swap space issues

[Greg 'groggy' Lehey]

On Wednesday, 24 June 2020 at 18:51:04 -0700, Donald Wilde wrote:
> On 6/24/20, Greg 'groggy' Lehey <grog at freebsd.org> wrote:
>> On Wednesday, 24 June 2020 at  9:36:23 -0700, Donald Wilde wrote:
>>> All,
>>>
>>> I recently upgraded my 12-STABLE system to the latest, and now my
>>> swap subsystems aren't working. I deliberately set up a 40GB
>>> partition for swap, and when I do 'top -t' I am only seeing 7906M
>>> total.
>>
>> That looks suspiciously like the difference from 32 GB.  Could it be
>> numeric overflow?  And if so, where?  What does pstat -s say?
>
> Well, hi Greg! LTNT2!

Indeed.

> pstat -shm:
>
> /dev/ada0s1b  65536 (1M blocks), Used: 1.5G, Avail: 63G, Capacity: 2%

Now that's really puzzling.  Why does it say 64 G when you said 40 G,
and the error from top tends to confirm it?  How big is the partition
(gpart output)?

>>> When using synth, it shows swap usage of < 2%, but then it gives the
>>> 'out of swap' complaint and tosses all my users out into neverland.
>>
>> Unless this also causes kernel messages to that effect, this, too,
>> could be an issue with synth.
>
> I believe the messages about 'out of swap' were from the kernel as
> it died, not synth. As I say, it killed all my active users, both
> root and non-root.

Hmm.

> Why does _top_ show the 7906M number? I suspect that it's deeper
> than just synth.

If top counts swap in a form that overflows at 32 GB, 40 GB could show
up as 8 GB.

> What else can I share to help diagnose this?

Background, maybe?  You say that you upgraded your system.  Did you
change the swap size when you did?  What were swap and RAM sizes
before and after?

FWIW, I've had a very large number of issues with -STABLE in recent
months, though not this one.  I should send a separate message.

Greg
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