Re: [RFC PATCH] mm/oom_kill: allow oom kill allocating task for non-global case

[Waiman Long]

On 6/7/21 3:04 PM, Shakeel Butt wrote:
> On Mon, Jun 7, 2021 at 11:51 AM Waiman Long <llong@xxxxxxxxxx> wrote:
> > On 6/7/21 2:43 PM, Shakeel Butt wrote:
> > > On Mon, Jun 7, 2021 at 9:45 AM Waiman Long <llong@xxxxxxxxxx> wrote:
> > > > On 6/7/21 12:31 PM, Aaron Tomlin wrote:
> > > > > At the present time, in the context of memcg OOM, even when
> > > > > sysctl_oom_kill_allocating_task is enabled/or set, the "allocating"
> > > > > task cannot be selected, as a target for the OOM killer.
> > > > >
> > > > > This patch removes the restriction entirely.
> > > > >
> > > > > Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
> > > > > ---
> > > > >     mm/oom_kill.c | 6 +++---
> > > > >     1 file changed, 3 insertions(+), 3 deletions(-)
> > > > >
> > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > > > > index eefd3f5fde46..3bae33e2d9c2 100644
> > > > > --- a/mm/oom_kill.c
> > > > > +++ b/mm/oom_kill.c
> > > > > @@ -1089,9 +1089,9 @@ bool out_of_memory(struct oom_control *oc)
> > > > >                 oc->nodemask = NULL;
> > > > >         check_panic_on_oom(oc);
> > > > >
> > > > > -     if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
> > > > > -         current->mm && !oom_unkillable_task(current) &&
> > > > > -         oom_cpuset_eligible(current, oc) &&
> > > > > +     if (sysctl_oom_kill_allocating_task && current->mm &&
> > > > > +            !oom_unkillable_task(current) &&
> > > > > +            oom_cpuset_eligible(current, oc) &&
> > > > >             current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
> > > > >                 get_task_struct(current);
> > > > >                 oc->chosen = current;
> > > > To provide more context for this patch, we are actually seeing that in a
> > > > customer report about OOM happened in a container where the dominating
> > > > task used up most of the memory and it happened to be the task that
> > > > triggered the OOM with the result that no killable process could be
> > > > found.
> > > Why was there no killable process? What about the process allocating
> > > the memory or is this remote memcg charging?
> > It is because the other processes have a oom_adjust_score of -1000. So
> > they are non-killable. Anyway, they don't consume that much memory and
> > killing them won't free up that much.
> >
> > The other process that uses most of the memory is the one that trigger
> > the OOM kill in the first place because the memory limit has been
> > reached in new memory allocation. Based on the current logic, this
> > process cannot be killed at all even if we set the
> > oom_kill_allocating_task to 1 if the OOM happens only within the memcg
> > context, not in a global OOM situation.
> I am not really against the patch but I am still not able to
> understand why select_bad_process() was not able to select the current
> process. mem_cgroup_scan_tasks() traverses all the processes in the
> target memcg hierarchy, so why the current was skipped.

Yes, you are right. Probably there is some problem with reaping so that 
the MMF_OOM_SKIP bit gets set. I don't have the answer yet.

Regards,
Longman