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

[Mark Millard]

On 2018-Jun-26, at 3:28 PM, bob prohaska <fbsd at www.zefox.net> wrote:

> On Tue, Jun 26, 2018 at 01:15:54PM -0700, Mark Millard wrote:
>> 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.
>> 
> 
> I just didn't bother to record successful runs. I'm logging one now.
> 
>> 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.
>> 
> Not sure I understand here. Basically there seem to be three cases:
> Enough swap not on da0, -j4 buildworld completes.
> Any swap on da0, -j4 buildworld is killed by OOMA
> Not enough swap not on da0, -j4 buildworld crashes the machine eventually.
> 
> Are there other combinations I've overlooked? The first two don't seem 
> worth repeating, at least not often.

"buildworld completes with /dev/da0 errors" vs. "buildworld completes
without /dev/da0 errors" (for: enough swap not on /dev/da0 with no
swap on /dev/da0 ).

That is a little simplistic, as there can be multiple retries
before FreeBSD gives up. Normal is no retries needed. Going
from rare single retries to frequent multiple retries but no
giving-up to it giving up sometimes is all abnormal as I
understand. But there are degrees of abnormal.

And, yes, I have had past examples of significant drive reports
during buildworld that let buildworld appear to complete. (Not
that I trusted the result or the drive involved after such, at
least as the drive was powered/connected at the time.)

For "any swap on da0" and "not enough swap not on da0" (with
no swap on da0) I'd add to your descriptions: "with /dev/da0
errors" (again simplistic).

This goes along with my suggestion to split the /dev/da0
error investigation from the investigations of OMMA behavior
and crashing-the-machine: avoiding any confounding.

(For now I do not have access to a context for doing rpi3
examples myself.)


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