Memory management issue on RPi?

[Michael Tuexen]

> On 13 Nov 2015, at 16:12, Warner Losh <imp at bsdimp.com> wrote:
> 
> 
> 
> On Fri, Nov 13, 2015 at 1:23 AM, Michael Tuexen <tuexen at freebsd.org> wrote:
> > On 12 Nov 2015, at 21:03, Konstantin Belousov <kostikbel at gmail.com> wrote:
> >
> > On Thu, Nov 12, 2015 at 08:47:29PM +0100, Michael Tuexen wrote:
> >>> On 12 Nov 2015, at 19:09, Konstantin Belousov <kostikbel at gmail.com> wrote:
> >>>
> >>> On Thu, Nov 12, 2015 at 06:57:03PM +0100, Michael Tuexen wrote:
> >>>>> On 12 Nov 2015, at 18:12, Konstantin Belousov <kostikbel at gmail.com> wrote:
> >>>>>
> >>>>> On Thu, Nov 12, 2015 at 05:25:37PM +0100, Michael Tuexen wrote:
> >>>>>>> On 12 Nov 2015, at 13:18, Konstantin Belousov <kostikbel at gmail.com> wrote:
> >>>>>>> This is a known problem with the swap-less OOM.  The following patch
> >>>>>>> should give you an immediate relief.  You might want to tweak
> >>>>>>> sysctl vm.pageout_oom_seq if default value is not right, it was selected
> >>>>>>> by 'try and see' approach on very small (32 or 64MB) i386 VM.
> >>>>>> It just works... Will do some more testing...
> >>>>>
> >>>>> I am more interested in report if OOM was triggered when it should.
> >>>> How do I know? What output do you want to see?
> >>>>
> >>>> Best regards
> >>>> Michael
> >>>>>
> >>>>> Try running several instances of 'sort /dev/zero'.
> >>> ^^^^^^^^^^^^^ I already answered this.
> >>> Run sort /dev/zero, and see whether OOM fires.
> >> OK, now I understand. You want to see if some processes are getting killed.
> >> (I was thinking that you might want to see some sysctl counters or so).
> >>
> >> Results:
> >> * I'm able to compile/link/install a kernel from source. This was not
> >>  possible before.
> >> * When running three instances of sort /dev/zero, two of them get killed
> >>  after a while (less than a minute). One continued to run, but got also
> >>  kill eventually. All via ssh login.
> > Exactly, this is the experiment I want to occur, and even more, the results
> > are good.
> Any plans to commit it?
> 
> These changes are good as an experiment. The RPi's relative speed of the CPU
> to the extremely slow SD card where pages are laundered to. Deferring the calls
> to the actual OOM a bit is useful. However, a simple count won't self-scale. What's
> good for the RPi likely is likely poor for a CPU connected to faster storage. The OOM
> won't kill things quickly enough in those circumstances. I imagine that there may
> be a more complicated relationship between the rate of page dirtying and laundering.
> 
> I'd hope that there'd be some kind of scaling that would take this variation into
> account.
> 
> At Netflix, we're developing some patches to do more pro-active laundering of pages
> rather than waiting for the page daemon to kick in. We do this primarily to avoid
> flushing the uma caches which have performance implications that we need to
> address to smooth out the performance. Perhaps something like this would be a
> more general way to cope with this situation?
I'm happy to test patches...

Best regards
Michael
> 
> Warner