[RFC PATCH] mm, memcg: fix (Re: OOM: Better, but still there on)

[Michal Hocko <mhocko@kernel.org>]

[Add Mel, Johannes and Vladimir - the email thread started here
http://lkml.kernel.org/r/20161215225702.GA27944@boerne.fritz.box
The long story short, the zone->node reclaim change has broken active
list aging for lowmem requests when memory cgroups are enabled. More
details below.

On Fri 23-12-16 13:57:28, Michal Hocko wrote:
> On Fri 23-12-16 13:18:51, Nils Holland wrote:
> > On Fri, Dec 23, 2016 at 11:51:57AM +0100, Michal Hocko wrote:
> > > TL;DR
> > > drop the last patch, check whether memory cgroup is enabled and retest
> > > with cgroup_disable=memory to see whether this is memcg related and if
> > > it is _not_ then try to test with the patch below
> > 
> > Right, it seems we might be looking in the right direction! So I
> > removed the previous patch from my kernel and verified if memory
> > cgroup was enabled, and indeed, it was. So I booted with
> > cgroup_disable=memory and ran my ordinary test again ... and in fact,
> > no ooms!
> 
> OK, thanks for confirmation. I could have figured that earlier. The
> pagecache differences in such a short time should have raised the red
> flag and point towards memcgs...
> 
> [...]
> > > I would appreciate to stick with your setup to not pull new unknows into
> > > the picture.
> > 
> > No problem! It's just likely that I won't be able to test during the
> > following days until Dec 27th, but after that I should be back to
> > normal and thus be able to run further tests in a timely fashion. :-)
> 
> no problem at all. I will try to cook up a patch in the mean time.

So here is my attempt. Only compile tested so be careful, it might eat
your kittens or do more harm. I would appreciate other guys to have a
look to see whether this is sane. There are probably other places which
would need some tweaks. I think that get_scan_count needs some tweaks
as well because we should only consider eligible zones when counting the
number of pages to scan. This would be for a separate patch which I will
send later. I just want to fix this one first.

Nils, even though this is still highly experimental, could you give it a
try please?
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