Re: [PATCH v6 2/6] mm/cma: introduce new zone, ZONE_CMA

[Chen Feng]

On 2016/11/8 11:59, Joonsoo Kim wrote:
> On Mon, Nov 07, 2016 at 03:46:02PM +0800, Chen Feng wrote:
>>
>>
>> On 2016/11/7 15:44, Chen Feng wrote:
>>> On 2016/11/7 15:27, Joonsoo Kim wrote:
>>>> On Mon, Nov 07, 2016 at 03:08:49PM +0800, Chen Feng wrote:
>>>>>
>>>>>
>>>>> On 2016/11/7 14:15, Joonsoo Kim wrote:
>>>>>> On Tue, Nov 01, 2016 at 03:58:32PM +0800, Chen Feng wrote:
>>>>>>> Hello, I hava a question on cma zone.
>>>>>>>
>>>>>>> When we have cma zone, cma zone will be the highest zone of system.
>>>>>>>
>>>>>>> In android system, the most memory allocator is ION. Media system will
>>>>>>> alloc unmovable memory from it.
>>>>>>>
>>>>>>> On low memory scene, will the CMA zone always do balance?
>>>>>>
>>>>>> Allocation request for low zone (normal zone) would not cause CMA zone
>>>>>> to be balanced since it isn't helpful.
>>>>>>
>>>>> Yes. But the cma zone will run out soon. And it always need to do balance.
>>>>>
>>>>> How about use migrate cma before movable and let cma type to fallback movable.
>>>>>
>>>>> https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1263745.html
>>>>
>>>> ZONE_CMA approach will act like as your solution. Could you elaborate
>>>> more on the problem of zone approach?
>>>>
>>>
>>> The ZONE approach is that makes cma pages in a zone. It can cause a higher swapin/out
>>> than use migrate cma first.
> 
> Interesting result. I should look at it more deeply. Could you explain
> me why the ZONE approach causes a higher swapin/out?
> 
The result is that. I don't have a obvious reason. Maybe add a zone, need to do more balance
to keep the watermark of cma-zone. cma-zone is always used firstly. Since the test-case
alloced the same memory in total.

>>>
>>> The higher swapin/out may have a performance effect to application. The application may
>>> use too much time swapin memory.
>>>
>>> You can see my tested result attached for detail. And the baseline is result of [1].
>>>
>>>
>> My test case is run 60 applications and alloc 512MB ION memory.
>>
>> Repeat this action 50 times
> 
> Could you tell me more detail about your test?
> Kernel version? Total Memory? Total CMA Memory? Android system? What
> type of memory does ION uses? Other statistics? Etc...

Tested on 4.1, android 7, 512MB-cma in 4G memory.
ION use normal unmovable memory, I use it to simulate a camera open operator.
> 
> If it tested on the Android, I'm not sure that we need to consider
> it's result. Android has a lowmemory killer which is quitely different
> with normal reclaim behaviour.
Why?
> 
> Thanks.
> 
> 
> .
>