On Thu 19-10-17 15:45:34, Johannes Weiner wrote:

On Thu, Oct 19, 2017 at 07:52:12PM +0100, Roman Gushchin wrote:

quoted

This patchset makes the OOM killer cgroup-aware.

Hi Andrew,

I believe this code is ready for merging upstream, and it seems Michal
is in agreement. There are two main things to consider, however.

David would have really liked for this patchset to include knobs to
influence how the algorithm picks cgroup victims. The rest of us
agreed that this is beyond the scope of these patches, that the
patches don't need it to be useful, and that there is nothing
preventing anyone from adding configurability later on. David
subsequently nacked the series as he considers it incomplete. Neither
Michal nor I see technical merit in David's nack.

agreed

Michal acked the implementation, but on the condition that the new
behavior be opt-in, to not surprise existing users.

and just to make it clear I have also said I will _not_ nack if that is
not the case.

I *think* we agree
that respecting the cgroup topography during global OOM is what we
should have been doing when cgroups were initially introduced;

We do not agree here though. I am not convinced that respecting the
cgroup topography is an universal win. It is true that there is no best
OOM victim selection strategy but what we have currently is the simplest
option and as such the most robust one. I can tell from the past year
experience that many of those clever heuristics actually contributed to
lockups and non-deterministic behavior.

where
we disagree is that I think users shouldn't have to opt in to
improvements. We have done much more invasive changes to the victim
selection without actual regressions in the past. Further, this change
only applies to mounts of the new cgroup2.

which basically means that the behavior will change under many users
feet because the respecitve cgroup configuration is chosen by somebody
else (e.g. systemd) so I do not really buy "only v2 behavior"

Tejun also wasn't convinced
of the risk for regression, and too would prefer cgroup-awareness to
be the default in cgroup2. I would ask for patch 5/6 to be dropped.

-- 
Michal Hocko
SUSE Labs

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