Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()

[Minchan Kim <minchan.kim@gmail.com>]

On Fri, Mar 11, 2011 at 3:08 PM, avagin@gmail.com <avagin@gmail.com> wrote:
> On 03/11/2011 03:18 AM, Minchan Kim wrote:
>>
>> On Fri, Mar 11, 2011 at 8:58 AM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@jp.fujitsu.com>  wrote:
>>>
>>> On Thu, 10 Mar 2011 15:58:29 +0900
>>> Minchan Kim<minchan.kim@gmail.com>  wrote:
>>>
>>>> Hi Kame,
>>>>
>>>> Sorry for late response.
>>>> I had a time to test this issue shortly because these day I am very
>>>> busy.
>>>> This issue was interesting to me.
>>>> So I hope taking a time for enough testing when I have a time.
>>>> I should find out root cause of livelock.
>>>>
>>>
>>> Thanks. I and Kosaki-san reproduced the bug with swapless system.
>>> Now, Kosaki-san is digging and found some issue with scheduler boost at
>>> OOM
>>> and lack of enough "wait" in vmscan.c.
>>>
>>> I myself made patch like attached one. This works well for returning TRUE
>>> at
>>> all_unreclaimable() but livelock(deadlock?) still happens.
>>
>> I saw the deadlock.
>> It seems to happen by following code by my quick debug but not sure. I
>> need to investigate further but don't have a time now. :(
>>
>>
>>                  * Note: this may have a chance of deadlock if it gets
>>                  * blocked waiting for another task which itself is
>> waiting
>>                  * for memory. Is there a better alternative?
>>                  */
>>                 if (test_tsk_thread_flag(p, TIF_MEMDIE))
>>                         return ERR_PTR(-1UL);
>> It would be wait to die the task forever without another victim selection.
>> If it's right, It's a known BUG and we have no choice until now. Hmm.
>
>
> I fixed this bug too and sent patch "mm: skip zombie in OOM-killer".
>
> http://groups.google.com/group/linux.kernel/browse_thread/thread/b9c6ddf34d1671ab/2941e1877ca4f626?lnk=raot&pli=1
>
> -               if (test_tsk_thread_flag(p, TIF_MEMDIE))
> +               if (test_tsk_thread_flag(p, TIF_MEMDIE) && p->mm)
>                        return ERR_PTR(-1UL);
>
> It is not committed yet, because Devid Rientjes and company think what to do
> with "[patch] oom: prevent unnecessary oom kills or kernel panics.".

Thanks, Andrey.
The patch "mm: skip zombie in OOM-killer"  solves my livelock issue
but I didn't look effectiveness of "mm: check zone->all_unreclaimable
in all_unreclaimable". I have to look further.

But your patch  "mm: skip zombie in OOM-killer" is very controversial
because It breaks multi-thread case.
Since find_lock_task_mm is introduced, we have considered mt cases but
I think it doesn't cover completely all cases like discussing
TIF_MEMDIE now.

I will watch the discussion.
-- 
Kind regards,
Minchan Kim

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