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

[Mark Johnston]

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.

> 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.