Answering my own question (getting help from Pavan), I see that all
the details are in this PR: https://github.com/ceph/ceph/pull/11051
So, the zone was updated to set metadata_heap: "" with
$ radosgw-admin zone get --rgw-zone=default > zone.json
[edit zone.json]
$ radosgw-admin zone set
Hi all,
We have an S3 cluster with >10 million objects in default.rgw.meta.
# radosgw-admin zone get | jq .metadata_heap
"default.rgw.meta"
In these old tickets I realized that this setting is obsolete, and
those objects are probably useless:
http://tracker.ceph.com/issues/17256
