Re: Suspicious error for CMA stress test

Joonsoo Kim
2016-03-11T15:00:39Z

2016-03-09 10:23 GMT+09:00 Leizhen (ThunderTown) <thunder.leizhen@huawei.com>:
>
>
> On 2016/3/8 9:54, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2016/3/8 2:42, Laura Abbott wrote:
>>> On 03/07/2016 12:16 AM, Leizhen (ThunderTown) wrote:
>>>>
>>>>
>>>> On 2016/3/7 12:34, Joonsoo Kim wrote:
>>>>> On Fri, Mar 04, 2016 at 03:35:26PM +0800, Hanjun Guo wrote:
>>>>>> On 2016/3/4 14:38, Joonsoo Kim wrote:
>>>>>>> On Fri, Mar 04, 2016 at 02:05:09PM +0800, Hanjun Guo wrote:
>>>>>>>> On 2016/3/4 12:32, Joonsoo Kim wrote:
>>>>>>>>> On Fri, Mar 04, 2016 at 11:02:33AM +0900, Joonsoo Kim wrote:
>>>>>>>>>> On Thu, Mar 03, 2016 at 08:49:01PM +0800, Hanjun Guo wrote:
>>>>>>>>>>> On 2016/3/3 15:42, Joonsoo Kim wrote:
>>>>>>>>>>>> 2016-03-03 10:25 GMT+09:00 Laura Abbott <labbott@redhat.com>:
>>>>>>>>>>>>> (cc -mm and Joonsoo Kim)
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> On 03/02/2016 05:52 AM, Hanjun Guo wrote:
>>>>>>>>>>>>>> Hi,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I came across a suspicious error for CMA stress test:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Before the test, I got:
>>>>>>>>>>>>>> -bash-4.3# cat /proc/meminfo | grep Cma
>>>>>>>>>>>>>> CmaTotal: 204800 kB
>>>>>>>>>>>>>> CmaFree: 195044 kB
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> After running the test:
>>>>>>>>>>>>>> -bash-4.3# cat /proc/meminfo | grep Cma
>>>>>>>>>>>>>> CmaTotal: 204800 kB
>>>>>>>>>>>>>> CmaFree: 6602584 kB
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> So the freed CMA memory is more than total..
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Also the the MemFree is more than mem total:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> -bash-4.3# cat /proc/meminfo
>>>>>>>>>>>>>> MemTotal: 16342016 kB
>>>>>>>>>>>>>> MemFree: 22367268 kB
>>>>>>>>>>>>>> MemAvailable: 22370528 kB
>>>>>>>>>>> [...]
>>>>>>>>>>>>> I played with this a bit and can see the same problem. The sanity
>>>>>>>>>>>>> check of CmaFree < CmaTotal generally triggers in
>>>>>>>>>>>>> __move_zone_freepage_state in unset_migratetype_isolate.
>>>>>>>>>>>>> This also seems to be present as far back as v4.0 which was the
>>>>>>>>>>>>> first version to have the updated accounting from Joonsoo.
>>>>>>>>>>>>> Were there known limitations with the new freepage accounting,
>>>>>>>>>>>>> Joonsoo?
>>>>>>>>>>>> I don't know. I also played with this and looks like there is
>>>>>>>>>>>> accounting problem, however, for my case, number of free page is slightly less
>>>>>>>>>>>> than total. I will take a look.
>>>>>>>>>>>>
>>>>>>>>>>>> Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't
>>>>>>>>>>>> look like your case.
>>>>>>>>>>> I tested with malloc_size with 2M, and it grows much bigger than 1M, also I
>>>>>>>>>>> did some other test:
>>>>>>>>>> Thanks! Now, I can re-generate erronous situation you mentioned.
>>>>>>>>>>
>>>>>>>>>>> - run with single thread with 100000 times, everything is fine.
>>>>>>>>>>>
>>>>>>>>>>> - I hack the cam_alloc() and free as below [1] to see if it's lock issue, with
>>>>>>>>>>> the same test with 100 multi-thread, then I got:
>>>>>>>>>> [1] would not be sufficient to close this race.
>>>>>>>>>>
>>>>>>>>>> Try following things [A]. And, for more accurate test, I changed code a bit more
>>>>>>>>>> to prevent kernel page allocation from cma area [B]. This will prevent kernel
>>>>>>>>>> page allocation from cma area completely so we can focus cma_alloc/release race.
>>>>>>>>>>
>>>>>>>>>> Although, this is not correct fix, it could help that we can guess
>>>>>>>>>> where the problem is.
>>>>>>>>> More correct fix is something like below.
>>>>>>>>> Please test it.
>>>>>>>> Hmm, this is not working:
>>>>>>> Sad to hear that.
>>>>>>>
>>>>>>> Could you tell me your system's MAX_ORDER and pageblock_order?
>>>>>>>
>>>>>>
>>>>>> MAX_ORDER is 11, pageblock_order is 9, thanks for your help!
>>>>>
>>>>> Hmm... that's same with me.
>>>>>
>>>>> Below is similar fix that prevents buddy merging when one of buddy's
>>>>> migrate type, but, not both, is MIGRATE_ISOLATE. In fact, I have
>>>>> no idea why previous fix (more correct fix) doesn't work for you.
>>>>> (It works for me.) But, maybe there is a bug on the fix
>>>>> so I make new one which is more general form. Please test it.
>>>>
>>>> Hi,
>>>> Hanjun Guo has gone to Tailand on business, so I help him to run this patch. The result
>>>> shows that the count of "CmaFree:" is OK now. But sometimes printed some information as below:
>>>>
>>>> alloc_contig_range: [28500, 28600) PFNs busy
>>>> alloc_contig_range: [28300, 28380) PFNs busy
>>>>
>>>
>>> Those messages aren't necessarily a problem. Those messages indicate that
>> OK.
>>
>>> those pages weren't able to be isolated. Given the test here is a
>>> concurrency test, I suspect some concurrent allocation or free prevented
>>> isolation which is to be expected some times. I'd only be concerned if
>>> seeing those messages cause allocation failure or some other notable impact.
>> I chose memory block size: 512K, 1M, 2M ran serveral times, there was no memory allocation failure.
>
> Hi, Joonsoo:
> This new patch worked well. Do you plan to upstream it in the near furture?

Of course!
But, I should think more because it touches allocator's fastpatch and
I'd like to detour.
If I fail to think a better solution, I will send it as is, soon.

Thanks.