Re: [patch -mm v2 2/3] mm, memcg: replace cgroup aware oom killer mount option with tunable

[Michal Hocko]

On Tue 30-01-18 12:13:22, Roman Gushchin wrote:
> On Tue, Jan 30, 2018 at 01:08:52PM +0100, Michal Hocko wrote:
> > On Tue 30-01-18 11:58:51, Roman Gushchin wrote:
> > > On Tue, Jan 30, 2018 at 09:54:45AM +0100, Michal Hocko wrote:
> > > > On Mon 29-01-18 11:11:39, Tejun Heo wrote:
> > > 
> > > Hello, Michal!
> > > 
> > > > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> > > > index 2eaed1e2243d..67bdf19f8e5b 100644
> > > > --- a/Documentation/cgroup-v2.txt
> > > > +++ b/Documentation/cgroup-v2.txt
> > > > @@ -1291,8 +1291,14 @@ This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM
> > > >  the memory controller considers only cgroups belonging to the sub-tree
> > > >  of the OOM'ing cgroup.
> > > >  
> > > > -The root cgroup is treated as a leaf memory cgroup, so it's compared
> > > > -with other leaf memory cgroups and cgroups with oom_group option set.
> > >                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > IMO, this statement is important. Isn't it?
> > > 
> > > > +Leaf cgroups are compared based on their cumulative memory usage. The
> > > > +root cgroup is treated as a leaf memory cgroup as well, so it's
> > > > +compared with other leaf memory cgroups. Due to internal implementation
> > > > +restrictions the size of the root cgroup is a cumulative sum of
> > > > +oom_badness of all its tasks (in other words oom_score_adj of each task
> > > > +is obeyed). Relying on oom_score_adj (appart from OOM_SCORE_ADJ_MIN)
> > > > +can lead to overestimating of the root cgroup consumption and it is
> > > 
> > > Hm, and underestimating too. Also OOM_SCORE_ADJ_MIN isn't any different
> > > in this case. Say, all tasks except a small one have OOM_SCORE_ADJ set to
> > > -999, this means the root croup has extremely low chances to be elected.
> > > 
> > > > +therefore discouraged. This might change in the future, though.
> > > 
> > > Other than that looks very good to me.
> > 
> > This?
> > 
> > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> > index 2eaed1e2243d..34ad80ee90f2 100644
> > --- a/Documentation/cgroup-v2.txt
> > +++ b/Documentation/cgroup-v2.txt
> > @@ -1291,8 +1291,15 @@ This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM
> >  the memory controller considers only cgroups belonging to the sub-tree
> >  of the OOM'ing cgroup.
> >  
> > -The root cgroup is treated as a leaf memory cgroup, so it's compared
> > -with other leaf memory cgroups and cgroups with oom_group option set.
> > +Leaf cgroups and cgroups with oom_group option set are compared based
> > +on their cumulative memory usage. The root cgroup is treated as a
> > +leaf memory cgroup as well, so it's compared with other leaf memory
> > +cgroups. Due to internal implementation restrictions the size of
> > +the root cgroup is a cumulative sum of oom_badness of all its tasks
> > +(in other words oom_score_adj of each task is obeyed). Relying on
> > +oom_score_adj (appart from OOM_SCORE_ADJ_MIN) can lead to over or
> > +underestimating of the root cgroup consumption and it is therefore
> > +discouraged. This might change in the future, though.
> 
> Acked-by: Roman Gushchin <guro@xxxxxx>

Andrew?