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

[Waiman Long <llong@redhat.com>]

On 6/7/21 3:36 PM, Michal Hocko wrote:
> On Mon 07-06-21 15:18:38, Waiman Long wrote:
>> On 6/7/21 3:04 PM, Michal Hocko wrote:
>>> On Mon 07-06-21 14:51:05, Waiman Long wrote:
>>>> On 6/7/21 2:43 PM, Shakeel Butt wrote:
>>>>> On Mon, Jun 7, 2021 at 9:45 AM Waiman Long <llong@redhat.com> 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@redhat.com>
>>>>>>> ---
>>>>>>>      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. This patch is
>>>> to allow this process to be killed under this circumstance.
>>> Do you have the oom report? I do not see why the allocating task hasn't
>>> been chosen.
>> A partial OOM report below:
> Do you happen to have the full report?
I need to ask to see if I can release the full report.
>
>> [ 8221.433608] memory: usage 21280kB, limit 204800kB, failcnt 49116
>>    :
>> [ 8227.239769] [ pid ]   uid  tgid total_vm      rss pgtables_bytes swapents  oom_score_adj name
>> [ 8227.242495] [1611298]     0 1611298    35869      635 167936        0         -1000 conmon
>> [ 8227.242518] [1702509]     0 1702509    35869      701 176128        0         -1000 conmon
>> [ 8227.242522] [1703345] 1001050000 1703294   183440        0 2125824        0           999 node
>> [ 8227.242706] Out of memory and no killable processes...
>> [ 8227.242731] node invoked oom-killer: gfp_mask=0x6000c0(GFP_KERNEL), nodemask=(null), order=0, oom_score_adj=999
>> [ 8227.242732] node cpuset=crio-b8ac7e23f7b520c0365461defb66738231918243586e287bfb9e206bb3a0227a.scope mems_allowed=0-1
>>
>> So in this case, node cannot kill itself and no other processes are
>> available to be killed.
> The process is clearly listed as eligible so the oom killer should find
> it and if it hasn't then this should be investigated. Which kernel is
> this?

Right. I don't know why the current cannot be selected. I think we may 
need to enhance the OOM but no killable process report to list the 
reason a task is skipped other than oom_score_adj. The kernel is a 
RHEL8.2 kernel which has OOM code pretty close to upstream.

Cheers,
Longman