Re: spurious out of swap kills

On Thu, Sep 12, 2019 at 05:42:00PM -0700, Don Lewis wrote:
> 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.
If you are sure that you cannot exhaust your swap space, set
attempts to -1 to disable this mechanism.

Basically, page fault handler waits for vm.pfault_oom_wait *
vm.pfault_oom_attempts for a page allocation before killing the process.
Default is 30 secs, and if you cannot get a page for 30 secs, there is
something very wrong with the machine.