diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 674e2f4..20fe96c 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -384,8 +384,6 @@
 	void			*private;
 };
 
-typedef bool (keybuf_pred_fn)(struct keybuf *, struct bkey *);
-
 struct keybuf {
 	struct bkey		last_scanned;
 	spinlock_t		lock;
diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index d0512e4..14c2a23 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -842,6 +842,13 @@
 
 /* Btree iterator */
 
+/*
+ * Returns true if l > r - unless l == r, in which case returns true if l is
+ * older than r.
+ *
+ * Necessary for btree_sort_fixup() - if there are multiple keys that compare
+ * equal in different sets, we have to process them newest to oldest.
+ */
 static inline bool btree_iter_cmp(struct btree_iter_set l,
 				  struct btree_iter_set r)
 {
@@ -1146,16 +1153,16 @@
 /* Sysfs stuff */
 
 struct bset_stats {
+	struct btree_op op;
 	size_t nodes;
 	size_t sets_written, sets_unwritten;
 	size_t bytes_written, bytes_unwritten;
 	size_t floats, failed;
 };
 
-static int bch_btree_bset_stats(struct btree *b, struct btree_op *op,
-			    struct bset_stats *stats)
+static int btree_bset_stats(struct btree_op *op, struct btree *b)
 {
-	struct bkey *k;
+	struct bset_stats *stats = container_of(op, struct bset_stats, op);
 	unsigned i;
 
 	stats->nodes++;
@@ -1180,30 +1187,20 @@
 		}
 	}
 
-	if (b->level) {
-		struct btree_iter iter;
-
-		for_each_key_filter(b, k, &iter, bch_ptr_bad) {
-			int ret = btree(bset_stats, k, b, op, stats);
-			if (ret)
-				return ret;
-		}
-	}
-
-	return 0;
+	return MAP_CONTINUE;
 }
 
 int bch_bset_print_stats(struct cache_set *c, char *buf)
 {
-	struct btree_op op;
 	struct bset_stats t;
 	int ret;
 
-	bch_btree_op_init_stack(&op);
 	memset(&t, 0, sizeof(struct bset_stats));
+	bch_btree_op_init_stack(&t.op);
+	t.op.c = c;
 
-	ret = btree_root(bset_stats, c, &op, &t);
-	if (ret)
+	ret = bch_btree_map_nodes(&t.op, c, &ZERO_KEY, btree_bset_stats);
+	if (ret < 0)
 		return ret;
 
 	return snprintf(buf, PAGE_SIZE,
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 17bfd87..cfbdcf3 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -2296,6 +2296,82 @@
 	return ret;
 }
 
+/* Map across nodes or keys */
+
+static int bch_btree_map_nodes_recurse(struct btree *b, struct btree_op *op,
+				       struct bkey *from,
+				       btree_map_nodes_fn *fn, int flags)
+{
+	int ret = MAP_CONTINUE;
+
+	if (b->level) {
+		struct bkey *k;
+		struct btree_iter iter;
+
+		bch_btree_iter_init(b, &iter, from);
+
+		while ((k = bch_btree_iter_next_filter(&iter, b,
+						       bch_ptr_bad))) {
+			ret = btree(map_nodes_recurse, k, b,
+				    op, from, fn, flags);
+			from = NULL;
+
+			if (ret != MAP_CONTINUE)
+				return ret;
+		}
+	}
+
+	if (!b->level || flags == MAP_ALL_NODES)
+		ret = fn(op, b);
+
+	return ret;
+}
+
+int __bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
+			  struct bkey *from, btree_map_nodes_fn *fn, int flags)
+{
+	int ret = btree_root(map_nodes_recurse, c, op, from, fn, flags);
+	if (closure_blocking(&op->cl))
+		closure_sync(&op->cl);
+	return ret;
+}
+
+static int bch_btree_map_keys_recurse(struct btree *b, struct btree_op *op,
+				      struct bkey *from, btree_map_keys_fn *fn,
+				      int flags)
+{
+	int ret = MAP_CONTINUE;
+	struct bkey *k;
+	struct btree_iter iter;
+
+	bch_btree_iter_init(b, &iter, from);
+
+	while ((k = bch_btree_iter_next_filter(&iter, b, bch_ptr_bad))) {
+		ret = !b->level
+			? fn(op, b, k)
+			: btree(map_keys_recurse, k, b, op, from, fn, flags);
+		from = NULL;
+
+		if (ret != MAP_CONTINUE)
+			return ret;
+	}
+
+	if (!b->level && (flags & MAP_END_KEY))
+		ret = fn(op, b, &KEY(KEY_INODE(&b->key),
+				     KEY_OFFSET(&b->key), 0));
+
+	return ret;
+}
+
+int bch_btree_map_keys(struct btree_op *op, struct cache_set *c,
+		       struct bkey *from, btree_map_keys_fn *fn, int flags)
+{
+	int ret = btree_root(map_keys_recurse, c, op, from, fn, flags);
+	if (closure_blocking(&op->cl))
+		closure_sync(&op->cl);
+	return ret;
+}
+
 /* Keybuf code */
 
 static inline int keybuf_cmp(struct keybuf_key *l, struct keybuf_key *r)
@@ -2314,74 +2390,70 @@
 	return clamp_t(int64_t, bkey_cmp(&l->key, &r->key), -1, 1);
 }
 
-static int bch_btree_refill_keybuf(struct btree *b, struct btree_op *op,
-				   struct keybuf *buf, struct bkey *end,
-				   keybuf_pred_fn *pred)
+struct refill {
+	struct btree_op	op;
+	struct keybuf	*buf;
+	struct bkey	*end;
+	keybuf_pred_fn	*pred;
+};
+
+static int refill_keybuf_fn(struct btree_op *op, struct btree *b,
+			    struct bkey *k)
 {
-	struct btree_iter iter;
-	bch_btree_iter_init(b, &iter, &buf->last_scanned);
+	struct refill *refill = container_of(op, struct refill, op);
+	struct keybuf *buf = refill->buf;
+	int ret = MAP_CONTINUE;
 
-	while (!array_freelist_empty(&buf->freelist)) {
-		struct bkey *k = bch_btree_iter_next_filter(&iter, b,
-							    bch_ptr_bad);
-
-		if (!b->level) {
-			if (!k) {
-				buf->last_scanned = b->key;
-				break;
-			}
-
-			buf->last_scanned = *k;
-			if (bkey_cmp(&buf->last_scanned, end) >= 0)
-				break;
-
-			if (pred(buf, k)) {
-				struct keybuf_key *w;
-
-				spin_lock(&buf->lock);
-
-				w = array_alloc(&buf->freelist);
-
-				w->private = NULL;
-				bkey_copy(&w->key, k);
-
-				if (RB_INSERT(&buf->keys, w, node, keybuf_cmp))
-					array_free(&buf->freelist, w);
-
-				spin_unlock(&buf->lock);
-			}
-		} else {
-			if (!k)
-				break;
-
-			btree(refill_keybuf, k, b, op, buf, end, pred);
-			/*
-			 * Might get an error here, but can't really do anything
-			 * and it'll get logged elsewhere. Just read what we
-			 * can.
-			 */
-
-			if (bkey_cmp(&buf->last_scanned, end) >= 0)
-				break;
-
-			cond_resched();
-		}
+	if (bkey_cmp(k, refill->end) >= 0) {
+		ret = MAP_DONE;
+		goto out;
 	}
 
-	return 0;
+	if (!KEY_SIZE(k)) /* end key */
+		goto out;
+
+	if (refill->pred(buf, k)) {
+		struct keybuf_key *w;
+
+		spin_lock(&buf->lock);
+
+		w = array_alloc(&buf->freelist);
+		if (!w) {
+			spin_unlock(&buf->lock);
+			return MAP_DONE;
+		}
+
+		w->private = NULL;
+		bkey_copy(&w->key, k);
+
+		if (RB_INSERT(&buf->keys, w, node, keybuf_cmp))
+			array_free(&buf->freelist, w);
+
+		if (array_freelist_empty(&buf->freelist))
+			ret = MAP_DONE;
+
+		spin_unlock(&buf->lock);
+	}
+out:
+	buf->last_scanned = *k;
+	return ret;
 }
 
 void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf,
 		       struct bkey *end, keybuf_pred_fn *pred)
 {
 	struct bkey start = buf->last_scanned;
-	struct btree_op op;
-	bch_btree_op_init_stack(&op);
+	struct refill refill;
 
 	cond_resched();
 
-	btree_root(refill_keybuf, c, &op, buf, end, pred);
-	closure_sync(&op.cl);
+	bch_btree_op_init_stack(&refill.op);
+	refill.buf = buf;
+	refill.end = end;
+	refill.pred = pred;
+
+	bch_btree_map_keys(&refill.op, c, &buf->last_scanned,
+			   refill_keybuf_fn, MAP_END_KEY);
 
 	pr_debug("found %s keys from %llu:%llu to %llu:%llu",
 		 RB_EMPTY_ROOT(&buf->keys) ? "no" :
@@ -2465,9 +2537,9 @@
 }
 
 struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
-					     struct keybuf *buf,
-					     struct bkey *end,
-					     keybuf_pred_fn *pred)
+					  struct keybuf *buf,
+					  struct bkey *end,
+					  keybuf_pred_fn *pred)
 {
 	struct keybuf_key *ret;
 
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index fa9641a..cafdeb0 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -400,9 +400,42 @@
 		wake_up_process(c->gc_thread);
 }
 
+#define MAP_DONE	0
+#define MAP_CONTINUE	1
+
+#define MAP_ALL_NODES	0
+#define MAP_LEAF_NODES	1
+
+#define MAP_END_KEY	1
+
+typedef int (btree_map_nodes_fn)(struct btree_op *, struct btree *);
+int __bch_btree_map_nodes(struct btree_op *, struct cache_set *,
+			  struct bkey *, btree_map_nodes_fn *, int);
+
+static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
+				      struct bkey *from, btree_map_nodes_fn *fn)
+{
+	return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES);
+}
+
+static inline int bch_btree_map_leaf_nodes(struct btree_op *op,
+					   struct cache_set *c,
+					   struct bkey *from,
+					   btree_map_nodes_fn *fn)
+{
+	return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES);
+}
+
+typedef int (btree_map_keys_fn)(struct btree_op *, struct btree *,
+				struct bkey *);
+int bch_btree_map_keys(struct btree_op *, struct cache_set *,
+		       struct bkey *, btree_map_keys_fn *, int);
+
+typedef bool (keybuf_pred_fn)(struct keybuf *, struct bkey *);
+
 void bch_keybuf_init(struct keybuf *);
-void bch_refill_keybuf(struct cache_set *, struct keybuf *, struct bkey *,
-		       keybuf_pred_fn *);
+void bch_refill_keybuf(struct cache_set *, struct keybuf *,
+		       struct bkey *, keybuf_pred_fn *);
 bool bch_keybuf_check_overlapping(struct keybuf *, struct bkey *,
 				  struct bkey *);
 void bch_keybuf_del(struct keybuf *, struct keybuf_key *);
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 4392f3f..c68de9f 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -433,31 +433,17 @@
 
 /* Init */
 
-static int bch_btree_sectors_dirty_init(struct btree *b, struct btree_op *op,
-					struct cached_dev *dc)
+static int sectors_dirty_init_fn(struct btree_op *op, struct btree *b,
+				 struct bkey *k)
 {
-	struct bkey *k;
-	struct btree_iter iter;
+	if (KEY_INODE(k) > op->inode)
+		return MAP_DONE;
 
-	bch_btree_iter_init(b, &iter, &KEY(dc->disk.id, 0, 0));
-	while ((k = bch_btree_iter_next_filter(&iter, b, bch_ptr_bad)))
-		if (!b->level) {
-			if (KEY_INODE(k) > dc->disk.id)
-				break;
+	if (KEY_DIRTY(k))
+		bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
+					     KEY_START(k), KEY_SIZE(k));
 
-			if (KEY_DIRTY(k))
-				bcache_dev_sectors_dirty_add(b->c, dc->disk.id,
-							     KEY_START(k),
-							     KEY_SIZE(k));
-		} else {
-			btree(sectors_dirty_init, k, b, op, dc);
-			if (KEY_INODE(k) > dc->disk.id)
-				break;
-
-			cond_resched();
-		}
-
-	return 0;
+	return MAP_CONTINUE;
 }
 
 void bch_sectors_dirty_init(struct cached_dev *dc)
@@ -465,7 +451,10 @@
 	struct btree_op op;
 
 	bch_btree_op_init_stack(&op);
-	btree_root(sectors_dirty_init, dc->disk.c, &op, dc);
+	op.inode = dc->disk.id;
+
+	bch_btree_map_keys(&op, dc->disk.c, &KEY(op.inode, 0, 0),
+			   sectors_dirty_init_fn, 0);
 }
 
 int bch_cached_dev_writeback_init(struct cached_dev *dc)