On Mon, Apr 13, 2020 at 5:36 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> On Tue, Apr 14, 2020 at 1:06 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> >
> > On Sun, Apr 12, 2020 at 7:04 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> > >
> > > A recent commit 9852ae3fe529 ("mm, memcg: consider subtrees in
> > > memory.events") changes the behavior of memcg events, which will
> > > consider subtrees in memory.events. But oom_kill event is a special one
> > > as it is used in both cgroup1 and cgroup2. In cgroup1, it is displayed
> > > in memory.oom_control. The file memory.oom_control is in both root memcg
> > > and non root memcg, that is different with memory.event as it only in
> > > non-root memcg. That commit is okay for cgroup2, but it is not okay for
> > > cgroup1 as it will cause inconsistent behavior between root memcg and
> > > non-root memcg.
> >
> > I still couldn't understand the cgroup v1's root vs non_root behavior
> > change. The behavior change I see is the hierarchical one i.e.
> > MEMCG_OOM_KILL event in the descendant will cause the notification and
> > count increment in the ancestors even in the cgroup v1.
>
> For the non-root memcg, its memory.oom_control(oom_kill) includes its
> descendants' oom_kill, but for root memcg, it doesn't include its
> descendants' oom_kill. That means, memory.oom_control(oom_kill) has
> different meanings in different memcgs. That is inconsistent.
>
> [snip]
> > I suppose we
> > don't want that behavior change in v1.
> >
>
> That is another topic. I think this feature is welcomed to cgroup1, if
> we can fully support it, for example by adding memory.events.local
> into cgroup1 as well, but as far as I know the cgroup1 is frozen.
>
Please note that after your patch the non-root memcg's
memory.oom_control(oom_kill) will not include the descendant's
oom_kill anymore. The non-root and root memcg's
memory.oom_control(oom_kill) will not be hierarchical anymore but
consistent. I think that was the intention of the patch, right?
> > > Let's recover the original behavior for cgroup1.
> > >
> > > Fixes: 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events")
> > > Cc: Chris Down <chris@xxxxxxxxxxxxxx>
> > > Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> > > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > > ---
> > > include/linux/memcontrol.h | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > > index 8c340e6b347f..a0ae080a67d1 100644
> > > --- a/include/linux/memcontrol.h
> > > +++ b/include/linux/memcontrol.h
> > > @@ -798,7 +798,8 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg,
> > > atomic_long_inc(&memcg->memory_events[event]);
> > > cgroup_file_notify(&memcg->events_file);
> > >
> > > - if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
> > > + if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS ||
> > > + !cgroup_subsys_on_dfl(memory_cgrp_subsys))
> > > break;
> > > } while ((memcg = parent_mem_cgroup(memcg)) &&
> > > !mem_cgroup_is_root(memcg));
> > > --
> > > 2.18.2
> > >
>
>
> Thanks
> Yafang
