Re: DAMON VA regions don't split on an large Android APP

Rongwei Wang
2022-04-27T12:06:52Z

On 4/27/22 3:44 PM, Barry Song wrote:
> On Wed, Apr 27, 2022 at 6:56 PM Rongwei Wang
> <rongwei.wang@linux.alibaba.com> wrote:
>>
>>
>>
>> On 4/27/22 7:19 AM, Barry Song wrote:
>>> Hi SeongJae & Andrew,
>>> (also Cc-ed main damon developers)
>>> On an Android phone, I tried to use the DAMON vaddr monitor and found
>>> that vaddr regions don't split well on large Android Apps though
>>> everything works well on native Apps.
>>>
>>> I have tried the below two cases on an Android phone with 12GB memory
>>> and snapdragon 888 CPU.
>>> 1. a native program with small memory working set as below,
>>> #define size (1024*1024*100)
>>> main()
>>> {
>>> volatile int *p = malloc(size);
>>> memset(p, 0x55, size);
>>>
>>> while(1) {
>>> int i;
>>> for (i = 0; i < size / 4; i++)
>>> (void)*(p + i);
>>> usleep(1000);
>>>
>>> for (i = 0; i < size / 16; i++)
>>> (void)*(p + i);
>>> usleep(1000);
>>>
>>> }
>>> }
>>> For this application, the Damon vaddr monitor works very well.
>>> I have modified monitor.py in the damo userspace tool a little bit to
>>> show the raw data getting from the kernel.
>>> Regions can split decently on this kind of applications, a typical raw
>>> data is as below,
>>>
>>> monitoring_start: 2.224 s
>>> monitoring_end: 2.329 s
>>> monitoring_duration: 104.336 ms
>>> target_id: 0
>>> nr_regions: 24
>>> 005fb37b2000-005fb734a000( 59.594 MiB): 0
>>> 005fb734a000-005fbaf95000( 60.293 MiB): 0
>>> 005fbaf95000-005fbec0b000( 60.461 MiB): 0
>>> 005fbec0b000-005fc2910000( 61.020 MiB): 0
>>> 005fc2910000-005fc6769000( 62.348 MiB): 0
>>> 005fc6769000-005fca33f000( 59.836 MiB): 0
>>> 005fca33f000-005fcdc8b000( 57.297 MiB): 0
>>> 005fcdc8b000-005fd115a000( 52.809 MiB): 0
>>> 005fd115a000-005fd45bd000( 52.387 MiB): 0
>>> 007661c59000-007661ee4000( 2.543 MiB): 2
>>> 007661ee4000-0076623e4000( 5.000 MiB): 3
>>> 0076623e4000-007662837000( 4.324 MiB): 2
>>> 007662837000-0076630f1000( 8.727 MiB): 3
>>> 0076630f1000-007663494000( 3.637 MiB): 2
>>> 007663494000-007663753000( 2.746 MiB): 1
>>> 007663753000-007664251000( 10.992 MiB): 3
>>> 007664251000-0076666fd000( 36.672 MiB): 2
>>> 0076666fd000-007666e73000( 7.461 MiB): 1
>>> 007666e73000-007667c89000( 14.086 MiB): 2
>>> 007667c89000-007667f97000( 3.055 MiB): 0
>>> 007667f97000-007668112000( 1.480 MiB): 1
>>> 007668112000-00766820f000(1012.000 KiB): 0
>>> 007ff27b7000-007ff27d6000( 124.000 KiB): 0
>>> 007ff27d6000-007ff27d8000( 8.000 KiB): 8
>>>
>>> 2. a large Android app like Asphalt 9
>>> For this case, basically regions can't split very well, but monitor
>>> works on small vma:
>>>
>>> monitoring_start: 2.220 s
>>> monitoring_end: 2.318 s
>>> monitoring_duration: 98.576 ms
>>> target_id: 0
>>> nr_regions: 15
>>> 000012c00000-0001c301e000( 6.754 GiB): 0
>>> 0001c301e000-000371b6c000( 6.730 GiB): 0
>>> 000371b6c000-000400000000( 2.223 GiB): 0
>>> 005c6759d000-005c675a2000( 20.000 KiB): 0
>>> 005c675a2000-005c675a3000( 4.000 KiB): 3
>>> 005c675a3000-005c675a7000( 16.000 KiB): 0
>>> 0072f1e14000-0074928d4000( 6.510 GiB): 0
>>> 0074928d4000-00763c71f000( 6.655 GiB): 0
>>> 00763c71f000-0077e863e000( 6.687 GiB): 0
>>> 0077e863e000-00798e214000( 6.590 GiB): 0
>>> 00798e214000-007b0e48a000( 6.002 GiB): 0
>>> 007b0e48a000-007c62f00000( 5.323 GiB): 0
>>> 007c62f00000-007defb19000( 6.199 GiB): 0
>>> 007defb19000-007f794ef000( 6.150 GiB): 0
>>> 007f794ef000-007fe8f53000( 1.745 GiB): 0
>>>
>>> As you can see, we have some regions which are very very big and they
>>> are losing the chance to be splitted. But
>>> Damon can still monitor memory access for those small VMA areas very well like:
>>> 005c675a2000-005c675a3000( 4.000 KiB): 3
>> Hi, Barry
>>
>> Actually, we also had found the same problem in redis by ourselves
>> tool[1]. The DAMON can not split the large anon VMA well, and the anon
>> VMA has 10G~20G memory. I guess the whole region doesn't have sufficient
>> hot areas to been monitored or found by DAMON, likes one or more address
>> choose by DAMON not been accessed during sample period.
>
> Hi Rongwei,
> Thanks for your comments and thanks for sharing your tools.
>
> I guess the cause might be:
> in case a region is very big like 10GiB, we have only 1MiB hot pages
> in this large region.
> damon will randomly pick one page to sample, but the page has only
> 1MiB/10GiB, thus
> less than 1/10000 chance to hit the hot 1MiB. so probably we need
> 10000 sample periods
> to hit the hot 1MiB in order to split this large region?
>
> @SeongJae, please correct me if I am wrong.
>
>>
>> I'm not sure whether sets init_regions can deal with the above problem,
>> or dynamic choose one or limited number VMA to monitor.
>>
>
> I won't set a limited number of VMA as this will make the damon too hard to use
> as nobody wants to make such complex operations, especially an Android
> app might have more than 8000 VMAs.
>
> I agree init_regions might be the right place to enhance the situation.
>
>> I'm not sure, just share my idea.
>>
>> [1] https://github.com/aliyun/data-profile-tools.git
>
> I suppose this tool is based on damon? How do you finally resolve the problem
Yes, and we plan to design it to be a user agent.
> that large anon VMAs can't be splitted?
I see your have different environment with mine. Finally, I just monitor
the anon VMA and set a large regions number.
There is one or two large anon VMAs in my environment. It seems
different with your.

> Anyway, I will give your tool a try.
>
>>>
>>> Typical characteristics of a large Android app is that it has
>>> thousands of vma and very large virtual address spaces:
>>> ~/damo # pmap 2550 | wc -l
>>> 8522
>>>
>>> ~/damo # pmap 2550
>>> ...
>>> 0000007992bbe000 4K r---- [ anon ]
>>> 0000007992bbf000 24K rw--- [ anon ]
>>> 0000007fe8753000 4K ----- [ anon ]
>>> 0000007fe8754000 8188K rw--- [ stack ]
>>> total 36742112K
>>>
>>> Because the whole vma list is too long, I have put the list here for
>>> you to download:
>>> wget http://www.linuxep.com/patches/android-app-vmas
>>>
>>> I can reproduce this problem on other Apps like youtube as well.
>>> I suppose we need to boost the algorithm of splitting regions for this
>>> kind of application.
>>> Any thoughts?
>>>
>
> Thanks
> Barry