swap space issues

[Donald Wilde]

On 6/26/20, Peter Jeremy <peter at rulingia.com> wrote:
> On 2020-Jun-25 11:30:31 -0700, Donald Wilde <dwilde1 at gmail.com> wrote:
>>Here's 'pstat -s' on the i3 (which registers as cpu HAMMER):
>>
>>Device          1K-blocks     Used    Avail Capacity
>>/dev/ada0s1b     33554432        0 33554432     0%
>>/dev/ada0s1d     33554432        0 33554432     0%
>>Total            67108864        0 67108864     0%
>
> I strongly suggest you don't have more than one swap device on spinning
> rust - the VM system will stripe I/O across the available devices and
> that will give particularly poor results when it has to seek between the
> partitions.

My intent is to make this machine function -- getting the bear
dancing. How deftly she dances is less important than that she dances
at all. My for-real boxen will have real HP and real cores and RAM.

>
> Also, you can't actually use 64GB swap with 4GB RAM.  If you look back
> through your boot messages, I expect you'll find messages like:
> warning: total configured swap (524288 pages) exceeds maximum recommended
> amount (498848 pages).
> warning: increase kern.maxswzone or reduce amount of swap.

Yes, as I posted, those were part of the failure stream from the synth
program. When I had kern.maxswzone increased, it got through boot
without complaining.

> or maybe:
> WARNING: reducing swap size to maximum of xxxxMB per unit

The warnings were there, in the as-it-failed complaints.

> The absolute limit on swap space is vm.swap_maxpages pages but the
> realistic
> limit is about half that.  By default the realistic limit is about 4×RAM
> (on
> 64-bit architectures), but this can be adjusted via kern.maxswzone (which
> defines the #bytes of RAM to allocate to swzone structures - the actual
> space allocated is vm.swzone).
>
> As a further piece of arcana, vm.pageout_oom_seq is a count that controls
> the number of passes before the pageout daemon gives up and starts killing
> processes when it can't free up enough RAM.  "out of swap space" messages
> generally mean that this number is too low, rather than there being a
> shortage of swap - particularly if your swap device is rather slow.
>
Thanks, Peter!
-- 
Don Wilde
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