RPI3 swap experiments, was Re: GPT vs MBR for swap devices

[Mark Millard]

On 2018-Jun-26, at 8:18 AM, bob prohaska <fbsd at www.zefox.net> wrote:

> On Tue, Jun 26, 2018 at 07:37:59AM -0700, Mark Millard wrote:
>> 
>> 
>> . . .
>> 
>> As I remember, Bob P. Did reproduce drive errors even without
>> the problem drive being used for swapping. This too suggests
>> (A) as separate activity.
>> 
> Indeed, it is a requirement. If the suspect device is used for swapping
> OOMA kills prevent the test from progressing to the point of failure.
> 

Looking back at http://www.zefox.net/~fbsd/rpi3/swaptests/
and information about /dev/da0 rive errors it does not
appear that a combination with:

A) sufficient swap (> 1.5 GiByte total?) but no use of swap on
   any partition on /dev/da0
and:
B) use of /dev/da0 for /usr/ and /var/
and:
C) Records from the console showing errors (or notes
   indicating lack of such errors).

exists. So I was remembering incorrectly.

I'm not claiming such a combination is the best direction for
the next tests, but absent such tests there is no
compare/contrast to know if /dev/da0 would still get errors
despite the system having sufficient swap present on other
drives. Thus, I would not go so far as "is a requirement" on
the evidence available.

We do have evidence for the system having insufficient swap
space: this context seems to have the current status "is
sufficient but might not be necessary" for /dev/da0
getting drive errors.


As for simpler contexts, one that would swap but would be
far simpler a context than buildworld buildkernel might be
something like using the stress port via options like:

stress -d 2 -m 3 --vm-keep

(The option values likely could need adjustment from context
to context to match available resources. The above is not
carefully tailored to your context or a modern context.
It dates back to 2016-Jan-22 for showing vnode based swap
failures in a 1 GiByte RAM + 1 GiByte swap-file context
[inside virtualbox on amd64 hardware]: see comment 3 of
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=206048 .)



===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)