RPI3 swap experiments

[Mark Millard]

On 2018-Jun-27, at 12:42 PM, bob prohaska <fbsd at www.zefox.net> wrote:

> On Tue, Jun 26, 2018 at 11:30:52PM -0700, Mark Millard wrote:
>> On 2018-Jun-26, at 10:40 PM, bob prohaska <fbsd at www.zefox.net> wrote:
>> 
>> . . .
>> For (A), have you tried any examples of:
>> 
>> sufficient swap on mmcsd0 (or other such) with no swap
>> on da0 (but /usr and /var on /dev/da0)?
> Yes, that is the configuration which completes successfully.
>> 
>> If yes, did you check on if there were /dev/da0 errors
>> logged? What, if any, /dev/da0 errors where logged?
>> None?
> Correct, no errors on da0 when -j4 buildworld is successful.

Good to know. Thanks.

>> For (B), have you tried any examples of:
>> 
>> insufficient swap on (say) mmcsd0 and no use of the
>> /dev/da0 drive that has reported errors at all,
>> /usr/ and /var not on mmcsd0 (or whatever was used
>> for swap) either? Did some drive end up reporting
>> errors? Which? Did the system still crash as well?
>> 
> I think this is the standard test case:
> /usr and /var on /dev/da0
> /tmp on /dev/mmcsd0s3a
> swap on /dev/mmcsd0s3b
> 
> This configuration has crashed reliably with errors on /dev/da0 but no other "disk" errors.
> Did I understand the question correctly?

I intended for "no use of /dev/da0" to indicate
that not even /usr or /var were from the device
that has been logging the errors. For example:
having /usr or /var on the mechanical disk and
the known-problem disk not connected at all.

This would get either no-errors or some other
device would get errors, possibly the mechanical
disk (if that was the type used for a test).

>> 
>> 
>> Have such test-context combinations been tried?
>> 
>> Without any logs to look at for such alternatives, I
>> can not try to compare/contrast such to the others
>> examples.
>> 
> 
> Understood. The matrix of test conditions is not completely filled,
> and the test of different media for /dev/da0 has not yet been made.
> I'd like to play with stress2 and ports/sysutils/stress before doing
> that.

It would be handy for something simpler than buildworld to be
able to induce some of the types of problems, for sure.

> There is a new, successful -j4 buildworld swapuse.log for the case
> of 3 GB of USB flash swap at
> 
> http://www.zefox.net/~fbsd/rpi3/swaptests/r335576/3gbusbflash/
> 

I do not see a console.log or notes about the console messages
(or lack of such). Where there any messages there of note? No
device errors? Was such checked for?

> The system is now up to r335655 and I'm trying to replicate 
> earlier crash behavior before proceeding further. 
> 

Sounds good.

I will note that the following might help memory handling
for your context (small memory context):

Author: alc
Date: Tue Jun 26 18:29:56 2018
New Revision: 335674
URL: https://svnweb.freebsd.org/changeset/base/335674

Log:
  Update the physical page selection strategy used by vm_page_import() so
  that it does not cause rapid fragmentation of the free physical memory.
  
  Reviewed by:	jeff, markj (an earlier version)
  Differential Revision:	https://reviews.freebsd.org/D15976


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