This solves the issue of multiple mdirs/rbyds in lfsr_mtree_gc, where
it's easy for traversal state to fall out of sync when mutating parts of
the filesystem.
Is it good design, with self-referential pointers making everything more
entangled? Not sure!
This saves a bit of stack, but adds a bit of code, which makes sense,
pointer chasing can be costly. But both of these changes are well below
the compiler noise floor:
code stack
before: 35228 2688
after: 35256 (+0.1%) 2680 (-0.3%)
Christopher Haster
3c7b462659