[linux-lvm] system boot time regression when using lvm2-2.03.05

[Heming Zhao]

Hello List,

I found lvm2-2.03 has some performance regression when system booting.

My env as below:
```
x86-64 qemu vm, 2vcpu, 8G memory,  7 disks (per disk 1GB)
each disk have 128 primary partition, each partition size is 6MB.
total pvs: 896 (each partition create a pv),  vgs 56 (every 16 pvs 
create a vg), lvs 56 (each vg create a lv).
```

When using lvm2-2.02, it only took about a few seconds to enter login 
prompt, but lvm2-2.03 took about 2mins.


## how to create lvm2-2.03.05

In fedora system,
go to website: https://src.fedoraproject.org/rpms/lvm2/tree/master
git clone https://src.fedoraproject.org/rpms/lvm2.git
To use rpmbuild to create rpm package and install.
And to run mkinitrd after changing the lvm.conf.

## teset result

below time got from the command: systemd-analyze --no-pager blame
the time line of "lvm2-pvscan at major:minor.service"

centos 7.6 (lvm2-2.02.180):
disable lvmetad:  2.341s
enable lvmetad:  I wait about more than two hours, the system can't 
enter login phase.

fedora-server (kernel: 5.2.9-200  with default installed lvm2: 
lvm2-2.02.183-3)
use_lvmetad=0: 187ms
use_lvmetad=1: (no test)

fedora-server (kernel: 5.2.9-200  with rpmbuild: lvm2-2.03.05)
event_activation=1: 2min 3.661s
event_activation=0: 1min 57.478s


Could you give me some advice to locate this issue?

Thank you.