RPI3 swap experiments ["was killed: out of swap space" with: "v_free_count: 5439, v_inactive_count: 1"]

[Mark Millard]

On 2018-Aug-8, at 1:48 PM, Mark Johnston <markj at FreeBSD.org> wrote:

> On Wed, Aug 08, 2018 at 08:38:00AM -0700, bob prohaska wrote:
>> The patched kernel ran longer than default but OOMA still halted buildworld around
>> 13 MB. That's considerably farther than a default build world have run but less than
>> observed when setting vm.pageout_oom_seq=120 alone. Log files are at
>> http://www.zefox.net/~fbsd/rpi3/swaptests/r337226M/1gbsdflash_1gbusbflash/batchqueue/
>> 
>> Both changes are now in place and -j4 buildworld has been restarted. 
> 
> Looking through the gstat output, I'm seeing some pretty abysmal average
> write latencies for da0, the flash drive.  I also realized that my
> reference to r329882 lowering the pagedaemon sleep period was wrong -
> things have been this way for much longer than that.  Moreover, as you
> pointed out, bumping oom_seq to a much larger value wasn't quite
> sufficient.

My understanding is that some other folks involved in the message
exchange replicated the OOM kills without having evidence of issues
like Bob P. has with large latencies for his hardware. The latencies
may be sufficient but not necessary.

Getting some of the other folks to run your tests would likely be
good.

> I'm curious as to what the worst case swap I/O latencies are in your
> test, since the average latencies reported in your logs are high enough
> to trigger OOM kills even with the increased oom_seq value.  When the
> current test finishes, could you try repeating it with this patch
> applied on top? https://people.freebsd.org/~markj/patches/slow_swap.diff
> That is, keep the non-default oom_seq setting and modification to
> VM_BATCHQUEUE_SIZE, and apply this patch on top.  It'll cause the kernel
> to print messages to the console under certain conditions, so a log of
> console output will be interesting.

Sounds like anyone else running tests should also have all 3
changes in place.

I've CC'd some folks from the exchange that I think were running
some tests.

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