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

[Mark Millard]

[Your old changes for reporting information no longer matches
sys/vm/swap_pager.c as of head -r343030 and later.]

On 2018-Aug-9, at 10:09, Mark Johnston <markj at FreeBSD.org> wrote:

> On Thu, Aug 09, 2018 at 09:21:38AM -0700, Mark Millard wrote:
>> Would something like the patch that produced the messages
>> like:
>> 
>> waited 3s for async swap write
>> waited 3s for swap buffer
>> 
>> be appropriate as able to be enabled via a sysctl or in
>> some other way? In other words: in the source code by standard,
>> off by default, but able to be enabled without patching,
>> possibly without rebuilding?
> 
> Yes, I think so.  We don't have a lot of visibility into the behaviour
> of the pageout threads, and I have some ideas on how to improve that.
> Swap I/O latency measurements are something I've wanted in the past.

Your old changes for reporting information no longer matches
sys/vm/swap_pager.c as of head -r343030 and later and nothing
for this was merged into head or stable/12.

Are you still planning to have an update for monitoring for such
issues at some point?

>> I ask because I've been thinking of having such on the
>> FreeBSD's where I buildworld buildkernel and use poudriere-devel
>> for port builds. It might warning me of marginal contexts and
>> help explain any OOM kills that might occur. (Somethings
>> things are difficult or time consuming to reproduce.)
>> 
>> If monitored at the time, it might even help identify contexts
>> that "machine-gun down requests" in environments were such can
>> be a problem for swapping.

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