Re: Extremely high OSD memory utilization on Kraken 11.2.0 (with XFS -or- bluestore)

[Sage Weil <sage-BnTBU8nroG7k1uMJSBkQmQ@public.gmane.org>]

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On Sat, 15 Apr 2017, Aaron Ten Clay wrote:
> Hi all,
> 
> Our cluster is experiencing a very odd issue and I'm hoping for some
> guidance on troubleshooting steps and/or suggestions to mitigate the issue.
> tl;dr: Individual ceph-osd processes try to allocate > 90GiB of RAM and are
> eventually nuked by oom_killer.

My guess is that there there is a bug in a decoding path and it's 
trying to allocate some huge amount of memory.  Can you try setting a 
memory ulimit to something like 40gb and then enabling core dumps so you 
can get a core?  Something like

ulimit -c unlimited
ulimit -m 20000000

or whatever the corresponding systemd unit file options are...

Once we have a core file it will hopefully be clear who is 
doing the bad allocation...

sage



> 
> I'll try to explain the situation in detail:
> 
> We have 24-4TB bluestore HDD OSDs, and 4-600GB SSD OSDs. The SSD OSDs are in
> a different CRUSH "root", used as a cache tier for the main storage pools,
> which are erasure coded and used for cephfs. The OSDs are spread across two
> identical machines with 128GiB of RAM each, and there are three monitor
> nodes on different hardware.
> 
> Several times we've encountered crippling bugs with previous Ceph releases
> when we were on RC or betas, or using non-recommended configurations, so in
> January we abandoned all previous Ceph usage, deployed LTS Ubuntu 16.04, and
> went with stable Kraken 11.2.0 with the configuration mentioned above.
> Everything was fine until the end of March, when one day we find all but a
> couple of OSDs are "down" inexplicably. Investigation reveals oom_killer
> came along and nuked almost all the ceph-osd processes.
> 
> We've gone through a bunch of iterations of restarting the OSDs, trying to
> bring them up one at a time gradually, all at once, various configuration
> settings to reduce cache size as suggested in this ticket:
> http://tracker.ceph.com/issues/18924...
> 
> I don't know if that ticket really pertains to our situation or not, I have
> no experience with memory allocation debugging. I'd be willing to try if
> someone can point me to a guide or walk me through the process.
> 
> I've even tried, just to see if the situation was  transitory, adding over
> 300GiB of swap to both OSD machines. The OSD procs managed to allocate, in a
> matter of 5-10 minutes, more than 300GiB of RAM pressure and became
> oom_killer victims once again.
> 
> No software or hardware changes took place around the time this problem
> started, and no significant data changes occurred either. We added about
> 40GiB of ~1GiB files a week or so before the problem started and that's the
> last time data was written.
> 
> I can only assume we've found another crippling bug of some kind, this level
> of memory usage is entirely unprecedented. What can we do?
> 
> Thanks in advance for any suggestions.
> -Aaron
> 
> 

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