Re: [patch] mm, oom: prevent soft lockup on memcg oom for UP systems

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

On 2020/03/11 7:55, David Rientjes wrote:
> On Wed, 11 Mar 2020, Tetsuo Handa wrote:
> 
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -2637,6 +2637,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
>>>  		unsigned long reclaimed;
>>>  		unsigned long scanned;
>>>  
>>> +		cond_resched();
>>> +
>>
>> Is this safe for CONFIG_PREEMPTION case? If current thread has realtime priority,
>> can we guarantee that the OOM victim (well, the OOM reaper kernel thread rather
>> than the OOM victim ?) gets scheduled?
>>
> 
> I think it's the best we can do that immediately solves the issue unless 
> you have another idea in mind?

"schedule_timeout_killable(1) outside of oom_lock" or "the OOM reaper grabs oom_lock
so that allocating threads guarantee that the OOM reaper gets scheduled" or "direct OOM
reaping so that allocating threads guarantee that some memory is reclaimed".

> 
>>>  		switch (mem_cgroup_protected(target_memcg, memcg)) {
>>>  		case MEMCG_PROT_MIN:
>>>  			/*
>>>
>>