mds: consider subtree setting to enable LAZYIO automatically (RFC)
See discussion here: https://github.com/ceph/ceph/pull/22450#issuecomment-400614296
This should be one avenue to explore to relax consistency requirements across a subtree for performance.
One open question is how do we handle a client that wants to open a file without LAZYIO (i.e. O_SYNC)? Should we just ignore the flag? Or just force recall of Flwr from other clients and give out Fwr?