		: (path->level > 1 ? 1 : 16);
 	bool was_locked = btree_node_locked(path, path->level);
@@ -884,7 +897,8 @@ static noinline int btree_node_iter_and_journal_peek(struct btree_trans *trans,
 
 	bch2_bkey_buf_reassemble(out, c, k);
 
-	if (flags & BTREE_ITER_PREFETCH)
+	if ((flags & BTREE_ITER_PREFETCH) &&
+	    c->opts.btree_node_prefetch)
 		ret = btree_path_prefetch_j(trans, path, &jiter);
 
 	bch2_btree_and_journal_iter_exit(&jiter);
@@ -916,7 +930,8 @@ static __always_inline int btree_path_down(struct btree_trans *trans,
 		bch2_bkey_buf_unpack(&tmp, c, l->b,
 				 bch2_btree_node_iter_peek(&l->iter, l->b));
 
-		if (flags & BTREE_ITER_PREFETCH) {
+		if ((flags & BTREE_ITER_PREFETCH) &&
+		    c->opts.btree_node_prefetch) {
 			ret = btree_path_prefetch(trans, path);
 			if (ret)
 				goto err;
@@ -953,7 +968,8 @@ static int bch2_btree_path_traverse_all(struct btree_trans *trans)
 	struct bch_fs *c = trans->c;
 	struct btree_path *path;
 	unsigned long trace_ip = _RET_IP_;
-	int i, ret = 0;
+	unsigned i;
+	int ret = 0;
 
 	if (trans->in_traverse_all)
 		return -BCH_ERR_transaction_restart_in_traverse_all;
@@ -963,7 +979,7 @@ retry_all:
 	trans->restarted = 0;
 	trans->last_restarted_ip = 0;
 
-	trans_for_each_path(trans, path)
+	trans_for_each_path(trans, path, i)
 		path->should_be_locked = false;
 
 	btree_trans_sort_paths(trans);
@@ -977,7 +993,7 @@ retry_all:
 		closure_init_stack(&cl);
 
 		do {
-			ret = bch2_btree_cache_cannibalize_lock(c, &cl);
+			ret = bch2_btree_cache_cannibalize_lock(trans, &cl);
 			closure_sync(&cl);
 		} while (ret);
 	}
@@ -985,16 +1001,16 @@ retry_all:
 	/* Now, redo traversals in correct order: */
 	i = 0;
 	while (i < trans->nr_sorted) {
-		path = trans->paths + trans->sorted[i];
+		btree_path_idx_t idx = trans->sorted[i];
 
 		/*
 		 * Traversing a path can cause another path to be added at about
 		 * the same position:
 		 */
-		if (path->uptodate) {
-			__btree_path_get(path, false);
-			ret = bch2_btree_path_traverse_one(trans, path, 0, _THIS_IP_);
-			__btree_path_put(path, false);
+		if (trans->paths[idx].uptodate) {
+			__btree_path_get(&trans->paths[idx], false);
+			ret = bch2_btree_path_traverse_one(trans, idx, 0, _THIS_IP_);
+			__btree_path_put(&trans->paths[idx], false);
 
 			if (bch2_err_matches(ret, BCH_ERR_transaction_restart) ||
 			    bch2_err_matches(ret, ENOMEM))
@@ -1013,7 +1029,7 @@ retry_all:
 	 * then failed to relock a path - that's fine.
 	 */
 err:
-	bch2_btree_cache_cannibalize_unlock(c);
+	bch2_btree_cache_cannibalize_unlock(trans);
 
 	trans->in_traverse_all = false;
 
@@ -1099,10 +1115,11 @@ static inline unsigned btree_path_up_until_good_node(struct btree_trans *trans,
  * stashed in the iterator and returned from bch2_trans_exit().
  */
 int bch2_btree_path_traverse_one(struct btree_trans *trans,
-				 struct btree_path *path,
+				 btree_path_idx_t path_idx,
 				 unsigned flags,
 				 unsigned long trace_ip)
 {
+	struct btree_path *path = &trans->paths[path_idx];
 	unsigned depth_want = path->level;
 	int ret = -((int) trans->restarted);
 
@@ -1126,6 +1143,8 @@ int bch2_btree_path_traverse_one(struct btree_trans *trans,
 		goto out;
 	}
 
+	path = &trans->paths[path_idx];
+
 	if (unlikely(path->level >= BTREE_MAX_DEPTH))
 		goto out;
 
@@ -1188,39 +1207,38 @@ static inline void btree_path_copy(struct btree_trans *trans, struct btree_path
 	}
 }
 
-static struct btree_path *btree_path_clone(struct btree_trans *trans, struct btree_path *src,
-					   bool intent)
+static btree_path_idx_t btree_path_clone(struct btree_trans *trans, btree_path_idx_t src,
+					 bool intent)
 {
-	struct btree_path *new = btree_path_alloc(trans, src);
-
-	btree_path_copy(trans, new, src);
-	__btree_path_get(new, intent);
+	btree_path_idx_t new = btree_path_alloc(trans, src);
+	btree_path_copy(trans, trans->paths + new, trans->paths + src);
+	__btree_path_get(trans->paths + new, intent);
 	return new;
 }
 
 __flatten
-struct btree_path *__bch2_btree_path_make_mut(struct btree_trans *trans,
-			 struct btree_path *path, bool intent,
-			 unsigned long ip)
+btree_path_idx_t __bch2_btree_path_make_mut(struct btree_trans *trans,
+			btree_path_idx_t path, bool intent, unsigned long ip)
 {
-	__btree_path_put(path, intent);
+	__btree_path_put(trans->paths + path, intent);
 	path = btree_path_clone(trans, path, intent);
-	path->preserve = false;
+	trans->paths[path].preserve = false;
 	return path;
 }
 
-struct btree_path * __must_check
+btree_path_idx_t __must_check
 __bch2_btree_path_set_pos(struct btree_trans *trans,
-		   struct btree_path *path, struct bpos new_pos,
-		   bool intent, unsigned long ip, int cmp)
+			  btree_path_idx_t path_idx, struct bpos new_pos,
+			  bool intent, unsigned long ip)
 {
-	unsigned level = path->level;
+	int cmp = bpos_cmp(new_pos, trans->paths[path_idx].pos);
 
 	bch2_trans_verify_not_in_restart(trans);
-	EBUG_ON(!path->ref);
+	EBUG_ON(!trans->paths[path_idx].ref);
 
-	path = bch2_btree_path_make_mut(trans, path, intent, ip);
+	path_idx = bch2_btree_path_make_mut(trans, path_idx, intent, ip);
 
+	struct btree_path *path = trans->paths + path_idx;
 	path->pos		= new_pos;
 	trans->paths_sorted	= false;
 
@@ -1231,7 +1249,7 @@ __bch2_btree_path_set_pos(struct btree_trans *trans,
 		goto out;
 	}
 
-	level = btree_path_up_until_good_node(trans, path, cmp);
+	unsigned level = btree_path_up_until_good_node(trans, path, cmp);
 
 	if (btree_path_node(path, level)) {
 		struct btree_path_level *l = &path->l[level];
@@ -1261,7 +1279,7 @@ __bch2_btree_path_set_pos(struct btree_trans *trans,
 	}
 out:
 	bch2_btree_path_verify(trans, path);
-	return path;
+	return path_idx;
 }
 
 /* Btree path: main interface: */
@@ -1296,19 +1314,16 @@ static struct btree_path *have_node_at_pos(struct btree_trans *trans, struct btr
 	return NULL;
 }
 
-static inline void __bch2_path_free(struct btree_trans *trans, struct btree_path *path)
+static inline void __bch2_path_free(struct btree_trans *trans, btree_path_idx_t path)
 {
-	__bch2_btree_path_unlock(trans, path);
-	btree_path_list_remove(trans, path);
-	trans->paths_allocated &= ~(1ULL << path->idx);
+	__bch2_btree_path_unlock(trans, trans->paths + path);
+	btree_path_list_remove(trans, trans->paths + path);
+	__clear_bit(path, trans->paths_allocated);
 }
 
-void bch2_path_put(struct btree_trans *trans, struct btree_path *path, bool intent)
+void bch2_path_put(struct btree_trans *trans, btree_path_idx_t path_idx, bool intent)
 {
-	struct btree_path *dup;
-
-	EBUG_ON(trans->paths + path->idx != path);
-	EBUG_ON(!path->ref);
+	struct btree_path *path = trans->paths + path_idx, *dup;
 
 	if (!__btree_path_put(path, intent))
 		return;
@@ -1322,7 +1337,7 @@ void bch2_path_put(struct btree_trans *trans, struct btree_path *path, bool inte
 
 	if (path->should_be_locked &&
 	    !trans->restarted &&
-	    (!dup || !bch2_btree_path_relock_norestart(trans, dup, _THIS_IP_)))
+	    (!dup || !bch2_btree_path_relock_norestart(trans, dup)))
 		return;
 
 	if (dup) {
@@ -1330,16 +1345,13 @@ void bch2_path_put(struct btree_trans *trans, struct btree_path *path, bool inte
 		dup->should_be_locked	|= path->should_be_locked;
 	}
 
-	__bch2_path_free(trans, path);
+	__bch2_path_free(trans, path_idx);
 }
 
-static void bch2_path_put_nokeep(struct btree_trans *trans, struct btree_path *path,
+static void bch2_path_put_nokeep(struct btree_trans *trans, btree_path_idx_t path,
 				 bool intent)
 {
-	EBUG_ON(trans->paths + path->idx != path);
-	EBUG_ON(!path->ref);
-
-	if (!__btree_path_put(path, intent))
+	if (!__btree_path_put(trans->paths + path, intent))
 		return;
 
 	__bch2_path_free(trans, path);
@@ -1362,9 +1374,6 @@ void __noreturn bch2_trans_in_restart_error(struct btree_trans *trans)
 noinline __cold
 void bch2_trans_updates_to_text(struct printbuf *buf, struct btree_trans *trans)
 {
-	struct btree_insert_entry *i;
-	struct btree_write_buffered_key *wb;
-
 	prt_printf(buf, "transaction updates for %s journal seq %llu",
 	       trans->fn, trans->journal_res.seq);
 	prt_newline(buf);
@@ -1388,16 +1397,10 @@ void bch2_trans_updates_to_text(struct printbuf *buf, struct btree_trans *trans)
 		prt_newline(buf);
 	}
 
-	trans_for_each_wb_update(trans, wb) {
-		prt_printf(buf, "update: btree=%s wb=1 %pS",
-		       bch2_btree_id_str(wb->btree),
-		       (void *) i->ip_allocated);
-		prt_newline(buf);
-
-		prt_printf(buf, "  new ");
-		bch2_bkey_val_to_text(buf, trans->c, bkey_i_to_s_c(&wb->k));
-		prt_newline(buf);
-	}
+	for (struct jset_entry *e = trans->journal_entries;
+	     e != btree_trans_journal_entries_top(trans);
+	     e = vstruct_next(e))
+		bch2_journal_entry_to_text(buf, trans->c, e);
 
 	printbuf_indent_sub(buf, 2);
 }
@@ -1412,11 +1415,12 @@ void bch2_dump_trans_updates(struct btree_trans *trans)
 	printbuf_exit(&buf);
 }
 
-noinline __cold
-void bch2_btree_path_to_text(struct printbuf *out, struct btree_path *path)
+static void bch2_btree_path_to_text(struct printbuf *out, struct btree_trans *trans, btree_path_idx_t path_idx)
 {
+	struct btree_path *path = trans->paths + path_idx;
+
 	prt_printf(out, "path: idx %2u ref %u:%u %c %c btree=%s l=%u pos ",
-		   path->idx, path->ref, path->intent_ref,
+		   path_idx, path->ref, path->intent_ref,
 		   path->preserve ? 'P' : ' ',
 		   path->should_be_locked ? 'S' : ' ',
 		   bch2_btree_id_str(path->btree_id),
@@ -1434,14 +1438,13 @@ static noinline __cold
 void __bch2_trans_paths_to_text(struct printbuf *out, struct btree_trans *trans,
 				bool nosort)
 {
-	struct btree_path *path;
-	unsigned idx;
+	struct trans_for_each_path_inorder_iter iter;
 
 	if (!nosort)
 		btree_trans_sort_paths(trans);
 
-	trans_for_each_path_inorder(trans, path, idx)
-		bch2_btree_path_to_text(out, path);
+	trans_for_each_path_idx_inorder(trans, iter)
+		bch2_btree_path_to_text(out, trans, iter.path_idx);
 }
 
 noinline __cold
@@ -1473,17 +1476,14 @@ static void bch2_trans_update_max_paths(struct btree_trans *trans)
 {
 	struct btree_transaction_stats *s = btree_trans_stats(trans);
 	struct printbuf buf = PRINTBUF;
-
-	if (!s)
-		return;
+	size_t nr = bitmap_weight(trans->paths_allocated, trans->nr_paths);
 
 	bch2_trans_paths_to_text(&buf, trans);
 
 	if (!buf.allocation_failure) {
 		mutex_lock(&s->lock);
-		if (s->nr_max_paths < hweight64(trans->paths_allocated)) {
-			s->nr_max_paths = trans->nr_max_paths =
-				hweight64(trans->paths_allocated);
+		if (nr > s->nr_max_paths) {
+			s->nr_max_paths = nr;
 			swap(s->max_paths_text, buf.buf);
 		}
 		mutex_unlock(&s->lock);
@@ -1491,64 +1491,121 @@ static void bch2_trans_update_max_paths(struct btree_trans *trans)
 
 	printbuf_exit(&buf);
 
-	trans->nr_max_paths = hweight64(trans->paths_allocated);
+	trans->nr_paths_max = nr;
+}
+
+noinline __cold
+int __bch2_btree_trans_too_many_iters(struct btree_trans *trans)
+{
+	if (trace_trans_restart_too_many_iters_enabled()) {
+		struct printbuf buf = PRINTBUF;
+
+		bch2_trans_paths_to_text(&buf, trans);
+		trace_trans_restart_too_many_iters(trans, _THIS_IP_, buf.buf);
+		printbuf_exit(&buf);
+	}
+
+	count_event(trans->c, trans_restart_too_many_iters);
+
+	return btree_trans_restart(trans, BCH_ERR_transaction_restart_too_many_iters);
 }
 
 static noinline void btree_path_overflow(struct btree_trans *trans)
 {
 	bch2_dump_trans_paths_updates(trans);
-	panic("trans path overflow\n");
+	bch_err(trans->c, "trans path overflow");
 }
 
-static inline struct btree_path *btree_path_alloc(struct btree_trans *trans,
-						  struct btree_path *pos)
+static noinline void btree_paths_realloc(struct btree_trans *trans)
 {
-	struct btree_path *path;
-	unsigned idx;
+	unsigned nr = trans->nr_paths * 2;
+
+	void *p = kzalloc(BITS_TO_LONGS(nr) * sizeof(unsigned long) +
+			  sizeof(struct btree_trans_paths) +
+			  nr * sizeof(struct btree_path) +
+			  nr * sizeof(btree_path_idx_t) + 8 +
+			  nr * sizeof(struct btree_insert_entry), GFP_KERNEL|__GFP_NOFAIL);
+
+	unsigned long *paths_allocated = p;
+	memcpy(paths_allocated, trans->paths_allocated, BITS_TO_LONGS(trans->nr_paths) * sizeof(unsigned long));
+	p += BITS_TO_LONGS(nr) * sizeof(unsigned long);
+
+	p += sizeof(struct btree_trans_paths);
+	struct btree_path *paths = p;
+	*trans_paths_nr(paths) = nr;
+	memcpy(paths, trans->paths, trans->nr_paths * sizeof(struct btree_path));
+	p += nr * sizeof(struct btree_path);
+
+	btree_path_idx_t *sorted = p;
+	memcpy(sorted, trans->sorted, trans->nr_sorted * sizeof(btree_path_idx_t));
+	p += nr * sizeof(btree_path_idx_t) + 8;
+
+	struct btree_insert_entry *updates = p;
+	memcpy(updates, trans->updates, trans->nr_paths * sizeof(struct btree_insert_entry));
+
+	unsigned long *old = trans->paths_allocated;
 
-	if (unlikely(trans->paths_allocated ==
-		     ~((~0ULL << 1) << (BTREE_ITER_MAX - 1))))
-		btree_path_overflow(trans);
+	rcu_assign_pointer(trans->paths_allocated,	paths_allocated);
+	rcu_assign_pointer(trans->paths,		paths);
+	rcu_assign_pointer(trans->sorted,		sorted);
+	rcu_assign_pointer(trans->updates,		updates);
 
-	idx = __ffs64(~trans->paths_allocated);
+	trans->nr_paths		= nr;
+
+	if (old != trans->_paths_allocated)
+		kfree_rcu_mightsleep(old);
+}
+
+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, trans->nr_paths);
+
+	if (unlikely(idx == trans->nr_paths)) {
+		if (trans->nr_paths == BTREE_ITER_MAX) {
+			btree_path_overflow(trans);
+			return 0;
+		}
+
+		btree_paths_realloc(trans);
+	}
 
 	/*
 	 * Do this before marking the new path as allocated, since it won't be
 	 * initialized yet:
 	 */
-	if (unlikely(idx > trans->nr_max_paths))
+	if (unlikely(idx > trans->nr_paths_max))
 		bch2_trans_update_max_paths(trans);
 
-	trans->paths_allocated |= 1ULL << idx;
+	__set_bit(idx, trans->paths_allocated);
 
-	path = &trans->paths[idx];
-	path->idx		= idx;
+	struct btree_path *path = &trans->paths[idx];
 	path->ref		= 0;
 	path->intent_ref	= 0;
 	path->nodes_locked	= 0;
-	path->alloc_seq++;
 
-	btree_path_list_add(trans, pos, path);
+	btree_path_list_add(trans, pos, idx);
 	trans->paths_sorted = false;
-	return path;
+	return idx;
 }
 
-struct btree_path *bch2_path_get(struct btree_trans *trans,
-				 enum btree_id btree_id, struct bpos pos,
-				 unsigned locks_want, unsigned level,
-				 unsigned flags, unsigned long ip)
+btree_path_idx_t bch2_path_get(struct btree_trans *trans,
+			     enum btree_id btree_id, struct bpos pos,
+			     unsigned locks_want, unsigned level,
+			     unsigned flags, unsigned long ip)
 {
-	struct btree_path *path, *path_pos = NULL;
+	struct btree_path *path;
 	bool cached = flags & BTREE_ITER_CACHED;
 	bool intent = flags & BTREE_ITER_INTENT;
-	int i;
+	struct trans_for_each_path_inorder_iter iter;
+	btree_path_idx_t path_pos = 0, path_idx;
 
 	bch2_trans_verify_not_in_restart(trans);
 	bch2_trans_verify_locks(trans);
 
 	btree_trans_sort_paths(trans);
 
-	trans_for_each_path_inorder(trans, path, i) {
+	trans_for_each_path_inorder(trans, path, iter) {
 		if (__btree_path_cmp(path,
 				     btree_id,
 				     cached,
@@ -1556,18 +1613,19 @@ struct btree_path *bch2_path_get(struct btree_trans *trans,
 				     level) > 0)
 			break;
 
-		path_pos = path;
+		path_pos = iter.path_idx;
 	}
 
 	if (path_pos &&
-	    path_pos->cached	== cached &&
-	    path_pos->btree_id	== btree_id &&
-	    path_pos->level	== level) {
-		__btree_path_get(path_pos, intent);
-		path = bch2_btree_path_set_pos(trans, path_pos, pos, intent, ip);
+	    trans->paths[path_pos].cached	== cached &&
+	    trans->paths[path_pos].btree_id	== btree_id &&
+	    trans->paths[path_pos].level	== level) {
+		__btree_path_get(trans->paths + path_pos, intent);
+		path_idx = bch2_btree_path_set_pos(trans, path_pos, pos, intent, ip);
+		path = trans->paths + path_idx;
 	} else {
-		path = btree_path_alloc(trans, path_pos);
-		path_pos = NULL;
+		path_idx = btree_path_alloc(trans, path_pos);
+		path = trans->paths + path_idx;
 
 		__btree_path_get(path, intent);
 		path->pos			= pos;
@@ -1578,7 +1636,7 @@ struct btree_path *bch2_path_get(struct btree_trans *trans,
 		path->level			= level;
 		path->locks_want		= locks_want;
 		path->nodes_locked		= 0;
-		for (i = 0; i < ARRAY_SIZE(path->l); i++)
+		for (unsigned i = 0; i < ARRAY_SIZE(path->l); i++)
 			path->l[i].b		= ERR_PTR(-BCH_ERR_no_btree_node_init);
 #ifdef TRACK_PATH_ALLOCATED
 		path->ip_allocated		= ip;
@@ -1604,7 +1662,7 @@ struct btree_path *bch2_path_get(struct btree_trans *trans,
 	if (locks_want > path->locks_want)
 		bch2_btree_path_upgrade_noupgrade_sibs(trans, path, locks_want, NULL);
 
-	return path;
+	return path_idx;
 }
 
 struct bkey_s_c bch2_btree_path_peek_slot(struct btree_path *path, struct bkey *u)
@@ -1659,9 +1717,10 @@ __bch2_btree_iter_traverse(struct btree_iter *iter)
 int __must_check
 bch2_btree_iter_traverse(struct btree_iter *iter)
 {
+	struct btree_trans *trans = iter->trans;
 	int ret;
 
-	iter->path = bch2_btree_path_set_pos(iter->trans, iter->path,
+	iter->path = bch2_btree_path_set_pos(trans, iter->path,
 					btree_iter_search_key(iter),
 					iter->flags & BTREE_ITER_INTENT,
 					btree_iter_ip_allocated(iter));
@@ -1670,7 +1729,7 @@ bch2_btree_iter_traverse(struct btree_iter *iter)
 	if (ret)
 		return ret;
 
-	btree_path_set_should_be_locked(iter->path);
+	btree_path_set_should_be_locked(trans->paths + iter->path);
 	return 0;
 }
 
@@ -1682,14 +1741,15 @@ struct btree *bch2_btree_iter_peek_node(struct btree_iter *iter)
 	struct btree *b = NULL;
 	int ret;
 
-	EBUG_ON(iter->path->cached);
+	EBUG_ON(trans->paths[iter->path].cached);
 	bch2_btree_iter_verify(iter);
 
 	ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
 	if (ret)
 		goto err;
 
-	b = btree_path_node(iter->path, iter->path->level);
+	struct btree_path *path = btree_iter_path(trans, iter);
+	b = btree_path_node(path, path->level);
 	if (!b)
 		goto out;
 
@@ -1701,7 +1761,7 @@ struct btree *bch2_btree_iter_peek_node(struct btree_iter *iter)
 	iter->path = bch2_btree_path_set_pos(trans, iter->path, b->key.k.p,
 					iter->flags & BTREE_ITER_INTENT,
 					btree_iter_ip_allocated(iter));
-	btree_path_set_should_be_locked(iter->path);
+	btree_path_set_should_be_locked(btree_iter_path(trans, iter));
 out:
 	bch2_btree_iter_verify_entry_exit(iter);
 	bch2_btree_iter_verify(iter);
@@ -1726,14 +1786,15 @@ struct btree *bch2_btree_iter_peek_node_and_restart(struct btree_iter *iter)
 struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
 {
 	struct btree_trans *trans = iter->trans;
-	struct btree_path *path = iter->path;
 	struct btree *b = NULL;
 	int ret;
 
+	EBUG_ON(trans->paths[iter->path].cached);
 	bch2_trans_verify_not_in_restart(trans);
-	EBUG_ON(iter->path->cached);
 	bch2_btree_iter_verify(iter);
 
+	struct btree_path *path = btree_iter_path(trans, iter);
+
 	/* already at end? */
 	if (!btree_path_node(path, path->level))
 		return NULL;
@@ -1763,17 +1824,19 @@ struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
 		 * Haven't gotten to the end of the parent node: go back down to
 		 * the next child node
 		 */
-		path = iter->path =
-			bch2_btree_path_set_pos(trans, path, bpos_successor(iter->pos),
-					   iter->flags & BTREE_ITER_INTENT,
-					   btree_iter_ip_allocated(iter));
+		iter->path = bch2_btree_path_set_pos(trans, iter->path,
+					bpos_successor(iter->pos),
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
 
+		path = btree_iter_path(trans, iter);
 		btree_path_set_level_down(trans, path, iter->min_depth);
 
-		ret = bch2_btree_path_traverse(trans, path, iter->flags);
+		ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
 		if (ret)
 			goto err;
 
+		path = btree_iter_path(trans, iter);
 		b = path->l[path->level].b;
 	}
 
@@ -1783,8 +1846,8 @@ struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
 	iter->path = bch2_btree_path_set_pos(trans, iter->path, b->key.k.p,
 					iter->flags & BTREE_ITER_INTENT,
 					btree_iter_ip_allocated(iter));
-	btree_path_set_should_be_locked(iter->path);
-	BUG_ON(iter->path->uptodate);
+	btree_path_set_should_be_locked(btree_iter_path(trans, iter));
+	EBUG_ON(btree_iter_path(trans, iter)->uptodate);
 out:
 	bch2_btree_iter_verify_entry_exit(iter);
 	bch2_btree_iter_verify(iter);
@@ -1799,23 +1862,15 @@ err:
 
 inline bool bch2_btree_iter_advance(struct btree_iter *iter)
 {
-	if (likely(!(iter->flags & BTREE_ITER_ALL_LEVELS))) {
-		struct bpos pos = iter->k.p;
-		bool ret = !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS
-			     ? bpos_eq(pos, SPOS_MAX)
-			     : bkey_eq(pos, SPOS_MAX));
-
-		if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
-			pos = bkey_successor(iter, pos);
-		bch2_btree_iter_set_pos(iter, pos);
-		return ret;
-	} else {
-		if (!btree_path_node(iter->path, iter->path->level))
-			return true;
+	struct bpos pos = iter->k.p;
+	bool ret = !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS
+		     ? bpos_eq(pos, SPOS_MAX)
+		     : bkey_eq(pos, SPOS_MAX));
 
-		iter->advanced = true;
-		return false;
-	}
+	if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
+		pos = bkey_successor(iter, pos);
+	bch2_btree_iter_set_pos(iter, pos);
+	return ret;
 }
 
 inline bool bch2_btree_iter_rewind(struct btree_iter *iter)
@@ -1832,58 +1887,70 @@ inline bool bch2_btree_iter_rewind(struct btree_iter *iter)
 }
 
 static noinline
-struct bkey_i *__bch2_btree_trans_peek_updates(struct btree_iter *iter)
+void bch2_btree_trans_peek_prev_updates(struct btree_trans *trans, struct btree_iter *iter,
+					struct bkey_s_c *k)
 {
-	struct btree_insert_entry *i;
-	struct bkey_i *ret = NULL;
+	struct bpos end = path_l(btree_iter_path(trans, iter))->b->data->min_key;
 
-	trans_for_each_update(iter->trans, i) {
-		if (i->btree_id < iter->btree_id)
-			continue;
-		if (i->btree_id > iter->btree_id)
-			break;
-		if (bpos_lt(i->k->k.p, iter->path->pos))
-			continue;
-		if (i->key_cache_already_flushed)
-			continue;
-		if (!ret || bpos_lt(i->k->k.p, ret->k.p))
-			ret = i->k;
-	}
+	trans_for_each_update(trans, i)
+		if (!i->key_cache_already_flushed &&
+		    i->btree_id == iter->btree_id &&
+		    bpos_le(i->k->k.p, iter->pos) &&
+		    bpos_ge(i->k->k.p, k->k ? k->k->p : end)) {
+			iter->k = i->k->k;
+			*k = bkey_i_to_s_c(i->k);
+		}
+}
 
-	return ret;
+static noinline
+void bch2_btree_trans_peek_updates(struct btree_trans *trans, struct btree_iter *iter,
+				   struct bkey_s_c *k)
+{
+	struct btree_path *path = btree_iter_path(trans, iter);
+	struct bpos end = path_l(path)->b->key.k.p;
+
+	trans_for_each_update(trans, i)
+		if (!i->key_cache_already_flushed &&
+		    i->btree_id == iter->btree_id &&
+		    bpos_ge(i->k->k.p, path->pos) &&
+		    bpos_le(i->k->k.p, k->k ? k->k->p : end)) {
+			iter->k = i->k->k;
+			*k = bkey_i_to_s_c(i->k);
+		}
 }
 
-static inline struct bkey_i *btree_trans_peek_updates(struct btree_iter *iter)
+static noinline
+void bch2_btree_trans_peek_slot_updates(struct btree_trans *trans, struct btree_iter *iter,
+					struct bkey_s_c *k)
 {
-	return iter->flags & BTREE_ITER_WITH_UPDATES
-		? __bch2_btree_trans_peek_updates(iter)
-		: NULL;
+	trans_for_each_update(trans, i)
+		if (!i->key_cache_already_flushed &&
+		    i->btree_id == iter->btree_id &&
+		    bpos_eq(i->k->k.p, iter->pos)) {
+			iter->k = i->k->k;
+			*k = bkey_i_to_s_c(i->k);
+		}
 }
 
 static struct bkey_i *bch2_btree_journal_peek(struct btree_trans *trans,
 					      struct btree_iter *iter,
 					      struct bpos end_pos)
 {
-	struct bkey_i *k;
-
-	if (bpos_lt(iter->path->pos, iter->journal_pos))
-		iter->journal_idx = 0;
+	struct btree_path *path = btree_iter_path(trans, iter);
 
-	k = bch2_journal_keys_peek_upto(trans->c, iter->btree_id,
-					iter->path->level,
-					iter->path->pos,
-					end_pos,
-					&iter->journal_idx);
-
-	iter->journal_pos = k ? k->k.p : end_pos;
-	return k;
+	return bch2_journal_keys_peek_upto(trans->c, iter->btree_id,
+					   path->level,
+					   path->pos,
+					   end_pos,
+					   &iter->journal_idx);
 }
 
 static noinline
 struct bkey_s_c btree_trans_peek_slot_journal(struct btree_trans *trans,
 					      struct btree_iter *iter)
 {
-	struct bkey_i *k = bch2_btree_journal_peek(trans, iter, iter->path->pos);
+	struct btree_path *path = btree_iter_path(trans, iter);
+	struct bkey_i *k = bch2_btree_journal_peek(trans, iter, path->pos);
 
 	if (k) {
 		iter->k = k->k;
@@ -1898,9 +1965,10 @@ struct bkey_s_c btree_trans_peek_journal(struct btree_trans *trans,
 					 struct btree_iter *iter,
 					 struct bkey_s_c k)
 {
+	struct btree_path *path = btree_iter_path(trans, iter);
 	struct bkey_i *next_journal =
 		bch2_btree_journal_peek(trans, iter,
-				k.k ? k.k->p : path_l(iter->path)->b->key.k.p);
+				k.k ? k.k->p : path_l(path)->b->key.k.p);
 
 	if (next_journal) {
 		iter->k = next_journal->k;
@@ -1943,13 +2011,13 @@ struct bkey_s_c btree_trans_peek_key_cache(struct btree_iter *iter, struct bpos
 
 	ret =   bch2_btree_path_traverse(trans, iter->key_cache_path,
 					 iter->flags|BTREE_ITER_CACHED) ?:
-		bch2_btree_path_relock(trans, iter->path, _THIS_IP_);
+		bch2_btree_path_relock(trans, btree_iter_path(trans, iter), _THIS_IP_);
 	if (unlikely(ret))
 		return bkey_s_c_err(ret);
 
-	btree_path_set_should_be_locked(iter->key_cache_path);
+	btree_path_set_should_be_locked(trans->paths + iter->key_cache_path);
 
-	k = bch2_btree_path_peek_slot(iter->key_cache_path, &u);
+	k = bch2_btree_path_peek_slot(trans->paths + iter->key_cache_path, &u);
 	if (k.k && !bkey_err(k)) {
 		iter->k = u;
 		k.k = &iter->k;
@@ -1960,11 +2028,10 @@ struct bkey_s_c btree_trans_peek_key_cache(struct btree_iter *iter, struct bpos
 static struct bkey_s_c __bch2_btree_iter_peek(struct btree_iter *iter, struct bpos search_key)
 {
 	struct btree_trans *trans = iter->trans;
-	struct bkey_i *next_update;
 	struct bkey_s_c k, k2;
 	int ret;
 
-	EBUG_ON(iter->path->cached);
+	EBUG_ON(btree_iter_path(trans, iter)->cached);
 	bch2_btree_iter_verify(iter);
 
 	while (1) {
@@ -1982,7 +2049,8 @@ static struct bkey_s_c __bch2_btree_iter_peek(struct btree_iter *iter, struct bp
 			goto out;
 		}
 
-		l = path_l(iter->path);
+		struct btree_path *path = btree_iter_path(trans, iter);
+		l = path_l(path);
 
 		if (unlikely(!l->b)) {
 			/* No btree nodes at requested level: */
@@ -1991,7 +2059,7 @@ static struct bkey_s_c __bch2_btree_iter_peek(struct btree_iter *iter, struct bp
 			goto out;
 		}
 
-		btree_path_set_should_be_locked(iter->path);
+		btree_path_set_should_be_locked(path);
 
 		k = btree_path_level_peek_all(trans->c, l, &iter->k);
 
@@ -2009,14 +2077,9 @@ static struct bkey_s_c __bch2_btree_iter_peek(struct btree_iter *iter, struct bp
 		if (unlikely(iter->flags & BTREE_ITER_WITH_JOURNAL))
 			k = btree_trans_peek_journal(trans, iter, k);
 
-		next_update = btree_trans_peek_updates(iter);
-
-		if (next_update &&
-		    bpos_le(next_update->k.p,
-			    k.k ? k.k->p : l->b->key.k.p)) {
-			iter->k = next_update->k;
-			k = bkey_i_to_s_c(next_update);
-		}
+		if (unlikely((iter->flags & BTREE_ITER_WITH_UPDATES) &&
+			     trans->nr_updates))
+			bch2_btree_trans_peek_updates(trans, iter, &k);
 
 		if (k.k && bkey_deleted(k.k)) {
 			/*
@@ -2066,13 +2129,12 @@ struct bkey_s_c bch2_btree_iter_peek_upto(struct btree_iter *iter, struct bpos e
 	struct bpos iter_pos;
 	int ret;
 
-	EBUG_ON(iter->flags & BTREE_ITER_ALL_LEVELS);
 	EBUG_ON((iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) && bkey_eq(end, POS_MAX));
 
 	if (iter->update_path) {
 		bch2_path_put_nokeep(trans, iter->update_path,
 				     iter->flags & BTREE_ITER_INTENT);
-		iter->update_path = NULL;
+		iter->update_path = 0;
 	}
 
 	bch2_btree_iter_verify_entry_exit(iter);
@@ -2100,10 +2162,10 @@ struct bkey_s_c bch2_btree_iter_peek_upto(struct btree_iter *iter, struct bpos e
 			goto end;
 
 		if (iter->update_path &&
-		    !bkey_eq(iter->update_path->pos, k.k->p)) {
+		    !bkey_eq(trans->paths[iter->update_path].pos, k.k->p)) {
 			bch2_path_put_nokeep(trans, iter->update_path,
 					     iter->flags & BTREE_ITER_INTENT);
-			iter->update_path = NULL;
+			iter->update_path = 0;
 		}
 
 		if ((iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) &&
@@ -2123,7 +2185,7 @@ struct bkey_s_c bch2_btree_iter_peek_upto(struct btree_iter *iter, struct bpos e
 			 * advance, same as on exit for iter->path, but only up
 			 * to snapshot
 			 */
-			__btree_path_get(iter->path, iter->flags & BTREE_ITER_INTENT);
+			__btree_path_get(trans->paths + iter->path, iter->flags & BTREE_ITER_INTENT);
 			iter->update_path = iter->path;
 
 			iter->update_path = bch2_btree_path_set_pos(trans,
@@ -2179,14 +2241,14 @@ struct bkey_s_c bch2_btree_iter_peek_upto(struct btree_iter *iter, struct bpos e
 				iter->flags & BTREE_ITER_INTENT,
 				btree_iter_ip_allocated(iter));
 
-	btree_path_set_should_be_locked(iter->path);
+	btree_path_set_should_be_locked(btree_iter_path(trans, iter));
 out_no_locked:
 	if (iter->update_path) {
-		ret = bch2_btree_path_relock(trans, iter->update_path, _THIS_IP_);
+		ret = bch2_btree_path_relock(trans, trans->paths + iter->update_path, _THIS_IP_);
 		if (unlikely(ret))
 			k = bkey_s_c_err(ret);
 		else
-			btree_path_set_should_be_locked(iter->update_path);
+			btree_path_set_should_be_locked(trans->paths + iter->update_path);
 	}
 
 	if (!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS))
@@ -2208,103 +2270,6 @@ end:
 }
 
 /**
- * bch2_btree_iter_peek_all_levels() - returns the first key greater than or
- * equal to iterator's current position, returning keys from every level of the
- * btree. For keys at different levels of the btree that compare equal, the key
- * from the lower level (leaf) is returned first.
- * @iter:	iterator to peek from
- *
- * Returns:	key if found, or an error extractable with bkey_err().
- */
-struct bkey_s_c bch2_btree_iter_peek_all_levels(struct btree_iter *iter)
-{
-	struct btree_trans *trans = iter->trans;
-	struct bkey_s_c k;
-	int ret;
-
-	EBUG_ON(iter->path->cached);
-	bch2_btree_iter_verify(iter);
-	BUG_ON(iter->path->level < iter->min_depth);
-	BUG_ON(!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS));
-	EBUG_ON(!(iter->flags & BTREE_ITER_ALL_LEVELS));
-
-	while (1) {
-		iter->path = bch2_btree_path_set_pos(trans, iter->path, iter->pos,
-					iter->flags & BTREE_ITER_INTENT,
-					btree_iter_ip_allocated(iter));
-
-		ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
-		if (unlikely(ret)) {
-			/* ensure that iter->k is consistent with iter->pos: */
-			bch2_btree_iter_set_pos(iter, iter->pos);
-			k = bkey_s_c_err(ret);
-			goto out_no_locked;
-		}
-
-		/* Already at end? */
-		if (!btree_path_node(iter->path, iter->path->level)) {
-			k = bkey_s_c_null;
-			goto out_no_locked;
-		}
-
-		k = btree_path_level_peek_all(trans->c,
-				&iter->path->l[iter->path->level], &iter->k);
-
-		/* Check if we should go up to the parent node: */
-		if (!k.k ||
-		    (iter->advanced &&
-		     bpos_eq(path_l(iter->path)->b->key.k.p, iter->pos))) {
-			iter->pos = path_l(iter->path)->b->key.k.p;
-			btree_path_set_level_up(trans, iter->path);
-			iter->advanced = false;
-			continue;
-		}
-
-		/*
-		 * Check if we should go back down to a leaf:
-		 * If we're not in a leaf node, we only return the current key
-		 * if it exactly matches iter->pos - otherwise we first have to
-		 * go back to the leaf:
-		 */
-		if (iter->path->level != iter->min_depth &&
-		    (iter->advanced ||
-		     !k.k ||
-		     !bpos_eq(iter->pos, k.k->p))) {
-			btree_path_set_level_down(trans, iter->path, iter->min_depth);
-			iter->pos = bpos_successor(iter->pos);
-			iter->advanced = false;
-			continue;
-		}
-
-		/* Check if we should go to the next key: */
-		if (iter->path->level == iter->min_depth &&
-		    iter->advanced &&
-		    k.k &&
-		    bpos_eq(iter->pos, k.k->p)) {
-			iter->pos = bpos_successor(iter->pos);
-			iter->advanced = false;
-			continue;
-		}
-
-		if (iter->advanced &&
-		    iter->path->level == iter->min_depth &&
-		    !bpos_eq(k.k->p, iter->pos))
-			iter->advanced = false;
-
-		BUG_ON(iter->advanced);
-		BUG_ON(!k.k);
-		break;
-	}
-
-	iter->pos = k.k->p;
-	btree_path_set_should_be_locked(iter->path);
-out_no_locked:
-	bch2_btree_iter_verify(iter);
-
-	return k;
-}
-
-/**
  * bch2_btree_iter_next() - returns first key greater than iterator's current
  * position
  * @iter:	iterator to peek from
@@ -2330,14 +2295,14 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 {
 	struct btree_trans *trans = iter->trans;
 	struct bpos search_key = iter->pos;
-	struct btree_path *saved_path = NULL;
 	struct bkey_s_c k;
 	struct bkey saved_k;
 	const struct bch_val *saved_v;
+	btree_path_idx_t saved_path = 0;
 	int ret;
 
-	EBUG_ON(iter->path->cached || iter->path->level);
-	EBUG_ON(iter->flags & BTREE_ITER_WITH_UPDATES);
+	EBUG_ON(btree_iter_path(trans, iter)->cached ||
+		btree_iter_path(trans, iter)->level);
 
 	if (iter->flags & BTREE_ITER_WITH_JOURNAL)
 		return bkey_s_c_err(-EIO);
@@ -2361,14 +2326,18 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 			goto out_no_locked;
 		}
 
-		k = btree_path_level_peek(trans, iter->path,
-					  &iter->path->l[0], &iter->k);
+		struct btree_path *path = btree_iter_path(trans, iter);
+
+		k = btree_path_level_peek(trans, path, &path->l[0], &iter->k);
 		if (!k.k ||
 		    ((iter->flags & BTREE_ITER_IS_EXTENTS)
 		     ? bpos_ge(bkey_start_pos(k.k), search_key)
 		     : bpos_gt(k.k->p, search_key)))
-			k = btree_path_level_prev(trans, iter->path,
-						  &iter->path->l[0], &iter->k);
+			k = btree_path_level_prev(trans, path, &path->l[0], &iter->k);
+
+		if (unlikely((iter->flags & BTREE_ITER_WITH_UPDATES) &&
+			     trans->nr_updates))
+			bch2_btree_trans_peek_prev_updates(trans, iter, &k);
 
 		if (likely(k.k)) {
 			if (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) {
@@ -2384,13 +2353,13 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 					bch2_path_put_nokeep(trans, iter->path,
 						      iter->flags & BTREE_ITER_INTENT);
 					iter->path = saved_path;
-					saved_path = NULL;
+					saved_path = 0;
 					iter->k	= saved_k;
 					k.v	= saved_v;
 					goto got_key;
 				}
 
-				if (bch2_snapshot_is_ancestor(iter->trans->c,
+				if (bch2_snapshot_is_ancestor(trans->c,
 							      iter->snapshot,
 							      k.k->p.snapshot)) {
 					if (saved_path)
@@ -2398,6 +2367,7 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 						      iter->flags & BTREE_ITER_INTENT);
 					saved_path = btree_path_clone(trans, iter->path,
 								iter->flags & BTREE_ITER_INTENT);
+					path = btree_iter_path(trans, iter);
 					saved_k = *k.k;
 					saved_v = k.v;
 				}
@@ -2414,10 +2384,11 @@ got_key:
 				continue;
 			}
 
+			btree_path_set_should_be_locked(path);
 			break;
-		} else if (likely(!bpos_eq(iter->path->l[0].b->data->min_key, POS_MIN))) {
+		} else if (likely(!bpos_eq(path->l[0].b->data->min_key, POS_MIN))) {
 			/* Advance to previous leaf node: */
-			search_key = bpos_predecessor(iter->path->l[0].b->data->min_key);
+			search_key = bpos_predecessor(path->l[0].b->data->min_key);
 		} else {
 			/* Start of btree: */
 			bch2_btree_iter_set_pos(iter, POS_MIN);
@@ -2434,8 +2405,6 @@ got_key:
 
 	if (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS)
 		iter->pos.snapshot = iter->snapshot;
-
-	btree_path_set_should_be_locked(iter->path);
 out_no_locked:
 	if (saved_path)
 		bch2_path_put_nokeep(trans, saved_path, iter->flags & BTREE_ITER_INTENT);
@@ -2470,8 +2439,7 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 
 	bch2_btree_iter_verify(iter);
 	bch2_btree_iter_verify_entry_exit(iter);
-	EBUG_ON(iter->flags & BTREE_ITER_ALL_LEVELS);
-	EBUG_ON(iter->path->level && (iter->flags & BTREE_ITER_WITH_KEY_CACHE));
+	EBUG_ON(btree_iter_path(trans, iter)->level && (iter->flags & BTREE_ITER_WITH_KEY_CACHE));
 
 	/* extents can't span inode numbers: */
 	if ((iter->flags & BTREE_ITER_IS_EXTENTS) &&
@@ -2495,13 +2463,13 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 
 	if ((iter->flags & BTREE_ITER_CACHED) ||
 	    !(iter->flags & (BTREE_ITER_IS_EXTENTS|BTREE_ITER_FILTER_SNAPSHOTS))) {
-		struct bkey_i *next_update;
+		k = bkey_s_c_null;
 
-		if ((next_update = btree_trans_peek_updates(iter)) &&
-		    bpos_eq(next_update->k.p, iter->pos)) {
-			iter->k = next_update->k;
-			k = bkey_i_to_s_c(next_update);
-			goto out;
+		if (unlikely((iter->flags & BTREE_ITER_WITH_UPDATES) &&
+			     trans->nr_updates)) {
+			bch2_btree_trans_peek_slot_updates(trans, iter, &k);
+			if (k.k)
+				goto out;
 		}
 
 		if (unlikely(iter->flags & BTREE_ITER_WITH_JOURNAL) &&
@@ -2516,7 +2484,7 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 			goto out_no_locked;
 		}
 
-		k = bch2_btree_path_peek_slot(iter->path, &iter->k);
+		k = bch2_btree_path_peek_slot(trans->paths + iter->path, &iter->k);
 		if (unlikely(!k.k))
 			goto out_no_locked;
 	} else {
@@ -2526,7 +2494,7 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 		if (iter->flags & BTREE_ITER_IS_EXTENTS)
 			end.offset = U64_MAX;
 
-		EBUG_ON(iter->path->level);
+		EBUG_ON(btree_iter_path(trans, iter)->level);
 
 		if (iter->flags & BTREE_ITER_INTENT) {
 			struct btree_iter iter2;
@@ -2572,7 +2540,7 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 		}
 	}
 out:
-	btree_path_set_should_be_locked(iter->path);
+	btree_path_set_should_be_locked(btree_iter_path(trans, iter));
 out_no_locked:
 	bch2_btree_iter_verify_entry_exit(iter);
 	bch2_btree_iter_verify(iter);
@@ -2619,17 +2587,17 @@ static void btree_trans_verify_sorted_refs(struct btree_trans *trans)
 	struct btree_path *path;
 	unsigned i;
 
-	BUG_ON(trans->nr_sorted != hweight64(trans->paths_allocated));
+	BUG_ON(trans->nr_sorted != bitmap_weight(trans->paths_allocated, trans->nr_paths) - 1);
 
-	trans_for_each_path(trans, path) {
+	trans_for_each_path(trans, path, i) {
 		BUG_ON(path->sorted_idx >= trans->nr_sorted);
-		BUG_ON(trans->sorted[path->sorted_idx] != path->idx);
+		BUG_ON(trans->sorted[path->sorted_idx] != i);
 	}
 
 	for (i = 0; i < trans->nr_sorted; i++) {
 		unsigned idx = trans->sorted[i];
 
-		EBUG_ON(!(trans->paths_allocated & (1ULL << idx)));
+		BUG_ON(!test_bit(idx, trans->paths_allocated));
 		BUG_ON(trans->paths[idx].sorted_idx != i);
 	}
 }
@@ -2637,12 +2605,12 @@ static void btree_trans_verify_sorted_refs(struct btree_trans *trans)
 static void btree_trans_verify_sorted(struct btree_trans *trans)
 {
 	struct btree_path *path, *prev = NULL;
-	unsigned i;
+	struct trans_for_each_path_inorder_iter iter;
 
 	if (!bch2_debug_check_iterators)
 		return;
 
-	trans_for_each_path_inorder(trans, path, i) {
+	trans_for_each_path_inorder(trans, path, iter) {
 		if (prev && btree_path_cmp(prev, path) > 0) {
 			__bch2_dump_trans_paths_updates(trans, true);
 			panic("trans paths out of order!\n");
@@ -2699,42 +2667,40 @@ out:
 static inline void btree_path_list_remove(struct btree_trans *trans,
 					  struct btree_path *path)
 {
-	unsigned i;
-
 	EBUG_ON(path->sorted_idx >= trans->nr_sorted);
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	trans->nr_sorted--;
 	memmove_u64s_down_small(trans->sorted + path->sorted_idx,
 				trans->sorted + path->sorted_idx + 1,
-				DIV_ROUND_UP(trans->nr_sorted - path->sorted_idx, 8));
+				DIV_ROUND_UP(trans->nr_sorted - path->sorted_idx,
+					     sizeof(u64) / sizeof(btree_path_idx_t)));
 #else
 	array_remove_item(trans->sorted, trans->nr_sorted, path->sorted_idx);
 #endif
-	for (i = path->sorted_idx; i < trans->nr_sorted; i++)
+	for (unsigned i = path->sorted_idx; i < trans->nr_sorted; i++)
 		trans->paths[trans->sorted[i]].sorted_idx = i;
-
-	path->sorted_idx = U8_MAX;
 }
 
 static inline void btree_path_list_add(struct btree_trans *trans,
-				       struct btree_path *pos,
-				       struct btree_path *path)
+				       btree_path_idx_t pos,
+				       btree_path_idx_t path_idx)
 {
-	unsigned i;
+	struct btree_path *path = trans->paths + path_idx;
 
-	path->sorted_idx = pos ? pos->sorted_idx + 1 : trans->nr_sorted;
+	path->sorted_idx = pos ? trans->paths[pos].sorted_idx + 1 : trans->nr_sorted;
 
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	memmove_u64s_up_small(trans->sorted + path->sorted_idx + 1,
 			      trans->sorted + path->sorted_idx,
-			      DIV_ROUND_UP(trans->nr_sorted - path->sorted_idx, 8));
+			      DIV_ROUND_UP(trans->nr_sorted - path->sorted_idx,
+					   sizeof(u64) / sizeof(btree_path_idx_t)));
 	trans->nr_sorted++;
-	trans->sorted[path->sorted_idx] = path->idx;
+	trans->sorted[path->sorted_idx] = path_idx;
 #else
-	array_insert_item(trans->sorted, trans->nr_sorted, path->sorted_idx, path->idx);
+	array_insert_item(trans->sorted, trans->nr_sorted, path->sorted_idx, path_idx);
 #endif
 
-	for (i = path->sorted_idx; i < trans->nr_sorted; i++)
+	for (unsigned i = path->sorted_idx; i < trans->nr_sorted; i++)
 		trans->paths[trans->sorted[i]].sorted_idx = i;
 
 	btree_trans_verify_sorted_refs(trans);
@@ -2751,9 +2717,10 @@ void bch2_trans_iter_exit(struct btree_trans *trans, struct btree_iter *iter)
 	if (iter->key_cache_path)
 		bch2_path_put(trans, iter->key_cache_path,
 			      iter->flags & BTREE_ITER_INTENT);
-	iter->path = NULL;
-	iter->update_path = NULL;
-	iter->key_cache_path = NULL;
+	iter->path		= 0;
+	iter->update_path	= 0;
+	iter->key_cache_path	= 0;
+	iter->trans		= NULL;
 }
 
 void bch2_trans_iter_init_outlined(struct btree_trans *trans,
@@ -2784,41 +2751,46 @@ void bch2_trans_node_iter_init(struct btree_trans *trans,
 
 	iter->min_depth	= depth;
 
-	BUG_ON(iter->path->locks_want	 < min(locks_want, BTREE_MAX_DEPTH));
-	BUG_ON(iter->path->level	!= depth);
-	BUG_ON(iter->min_depth		!= depth);
+	struct btree_path *path = btree_iter_path(trans, iter);
+	BUG_ON(path->locks_want	 < min(locks_want, BTREE_MAX_DEPTH));
+	BUG_ON(path->level	!= depth);
+	BUG_ON(iter->min_depth	!= depth);
 }
 
 void bch2_trans_copy_iter(struct btree_iter *dst, struct btree_iter *src)
 {
+	struct btree_trans *trans = src->trans;
+
 	*dst = *src;
 	if (src->path)
-		__btree_path_get(src->path, src->flags & BTREE_ITER_INTENT);
+		__btree_path_get(trans->paths + src->path, src->flags & BTREE_ITER_INTENT);
 	if (src->update_path)
-		__btree_path_get(src->update_path, src->flags & BTREE_ITER_INTENT);
-	dst->key_cache_path = NULL;
+		__btree_path_get(trans->paths + src->update_path, src->flags & BTREE_ITER_INTENT);
+	dst->key_cache_path = 0;
 }
 
 void *__bch2_trans_kmalloc(struct btree_trans *trans, size_t size)
 {
+	struct bch_fs *c = trans->c;
 	unsigned new_top = trans->mem_top + size;
-	size_t old_bytes = trans->mem_bytes;
-	size_t new_bytes = roundup_pow_of_two(new_top);
+	unsigned old_bytes = trans->mem_bytes;
+	unsigned new_bytes = roundup_pow_of_two(new_top);
 	int ret;
 	void *new_mem;
 	void *p;
 
-	trans->mem_max = max(trans->mem_max, new_top);
-
 	WARN_ON_ONCE(new_bytes > BTREE_TRANS_MEM_MAX);
 
+	struct btree_transaction_stats *s = btree_trans_stats(trans);
+	s->max_mem = max(s->max_mem, new_bytes);
+
 	new_mem = krealloc(trans->mem, new_bytes, GFP_NOWAIT|__GFP_NOWARN);
 	if (unlikely(!new_mem)) {
 		bch2_trans_unlock(trans);
 
 		new_mem = krealloc(trans->mem, new_bytes, GFP_KERNEL);
 		if (!new_mem && new_bytes <= BTREE_TRANS_MEM_MAX) {
-			new_mem = mempool_alloc(&trans->c->btree_trans_mem_pool, GFP_KERNEL);
+			new_mem = mempool_alloc(&c->btree_trans_mem_pool, GFP_KERNEL);
 			new_bytes = BTREE_TRANS_MEM_MAX;
 			kfree(trans->mem);
 		}
@@ -2838,7 +2810,7 @@ void *__bch2_trans_kmalloc(struct btree_trans *trans, size_t size)
 	trans->mem_bytes = new_bytes;
 
 	if (old_bytes) {
-		trace_and_count(trans->c, trans_restart_mem_realloced, trans, _RET_IP_, new_bytes);
+		trace_and_count(c, trans_restart_mem_realloced, trans, _RET_IP_, new_bytes);
 		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_mem_realloced));
 	}
 
@@ -2860,8 +2832,9 @@ void bch2_trans_srcu_unlock(struct btree_trans *trans)
 	if (trans->srcu_held) {
 		struct bch_fs *c = trans->c;
 		struct btree_path *path;
+		unsigned i;
 
-		trans_for_each_path(trans, path)
+		trans_for_each_path(trans, path, i)
 			if (path->cached && !btree_node_locked(path, 0))
 				path->l[0].b = ERR_PTR(-BCH_ERR_no_btree_node_srcu_reset);
 
@@ -2871,7 +2844,7 @@ void bch2_trans_srcu_unlock(struct btree_trans *trans)
 	}
 }
 
-void bch2_trans_srcu_lock(struct btree_trans *trans)
+static void bch2_trans_srcu_lock(struct btree_trans *trans)
 {
 	if (!trans->srcu_held) {
 		trans->srcu_idx = srcu_read_lock(&trans->c->btree_trans_barrier);
@@ -2893,14 +2866,16 @@ void bch2_trans_srcu_lock(struct btree_trans *trans)
 u32 bch2_trans_begin(struct btree_trans *trans)
 {
 	struct btree_path *path;
+	unsigned i;
 	u64 now;
 
 	bch2_trans_reset_updates(trans);
 
 	trans->restart_count++;
 	trans->mem_top			= 0;
+	trans->journal_entries		= NULL;
 
-	trans_for_each_path(trans, path) {
+	trans_for_each_path(trans, path, i) {
 		path->should_be_locked = false;
 
 		/*
@@ -2917,15 +2892,21 @@ u32 bch2_trans_begin(struct btree_trans *trans)
 		 * iterators if we do that
 		 */
 		if (!path->ref && !path->preserve)
-			__bch2_path_free(trans, path);
+			__bch2_path_free(trans, i);
 		else
 			path->preserve = false;
 	}
 
 	now = local_clock();
+
+	if (!IS_ENABLED(CONFIG_BCACHEFS_NO_LATENCY_ACCT) &&
+	    time_after64(now, trans->last_begin_time + 10))
+		__bch2_time_stats_update(&btree_trans_stats(trans)->duration,
+					 trans->last_begin_time, now);
+
 	if (!trans->restarted &&
 	    (need_resched() ||
-	     now - trans->last_begin_time > BTREE_TRANS_MAX_LOCK_HOLD_TIME_NS)) {
+	     time_after64(now, trans->last_begin_time + BTREE_TRANS_MAX_LOCK_HOLD_TIME_NS))) {
 		drop_locks_do(trans, (cond_resched(), 0));
 		now = local_clock();
 	}
@@ -2944,32 +2925,11 @@ u32 bch2_trans_begin(struct btree_trans *trans)
 	return trans->restart_count;
 }
 
-static struct btree_trans *bch2_trans_alloc(struct bch_fs *c)
-{
-	struct btree_trans *trans;
-
-	if (IS_ENABLED(__KERNEL__)) {
-		trans = this_cpu_xchg(c->btree_trans_bufs->trans, NULL);
-		if (trans)
-			return trans;
-	}
-
-	trans = mempool_alloc(&c->btree_trans_pool, GFP_NOFS);
-	/*
-	 * paths need to be zeroed, bch2_check_for_deadlock looks at
-	 * paths in other threads
-	 */
-	memset(&trans->paths, 0, sizeof(trans->paths));
-	return trans;
-}
-
-const char *bch2_btree_transaction_fns[BCH_TRANSACTIONS_NR];
+const char *bch2_btree_transaction_fns[BCH_TRANSACTIONS_NR] = { "(unknown)" };
 
 unsigned bch2_trans_get_fn_idx(const char *fn)
 {
-	unsigned i;
-
-	for (i = 0; i < ARRAY_SIZE(bch2_btree_transaction_fns); i++)
+	for (unsigned i = 0; i < ARRAY_SIZE(bch2_btree_transaction_fns); i++)
 		if (!bch2_btree_transaction_fns[i] ||
 		    bch2_btree_transaction_fns[i] == fn) {
 			bch2_btree_transaction_fns[i] = fn;
@@ -2977,76 +2937,92 @@ unsigned bch2_trans_get_fn_idx(const char *fn)
 		}
 
 	pr_warn_once("BCH_TRANSACTIONS_NR not big enough!");
-	return i;
+	return 0;
 }
 
 struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx)
 	__acquires(&c->btree_trans_barrier)
 {
 	struct btree_trans *trans;
-	struct btree_transaction_stats *s;
 
-	trans = bch2_trans_alloc(c);
-
-	memset(trans, 0, sizeof(*trans));
-	trans->c		= c;
-	trans->fn		= fn_idx < ARRAY_SIZE(bch2_btree_transaction_fns)
-		? bch2_btree_transaction_fns[fn_idx] : NULL;
-	trans->last_begin_time	= local_clock();
-	trans->fn_idx		= fn_idx;
-	trans->locking_wait.task = current;
-	trans->journal_replay_not_finished =
-		unlikely(!test_bit(JOURNAL_REPLAY_DONE, &c->journal.flags)) &&
-		atomic_inc_not_zero(&c->journal_keys.ref);
-	closure_init_stack(&trans->ref);
-
-	s = btree_trans_stats(trans);
-	if (s && s->max_mem) {
-		unsigned expected_mem_bytes = roundup_pow_of_two(s->max_mem);
-
-		trans->mem = kmalloc(expected_mem_bytes, GFP_KERNEL);
-
-		if (!unlikely(trans->mem)) {
-			trans->mem = mempool_alloc(&c->btree_trans_mem_pool, GFP_KERNEL);
-			trans->mem_bytes = BTREE_TRANS_MEM_MAX;
-		} else {
-			trans->mem_bytes = expected_mem_bytes;
+	if (IS_ENABLED(__KERNEL__)) {
+		trans = this_cpu_xchg(c->btree_trans_bufs->trans, NULL);
+		if (trans) {
+			memset(trans, 0, offsetof(struct btree_trans, list));
+			goto got_trans;
 		}
 	}
 
-	if (s) {
-		trans->nr_max_paths = s->nr_max_paths;
-		trans->wb_updates_size = s->wb_updates_size;
-	}
-
-	trans->srcu_idx		= srcu_read_lock(&c->btree_trans_barrier);
-	trans->srcu_lock_time	= jiffies;
-	trans->srcu_held	= true;
+	trans = mempool_alloc(&c->btree_trans_pool, GFP_NOFS);
+	memset(trans, 0, sizeof(*trans));
+	closure_init_stack(&trans->ref);
 
-	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
+	seqmutex_lock(&c->btree_trans_lock);
+	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG)) {
 		struct btree_trans *pos;
+		pid_t pid = current->pid;
+
+		trans->locking_wait.task = current;
 
-		seqmutex_lock(&c->btree_trans_lock);
 		list_for_each_entry(pos, &c->btree_trans_list, list) {
+			struct task_struct *pos_task = READ_ONCE(pos->locking_wait.task);
 			/*
 			 * We'd much prefer to be stricter here and completely
 			 * disallow multiple btree_trans in the same thread -
 			 * but the data move path calls bch2_write when we
 			 * already have a btree_trans initialized.
 			 */
-			BUG_ON(trans->locking_wait.task->pid == pos->locking_wait.task->pid &&
+			BUG_ON(pos_task &&
+			       pid == pos_task->pid &&
 			       bch2_trans_locked(pos));
 
-			if (trans->locking_wait.task->pid < pos->locking_wait.task->pid) {
+			if (pos_task && pid < pos_task->pid) {
 				list_add_tail(&trans->list, &pos->list);
 				goto list_add_done;
 			}
 		}
-		list_add_tail(&trans->list, &c->btree_trans_list);
+	}
+	list_add_tail(&trans->list, &c->btree_trans_list);
 list_add_done:
-		seqmutex_unlock(&c->btree_trans_lock);
+	seqmutex_unlock(&c->btree_trans_lock);
+got_trans:
+	trans->c		= c;
+	trans->last_begin_time	= local_clock();
+	trans->fn_idx		= fn_idx;
+	trans->locking_wait.task = current;
+	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;
+	trans->updates		= trans->_updates;
+
+	*trans_paths_nr(trans->paths) = BTREE_ITER_INITIAL;
+
+	trans->paths_allocated[0] = 1;
+
+	if (fn_idx < BCH_TRANSACTIONS_NR) {
+		trans->fn = bch2_btree_transaction_fns[fn_idx];
+
+		struct btree_transaction_stats *s = &c->btree_transaction_stats[fn_idx];
+
+		if (s->max_mem) {
+			unsigned expected_mem_bytes = roundup_pow_of_two(s->max_mem);
+
+			trans->mem = kmalloc(expected_mem_bytes, GFP_KERNEL);
+			if (likely(trans->mem))
+				trans->mem_bytes = expected_mem_bytes;
+		}
+
+		trans->nr_paths_max = s->nr_max_paths;
+		trans->journal_entries_size = s->journal_entries_size;
 	}
 
+	trans->srcu_idx		= srcu_read_lock(&c->btree_trans_barrier);
+	trans->srcu_lock_time	= jiffies;
+	trans->srcu_held	= true;
 	return trans;
 }
 
@@ -3055,14 +3031,15 @@ static void check_btree_paths_leaked(struct btree_trans *trans)
 #ifdef CONFIG_BCACHEFS_DEBUG
 	struct bch_fs *c = trans->c;
 	struct btree_path *path;
+	unsigned i;
 
-	trans_for_each_path(trans, path)
+	trans_for_each_path(trans, path, i)
 		if (path->ref)
 			goto leaked;
 	return;
 leaked:
 	bch_err(c, "btree paths leaked from %s!", trans->fn);
-	trans_for_each_path(trans, path)
+	trans_for_each_path(trans, path, i)
 		if (path->ref)
 			printk(KERN_ERR "  btree %s %pS\n",
 			       bch2_btree_id_str(path->btree_id),
@@ -3075,26 +3052,14 @@ leaked:
 void bch2_trans_put(struct btree_trans *trans)
 	__releases(&c->btree_trans_barrier)
 {
-	struct btree_insert_entry *i;
 	struct bch_fs *c = trans->c;
-	struct btree_transaction_stats *s = btree_trans_stats(trans);
 
 	bch2_trans_unlock(trans);
 
-	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
-		seqmutex_lock(&c->btree_trans_lock);
-		list_del(&trans->list);
-		seqmutex_unlock(&c->btree_trans_lock);
-	}
-
-	closure_sync(&trans->ref);
-
-	if (s)
-		s->max_mem = max(s->max_mem, trans->mem_max);
-
 	trans_for_each_update(trans, i)
-		__btree_path_put(i->path, true);
-	trans->nr_updates		= 0;
+		__btree_path_put(trans->paths + i->path, true);
+	trans->nr_updates	= 0;
+	trans->locking_wait.task = NULL;
 
 	check_btree_paths_leaked(trans);
 
@@ -3103,8 +3068,6 @@ void bch2_trans_put(struct btree_trans *trans)
 		srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx);
 	}
 
-	kfree(trans->extra_journal_entries.data);
-
 	if (trans->fs_usage_deltas) {
 		if (trans->fs_usage_deltas->size + sizeof(trans->fs_usage_deltas) ==
 		    REPLICAS_DELTA_LIST_MAX)
@@ -3117,6 +3080,13 @@ void bch2_trans_put(struct btree_trans *trans)
 	if (unlikely(trans->journal_replay_not_finished))
 		bch2_journal_keys_put(c);
 
+	unsigned long *paths_allocated = trans->paths_allocated;
+	trans->paths_allocated	= NULL;
+	trans->paths		= NULL;
+
+	if (paths_allocated != trans->_paths_allocated)
+		kfree_rcu_mightsleep(paths_allocated);
+
 	if (trans->mem_bytes == BTREE_TRANS_MEM_MAX)
 		mempool_free(trans->mem, &c->btree_trans_mem_pool);
 	else
@@ -3125,8 +3095,16 @@ void bch2_trans_put(struct btree_trans *trans)
 	/* Userspace doesn't have a real percpu implementation: */
 	if (IS_ENABLED(__KERNEL__))
 		trans = this_cpu_xchg(c->btree_trans_bufs->trans, trans);
-	if (trans)
+
+	if (trans) {
+		closure_sync(&trans->ref);
+
+		seqmutex_lock(&c->btree_trans_lock);
+		list_del(&trans->list);
+		seqmutex_unlock(&c->btree_trans_lock);
+
 		mempool_free(trans, &c->btree_trans_pool);
+	}
 }
 
 static void __maybe_unused
@@ -3154,24 +3132,38 @@ bch2_btree_bkey_cached_common_to_text(struct printbuf *out,
 
 void bch2_btree_trans_to_text(struct printbuf *out, struct btree_trans *trans)
 {
-	struct btree_path *path;
 	struct btree_bkey_cached_common *b;
 	static char lock_types[] = { 'r', 'i', 'w' };
+	struct task_struct *task = READ_ONCE(trans->locking_wait.task);
 	unsigned l, idx;
 
+	/* before rcu_read_lock(): */
+	bch2_printbuf_make_room(out, 4096);
+
 	if (!out->nr_tabstops) {
 		printbuf_tabstop_push(out, 16);
 		printbuf_tabstop_push(out, 32);
 	}
 
-	prt_printf(out, "%i %s\n", trans->locking_wait.task->pid, trans->fn);
+	prt_printf(out, "%i %s\n", task ? task->pid : 0, trans->fn);
+
+	/* trans->paths is rcu protected vs. freeing */
+	rcu_read_lock();
+	out->atomic++;
+
+	struct btree_path *paths = rcu_dereference(trans->paths);
+	if (!paths)
+		goto out;
+
+	unsigned long *paths_allocated = trans_paths_allocated(paths);
 
-	trans_for_each_path_safe(trans, path, idx) {
+	trans_for_each_path_idx_from(paths_allocated, *trans_paths_nr(paths), idx, 1) {
+		struct btree_path *path = paths + idx;
 		if (!path->nodes_locked)
 			continue;
 
 		prt_printf(out, "  path %u %c l=%u %s:",
-		       path->idx,
+		       idx,
 		       path->cached ? 'c' : 'b',
 		       path->level,
 		       bch2_btree_id_str(path->btree_id));
@@ -3199,6 +3191,9 @@ void bch2_btree_trans_to_text(struct printbuf *out, struct btree_trans *trans)
 		bch2_btree_bkey_cached_common_to_text(out, b);
 		prt_newline(out);
 	}
+out:
+	--out->atomic;
+	rcu_read_unlock();
 }
 
 void bch2_fs_btree_iter_exit(struct bch_fs *c)
@@ -3207,15 +3202,26 @@ void bch2_fs_btree_iter_exit(struct bch_fs *c)
 	struct btree_trans *trans;
 	int cpu;
 
+	if (c->btree_trans_bufs)
+		for_each_possible_cpu(cpu) {
+			struct btree_trans *trans =
+				per_cpu_ptr(c->btree_trans_bufs, cpu)->trans;
+
+			if (trans) {
+				closure_sync(&trans->ref);
+
+				seqmutex_lock(&c->btree_trans_lock);
+				list_del(&trans->list);
+				seqmutex_unlock(&c->btree_trans_lock);
+			}
+			kfree(trans);
+		}
+	free_percpu(c->btree_trans_bufs);
+
 	trans = list_first_entry_or_null(&c->btree_trans_list, struct btree_trans, list);
 	if (trans)
 		panic("%s leaked btree_trans\n", trans->fn);
 
-	if (c->btree_trans_bufs)
-		for_each_possible_cpu(cpu)
-			kfree(per_cpu_ptr(c->btree_trans_bufs, cpu)->trans);
-	free_percpu(c->btree_trans_bufs);
-
 	for (s = c->btree_transaction_stats;
 	     s < c->btree_transaction_stats + ARRAY_SIZE(c->btree_transaction_stats);
 	     s++) {
@@ -3236,6 +3242,7 @@ void bch2_fs_btree_iter_init_early(struct bch_fs *c)
 	for (s = c->btree_transaction_stats;
 	     s < c->btree_transaction_stats + ARRAY_SIZE(c->btree_transaction_stats);
 	     s++) {
+		bch2_time_stats_init(&s->duration);
 		bch2_time_stats_init(&s->lock_hold_times);
 		mutex_init(&s->lock);
 	}