ZFS memory management

Freddie Cash fjwcash at gmail.com
Tue Nov 27 20:22:16 UTC 2012

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


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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