spurious out of swap kills

[Don Lewis]

On 12 Sep, Mark Johnston wrote:
> On Thu, Sep 12, 2019 at 04:00:17PM -0700, Don Lewis wrote:
>> My poudriere machine is running 13.0-CURRENT and gets updated to the
>> latest version of -CURRENT periodically.  At least in the last week or
>> so, I've been seeing occasional port build failures when building my
>> default set of ports, and I finally had some time to do some
>> investigation.
>> 
>> It's a 16-thread Ryzen machine, with 64 GB of RAM and 40 GB of swap.
>> Poudriere is configured with
>>   USE_TMPFS="wrkdir data localbase"
>> and I have
>>   .if ${.CURDIR:M*/www/chromium}
>>   MAKE_JOBS_NUMBER=16
>>   .else
>>   MAKE_JOBS_NUMBER=7
>>   .endif
>> in /usr/local/etc/poudriere.d/make.conf, since this gives me the best
>> overall build time for my set of ports.  This hits memory pretty hard,
>> especially when chromium, firefox, libreoffice, and both versions of
>> openoffice are all building at the same time.  During this time, the
>> amount of space consumed by tmpfs for /wrkdir gets large when building
>> these large ports.  There is not enough RAM to hold it all, so some of
>> the older data spills over to swap.  Swap usage peaks at about 10 GB,
>> leaving about 30 GB of free swap.  Nevertheless, I see these errors,
>> with rustc being the usual victim:
>> 
>> Sep 11 23:21:43 zipper kernel: pid 16581 (rustc), jid 43, uid 65534, was killed: out of swap space
>> Sep 12 02:48:23 zipper kernel: pid 1209 (rustc), jid 62, uid 65534, was killed: out of swap space
>> 
>> Top shows the size of rustc being about 2 GB, so I doubt that it
>> suddenly needs an additional 30 GB of swap.
>> 
>> I'm wondering if there might be a transient kmem shortage that is
>> causing a malloc(..., M_NOWAIT) failure in the swap allocation path
>> that is the cause of the problem.
> 
> Perhaps this is a consequence of r351114?  To confirm this, you might
> try increasing the value of vm.pfault_oom_wait to a larger value, like
> 20 or 30, and see if the OOM kills still occur.

I wonder if increasing vm.pfault_oom_attempts might also be a good idea.