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

[David Teigland]

On Mon, Sep 09, 2019 at 11:42:17AM +0000, Heming Zhao wrote:
> Hello David,
> 
> You are right.  Without calling _online_pvscan_one(), the pv/vg/lv won't be actived.
> The activation jobs will be done by systemd calling lvm2-activation-*.services later.
> 
> Current code, the boot process is mainly blocked by:
> ```
> _pvscan_aa
>   vgchange_activate
>    _activate_lvs_in_vg
>     sync_local_dev_names
>      fs_unlock
>       dm_udev_wait <=== this point!
> ```

Thanks for debugging that.  With so many devices, one possibility that
comes to mind is this error you would probably have seen:
"Limit for the maximum number of semaphores reached"

> For fix this boot time regression, it looks lvm2 should have a config item in lvm2.conf
> i.e.: large_PV_boot_speedup.
> When this item is 1, pvcan won't call _online_pvscan_one, then let lvm2-activation*.service
> do the active jobs.
> Is it a workable solution?

We should look into fixing the udev problems.  I don't mind working around
udev when it won't do what we need; I'm not sure what the options are in
this case.