ZFS memory management

[Nikolay Denev]

On Nov 29, 2012, at 4:53 PM, Olivier Smedts <olivier at gid0.org> wrote:

> 2012/11/27 Freddie Cash <fjwcash at gmail.com>:
>> Read any ZFS tuning manual on the web, including the ones direct from
>> SUN/Oracle, and they all list:
>>  - if you are running processes that need a lot of memory, then limit the
>> ARC to allow the apps to have access to that memory
> 
> Or you could have at least a little swap (good practice) to allow ARC
> take the time to evict some memory when under pressure.
> 

Yes, this was already suggested off-list, and it seems like a solution.

Thanks to all for the input!

>> 
>> :)
>> 
>> 
>> On Tue, Nov 27, 2012 at 12:10 PM, Nikolay Denev <ndenev at gmail.com> wrote:
>> 
>>> Hello list,
>>> 
>>> I have the following question : I have several machines with 196G of RAM
>>> that are using
>>> RELENG_9 with ZFS, and are running a very memory intensive java
>>> applications - ElasticSearch
>>> The machines are without swap configured and have "vm.swap_enabled=0" in
>>> /etc/sysctl.conf.
>>> The ElasticSearch processes are using mlockall(2) to pin down their memory
>>> (configured at 40G).
>>> And at this point I thought that there would be no problems, but from time
>>> to time, when the machine grows it's
>>> ARC memory and there are some other running processes like nginx with
>>> passenger and uwsgi the ElasticSearch
>>> process would get killed by the kernel OOM killer with reason "no swap
>>> space available"
>>> 
>>> Of course, I've now tuned down arc_max in /boot/loader.conf, but isn't
>>> this supposed to work automatically? Like
>>> ZFS releasing some memory when there is a pressure, instead of the OOM
>>> killer going postal? (at the moment when
>>> the process was killed the ZFS ARC was 132G).
>>> 
>>> I understand that this might be problematic as AFAIK ZFS releases memory
>>> asynchronously when the arc_reclaim_thread() is run,
>>> which might take some time to be scheduled and complete.
>>> 
>>> Cheers,
>>> Nikolay
>>> 
>>> 
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>> 
>> 
>> 
>> --
>> Freddie Cash
>> fjwcash at gmail.com
>> _______________________________________________
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>> http://lists.freebsd.org/mailman/listinfo/freebsd-stable
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> 
> 
> 
> -- 
> Olivier Smedts                                                 _
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