Hammer OSD memory usage very high

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Hello all,

We have a small 160TB Ceph cluster used only as a test s3 storage repository for media content.

Problem
Since upgrading from Firefly to Hammer we are experiencing very high OSD memory use of 2-3 GB per TB of OSD storage - typical OSD memory 6-10GB.
We have had to increase swap space to bring the cluster to a basic functional state. Clearly this will significantly impact system performance and precludes starting all OSDs simultaneously.

Hardware
4 x storage nodes with 16 OSDs/node. OSD nodes are reasonable spec SMC storage servers with dual Xeon CPUs. Storage is 16 x 3TB SAS disks in each node.
Installed RAM is 72GB (2 nodes) & 80GB (2 nodes). (We note that the installed RAM is at least 50% higher than the Ceph recommended 1 GB RAM per TB of storage.)

Software
OSD node OS is CentOS 6.8 (with updates). One node has been updated to CentOS 7.2 - no change in memory usage was observed.

"ceph -v" -> ceph version 0.94.9 (fe6d859066244b97b24f09d46552afc2071e6f90)
(all Ceph packages downloaded from download.ceph.com)

The cluster has achieved status HEALTH_OK so we don’t believe this relates to increased memory due to recovery.

History
Emperor 0.72.2 -> Firefly 0.80.10 -> Hammer 0.94.6 -> Hammer 0.94.7 -> Hammer 0.94.9

OSD per process memory is observed to increase substantially during load_pgs phase.

Use of "ceph tell 'osd.*' heap release” has minimal effect - there is no substantial memory in the heap or cache freelists.

More information can be found in bug #17228 (link http://tracker.ceph.com/issues/17228)

Any feedback or guidance to further understanding the high memory usage would be welcomed.

Thanks

David


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