Re: OOM detection regressions since 4.7

[Markus Trippelsdorf]

On 2016.08.22 at 13:13 +0200, Michal Hocko wrote:
> On Mon 22-08-16 13:01:13, Markus Trippelsdorf wrote:
> > On 2016.08.22 at 12:56 +0200, Michal Hocko wrote:
> > > On Mon 22-08-16 12:16:14, Markus Trippelsdorf wrote:
> > > > On 2016.08.22 at 11:32 +0200, Michal Hocko wrote:
> > > > > [1] http://lkml.kernel.org/r/20160731051121.GB307@x4
> > > > 
> > > > For the report [1] above:
> > > > 
> > > > markus@x4 linux % cat .config | grep CONFIG_COMPACTION
> > > > # CONFIG_COMPACTION is not set
> > > 
> > > Hmm, without compaction and a heavy fragmentation then I am afraid we
> > > cannot really do much. What is the reason to disable compaction in the
> > > first place?
> > 
> > I don't recall. Must have been some issue in the past. I will re-enable
> > the option.
> 
> Well, without the compaction there is no source of high order pages at
> all. You can only reclaim and hope that some of the reclaimed pages will
> find its buddy on the list and form the higher order page. This can take
> for ever. We used to have the lumpy reclaim and that could help but this
> is long gone.
> 
> I do not think we can really sanely optimize for high-order heavy loads
> without COMPACTION sanely. At least not without reintroducing lumpy
> reclaim or something similar. To be honest I am even not sure which
> configurations should disable compaction - except for really highly
> controlled !mmu or other one purpose systems.

I now recall. It was an issue with CONFIG_TRANSPARENT_HUGEPAGE, so I
disabled that option. This then de-selected CONFIG_COMPACTION...

-- 
Markus