lightly loaded system eats swap space

[Adam]

On Mon, Jun 18, 2018 at 7:27 AM, tech-lists <tech-lists at zyxst.net> wrote:

> On 18/06/2018 09:08, Erich Dollansky wrote:
>
>> Hi,
>>
>> On Sun, 17 Jun 2018 23:19:02 +0100
>> tech-lists <tech-lists at zyxst.net> wrote:
>>
>> freebsd-11-stable r333874, ZFS raidz1-0 (3x4TB disks), 128GB RAM,
>>> Swap: 4096M Total, 3502M Used, 594M Free, 85% Inuse
>>>
>>
>> this might not be related but I noticed that your swap space is small
>> compared to RAM size. I noticed on a much smaller Raspberry Pi, that it
>> runs into trouble when there is no swap even there is enough RAM
>> available. Is it easily possible for you to add some GB of swap space
>> and let the machine run then?
>>
>> How much swap do the other machines have?
>>
>
> Hi,
>
> Yes, the machine with the problem uses the default 4GB swap. That's all
> the swap it has. The machine without issue has a swapfile installed on a
> SSD in addition to the default 4GB swap.
>
> problematic machine:
> Device          512-blocks     Used    Avail Capacity
> /dev/ada0p3        8388608     3.3G     714M    83%
>
> machine without a problem, it has swapfile installed:
> Device          512-blocks     Used    Avail Capacity
> /dev/ada0s1b       8262248     1.7G     2.2G    44%
> /dev/md0          65536000     1.9G      29G     6%
> Total             73798248     3.7G      32G    10%
>
> I added the swapfile a long time ago on this machine due to the same issue.
>
> But my problem isn't so much an out of swapspace problem; all this is, is
> a symptom. My problem is "why is it swapping out at all on a 128GB system
> and why is what's swapped out not being swapped back in again".
>

What is the output of sysctl vm.overcommit? If this system is intended on
being a VM host, then why don't you limit ARC to something reasonable like
Total Mem - Projected VM Mem - Overhead = Ideal ARC .

-- 
Adam