Ceph » CephFS

Sidharth Anupkrishnan wrote:

In the current MDS code, the migration of empty directories is prohibited but it is actually exported during the migration process and a check on the importer side during import_finish() (https://github.com/ceph/ceph/blob/master/src/mds/Migrator.cc#L3175) determines whether the directory empty and if so exports it back to the original exporter.

Why is this check not done on the exporter side? We can avoid unnecessary round trips between the exporter and the importing mds.

Zheng and Patrick. Please take a look

you are right. we can do the check a export_dir and export_frozen. If directory is empty, abort. But we still need to consider export_pin

Zheng Yan wrote:

you are right. we can do the check a export_dir and export_frozen. If directory is empty, abort. But we still need to consider export_pin

As I discussed with Sidharth, it appears to me the prohibition on exporting empty directories is just a premature optimization to prevent moving metadata unnecessarily. I think it does make sense for a pinned directory. I'm suggesting we just undo this restriction entirely.

Sidharth, please submit a PR when you have time.