[ceph-users] Unexplainable high memory usage OSD with BlueStore

Wido den Hollander wido at 42on.com
Thu Nov 8 00:52:48 PST 2018


Recently I've seen a Ceph cluster experience a few outages due to memory

The machines:

- Intel Xeon E3 CPU
- 32GB Memory
- 8x 1.92TB SSD
- Ubuntu 16.04
- Ceph 12.2.8

Looking at one of the machines:

root at ceph22:~# free -h
              total        used        free      shared  buff/cache
Mem:            31G         22G        8.2G        9.8M        809M
Swap:          1.9G          0B        1.9G
root at ceph22:~#

As you can see, it's using 22GB of the 32GB in the system.

bluestore_cache_size_ssd = 1G

The BlueStore Cache size for SSD has been set to 1GB, so the OSDs
shouldn't use more then that.

When dumping the mem pools each OSD claims to be using between 1.8GB and
2.2GB of memory.

$ ceph daemon osd.X dump_mempools|jq '.total.bytes'

Summing up all the values I get to a total of 15.8GB and the system is
using 22GB.

Looking at 'ps aux --sort rss' I see OSDs using almost 10% of the
memory, which would be ~3GB for a single daemon.

Sometimes these machines go OOM without a really good reason. After all
the OSDs have been restarted it runs fine, but about 10 days later the
same problem arrises again.

I know that BlueStore uses more memory, but 32GB with 8 OSDs should be a
workable setup.

Any ideas?


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