Re: DAMON VA regions don't split on an large Android APP
From: Rongwei Wang
Date: Wed Apr 27 2022 - 08:06:52 EST
On 4/27/22 3:44 PM, Barry Song wrote:
On Wed, Apr 27, 2022 at 6:56 PM Rongwei Wang
<rongwei.wang@xxxxxxxxxxxxxxxxx> 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