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

[Waiman Long <llong@redhat.com>]

On 6/7/21 3:04 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:

[ 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.

Cheers,
Longman