[ceph-users] Re: PG lock contention? CephFS metadata pool rebalance

Hi, Like I said in an earlier mail to this list, we re-balanced ~ 60% of the CephFS metadata pool to NVMe backed devices. Roughly 422 M objects (1.2 Billion replicated). We have 512 PGs allocated to them. While rebalancing we suffered from quite a few SLOW_OPS. Memory, CPU and device IOPS capacity were not a limiting factor as far as we can see (plenty of them available ... nowhere near max capacity). We saw quite a few slow ops with the following events: "time": "2019-12-19 09:41:02.712010", "event": "reached_pg" }, { "time": "2019-12-19 09:41:02.712014", "event": "waiting for rw locks" }, { "time": "2019-12-19 09:41:02.881939", "event": "reached_pg" ... and this repeated 100's of times taking ~ 30 seconds to complete Does this indicate PG lock contention? If so ... would we need to provide more PGs to the metadata pool to avoid this? The metadata pool is only ~ 166 MiB big ... but with loads of OMAPs ... Most advice on PG planning is concerned with the _amount_ of data ... but the metadata pool (and this might also be true for RGW index pools) seem to be a special case.