]> git.sesse.net Git - bcachefs-tools-debian/blobdiff - libbcachefs/btree_iter.c
New upstream snapshot
[bcachefs-tools-debian] / libbcachefs / btree_iter.c
index 6fab76c3220c55f64687d93299ac942d941cb84d..425c9ad779e326b7b3ea32c01f54046bd0b73891 100644 (file)
@@ -2,18 +2,53 @@
 
 #include "bcachefs.h"
 #include "bkey_methods.h"
+#include "bkey_buf.h"
 #include "btree_cache.h"
 #include "btree_iter.h"
 #include "btree_key_cache.h"
 #include "btree_locking.h"
 #include "btree_update.h"
 #include "debug.h"
+#include "error.h"
 #include "extents.h"
 #include "journal.h"
+#include "replicas.h"
 
 #include <linux/prefetch.h>
 #include <trace/events/bcachefs.h>
 
+static void btree_iter_set_search_pos(struct btree_iter *, struct bpos);
+
+static inline struct bpos bkey_successor(struct btree_iter *iter, struct bpos p)
+{
+       EBUG_ON(btree_iter_type(iter) == BTREE_ITER_NODES);
+
+       /* Are we iterating over keys in all snapshots? */
+       if (iter->flags & BTREE_ITER_ALL_SNAPSHOTS) {
+               p = bpos_successor(p);
+       } else {
+               p = bpos_nosnap_successor(p);
+               p.snapshot = iter->snapshot;
+       }
+
+       return p;
+}
+
+static inline struct bpos bkey_predecessor(struct btree_iter *iter, struct bpos p)
+{
+       EBUG_ON(btree_iter_type(iter) == BTREE_ITER_NODES);
+
+       /* Are we iterating over keys in all snapshots? */
+       if (iter->flags & BTREE_ITER_ALL_SNAPSHOTS) {
+               p = bpos_predecessor(p);
+       } else {
+               p = bpos_nosnap_predecessor(p);
+               p.snapshot = iter->snapshot;
+       }
+
+       return p;
+}
+
 static inline bool is_btree_node(struct btree_iter *iter, unsigned l)
 {
        return l < BTREE_MAX_DEPTH &&
@@ -26,20 +61,20 @@ static inline struct bpos btree_iter_search_key(struct btree_iter *iter)
 
        if ((iter->flags & BTREE_ITER_IS_EXTENTS) &&
            bkey_cmp(pos, POS_MAX))
-               pos = bkey_successor(pos);
+               pos = bkey_successor(iter, pos);
        return pos;
 }
 
 static inline bool btree_iter_pos_before_node(struct btree_iter *iter,
                                              struct btree *b)
 {
-       return bkey_cmp(btree_iter_search_key(iter), b->data->min_key) < 0;
+       return bpos_cmp(iter->real_pos, b->data->min_key) < 0;
 }
 
 static inline bool btree_iter_pos_after_node(struct btree_iter *iter,
                                             struct btree *b)
 {
-       return bkey_cmp(b->key.k.p, btree_iter_search_key(iter)) < 0;
+       return bpos_cmp(b->key.k.p, iter->real_pos) < 0;
 }
 
 static inline bool btree_iter_pos_in_node(struct btree_iter *iter,
@@ -197,13 +232,14 @@ static struct bpos btree_node_pos(struct btree_bkey_cached_common *_b,
 bool __bch2_btree_node_lock(struct btree *b, struct bpos pos,
                            unsigned level, struct btree_iter *iter,
                            enum six_lock_type type,
-                           six_lock_should_sleep_fn should_sleep_fn,
-                           void *p)
+                           six_lock_should_sleep_fn should_sleep_fn, void *p,
+                           unsigned long ip)
 {
        struct btree_trans *trans = iter->trans;
-       struct btree_iter *linked;
+       struct btree_iter *linked, *deadlock_iter = NULL;
        u64 start_time = local_clock();
-       bool ret = true;
+       unsigned reason = 9;
+       bool ret;
 
        /* Check if it's safe to block: */
        trans_for_each_iter(trans, linked) {
@@ -224,15 +260,33 @@ bool __bch2_btree_node_lock(struct btree *b, struct bpos pos,
                 */
                if (type == SIX_LOCK_intent &&
                    linked->nodes_locked != linked->nodes_intent_locked) {
-                       if (!(trans->nounlock)) {
-                               linked->locks_want = max_t(unsigned,
-                                               linked->locks_want,
-                                               __fls(linked->nodes_locked) + 1);
-                               if (!btree_iter_get_locks(linked, true, false))
-                                       ret = false;
-                       } else {
-                               ret = false;
+                       linked->locks_want = max_t(unsigned,
+                                       linked->locks_want,
+                                       __fls(linked->nodes_locked) + 1);
+                       if (!btree_iter_get_locks(linked, true, false)) {
+                               deadlock_iter = linked;
+                               reason = 1;
+                       }
+               }
+
+               if (linked->btree_id != iter->btree_id) {
+                       if (linked->btree_id > iter->btree_id) {
+                               deadlock_iter = linked;
+                               reason = 3;
                        }
+                       continue;
+               }
+
+               /*
+                * Within the same btree, cached iterators come before non
+                * cached iterators:
+                */
+               if (btree_iter_is_cached(linked) != btree_iter_is_cached(iter)) {
+                       if (btree_iter_is_cached(iter)) {
+                               deadlock_iter = linked;
+                               reason = 4;
+                       }
+                       continue;
                }
 
                /*
@@ -240,30 +294,24 @@ bool __bch2_btree_node_lock(struct btree *b, struct bpos pos,
                 * another iterator has possible descendants locked of the node
                 * we're about to lock, it must have the ancestors locked too:
                 */
-               if (linked->btree_id == iter->btree_id &&
-                   level > __fls(linked->nodes_locked)) {
-                       if (!(trans->nounlock)) {
-                               linked->locks_want =
-                                       max(level + 1, max_t(unsigned,
-                                           linked->locks_want,
-                                           iter->locks_want));
-                               if (!btree_iter_get_locks(linked, true, false))
-                                       ret = false;
-                       } else {
-                               ret = false;
+               if (level > __fls(linked->nodes_locked)) {
+                       linked->locks_want =
+                               max(level + 1, max_t(unsigned,
+                                   linked->locks_want,
+                                   iter->locks_want));
+                       if (!btree_iter_get_locks(linked, true, false)) {
+                               deadlock_iter = linked;
+                               reason = 5;
                        }
                }
 
                /* Must lock btree nodes in key order: */
-               if ((cmp_int(iter->btree_id, linked->btree_id) ?:
-                    -cmp_int(btree_iter_type(iter), btree_iter_type(linked))) < 0)
-                       ret = false;
-
-               if (iter->btree_id == linked->btree_id &&
-                   btree_node_locked(linked, level) &&
-                   bkey_cmp(pos, btree_node_pos((void *) linked->l[level].b,
-                                                btree_iter_type(linked))) <= 0)
-                       ret = false;
+               if (btree_node_locked(linked, level) &&
+                   bpos_cmp(pos, btree_node_pos((void *) linked->l[level].b,
+                                                btree_iter_type(linked))) <= 0) {
+                       deadlock_iter = linked;
+                       reason = 7;
+               }
 
                /*
                 * Recheck if this is a node we already have locked - since one
@@ -277,20 +325,36 @@ bool __bch2_btree_node_lock(struct btree *b, struct bpos pos,
                }
        }
 
-       if (unlikely(!ret)) {
-               trace_trans_restart_would_deadlock(iter->trans->ip);
+       if (unlikely(deadlock_iter)) {
+               trace_trans_restart_would_deadlock(iter->trans->ip, ip,
+                               reason,
+                               deadlock_iter->btree_id,
+                               btree_iter_type(deadlock_iter),
+                               iter->btree_id,
+                               btree_iter_type(iter));
                return false;
        }
 
        if (six_trylock_type(&b->c.lock, type))
                return true;
 
-       if (six_lock_type(&b->c.lock, type, should_sleep_fn, p))
-               return false;
+#ifdef CONFIG_BCACHEFS_DEBUG
+       trans->locking_iter_idx = iter->idx;
+       trans->locking_pos      = pos;
+       trans->locking_btree_id = iter->btree_id;
+       trans->locking_level    = level;
+       trans->locking          = b;
+#endif
 
-       bch2_time_stats_update(&trans->c->times[lock_to_time_stat(type)],
-                              start_time);
-       return true;
+       ret = six_lock_type(&b->c.lock, type, should_sleep_fn, p) == 0;
+
+#ifdef CONFIG_BCACHEFS_DEBUG
+       trans->locking = NULL;
+#endif
+       if (ret)
+               bch2_time_stats_update(&trans->c->times[lock_to_time_stat(type)],
+                                      start_time);
+       return ret;
 }
 
 /* Btree iterator locking: */
@@ -319,7 +383,7 @@ void bch2_btree_trans_verify_locks(struct btree_trans *trans)
 {
        struct btree_iter *iter;
 
-       trans_for_each_iter_all(trans, iter)
+       trans_for_each_iter(trans, iter)
                bch2_btree_iter_verify_locks(iter);
 }
 #else
@@ -360,50 +424,25 @@ bool __bch2_btree_iter_upgrade(struct btree_iter *iter,
        return false;
 }
 
-bool __bch2_btree_iter_upgrade_nounlock(struct btree_iter *iter,
-                                       unsigned new_locks_want)
+void __bch2_btree_iter_downgrade(struct btree_iter *iter,
+                                unsigned new_locks_want)
 {
-       unsigned l = iter->level;
+       unsigned l;
 
-       EBUG_ON(iter->locks_want >= new_locks_want);
+       EBUG_ON(iter->locks_want < new_locks_want);
 
        iter->locks_want = new_locks_want;
 
-       do {
-               if (!btree_iter_node(iter, l))
-                       break;
-
-               if (!bch2_btree_node_upgrade(iter, l)) {
-                       iter->locks_want = l;
-                       return false;
-               }
-
-               l++;
-       } while (l < iter->locks_want);
-
-       return true;
-}
-
-void __bch2_btree_iter_downgrade(struct btree_iter *iter,
-                                unsigned downgrade_to)
-{
-       unsigned l, new_locks_want = downgrade_to ?:
-               (iter->flags & BTREE_ITER_INTENT ? 1 : 0);
-
-       if (iter->locks_want < downgrade_to) {
-               iter->locks_want = new_locks_want;
-
-               while (iter->nodes_locked &&
-                      (l = __fls(iter->nodes_locked)) >= iter->locks_want) {
-                       if (l > iter->level) {
-                               btree_node_unlock(iter, l);
-                       } else {
-                               if (btree_node_intent_locked(iter, l)) {
-                                       six_lock_downgrade(&iter->l[l].b->c.lock);
-                                       iter->nodes_intent_locked ^= 1 << l;
-                               }
-                               break;
+       while (iter->nodes_locked &&
+              (l = __fls(iter->nodes_locked)) >= iter->locks_want) {
+               if (l > iter->level) {
+                       btree_node_unlock(iter, l);
+               } else {
+                       if (btree_node_intent_locked(iter, l)) {
+                               six_lock_downgrade(&iter->l[l].b->c.lock);
+                               iter->nodes_intent_locked ^= 1 << l;
                        }
+                       break;
                }
        }
 
@@ -423,13 +462,12 @@ void bch2_trans_downgrade(struct btree_trans *trans)
 bool bch2_trans_relock(struct btree_trans *trans)
 {
        struct btree_iter *iter;
-       bool ret = true;
 
        trans_for_each_iter(trans, iter)
-               if (iter->uptodate == BTREE_ITER_NEED_RELOCK)
-                       ret &= bch2_btree_iter_relock(iter, true);
-
-       return ret;
+               if (btree_iter_keep(trans, iter) &&
+                   !bch2_btree_iter_relock(iter, true))
+                       return false;
+       return true;
 }
 
 void bch2_trans_unlock(struct btree_trans *trans)
@@ -463,17 +501,20 @@ static void bch2_btree_iter_verify_cached(struct btree_iter *iter)
 static void bch2_btree_iter_verify_level(struct btree_iter *iter,
                                         unsigned level)
 {
-       struct bpos pos = btree_iter_search_key(iter);
-       struct btree_iter_level *l = &iter->l[level];
-       struct btree_node_iter tmp = l->iter;
-       bool locked = btree_node_locked(iter, level);
+       struct btree_iter_level *l;
+       struct btree_node_iter tmp;
+       bool locked;
        struct bkey_packed *p, *k;
-       char buf1[100], buf2[100];
+       char buf1[100], buf2[100], buf3[100];
        const char *msg;
 
-       if (!debug_check_iterators(iter->trans->c))
+       if (!bch2_debug_check_iterators)
                return;
 
+       l       = &iter->l[level];
+       tmp     = l->iter;
+       locked  = btree_node_locked(iter, level);
+
        if (btree_iter_type(iter) == BTREE_ITER_CACHED) {
                if (!level)
                        bch2_btree_iter_verify_cached(iter);
@@ -488,12 +529,7 @@ static void bch2_btree_iter_verify_level(struct btree_iter *iter,
        if (!bch2_btree_node_relock(iter, level))
                return;
 
-       /*
-        * Ideally this invariant would always be true, and hopefully in the
-        * future it will be, but for now set_pos_same_leaf() breaks it:
-        */
-       BUG_ON(iter->uptodate < BTREE_ITER_NEED_TRAVERSE &&
-              !btree_iter_pos_in_node(iter, l->b));
+       BUG_ON(!btree_iter_pos_in_node(iter, l->b));
 
        /*
         * node iterators don't use leaf node iterator:
@@ -512,16 +548,16 @@ static void bch2_btree_iter_verify_level(struct btree_iter *iter,
         * whiteouts)
         */
        p = level || btree_node_type_is_extents(iter->btree_id)
-               ? bch2_btree_node_iter_prev_filter(&tmp, l->b, KEY_TYPE_discard)
+               ? bch2_btree_node_iter_prev(&tmp, l->b)
                : bch2_btree_node_iter_prev_all(&tmp, l->b);
        k = bch2_btree_node_iter_peek_all(&l->iter, l->b);
 
-       if (p && bkey_iter_pos_cmp(l->b, p, &pos) >= 0) {
+       if (p && bkey_iter_pos_cmp(l->b, p, &iter->real_pos) >= 0) {
                msg = "before";
                goto err;
        }
 
-       if (k && bkey_iter_pos_cmp(l->b, k, &pos) < 0) {
+       if (k && bkey_iter_pos_cmp(l->b, k, &iter->real_pos) < 0) {
                msg = "after";
                goto err;
        }
@@ -530,44 +566,72 @@ unlock:
                btree_node_unlock(iter, level);
        return;
 err:
-       strcpy(buf1, "(none)");
        strcpy(buf2, "(none)");
+       strcpy(buf3, "(none)");
+
+       bch2_bpos_to_text(&PBUF(buf1), iter->real_pos);
 
        if (p) {
                struct bkey uk = bkey_unpack_key(l->b, p);
-               bch2_bkey_to_text(&PBUF(buf1), &uk);
+               bch2_bkey_to_text(&PBUF(buf2), &uk);
        }
 
        if (k) {
                struct bkey uk = bkey_unpack_key(l->b, k);
-               bch2_bkey_to_text(&PBUF(buf2), &uk);
+               bch2_bkey_to_text(&PBUF(buf3), &uk);
        }
 
        panic("iterator should be %s key at level %u:\n"
-             "iter pos %s %llu:%llu\n"
+             "iter pos %s\n"
              "prev key %s\n"
              "cur  key %s\n",
-             msg, level,
-             iter->flags & BTREE_ITER_IS_EXTENTS ? ">" : "=>",
-             iter->pos.inode, iter->pos.offset,
-             buf1, buf2);
+             msg, level, buf1, buf2, buf3);
 }
 
 static void bch2_btree_iter_verify(struct btree_iter *iter)
 {
+       enum btree_iter_type type = btree_iter_type(iter);
        unsigned i;
 
-       bch2_btree_trans_verify_locks(iter->trans);
+       EBUG_ON(iter->btree_id >= BTREE_ID_NR);
+
+       BUG_ON(!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS) &&
+              iter->pos.snapshot != iter->snapshot);
+
+       BUG_ON((iter->flags & BTREE_ITER_IS_EXTENTS) &&
+              (iter->flags & BTREE_ITER_ALL_SNAPSHOTS));
+
+       BUG_ON(type == BTREE_ITER_NODES &&
+              !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS));
+
+       BUG_ON(type != BTREE_ITER_NODES &&
+              (iter->flags & BTREE_ITER_ALL_SNAPSHOTS) &&
+              !btree_type_has_snapshots(iter->btree_id));
+
+       bch2_btree_iter_verify_locks(iter);
 
        for (i = 0; i < BTREE_MAX_DEPTH; i++)
                bch2_btree_iter_verify_level(iter, i);
 }
 
+static void bch2_btree_iter_verify_entry_exit(struct btree_iter *iter)
+{
+       enum btree_iter_type type = btree_iter_type(iter);
+
+       BUG_ON(!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS) &&
+              iter->pos.snapshot != iter->snapshot);
+
+       BUG_ON((type == BTREE_ITER_KEYS ||
+               type == BTREE_ITER_CACHED) &&
+              (bkey_cmp(iter->pos, bkey_start_pos(&iter->k)) < 0 ||
+               bkey_cmp(iter->pos, iter->k.p) > 0));
+}
+
 void bch2_btree_trans_verify_iters(struct btree_trans *trans, struct btree *b)
 {
        struct btree_iter *iter;
 
-       if (!debug_check_iterators(trans->c))
+       if (!bch2_debug_check_iterators)
                return;
 
        trans_for_each_iter_with_node(trans, b, iter)
@@ -578,6 +642,7 @@ void bch2_btree_trans_verify_iters(struct btree_trans *trans, struct btree *b)
 
 static inline void bch2_btree_iter_verify_level(struct btree_iter *iter, unsigned l) {}
 static inline void bch2_btree_iter_verify(struct btree_iter *iter) {}
+static inline void bch2_btree_iter_verify_entry_exit(struct btree_iter *iter) {}
 
 #endif
 
@@ -603,12 +668,11 @@ static void __bch2_btree_iter_fix_key_modified(struct btree_iter *iter,
                                               struct bkey_packed *where)
 {
        struct btree_iter_level *l = &iter->l[b->c.level];
-       struct bpos pos = btree_iter_search_key(iter);
 
        if (where != bch2_btree_node_iter_peek_all(&l->iter, l->b))
                return;
 
-       if (bkey_iter_pos_cmp(l->b, where, &pos) < 0)
+       if (bkey_iter_pos_cmp(l->b, where, &iter->real_pos) < 0)
                bch2_btree_node_iter_advance(&l->iter, l->b);
 
        btree_iter_set_dirty(iter, BTREE_ITER_NEED_PEEK);
@@ -643,7 +707,6 @@ static void __bch2_btree_node_iter_fix(struct btree_iter *iter,
        bool iter_current_key_modified =
                orig_iter_pos >= offset &&
                orig_iter_pos <= offset + clobber_u64s;
-       struct bpos iter_pos = btree_iter_search_key(iter);
 
        btree_node_iter_for_each(node_iter, set)
                if (set->end == old_end)
@@ -651,7 +714,7 @@ static void __bch2_btree_node_iter_fix(struct btree_iter *iter,
 
        /* didn't find the bset in the iterator - might have to readd it: */
        if (new_u64s &&
-           bkey_iter_pos_cmp(b, where, &iter_pos) >= 0) {
+           bkey_iter_pos_cmp(b, where, &iter->real_pos) >= 0) {
                bch2_btree_node_iter_push(node_iter, b, where, end);
                goto fixup_done;
        } else {
@@ -666,7 +729,7 @@ found:
                return;
 
        if (new_u64s &&
-           bkey_iter_pos_cmp(b, where, &iter_pos) >= 0) {
+           bkey_iter_pos_cmp(b, where, &iter->real_pos) >= 0) {
                set->k = offset;
        } else if (set->k < offset + clobber_u64s) {
                set->k = offset + new_u64s;
@@ -739,7 +802,7 @@ void bch2_btree_node_iter_fix(struct btree_iter *iter,
                __bch2_btree_node_iter_fix(iter, b, node_iter, t,
                                           where, clobber_u64s, new_u64s);
 
-               if (debug_check_iterators(iter->trans->c))
+               if (bch2_debug_check_iterators)
                        bch2_btree_node_iter_verify(node_iter, b);
        }
 
@@ -769,45 +832,50 @@ static inline struct bkey_s_c __btree_iter_unpack(struct btree_iter *iter,
 
        ret = bkey_disassemble(l->b, k, u);
 
-       if (debug_check_bkeys(iter->trans->c))
+       if (bch2_debug_check_bkeys)
                bch2_bkey_debugcheck(iter->trans->c, l->b, ret);
 
        return ret;
 }
 
 /* peek_all() doesn't skip deleted keys */
-static inline struct bkey_s_c __btree_iter_peek_all(struct btree_iter *iter,
-                                                   struct btree_iter_level *l,
-                                                   struct bkey *u)
+static inline struct bkey_s_c btree_iter_level_peek_all(struct btree_iter *iter,
+                                                       struct btree_iter_level *l,
+                                                       struct bkey *u)
 {
        return __btree_iter_unpack(iter, l, u,
                        bch2_btree_node_iter_peek_all(&l->iter, l->b));
 }
 
-static inline struct bkey_s_c __btree_iter_peek(struct btree_iter *iter,
-                                               struct btree_iter_level *l)
+static inline struct bkey_s_c btree_iter_level_peek(struct btree_iter *iter,
+                                                   struct btree_iter_level *l)
 {
-       return __btree_iter_unpack(iter, l, &iter->k,
+       struct bkey_s_c k = __btree_iter_unpack(iter, l, &iter->k,
                        bch2_btree_node_iter_peek(&l->iter, l->b));
+
+       iter->real_pos = k.k ? k.k->p : l->b->key.k.p;
+       return k;
 }
 
-static inline struct bkey_s_c __btree_iter_prev(struct btree_iter *iter,
-                                               struct btree_iter_level *l)
+static inline struct bkey_s_c btree_iter_level_prev(struct btree_iter *iter,
+                                                   struct btree_iter_level *l)
 {
-       return __btree_iter_unpack(iter, l, &iter->k,
+       struct bkey_s_c k = __btree_iter_unpack(iter, l, &iter->k,
                        bch2_btree_node_iter_prev(&l->iter, l->b));
+
+       iter->real_pos = k.k ? k.k->p : l->b->data->min_key;
+       return k;
 }
 
 static inline bool btree_iter_advance_to_pos(struct btree_iter *iter,
                                             struct btree_iter_level *l,
                                             int max_advance)
 {
-       struct bpos pos = btree_iter_search_key(iter);
        struct bkey_packed *k;
        int nr_advanced = 0;
 
        while ((k = bch2_btree_node_iter_peek_all(&l->iter, l->b)) &&
-              bkey_iter_pos_cmp(l->b, k, &pos) < 0) {
+              bkey_iter_pos_cmp(l->b, k, &iter->real_pos) < 0) {
                if (max_advance > 0 && nr_advanced >= max_advance)
                        return false;
 
@@ -845,12 +913,23 @@ static void btree_iter_verify_new_node(struct btree_iter *iter, struct btree *b)
        if (!k ||
            bkey_deleted(k) ||
            bkey_cmp_left_packed(l->b, k, &b->key.k.p)) {
-               char buf[100];
+               char buf1[100];
+               char buf2[100];
+               char buf3[100];
+               char buf4[100];
                struct bkey uk = bkey_unpack_key(b, k);
 
-               bch2_bkey_to_text(&PBUF(buf), &uk);
-               panic("parent iter doesn't point to new node:\n%s\n%llu:%llu\n",
-                     buf, b->key.k.p.inode, b->key.k.p.offset);
+               bch2_dump_btree_node(iter->trans->c, l->b);
+               bch2_bpos_to_text(&PBUF(buf1), iter->real_pos);
+               bch2_bkey_to_text(&PBUF(buf2), &uk);
+               bch2_bpos_to_text(&PBUF(buf3), b->data->min_key);
+               bch2_bpos_to_text(&PBUF(buf3), b->data->max_key);
+               panic("parent iter doesn't point to new node:\n"
+                     "iter pos %s %s\n"
+                     "iter key %s\n"
+                     "new node %s-%s\n",
+                     bch2_btree_ids[iter->btree_id], buf1,
+                     buf2, buf3, buf4);
        }
 
        if (!parent_locked)
@@ -860,10 +939,16 @@ static void btree_iter_verify_new_node(struct btree_iter *iter, struct btree *b)
 static inline void __btree_iter_init(struct btree_iter *iter,
                                     unsigned level)
 {
-       struct bpos pos = btree_iter_search_key(iter);
        struct btree_iter_level *l = &iter->l[level];
 
-       bch2_btree_node_iter_init(&l->iter, l->b, &pos);
+       bch2_btree_node_iter_init(&l->iter, l->b, &iter->real_pos);
+
+       /*
+        * Iterators to interior nodes should always be pointed at the first non
+        * whiteout:
+        */
+       if (level)
+               bch2_btree_node_iter_peek(&l->iter, l->b);
 
        btree_iter_set_dirty(iter, BTREE_ITER_NEED_PEEK);
 }
@@ -919,7 +1004,7 @@ void bch2_btree_iter_node_drop(struct btree_iter *iter, struct btree *b)
 
        trans_for_each_iter(iter->trans, linked)
                if (linked->l[level].b == b) {
-                       __btree_node_unlock(linked, level);
+                       btree_node_unlock(linked, level);
                        linked->l[level].b = BTREE_ITER_NO_NODE_DROP;
                }
 }
@@ -945,7 +1030,8 @@ static int lock_root_check_fn(struct six_lock *lock, void *p)
 }
 
 static inline int btree_iter_lock_root(struct btree_iter *iter,
-                                      unsigned depth_want)
+                                      unsigned depth_want,
+                                      unsigned long trace_ip)
 {
        struct bch_fs *c = iter->trans->c;
        struct btree *b, **rootp = &c->btree_roots[iter->btree_id].b;
@@ -974,7 +1060,8 @@ static inline int btree_iter_lock_root(struct btree_iter *iter,
                lock_type = __btree_lock_want(iter, iter->level);
                if (unlikely(!btree_node_lock(b, POS_MAX, iter->level,
                                              iter, lock_type,
-                                             lock_root_check_fn, rootp)))
+                                             lock_root_check_fn, rootp,
+                                             trace_ip)))
                        return -EINTR;
 
                if (likely(b == READ_ONCE(*rootp) &&
@@ -1002,27 +1089,32 @@ static void btree_iter_prefetch(struct btree_iter *iter)
        struct btree_iter_level *l = &iter->l[iter->level];
        struct btree_node_iter node_iter = l->iter;
        struct bkey_packed *k;
-       BKEY_PADDED(k) tmp;
+       struct bkey_buf tmp;
        unsigned nr = test_bit(BCH_FS_STARTED, &c->flags)
                ? (iter->level > 1 ? 0 :  2)
                : (iter->level > 1 ? 1 : 16);
        bool was_locked = btree_node_locked(iter, iter->level);
 
+       bch2_bkey_buf_init(&tmp);
+
        while (nr) {
                if (!bch2_btree_node_relock(iter, iter->level))
-                       return;
+                       break;
 
                bch2_btree_node_iter_advance(&node_iter, l->b);
                k = bch2_btree_node_iter_peek(&node_iter, l->b);
                if (!k)
                        break;
 
-               bch2_bkey_unpack(l->b, &tmp.k, k);
-               bch2_btree_node_prefetch(c, iter, &tmp.k, iter->level - 1);
+               bch2_bkey_buf_unpack(&tmp, c, l->b, k);
+               bch2_btree_node_prefetch(c, iter, tmp.k, iter->btree_id,
+                                        iter->level - 1);
        }
 
        if (!was_locked)
                btree_node_unlock(iter, iter->level);
+
+       bch2_bkey_buf_exit(&tmp, c);
 }
 
 static noinline void btree_node_mem_ptr_set(struct btree_iter *iter,
@@ -1046,45 +1138,45 @@ static noinline void btree_node_mem_ptr_set(struct btree_iter *iter,
                btree_node_unlock(iter, plevel);
 }
 
-static __always_inline int btree_iter_down(struct btree_iter *iter)
+static __always_inline int btree_iter_down(struct btree_iter *iter,
+                                          unsigned long trace_ip)
 {
        struct bch_fs *c = iter->trans->c;
        struct btree_iter_level *l = &iter->l[iter->level];
        struct btree *b;
        unsigned level = iter->level - 1;
        enum six_lock_type lock_type = __btree_lock_want(iter, level);
-       BKEY_PADDED(k) tmp;
+       struct bkey_buf tmp;
+       int ret;
 
        EBUG_ON(!btree_node_locked(iter, iter->level));
 
-       bch2_bkey_unpack(l->b, &tmp.k,
+       bch2_bkey_buf_init(&tmp);
+       bch2_bkey_buf_unpack(&tmp, c, l->b,
                         bch2_btree_node_iter_peek(&l->iter, l->b));
 
-       b = bch2_btree_node_get(c, iter, &tmp.k, level, lock_type);
-       if (unlikely(IS_ERR(b)))
-               return PTR_ERR(b);
+       b = bch2_btree_node_get(c, iter, tmp.k, level, lock_type, trace_ip);
+       ret = PTR_ERR_OR_ZERO(b);
+       if (unlikely(ret))
+               goto err;
 
        mark_btree_node_locked(iter, level, lock_type);
        btree_iter_node_set(iter, b);
 
-       if (tmp.k.k.type == KEY_TYPE_btree_ptr_v2 &&
-           unlikely(b != btree_node_mem_ptr(&tmp.k)))
+       if (tmp.k->k.type == KEY_TYPE_btree_ptr_v2 &&
+           unlikely(b != btree_node_mem_ptr(tmp.k)))
                btree_node_mem_ptr_set(iter, level + 1, b);
 
        if (iter->flags & BTREE_ITER_PREFETCH)
                btree_iter_prefetch(iter);
 
        iter->level = level;
-
-       return 0;
-}
-
-static void btree_iter_up(struct btree_iter *iter)
-{
-       btree_node_unlock(iter, iter->level++);
+err:
+       bch2_bkey_buf_exit(&tmp, c);
+       return ret;
 }
 
-static int btree_iter_traverse_one(struct btree_iter *);
+static int btree_iter_traverse_one(struct btree_iter *, unsigned long);
 
 static int __btree_iter_traverse_all(struct btree_trans *trans, int ret)
 {
@@ -1104,11 +1196,12 @@ retry_all:
                sorted[nr_sorted++] = iter->idx;
 
 #define btree_iter_cmp_by_idx(_l, _r)                          \
-               btree_iter_cmp(&trans->iters[_l], &trans->iters[_r])
+               btree_iter_lock_cmp(&trans->iters[_l], &trans->iters[_r])
 
        bubble_sort(sorted, nr_sorted, btree_iter_cmp_by_idx);
 #undef btree_iter_cmp_by_idx
        bch2_trans_unlock(trans);
+       cond_resched();
 
        if (unlikely(ret == -ENOMEM)) {
                struct closure cl;
@@ -1139,7 +1232,7 @@ retry_all:
                if (!(trans->iters_linked & (1ULL << idx)))
                        continue;
 
-               ret = btree_iter_traverse_one(&trans->iters[idx]);
+               ret = btree_iter_traverse_one(&trans->iters[idx], _THIS_IP_);
                if (ret)
                        goto retry_all;
        }
@@ -1171,9 +1264,9 @@ static inline bool btree_iter_good_node(struct btree_iter *iter,
            !bch2_btree_node_relock(iter, l))
                return false;
 
-       if (check_pos <= 0 && btree_iter_pos_before_node(iter, iter->l[l].b))
+       if (check_pos < 0 && btree_iter_pos_before_node(iter, iter->l[l].b))
                return false;
-       if (check_pos >= 0 && btree_iter_pos_after_node(iter, iter->l[l].b))
+       if (check_pos > 0 && btree_iter_pos_after_node(iter, iter->l[l].b))
                return false;
        return true;
 }
@@ -1202,7 +1295,8 @@ static inline unsigned btree_iter_up_until_good_node(struct btree_iter *iter,
  * On error, caller (peek_node()/peek_key()) must return NULL; the error is
  * stashed in the iterator and returned from bch2_trans_exit().
  */
-static int btree_iter_traverse_one(struct btree_iter *iter)
+static int btree_iter_traverse_one(struct btree_iter *iter,
+                                  unsigned long trace_ip)
 {
        unsigned depth_want = iter->level;
 
@@ -1223,24 +1317,8 @@ static int btree_iter_traverse_one(struct btree_iter *iter)
        if (unlikely(iter->level >= BTREE_MAX_DEPTH))
                return 0;
 
-       /*
-        * XXX: correctly using BTREE_ITER_UPTODATE should make using check_pos
-        * here unnecessary
-        */
        iter->level = btree_iter_up_until_good_node(iter, 0);
 
-       /*
-        * If we've got a btree node locked (i.e. we aren't about to relock the
-        * root) - advance its node iterator if necessary:
-        *
-        * XXX correctly using BTREE_ITER_UPTODATE should make this unnecessary
-        */
-       if (is_btree_node(iter, iter->level)) {
-               BUG_ON(!btree_iter_pos_in_node(iter, iter->l[iter->level].b));
-
-               btree_iter_advance_to_pos(iter, &iter->l[iter->level], -1);
-       }
-
        /*
         * Note: iter->nodes[iter->level] may be temporarily NULL here - that
         * would indicate to other code that we got to the end of the btree,
@@ -1249,8 +1327,8 @@ static int btree_iter_traverse_one(struct btree_iter *iter)
         */
        while (iter->level > depth_want) {
                int ret = btree_iter_node(iter, iter->level)
-                       ? btree_iter_down(iter)
-                       : btree_iter_lock_root(iter, depth_want);
+                       ? btree_iter_down(iter, trace_ip)
+                       : btree_iter_lock_root(iter, depth_want, trace_ip);
                if (unlikely(ret)) {
                        if (ret == 1)
                                return 0;
@@ -1275,32 +1353,41 @@ static int btree_iter_traverse_one(struct btree_iter *iter)
        return 0;
 }
 
-int __must_check __bch2_btree_iter_traverse(struct btree_iter *iter)
+static int __must_check __bch2_btree_iter_traverse(struct btree_iter *iter)
 {
        struct btree_trans *trans = iter->trans;
        int ret;
 
        ret =   bch2_trans_cond_resched(trans) ?:
-               btree_iter_traverse_one(iter);
+               btree_iter_traverse_one(iter, _RET_IP_);
        if (unlikely(ret))
                ret = __btree_iter_traverse_all(trans, ret);
 
        return ret;
 }
 
-static inline void bch2_btree_iter_checks(struct btree_iter *iter)
+/*
+ * Note:
+ * bch2_btree_iter_traverse() is for external users, btree_iter_traverse() is
+ * for internal btree iterator users
+ *
+ * bch2_btree_iter_traverse sets iter->real_pos to iter->pos,
+ * btree_iter_traverse() does not:
+ */
+static inline int __must_check
+btree_iter_traverse(struct btree_iter *iter)
 {
-       enum btree_iter_type type = btree_iter_type(iter);
-
-       EBUG_ON(iter->btree_id >= BTREE_ID_NR);
+       return iter->uptodate >= BTREE_ITER_NEED_RELOCK
+               ? __bch2_btree_iter_traverse(iter)
+               : 0;
+}
 
-       BUG_ON((type == BTREE_ITER_KEYS ||
-               type == BTREE_ITER_CACHED) &&
-              (bkey_cmp(iter->pos, bkey_start_pos(&iter->k)) < 0 ||
-               bkey_cmp(iter->pos, iter->k.p) > 0));
+int __must_check
+bch2_btree_iter_traverse(struct btree_iter *iter)
+{
+       btree_iter_set_search_pos(iter, btree_iter_search_key(iter));
 
-       bch2_btree_iter_verify_locks(iter);
-       bch2_btree_iter_verify_level(iter, iter->level);
+       return btree_iter_traverse(iter);
 }
 
 /* Iterate across nodes (leaf and interior nodes) */
@@ -1311,12 +1398,9 @@ struct btree *bch2_btree_iter_peek_node(struct btree_iter *iter)
        int ret;
 
        EBUG_ON(btree_iter_type(iter) != BTREE_ITER_NODES);
-       bch2_btree_iter_checks(iter);
-
-       if (iter->uptodate == BTREE_ITER_UPTODATE)
-               return iter->l[iter->level].b;
+       bch2_btree_iter_verify(iter);
 
-       ret = bch2_btree_iter_traverse(iter);
+       ret = btree_iter_traverse(iter);
        if (ret)
                return NULL;
 
@@ -1324,10 +1408,9 @@ struct btree *bch2_btree_iter_peek_node(struct btree_iter *iter)
        if (!b)
                return NULL;
 
-       BUG_ON(bkey_cmp(b->key.k.p, iter->pos) < 0);
+       BUG_ON(bpos_cmp(b->key.k.p, iter->pos) < 0);
 
-       iter->pos = b->key.k.p;
-       iter->uptodate = BTREE_ITER_UPTODATE;
+       iter->pos = iter->real_pos = b->key.k.p;
 
        bch2_btree_iter_verify(iter);
 
@@ -1340,7 +1423,7 @@ struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
        int ret;
 
        EBUG_ON(btree_iter_type(iter) != BTREE_ITER_NODES);
-       bch2_btree_iter_checks(iter);
+       bch2_btree_iter_verify(iter);
 
        /* already got to end? */
        if (!btree_iter_node(iter, iter->level))
@@ -1348,12 +1431,12 @@ struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
 
        bch2_trans_cond_resched(iter->trans);
 
-       btree_iter_up(iter);
+       btree_node_unlock(iter, iter->level);
+       iter->l[iter->level].b = BTREE_ITER_NO_NODE_UP;
+       iter->level++;
 
-       if (!bch2_btree_node_relock(iter, iter->level))
-               btree_iter_set_dirty(iter, BTREE_ITER_NEED_RELOCK);
-
-       ret = bch2_btree_iter_traverse(iter);
+       btree_iter_set_dirty(iter, BTREE_ITER_NEED_TRAVERSE);
+       ret = btree_iter_traverse(iter);
        if (ret)
                return NULL;
 
@@ -1362,34 +1445,28 @@ struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
        if (!b)
                return NULL;
 
-       if (bkey_cmp(iter->pos, b->key.k.p) < 0) {
+       if (bpos_cmp(iter->pos, b->key.k.p) < 0) {
                /*
                 * Haven't gotten to the end of the parent node: go back down to
                 * the next child node
                 */
+               btree_iter_set_search_pos(iter, bpos_successor(iter->pos));
 
-               /*
-                * We don't really want to be unlocking here except we can't
-                * directly tell btree_iter_traverse() "traverse to this level"
-                * except by setting iter->level, so we have to unlock so we
-                * don't screw up our lock invariants:
-                */
-               if (btree_node_read_locked(iter, iter->level))
-                       btree_node_unlock(iter, iter->level);
-
-               iter->pos       = bkey_successor(iter->pos);
-               iter->level     = iter->min_depth;
+               /* Unlock to avoid screwing up our lock invariants: */
+               btree_node_unlock(iter, iter->level);
 
+               iter->level = iter->min_depth;
                btree_iter_set_dirty(iter, BTREE_ITER_NEED_TRAVERSE);
-               ret = bch2_btree_iter_traverse(iter);
+               bch2_btree_iter_verify(iter);
+
+               ret = btree_iter_traverse(iter);
                if (ret)
                        return NULL;
 
                b = iter->l[iter->level].b;
        }
 
-       iter->pos = b->key.k.p;
-       iter->uptodate = BTREE_ITER_UPTODATE;
+       iter->pos = iter->real_pos = b->key.k.p;
 
        bch2_btree_iter_verify(iter);
 
@@ -1398,43 +1475,16 @@ struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
 
 /* Iterate across keys (in leaf nodes only) */
 
-void bch2_btree_iter_set_pos_same_leaf(struct btree_iter *iter, struct bpos new_pos)
-{
-       struct btree_iter_level *l = &iter->l[0];
-
-       EBUG_ON(iter->level != 0);
-       EBUG_ON(bkey_cmp(new_pos, iter->pos) < 0);
-       EBUG_ON(!btree_node_locked(iter, 0));
-       EBUG_ON(bkey_cmp(new_pos, l->b->key.k.p) > 0);
-
-       bkey_init(&iter->k);
-       iter->k.p = iter->pos = new_pos;
-       btree_iter_set_dirty(iter, BTREE_ITER_NEED_PEEK);
-
-       btree_iter_advance_to_pos(iter, l, -1);
-
-       /*
-        * XXX:
-        * keeping a node locked that's outside (even just outside) iter->pos
-        * breaks __bch2_btree_node_lock(). This seems to only affect
-        * bch2_btree_node_get_sibling so for now it's fixed there, but we
-        * should try to get rid of this corner case.
-        *
-        * (this behaviour is currently needed for BTREE_INSERT_NOUNLOCK)
-        */
-
-       if (bch2_btree_node_iter_end(&l->iter) &&
-           btree_iter_pos_after_node(iter, l->b))
-               btree_iter_set_dirty(iter, BTREE_ITER_NEED_TRAVERSE);
-}
-
-static void btree_iter_pos_changed(struct btree_iter *iter, int cmp)
+static void btree_iter_set_search_pos(struct btree_iter *iter, struct bpos new_pos)
 {
+       int cmp = bpos_cmp(new_pos, iter->real_pos);
        unsigned l = iter->level;
 
        if (!cmp)
                goto out;
 
+       iter->real_pos = new_pos;
+
        if (unlikely(btree_iter_type(iter) == BTREE_ITER_CACHED)) {
                btree_node_unlock(iter, 0);
                iter->l[0].b = BTREE_ITER_NO_NODE_UP;
@@ -1464,245 +1514,162 @@ out:
                btree_iter_set_dirty(iter, BTREE_ITER_NEED_TRAVERSE);
        else
                btree_iter_set_dirty(iter, BTREE_ITER_NEED_PEEK);
+
+       bch2_btree_iter_verify(iter);
 }
 
-void __bch2_btree_iter_set_pos(struct btree_iter *iter, struct bpos new_pos,
-                              bool strictly_greater)
+inline bool bch2_btree_iter_advance(struct btree_iter *iter)
 {
-       struct bpos old = btree_iter_search_key(iter);
-       int cmp;
-
-       iter->flags &= ~BTREE_ITER_IS_EXTENTS;
-       iter->flags |= strictly_greater ? BTREE_ITER_IS_EXTENTS : 0;
+       struct bpos pos = iter->k.p;
+       bool ret = bpos_cmp(pos, POS_MAX) != 0;
 
-       bkey_init(&iter->k);
-       iter->k.p = iter->pos = new_pos;
-
-       cmp = bkey_cmp(btree_iter_search_key(iter), old);
-
-       btree_iter_pos_changed(iter, cmp);
+       if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
+               pos = bkey_successor(iter, pos);
+       bch2_btree_iter_set_pos(iter, pos);
+       return ret;
 }
 
-void bch2_btree_iter_set_pos(struct btree_iter *iter, struct bpos new_pos)
+inline bool bch2_btree_iter_rewind(struct btree_iter *iter)
 {
-       int cmp = bkey_cmp(new_pos, iter->pos);
-
-       bkey_init(&iter->k);
-       iter->k.p = iter->pos = new_pos;
+       struct bpos pos = bkey_start_pos(&iter->k);
+       bool ret = bpos_cmp(pos, POS_MIN) != 0;
 
-       btree_iter_pos_changed(iter, cmp);
+       if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
+               pos = bkey_predecessor(iter, pos);
+       bch2_btree_iter_set_pos(iter, pos);
+       return ret;
 }
 
 static inline bool btree_iter_set_pos_to_next_leaf(struct btree_iter *iter)
 {
-       struct btree_iter_level *l = &iter->l[0];
-       bool ret;
-
-       bkey_init(&iter->k);
-       iter->k.p = iter->pos = l->b->key.k.p;
+       struct bpos next_pos = iter->l[0].b->key.k.p;
+       bool ret = bpos_cmp(next_pos, POS_MAX) != 0;
 
-       ret = bkey_cmp(iter->pos, POS_MAX) != 0;
-       if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
-               iter->k.p = iter->pos = bkey_successor(iter->pos);
+       /*
+        * Typically, we don't want to modify iter->pos here, since that
+        * indicates where we searched from - unless we got to the end of the
+        * btree, in that case we want iter->pos to reflect that:
+        */
+       if (ret)
+               btree_iter_set_search_pos(iter, bpos_successor(next_pos));
+       else
+               bch2_btree_iter_set_pos(iter, POS_MAX);
 
-       btree_iter_pos_changed(iter, 1);
        return ret;
 }
 
 static inline bool btree_iter_set_pos_to_prev_leaf(struct btree_iter *iter)
 {
-       struct btree_iter_level *l = &iter->l[0];
-       bool ret;
-
-       bkey_init(&iter->k);
-       iter->k.p = iter->pos = l->b->data->min_key;
-       iter->uptodate  = BTREE_ITER_NEED_TRAVERSE;
-
-       ret = bkey_cmp(iter->pos, POS_MIN) != 0;
-       if (ret) {
-               iter->k.p = iter->pos = bkey_predecessor(iter->pos);
+       struct bpos next_pos = iter->l[0].b->data->min_key;
+       bool ret = bpos_cmp(next_pos, POS_MIN) != 0;
 
-               if (iter->flags & BTREE_ITER_IS_EXTENTS)
-                       iter->k.p = iter->pos = bkey_predecessor(iter->pos);
-       }
+       if (ret)
+               btree_iter_set_search_pos(iter, bpos_predecessor(next_pos));
+       else
+               bch2_btree_iter_set_pos(iter, POS_MIN);
 
-       btree_iter_pos_changed(iter, -1);
        return ret;
 }
 
-/**
- * btree_iter_peek_uptodate - given an iterator that is uptodate, return the key
- * it currently points to
- */
-static inline struct bkey_s_c btree_iter_peek_uptodate(struct btree_iter *iter)
+static struct bkey_i *btree_trans_peek_updates(struct btree_trans *trans,
+                                              enum btree_id btree_id, struct bpos pos)
 {
-       struct btree_iter_level *l = &iter->l[0];
-       struct bkey_s_c ret = { .k = &iter->k };
-
-       if (!bkey_deleted(&iter->k)) {
-               struct bkey_packed *_k =
-                       __bch2_btree_node_iter_peek_all(&l->iter, l->b);
-
-               ret.v = bkeyp_val(&l->b->format, _k);
-
-               if (debug_check_iterators(iter->trans->c)) {
-                       struct bkey k = bkey_unpack_key(l->b, _k);
+       struct btree_insert_entry *i;
 
-                       BUG_ON(memcmp(&k, &iter->k, sizeof(k)));
+       trans_for_each_update2(trans, i)
+               if ((cmp_int(btree_id,  i->iter->btree_id) ?:
+                    bkey_cmp(pos,      i->k->k.p)) <= 0) {
+                       if (btree_id == i->iter->btree_id)
+                               return i->k;
+                       break;
                }
 
-               if (debug_check_bkeys(iter->trans->c))
-                       bch2_bkey_debugcheck(iter->trans->c, l->b, ret);
-       }
-
-       return ret;
+       return NULL;
 }
 
-/**
- * bch2_btree_iter_peek: returns first key greater than or equal to iterator's
- * current position
- */
-struct bkey_s_c bch2_btree_iter_peek(struct btree_iter *iter)
+static inline struct bkey_s_c __btree_iter_peek(struct btree_iter *iter, bool with_updates)
 {
-       struct btree_iter_level *l = &iter->l[0];
+       struct bpos search_key = btree_iter_search_key(iter);
+       struct bkey_i *next_update = with_updates
+               ? btree_trans_peek_updates(iter->trans, iter->btree_id, search_key)
+               : NULL;
        struct bkey_s_c k;
        int ret;
 
        EBUG_ON(btree_iter_type(iter) != BTREE_ITER_KEYS);
-       bch2_btree_iter_checks(iter);
+       bch2_btree_iter_verify(iter);
+       bch2_btree_iter_verify_entry_exit(iter);
 
-       if (iter->uptodate == BTREE_ITER_UPTODATE &&
-           !bkey_deleted(&iter->k))
-               return btree_iter_peek_uptodate(iter);
+       btree_iter_set_search_pos(iter, search_key);
 
        while (1) {
-               ret = bch2_btree_iter_traverse(iter);
+               ret = btree_iter_traverse(iter);
                if (unlikely(ret))
                        return bkey_s_c_err(ret);
 
-               k = __btree_iter_peek(iter, l);
-               if (likely(k.k))
+               k = btree_iter_level_peek(iter, &iter->l[0]);
+
+               if (next_update &&
+                   bpos_cmp(next_update->k.p, iter->real_pos) <= 0)
+                       k = bkey_i_to_s_c(next_update);
+
+               if (likely(k.k)) {
+                       if (bkey_deleted(k.k)) {
+                               btree_iter_set_search_pos(iter,
+                                               bkey_successor(iter, k.k->p));
+                               continue;
+                       }
+
                        break;
+               }
 
                if (!btree_iter_set_pos_to_next_leaf(iter))
                        return bkey_s_c_null;
        }
 
        /*
-        * iter->pos should always be equal to the key we just
-        * returned - except extents can straddle iter->pos:
+        * iter->pos should be mononotically increasing, and always be equal to
+        * the key we just returned - except extents can straddle iter->pos:
         */
-       if (!(iter->flags & BTREE_ITER_IS_EXTENTS) ||
-           bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0)
+       if (bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0)
                iter->pos = bkey_start_pos(k.k);
 
-       iter->uptodate = BTREE_ITER_UPTODATE;
-
-       bch2_btree_iter_verify_level(iter, 0);
+       bch2_btree_iter_verify_entry_exit(iter);
+       bch2_btree_iter_verify(iter);
        return k;
 }
 
+/**
+ * bch2_btree_iter_peek: returns first key greater than or equal to iterator's
+ * current position
+ */
+struct bkey_s_c bch2_btree_iter_peek(struct btree_iter *iter)
+{
+       return __btree_iter_peek(iter, false);
+}
+
 /**
  * bch2_btree_iter_next: returns first key greater than iterator's current
  * position
  */
 struct bkey_s_c bch2_btree_iter_next(struct btree_iter *iter)
 {
-       if (unlikely(!bkey_cmp(iter->k.p, POS_MAX)))
+       if (!bch2_btree_iter_advance(iter))
                return bkey_s_c_null;
 
-       bch2_btree_iter_set_pos(iter,
-               (iter->flags & BTREE_ITER_IS_EXTENTS)
-               ? iter->k.p
-               : bkey_successor(iter->k.p));
-
        return bch2_btree_iter_peek(iter);
 }
 
-static struct bkey_s_c __btree_trans_updates_peek(struct btree_iter *iter)
-{
-       struct bpos pos = btree_iter_search_key(iter);
-       struct btree_trans *trans = iter->trans;
-       struct btree_insert_entry *i;
-
-       trans_for_each_update2(trans, i)
-               if ((cmp_int(iter->btree_id,    i->iter->btree_id) ?:
-                    bkey_cmp(pos,              i->k->k.p)) <= 0)
-                       break;
-
-       return i < trans->updates2 + trans->nr_updates2 &&
-               iter->btree_id == i->iter->btree_id
-               ? bkey_i_to_s_c(i->k)
-               : bkey_s_c_null;
-}
-
-static struct bkey_s_c __bch2_btree_iter_peek_with_updates(struct btree_iter *iter)
-{
-       struct btree_iter_level *l = &iter->l[0];
-       struct bkey_s_c k = __btree_iter_peek(iter, l);
-       struct bkey_s_c u = __btree_trans_updates_peek(iter);
-
-       if (k.k && (!u.k || bkey_cmp(k.k->p, u.k->p) < 0))
-               return k;
-       if (u.k && bkey_cmp(u.k->p, l->b->key.k.p) <= 0) {
-               iter->k = *u.k;
-               return u;
-       }
-       return bkey_s_c_null;
-}
-
 struct bkey_s_c bch2_btree_iter_peek_with_updates(struct btree_iter *iter)
 {
-       struct bkey_s_c k;
-       int ret;
-
-       EBUG_ON(btree_iter_type(iter) != BTREE_ITER_KEYS);
-       bch2_btree_iter_checks(iter);
-
-       while (1) {
-               ret = bch2_btree_iter_traverse(iter);
-               if (unlikely(ret))
-                       return bkey_s_c_err(ret);
-
-               k = __bch2_btree_iter_peek_with_updates(iter);
-
-               if (k.k && bkey_deleted(k.k)) {
-                       bch2_btree_iter_set_pos(iter,
-                               (iter->flags & BTREE_ITER_IS_EXTENTS)
-                               ? iter->k.p
-                               : bkey_successor(iter->k.p));
-                       continue;
-               }
-
-               if (likely(k.k))
-                       break;
-
-               if (!btree_iter_set_pos_to_next_leaf(iter))
-                       return bkey_s_c_null;
-       }
-
-       /*
-        * iter->pos should always be equal to the key we just
-        * returned - except extents can straddle iter->pos:
-        */
-       if (!(iter->flags & BTREE_ITER_IS_EXTENTS) ||
-           bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0)
-               iter->pos = bkey_start_pos(k.k);
-
-       iter->uptodate = BTREE_ITER_UPTODATE;
-       return k;
+       return __btree_iter_peek(iter, true);
 }
 
 struct bkey_s_c bch2_btree_iter_next_with_updates(struct btree_iter *iter)
 {
-       if (unlikely(!bkey_cmp(iter->k.p, POS_MAX)))
+       if (!bch2_btree_iter_advance(iter))
                return bkey_s_c_null;
 
-       bch2_btree_iter_set_pos(iter,
-               (iter->flags & BTREE_ITER_IS_EXTENTS)
-               ? iter->k.p
-               : bkey_successor(iter->k.p));
-
        return bch2_btree_iter_peek_with_updates(iter);
 }
 
@@ -1712,38 +1679,57 @@ struct bkey_s_c bch2_btree_iter_next_with_updates(struct btree_iter *iter)
  */
 struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 {
-       struct bpos pos = iter->pos;
        struct btree_iter_level *l = &iter->l[0];
        struct bkey_s_c k;
        int ret;
 
        EBUG_ON(btree_iter_type(iter) != BTREE_ITER_KEYS);
-       bch2_btree_iter_checks(iter);
+       bch2_btree_iter_verify(iter);
+       bch2_btree_iter_verify_entry_exit(iter);
 
-       if (iter->uptodate == BTREE_ITER_UPTODATE &&
-           !bkey_deleted(&iter->k))
-               return btree_iter_peek_uptodate(iter);
+       btree_iter_set_search_pos(iter, iter->pos);
 
        while (1) {
-               ret = bch2_btree_iter_traverse(iter);
-               if (unlikely(ret))
-                       return bkey_s_c_err(ret);
+               ret = btree_iter_traverse(iter);
+               if (unlikely(ret)) {
+                       k = bkey_s_c_err(ret);
+                       goto no_key;
+               }
 
-               k = __btree_iter_peek(iter, l);
-               if (!k.k || bkey_cmp(bkey_start_pos(k.k), pos) > 0)
-                       k = __btree_iter_prev(iter, l);
+               k = btree_iter_level_peek(iter, l);
+               if (!k.k ||
+                   ((iter->flags & BTREE_ITER_IS_EXTENTS)
+                    ? bkey_cmp(bkey_start_pos(k.k), iter->pos) >= 0
+                    : bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0))
+                       k = btree_iter_level_prev(iter, l);
 
                if (likely(k.k))
                        break;
 
-               if (!btree_iter_set_pos_to_prev_leaf(iter))
-                       return bkey_s_c_null;
+               if (!btree_iter_set_pos_to_prev_leaf(iter)) {
+                       k = bkey_s_c_null;
+                       goto no_key;
+               }
        }
 
-       EBUG_ON(bkey_cmp(bkey_start_pos(k.k), pos) > 0);
-       iter->pos       = bkey_start_pos(k.k);
-       iter->uptodate  = BTREE_ITER_UPTODATE;
+       EBUG_ON(bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0);
+
+       /* Extents can straddle iter->pos: */
+       if (bkey_cmp(k.k->p, iter->pos) < 0)
+               iter->pos = k.k->p;
+out:
+       bch2_btree_iter_verify_entry_exit(iter);
+       bch2_btree_iter_verify(iter);
        return k;
+no_key:
+       /*
+        * btree_iter_level_peek() may have set iter->k to a key we didn't want, and
+        * then we errored going to the previous leaf - make sure it's
+        * consistent with iter->pos:
+        */
+       bkey_init(&iter->k);
+       iter->k.p = iter->pos;
+       goto out;
 }
 
 /**
@@ -1752,81 +1738,52 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
  */
 struct bkey_s_c bch2_btree_iter_prev(struct btree_iter *iter)
 {
-       struct bpos pos = bkey_start_pos(&iter->k);
-
-       EBUG_ON(btree_iter_type(iter) != BTREE_ITER_KEYS);
-       bch2_btree_iter_checks(iter);
-
-       if (unlikely(!bkey_cmp(pos, POS_MIN)))
+       if (!bch2_btree_iter_rewind(iter))
                return bkey_s_c_null;
 
-       bch2_btree_iter_set_pos(iter, bkey_predecessor(pos));
-
        return bch2_btree_iter_peek_prev(iter);
 }
 
 static inline struct bkey_s_c
 __bch2_btree_iter_peek_slot_extents(struct btree_iter *iter)
 {
-       struct btree_iter_level *l = &iter->l[0];
-       struct btree_node_iter node_iter;
        struct bkey_s_c k;
-       struct bkey n;
-       int ret;
+       struct bpos pos, next_start;
 
        /* keys & holes can't span inode numbers: */
        if (iter->pos.offset == KEY_OFFSET_MAX) {
                if (iter->pos.inode == KEY_INODE_MAX)
                        return bkey_s_c_null;
 
-               bch2_btree_iter_set_pos(iter, bkey_successor(iter->pos));
-
-               ret = bch2_btree_iter_traverse(iter);
-               if (unlikely(ret))
-                       return bkey_s_c_err(ret);
+               bch2_btree_iter_set_pos(iter, bkey_successor(iter, iter->pos));
        }
 
-       /*
-        * iterator is now at the correct position for inserting at iter->pos,
-        * but we need to keep iterating until we find the first non whiteout so
-        * we know how big a hole we have, if any:
-        */
-
-       node_iter = l->iter;
-       k = __btree_iter_unpack(iter, l, &iter->k,
-               bch2_btree_node_iter_peek(&node_iter, l->b));
-
-       if (k.k && bkey_cmp(bkey_start_pos(k.k), iter->pos) <= 0) {
-               /*
-                * We're not setting iter->uptodate because the node iterator
-                * doesn't necessarily point at the key we're returning:
-                */
+       pos = iter->pos;
+       k = bch2_btree_iter_peek(iter);
+       iter->pos = pos;
 
-               EBUG_ON(bkey_cmp(k.k->p, iter->pos) <= 0);
-               bch2_btree_iter_verify_level(iter, 0);
+       if (bkey_err(k))
                return k;
-       }
 
-       /* hole */
+       if (k.k && bkey_cmp(bkey_start_pos(k.k), iter->pos) <= 0)
+               return k;
 
-       if (!k.k)
-               k.k = &l->b->key.k;
+       next_start = k.k ? bkey_start_pos(k.k) : POS_MAX;
 
-       bkey_init(&n);
-       n.p = iter->pos;
-       bch2_key_resize(&n,
+       bkey_init(&iter->k);
+       iter->k.p = iter->pos;
+       bch2_key_resize(&iter->k,
                        min_t(u64, KEY_SIZE_MAX,
-                             (k.k->p.inode == n.p.inode
-                              ? bkey_start_offset(k.k)
+                             (next_start.inode == iter->pos.inode
+                              ? next_start.offset
                               : KEY_OFFSET_MAX) -
-                             n.p.offset));
+                             iter->pos.offset));
 
-       EBUG_ON(!n.size);
+       EBUG_ON(!iter->k.size);
 
-       iter->k = n;
-       iter->uptodate = BTREE_ITER_UPTODATE;
+       bch2_btree_iter_verify_entry_exit(iter);
+       bch2_btree_iter_verify(iter);
 
-       bch2_btree_iter_verify_level(iter, 0);
        return (struct bkey_s_c) { &iter->k, NULL };
 }
 
@@ -1837,19 +1794,19 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
        int ret;
 
        EBUG_ON(btree_iter_type(iter) != BTREE_ITER_KEYS);
-       bch2_btree_iter_checks(iter);
+       bch2_btree_iter_verify(iter);
+       bch2_btree_iter_verify_entry_exit(iter);
 
-       if (iter->uptodate == BTREE_ITER_UPTODATE)
-               return btree_iter_peek_uptodate(iter);
-
-       ret = bch2_btree_iter_traverse(iter);
-       if (unlikely(ret))
-               return bkey_s_c_err(ret);
+       btree_iter_set_search_pos(iter, btree_iter_search_key(iter));
 
        if (iter->flags & BTREE_ITER_IS_EXTENTS)
                return __bch2_btree_iter_peek_slot_extents(iter);
 
-       k = __btree_iter_peek_all(iter, l, &iter->k);
+       ret = btree_iter_traverse(iter);
+       if (unlikely(ret))
+               return bkey_s_c_err(ret);
+
+       k = btree_iter_level_peek_all(iter, l, &iter->k);
 
        EBUG_ON(k.k && bkey_deleted(k.k) && bkey_cmp(k.k->p, iter->pos) == 0);
 
@@ -1860,20 +1817,23 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
                k = (struct bkey_s_c) { &iter->k, NULL };
        }
 
-       iter->uptodate = BTREE_ITER_UPTODATE;
-       bch2_btree_iter_verify_level(iter, 0);
+       bch2_btree_iter_verify_entry_exit(iter);
+       bch2_btree_iter_verify(iter);
        return k;
 }
 
 struct bkey_s_c bch2_btree_iter_next_slot(struct btree_iter *iter)
 {
-       if (unlikely(!bkey_cmp(iter->k.p, POS_MAX)))
+       if (!bch2_btree_iter_advance(iter))
                return bkey_s_c_null;
 
-       bch2_btree_iter_set_pos(iter,
-               (iter->flags & BTREE_ITER_IS_EXTENTS)
-               ? iter->k.p
-               : bkey_successor(iter->k.p));
+       return bch2_btree_iter_peek_slot(iter);
+}
+
+struct bkey_s_c bch2_btree_iter_prev_slot(struct btree_iter *iter)
+{
+       if (!bch2_btree_iter_rewind(iter))
+               return bkey_s_c_null;
 
        return bch2_btree_iter_peek_slot(iter);
 }
@@ -1884,9 +1844,9 @@ struct bkey_s_c bch2_btree_iter_peek_cached(struct btree_iter *iter)
        int ret;
 
        EBUG_ON(btree_iter_type(iter) != BTREE_ITER_CACHED);
-       bch2_btree_iter_checks(iter);
+       bch2_btree_iter_verify(iter);
 
-       ret = bch2_btree_iter_traverse(iter);
+       ret = btree_iter_traverse(iter);
        if (unlikely(ret))
                return bkey_s_c_err(ret);
 
@@ -1900,26 +1860,17 @@ struct bkey_s_c bch2_btree_iter_peek_cached(struct btree_iter *iter)
 }
 
 static inline void bch2_btree_iter_init(struct btree_trans *trans,
-                       struct btree_iter *iter, enum btree_id btree_id,
-                       struct bpos pos, unsigned flags)
+                       struct btree_iter *iter, enum btree_id btree_id)
 {
        struct bch_fs *c = trans->c;
        unsigned i;
 
-       if (btree_node_type_is_extents(btree_id) &&
-           !(flags & BTREE_ITER_NODES))
-               flags |= BTREE_ITER_IS_EXTENTS;
-
        iter->trans                     = trans;
-       iter->pos                       = pos;
-       bkey_init(&iter->k);
-       iter->k.p                       = pos;
-       iter->flags                     = flags;
        iter->uptodate                  = BTREE_ITER_NEED_TRAVERSE;
        iter->btree_id                  = btree_id;
        iter->level                     = 0;
        iter->min_depth                 = 0;
-       iter->locks_want                = flags & BTREE_ITER_INTENT ? 1 : 0;
+       iter->locks_want                = 0;
        iter->nodes_locked              = 0;
        iter->nodes_intent_locked       = 0;
        for (i = 0; i < ARRAY_SIZE(iter->l); i++)
@@ -1948,6 +1899,7 @@ int bch2_trans_iter_put(struct btree_trans *trans,
                return 0;
 
        BUG_ON(trans->iters + iter->idx != iter);
+       BUG_ON(!btree_iter_live(trans, iter));
 
        ret = btree_iter_err(iter);
 
@@ -1965,115 +1917,51 @@ int bch2_trans_iter_free(struct btree_trans *trans,
        if (IS_ERR_OR_NULL(iter))
                return 0;
 
-       trans->iters_touched &= ~(1ULL << iter->idx);
+       set_btree_iter_dontneed(trans, iter);
 
        return bch2_trans_iter_put(trans, iter);
 }
 
-static int bch2_trans_realloc_iters(struct btree_trans *trans,
-                                   unsigned new_size)
+noinline __cold
+static void btree_trans_iter_alloc_fail(struct btree_trans *trans)
 {
-       void *p, *new_iters, *new_updates, *new_updates2;
-       size_t iters_bytes;
-       size_t updates_bytes;
-
-       new_size = roundup_pow_of_two(new_size);
-
-       BUG_ON(new_size > BTREE_ITER_MAX);
-
-       if (new_size <= trans->size)
-               return 0;
-
-       BUG_ON(trans->used_mempool);
 
-       bch2_trans_unlock(trans);
-
-       iters_bytes     = sizeof(struct btree_iter) * new_size;
-       updates_bytes   = sizeof(struct btree_insert_entry) * new_size;
-
-       p = kmalloc(iters_bytes +
-                   updates_bytes +
-                   updates_bytes, GFP_NOFS);
-       if (p)
-               goto success;
-
-       p = mempool_alloc(&trans->c->btree_iters_pool, GFP_NOFS);
-       new_size = BTREE_ITER_MAX;
-
-       trans->used_mempool = true;
-success:
-       new_iters       = p; p += iters_bytes;
-       new_updates     = p; p += updates_bytes;
-       new_updates2    = p; p += updates_bytes;
-
-       memcpy(new_iters, trans->iters,
-              sizeof(struct btree_iter) * trans->nr_iters);
-       memcpy(new_updates, trans->updates,
-              sizeof(struct btree_insert_entry) * trans->nr_updates);
-       memcpy(new_updates2, trans->updates2,
-              sizeof(struct btree_insert_entry) * trans->nr_updates2);
-
-       if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG))
-               memset(trans->iters, POISON_FREE,
-                      sizeof(struct btree_iter) * trans->nr_iters +
-                      sizeof(struct btree_insert_entry) * trans->nr_iters);
-
-       if (trans->iters != trans->iters_onstack)
-               kfree(trans->iters);
-
-       trans->iters            = new_iters;
-       trans->updates          = new_updates;
-       trans->updates2         = new_updates2;
-       trans->size             = new_size;
+       struct btree_iter *iter;
+       struct btree_insert_entry *i;
+       char buf[100];
 
-       if (trans->iters_live) {
-               trace_trans_restart_iters_realloced(trans->ip, trans->size);
-               return -EINTR;
+       trans_for_each_iter(trans, iter)
+               printk(KERN_ERR "iter: btree %s pos %s%s%s%s %pS\n",
+                      bch2_btree_ids[iter->btree_id],
+                      (bch2_bpos_to_text(&PBUF(buf), iter->pos), buf),
+                      btree_iter_live(trans, iter) ? " live" : "",
+                      (trans->iters_touched & (1ULL << iter->idx)) ? " touched" : "",
+                      iter->flags & BTREE_ITER_KEEP_UNTIL_COMMIT ? " keep" : "",
+                      (void *) iter->ip_allocated);
+
+       trans_for_each_update(trans, i) {
+               char buf[300];
+
+               bch2_bkey_val_to_text(&PBUF(buf), trans->c, bkey_i_to_s_c(i->k));
+               printk(KERN_ERR "update: btree %s %s\n",
+                      bch2_btree_ids[i->iter->btree_id], buf);
        }
-
-       return 0;
+       panic("trans iter oveflow\n");
 }
 
 static struct btree_iter *btree_trans_iter_alloc(struct btree_trans *trans)
 {
-       unsigned idx = __ffs64(~trans->iters_linked);
+       unsigned idx;
 
-       if (idx < trans->nr_iters)
-               goto got_slot;
+       if (unlikely(trans->iters_linked ==
+                    ~((~0ULL << 1) << (BTREE_ITER_MAX - 1))))
+               btree_trans_iter_alloc_fail(trans);
 
-       if (trans->nr_iters == trans->size) {
-               int ret;
-
-               if (trans->nr_iters >= BTREE_ITER_MAX) {
-                       struct btree_iter *iter;
-
-                       trans_for_each_iter(trans, iter) {
-                               pr_err("iter: btree %s pos %llu:%llu%s%s%s %ps",
-                                      bch2_btree_ids[iter->btree_id],
-                                      iter->pos.inode,
-                                      iter->pos.offset,
-                                      (trans->iters_live & (1ULL << iter->idx)) ? " live" : "",
-                                      (trans->iters_touched & (1ULL << iter->idx)) ? " touched" : "",
-                                      iter->flags & BTREE_ITER_KEEP_UNTIL_COMMIT ? " keep" : "",
-                                      (void *) iter->ip_allocated);
-                       }
-
-                       panic("trans iter oveflow\n");
-               }
+       idx = __ffs64(~trans->iters_linked);
 
-               ret = bch2_trans_realloc_iters(trans, trans->size * 2);
-               if (ret)
-                       return ERR_PTR(ret);
-       }
-
-       idx = trans->nr_iters++;
-       BUG_ON(trans->nr_iters > trans->size);
-
-       trans->iters[idx].idx = idx;
-got_slot:
-       BUG_ON(trans->iters_linked & (1ULL << idx));
-       trans->iters_linked |= 1ULL << idx;
-       trans->iters[idx].flags = 0;
+       trans->iters_linked     |= 1ULL << idx;
+       trans->iters[idx].idx    = idx;
+       trans->iters[idx].flags  = 0;
        return &trans->iters[idx];
 }
 
@@ -2095,21 +1983,21 @@ static inline void btree_iter_copy(struct btree_iter *dst,
        dst->flags &= ~BTREE_ITER_SET_POS_AFTER_COMMIT;
 }
 
-static inline struct bpos bpos_diff(struct bpos l, struct bpos r)
-{
-       if (bkey_cmp(l, r) > 0)
-               swap(l, r);
-
-       return POS(r.inode - l.inode, r.offset - l.offset);
-}
-
-static struct btree_iter *__btree_trans_get_iter(struct btree_trans *trans,
-                                                unsigned btree_id, struct bpos pos,
-                                                unsigned flags)
+struct btree_iter *__bch2_trans_get_iter(struct btree_trans *trans,
+                                        unsigned btree_id, struct bpos pos,
+                                        unsigned locks_want,
+                                        unsigned depth,
+                                        unsigned flags)
 {
        struct btree_iter *iter, *best = NULL;
 
-       BUG_ON(trans->nr_iters > BTREE_ITER_MAX);
+       if ((flags & BTREE_ITER_TYPE) != BTREE_ITER_NODES &&
+           !btree_type_has_snapshots(btree_id))
+               flags &= ~BTREE_ITER_ALL_SNAPSHOTS;
+
+       if (!(flags & BTREE_ITER_ALL_SNAPSHOTS))
+               pos.snapshot = btree_type_has_snapshots(btree_id)
+                       ? U32_MAX : 0;
 
        trans_for_each_iter(trans, iter) {
                if (btree_iter_type(iter) != (flags & BTREE_ITER_TYPE))
@@ -2119,8 +2007,8 @@ static struct btree_iter *__btree_trans_get_iter(struct btree_trans *trans,
                        continue;
 
                if (best &&
-                   bkey_cmp(bpos_diff(best->pos, pos),
-                            bpos_diff(iter->pos, pos)) < 0)
+                   bkey_cmp(bpos_diff(best->real_pos, pos),
+                            bpos_diff(iter->real_pos, pos)) > 0)
                        continue;
 
                best = iter;
@@ -2128,52 +2016,50 @@ static struct btree_iter *__btree_trans_get_iter(struct btree_trans *trans,
 
        if (!best) {
                iter = btree_trans_iter_alloc(trans);
-               if (IS_ERR(iter))
-                       return iter;
-
-               bch2_btree_iter_init(trans, iter, btree_id, pos, flags);
-       } else if ((trans->iters_live & (1ULL << best->idx)) ||
-                  (best->flags & BTREE_ITER_KEEP_UNTIL_COMMIT)) {
+               bch2_btree_iter_init(trans, iter, btree_id);
+       } else if (btree_iter_keep(trans, best)) {
                iter = btree_trans_iter_alloc(trans);
-               if (IS_ERR(iter))
-                       return iter;
-
                btree_iter_copy(iter, best);
        } else {
                iter = best;
        }
 
-       iter->flags &= ~BTREE_ITER_KEEP_UNTIL_COMMIT;
-       iter->flags &= ~BTREE_ITER_USER_FLAGS;
-       iter->flags |= flags & BTREE_ITER_USER_FLAGS;
+       trans->iters_live       |= 1ULL << iter->idx;
+       trans->iters_touched    |= 1ULL << iter->idx;
 
-       if (iter->flags & BTREE_ITER_INTENT)
-               bch2_btree_iter_upgrade(iter, 1);
-       else
-               bch2_btree_iter_downgrade(iter);
+       if ((flags & BTREE_ITER_TYPE) != BTREE_ITER_NODES &&
+           btree_node_type_is_extents(btree_id) &&
+           !(flags & BTREE_ITER_NOT_EXTENTS) &&
+           !(flags & BTREE_ITER_ALL_SNAPSHOTS))
+               flags |= BTREE_ITER_IS_EXTENTS;
 
-       BUG_ON(iter->btree_id != btree_id);
-       BUG_ON((iter->flags ^ flags) & BTREE_ITER_TYPE);
-       BUG_ON(iter->flags & BTREE_ITER_KEEP_UNTIL_COMMIT);
-       BUG_ON(iter->flags & BTREE_ITER_SET_POS_AFTER_COMMIT);
-       BUG_ON(trans->iters_live & (1ULL << iter->idx));
+       iter->flags = flags;
 
-       trans->iters_live       |= 1ULL << iter->idx;
-       trans->iters_touched    |= 1ULL << iter->idx;
+       iter->snapshot = pos.snapshot;
 
-       return iter;
-}
+       locks_want = min(locks_want, BTREE_MAX_DEPTH);
 
-struct btree_iter *__bch2_trans_get_iter(struct btree_trans *trans,
-                                        enum btree_id btree_id,
-                                        struct bpos pos, unsigned flags)
-{
-       struct btree_iter *iter =
-               __btree_trans_get_iter(trans, btree_id, pos, flags);
+       if (locks_want > iter->locks_want) {
+               iter->locks_want = locks_want;
+               btree_iter_get_locks(iter, true, false);
+       } else if (locks_want < iter->locks_want) {
+               __bch2_btree_iter_downgrade(iter, locks_want);
+       }
+
+       while (iter->level < depth) {
+               btree_node_unlock(iter, iter->level);
+               iter->l[iter->level].b = BTREE_ITER_NO_NODE_INIT;
+               iter->level++;
+       }
+
+       while (iter->level > depth)
+               iter->l[--iter->level].b = BTREE_ITER_NO_NODE_INIT;
+
+       iter->min_depth = depth;
+
+       bch2_btree_iter_set_pos(iter, pos);
+       btree_iter_set_search_pos(iter, btree_iter_search_key(iter));
 
-       if (!IS_ERR(iter))
-               __bch2_btree_iter_set_pos(iter, pos,
-                       btree_node_type_is_extents(btree_id));
        return iter;
 }
 
@@ -2185,20 +2071,18 @@ struct btree_iter *bch2_trans_get_node_iter(struct btree_trans *trans,
                                            unsigned flags)
 {
        struct btree_iter *iter =
-               __btree_trans_get_iter(trans, btree_id, pos,
-                                      flags|BTREE_ITER_NODES);
-       unsigned i;
+               __bch2_trans_get_iter(trans, btree_id, pos,
+                                     locks_want, depth,
+                                     BTREE_ITER_NODES|
+                                     BTREE_ITER_NOT_EXTENTS|
+                                     BTREE_ITER_ALL_SNAPSHOTS|
+                                     flags);
 
-       BUG_ON(IS_ERR(iter));
        BUG_ON(bkey_cmp(iter->pos, pos));
-
-       iter->locks_want = locks_want;
-       iter->level     = depth;
-       iter->min_depth = depth;
-
-       for (i = 0; i < ARRAY_SIZE(iter->l); i++)
-               iter->l[i].b            = NULL;
-       iter->l[iter->level].b          = BTREE_ITER_NO_NODE_INIT;
+       BUG_ON(iter->locks_want != min(locks_want, BTREE_MAX_DEPTH));
+       BUG_ON(iter->level      != depth);
+       BUG_ON(iter->min_depth  != depth);
+       iter->ip_allocated = _RET_IP_;
 
        return iter;
 }
@@ -2209,9 +2093,6 @@ struct btree_iter *__bch2_trans_copy_iter(struct btree_trans *trans,
        struct btree_iter *iter;
 
        iter = btree_trans_iter_alloc(trans);
-       if (IS_ERR(iter))
-               return iter;
-
        btree_iter_copy(iter, src);
 
        trans->iters_live |= 1ULL << iter->idx;
@@ -2219,7 +2100,7 @@ struct btree_iter *__bch2_trans_copy_iter(struct btree_trans *trans,
         * We don't need to preserve this iter since it's cheap to copy it
         * again - this will cause trans_iter_put() to free it right away:
         */
-       trans->iters_touched &= ~(1ULL << iter->idx);
+       set_btree_iter_dontneed(trans, iter);
 
        return iter;
 }
@@ -2286,11 +2167,11 @@ void bch2_trans_reset(struct btree_trans *trans, unsigned flags)
 
        trans->iters_touched &= trans->iters_live;
 
-       trans->need_reset               = 0;
        trans->nr_updates               = 0;
        trans->nr_updates2              = 0;
        trans->mem_top                  = 0;
 
+       trans->hooks                    = NULL;
        trans->extra_journal_entries    = NULL;
        trans->extra_journal_entry_u64s = 0;
 
@@ -2301,35 +2182,52 @@ void bch2_trans_reset(struct btree_trans *trans, unsigned flags)
                       (void *) &trans->fs_usage_deltas->memset_start);
        }
 
+       if (!(flags & TRANS_RESET_NOUNLOCK))
+               bch2_trans_cond_resched(trans);
+
        if (!(flags & TRANS_RESET_NOTRAVERSE))
                bch2_btree_iter_traverse_all(trans);
 }
 
+static void bch2_trans_alloc_iters(struct btree_trans *trans, struct bch_fs *c)
+{
+       size_t iters_bytes      = sizeof(struct btree_iter) * BTREE_ITER_MAX;
+       size_t updates_bytes    = sizeof(struct btree_insert_entry) * BTREE_ITER_MAX;
+       void *p = NULL;
+
+       BUG_ON(trans->used_mempool);
+
+#ifdef __KERNEL__
+       p = this_cpu_xchg(c->btree_iters_bufs->iter, NULL);
+#endif
+       if (!p)
+               p = mempool_alloc(&trans->c->btree_iters_pool, GFP_NOFS);
+
+       trans->iters            = p; p += iters_bytes;
+       trans->updates          = p; p += updates_bytes;
+       trans->updates2         = p; p += updates_bytes;
+}
+
 void bch2_trans_init(struct btree_trans *trans, struct bch_fs *c,
                     unsigned expected_nr_iters,
                     size_t expected_mem_bytes)
 {
-       memset(trans, 0, offsetof(struct btree_trans, iters_onstack));
+       memset(trans, 0, sizeof(*trans));
+       trans->c                = c;
+       trans->ip               = _RET_IP_;
 
        /*
         * reallocating iterators currently completely breaks
-        * bch2_trans_iter_put():
+        * bch2_trans_iter_put(), we always allocate the max:
         */
-       expected_nr_iters = BTREE_ITER_MAX;
-
-       trans->c                = c;
-       trans->ip               = _RET_IP_;
-       trans->size             = ARRAY_SIZE(trans->iters_onstack);
-       trans->iters            = trans->iters_onstack;
-       trans->updates          = trans->updates_onstack;
-       trans->updates2         = trans->updates2_onstack;
-       trans->fs_usage_deltas  = NULL;
+       bch2_trans_alloc_iters(trans, c);
 
-       if (expected_nr_iters > trans->size)
-               bch2_trans_realloc_iters(trans, expected_nr_iters);
+       if (expected_mem_bytes) {
+               trans->mem_bytes = roundup_pow_of_two(expected_mem_bytes);
+               trans->mem = kmalloc(trans->mem_bytes, GFP_KERNEL|__GFP_NOFAIL);
+       }
 
-       if (expected_mem_bytes)
-               bch2_trans_preload_mem(trans, expected_mem_bytes);
+       trans->srcu_idx = srcu_read_lock(&c->btree_trans_barrier);
 
 #ifdef CONFIG_BCACHEFS_DEBUG
        trans->pid = current->pid;
@@ -2341,37 +2239,74 @@ void bch2_trans_init(struct btree_trans *trans, struct bch_fs *c,
 
 int bch2_trans_exit(struct btree_trans *trans)
 {
+       struct bch_fs *c = trans->c;
+
        bch2_trans_unlock(trans);
 
 #ifdef CONFIG_BCACHEFS_DEBUG
+       if (trans->iters_live) {
+               struct btree_iter *iter;
+
+               bch_err(c, "btree iterators leaked!");
+               trans_for_each_iter(trans, iter)
+                       if (btree_iter_live(trans, iter))
+                               printk(KERN_ERR "  btree %s allocated at %pS\n",
+                                      bch2_btree_ids[iter->btree_id],
+                                      (void *) iter->ip_allocated);
+               /* Be noisy about this: */
+               bch2_fatal_error(c);
+       }
+
        mutex_lock(&trans->c->btree_trans_lock);
        list_del(&trans->list);
        mutex_unlock(&trans->c->btree_trans_lock);
 #endif
 
+       srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx);
+
        bch2_journal_preres_put(&trans->c->journal, &trans->journal_preres);
 
        kfree(trans->fs_usage_deltas);
        kfree(trans->mem);
-       if (trans->used_mempool)
+
+#ifdef __KERNEL__
+       /*
+        * Userspace doesn't have a real percpu implementation:
+        */
+       trans->iters = this_cpu_xchg(c->btree_iters_bufs->iter, trans->iters);
+#endif
+       if (trans->iters)
                mempool_free(trans->iters, &trans->c->btree_iters_pool);
-       else if (trans->iters != trans->iters_onstack)
-               kfree(trans->iters);
+
        trans->mem      = (void *) 0x1;
        trans->iters    = (void *) 0x1;
 
        return trans->error ? -EIO : 0;
 }
 
-static void bch2_btree_iter_node_to_text(struct printbuf *out,
-                                struct btree_bkey_cached_common *_b,
-                                enum btree_iter_type type)
+static void __maybe_unused
+bch2_btree_iter_node_to_text(struct printbuf *out,
+                            struct btree_bkey_cached_common *_b,
+                            enum btree_iter_type type)
 {
-       pr_buf(out, "    %px l=%u %s:",
-              _b, _b->level, bch2_btree_ids[_b->btree_id]);
+       pr_buf(out, "    l=%u %s:",
+              _b->level, bch2_btree_ids[_b->btree_id]);
        bch2_bpos_to_text(out, btree_node_pos(_b, type));
 }
 
+#ifdef CONFIG_BCACHEFS_DEBUG
+static bool trans_has_btree_nodes_locked(struct btree_trans *trans)
+{
+       struct btree_iter *iter;
+
+       trans_for_each_iter(trans, iter)
+               if (btree_iter_type(iter) != BTREE_ITER_CACHED &&
+                   iter->nodes_locked)
+                       return true;
+       return false;
+}
+#endif
+
 void bch2_btree_trans_to_text(struct printbuf *out, struct bch_fs *c)
 {
 #ifdef CONFIG_BCACHEFS_DEBUG
@@ -2382,14 +2317,18 @@ void bch2_btree_trans_to_text(struct printbuf *out, struct bch_fs *c)
 
        mutex_lock(&c->btree_trans_lock);
        list_for_each_entry(trans, &c->btree_trans_list, list) {
-               pr_buf(out, "%i %px %ps\n", trans->pid, trans, (void *) trans->ip);
+               if (!trans_has_btree_nodes_locked(trans))
+                       continue;
+
+               pr_buf(out, "%i %ps\n", trans->pid, (void *) trans->ip);
 
                trans_for_each_iter(trans, iter) {
                        if (!iter->nodes_locked)
                                continue;
 
-                       pr_buf(out, "  iter %u %s:",
+                       pr_buf(out, "  iter %u %c %s:",
                               iter->idx,
+                              btree_iter_type(iter) == BTREE_ITER_CACHED ? 'c' : 'b',
                               bch2_btree_ids[iter->btree_id]);
                        bch2_bpos_to_text(out, iter->pos);
                        pr_buf(out, "\n");
@@ -2408,17 +2347,18 @@ void bch2_btree_trans_to_text(struct printbuf *out, struct bch_fs *c)
 
                b = READ_ONCE(trans->locking);
                if (b) {
-                       pr_buf(out, "  locking iter %u l=%u %s:",
+                       iter = &trans->iters[trans->locking_iter_idx];
+                       pr_buf(out, "  locking iter %u %c l=%u %s:",
                               trans->locking_iter_idx,
+                              btree_iter_type(iter) == BTREE_ITER_CACHED ? 'c' : 'b',
                               trans->locking_level,
                               bch2_btree_ids[trans->locking_btree_id]);
                        bch2_bpos_to_text(out, trans->locking_pos);
 
-
                        pr_buf(out, " node ");
                        bch2_btree_iter_node_to_text(out,
                                        (void *) b,
-                                       btree_iter_type(&trans->iters[trans->locking_iter_idx]));
+                                       btree_iter_type(iter));
                        pr_buf(out, "\n");
                }
        }
@@ -2429,6 +2369,7 @@ void bch2_btree_trans_to_text(struct printbuf *out, struct bch_fs *c)
 void bch2_fs_btree_iter_exit(struct bch_fs *c)
 {
        mempool_exit(&c->btree_iters_pool);
+       cleanup_srcu_struct(&c->btree_trans_barrier);
 }
 
 int bch2_fs_btree_iter_init(struct bch_fs *c)
@@ -2438,7 +2379,8 @@ int bch2_fs_btree_iter_init(struct bch_fs *c)
        INIT_LIST_HEAD(&c->btree_trans_list);
        mutex_init(&c->btree_trans_lock);
 
-       return mempool_init_kmalloc_pool(&c->btree_iters_pool, 1,
+       return  init_srcu_struct(&c->btree_trans_barrier) ?:
+               mempool_init_kmalloc_pool(&c->btree_iters_pool, 1,
                        sizeof(struct btree_iter) * nr +
                        sizeof(struct btree_insert_entry) * nr +
                        sizeof(struct btree_insert_entry) * nr);