Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

(2011/05/24 20:55), Andrew Lutomirski wrote:
> On Tue, May 24, 2011 at 7:24 AM, Andrew Lutomirski <luto@mit.edu> wrote:
>> On Mon, May 23, 2011 at 9:34 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
>>> On Tue, May 24, 2011 at 10:19 AM, Andrew Lutomirski <luto@mit.edu> wrote:
>>>> On Sun, May 22, 2011 at 7:12 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
>>>>> Could you test below patch based on vanilla 2.6.38.6?
>>>>> The expect result is that system hang never should happen.
>>>>> I hope this is last test about hang.
>>>>>
>>>>> Thanks.
>>>>>
>>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>>>> index 292582c..1663d24 100644
>>>>> --- a/mm/vmscan.c
>>>>> +++ b/mm/vmscan.c
>>>>> @@ -231,8 +231,11 @@ unsigned long shrink_slab(struct shrink_control *shrink,
>>>>>       if (scanned == 0)
>>>>>               scanned = SWAP_CLUSTER_MAX;
>>>>>
>>>>> -       if (!down_read_trylock(&shrinker_rwsem))
>>>>> -               return 1;       /* Assume we'll be able to shrink next time */
>>>>> +       if (!down_read_trylock(&shrinker_rwsem)) {
>>>>> +               /* Assume we'll be able to shrink next time */
>>>>> +               ret = 1;
>>>>> +               goto out;
>>>>> +       }
>>>>>
>>>>>       list_for_each_entry(shrinker, &shrinker_list, list) {
>>>>>               unsigned long long delta;
>>>>> @@ -286,6 +289,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
>>>>>               shrinker->nr += total_scan;
>>>>>       }
>>>>>       up_read(&shrinker_rwsem);
>>>>> +out:
>>>>> +       cond_resched();
>>>>>       return ret;
>>>>>  }
>>>>>
>>>>> @@ -2331,7 +2336,7 @@ static bool sleeping_prematurely(pg_data_t
>>>>> *pgdat, int order, long remaining,
>>>>>        * must be balanced
>>>>>        */
>>>>>       if (order)
>>>>> -               return pgdat_balanced(pgdat, balanced, classzone_idx);
>>>>> +               return !pgdat_balanced(pgdat, balanced, classzone_idx);
>>>>>       else
>>>>>               return !all_zones_ok;
>>>>>  }
>>>>
>>>> So far with this patch I can't reproduce the hang or the bogus OOM.
>>>>
>>>> To be completely clear, I have COMPACTION, MIGRATION, and THP off, I'm
>>>> running 2.6.38.6, and I have exactly two patches applied.  One is the
>>>> attached patch and the other is a the fpu.ko/aesni_intel.ko merger
>>>> which I need to get dracut to boot my box.
>>>>
>>>> For fun, I also upgraded to 8GB of RAM and it still works.
>>>>
>>>
>>> Hmm. Could you test it with enable thp and 2G RAM?
>>> Isn't it a original test environment?
>>> Please don't change test environment. :)
>>
>> The test that passed last night was an environment (hardware and
>> config) that I had confirmed earlier as failing without the patch.
>>
>> I just re-tested my original config (from a backup -- migration,
>> compaction, and thp "always" are enabled).  I get bogus OOMs but not a
>> hang.  (I'm running with mem=2G right now -- I'll swap the DIMMs back
>> out later on if you want.)
>>
>> I attached the bogus OOM (actually several that happened in sequence).
>>  They look readahead-related.  There was plenty of free swap space.
> 
> Now with log actually attached.

Unfortnately, this log don't tell us why DM don't issue any swap io. ;-)
I doubt it's DM issue. Can you please try to make swap on out of DM?