bcachefs: Reduce would_deadlock restarts

We don't have to take locks in any particular ordering - we'll make
forward progress just fine - but if we try to stick to an ordering, it
can help to avoid excessive would_deadlock transaction restarts.

This tweaks the reflink path to take extents btree locks in the right
order.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/reflink.c b/fs/bcachefs/reflink.c
index 607010917421047d77415b7effeb0eacf7a363de..98255aa64e2261c504ebe0686c46b89589c36a6a 100644 (file)
--- a/fs/bcachefs/reflink.c
+++ b/fs/bcachefs/reflink.c
@@ -486,6 +486,13 @@ s64 bch2_remap_range(struct bch_fs *c,
 
                bch2_btree_iter_set_snapshot(&dst_iter, dst_snapshot);
 
+               if (dst_inum.inum < src_inum.inum) {
+                       /* Avoid some lock cycle transaction restarts */
+                       ret = bch2_btree_iter_traverse(&dst_iter);
+                       if (ret)
+                               continue;
+               }
+
                dst_done = dst_iter.pos.offset - dst_start.offset;
                src_want = POS(src_start.inode, src_start.offset + dst_done);
                bch2_btree_iter_set_pos(&src_iter, src_want);