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

[Andrew Lutomirski]

On Mon, May 23, 2011 at 9:34 PM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
> On Tue, May 24, 2011 at 10:19 AM, Andrew Lutomirski <luto@xxxxxxx> wrote:
>> On Sun, May 22, 2011 at 7:12 PM, Minchan Kim <minchan.kim@xxxxxxxxx> 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.

--Andy
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