[linux-lvm] Discussion: performance issue on event activation mode

[Martin Wilck]

On Di, 2021-06-08 at 14:29 +0200, Peter Rajnoha wrote:
> On Mon 07 Jun 2021 16:48, David Teigland wrote:
> > 
> > If there are say 1000 PVs already present on the system, there
> > could be
> > real savings in having one lvm command process all 1000, and then
> > switch
> > over to processing uevents for any further devices afterward.  The
> > switch
> > over would be delicate because of the obvious races involved with
> > new devs
> > appearing, but probably feasible.
> 
> Maybe to avoid the race, we could possibly write the proposed
> "/run/lvm2/boot-finished" right before we initiate scanning in
> "vgchange
> -aay" that is a part of the lvm2-activation-net.service (the last
> service to do the direct activation).
> 
> A few event-based pvscans could fire during the window between
> "scan initiated phase" in lvm2-activation-net.service's
> "ExecStart=vgchange -aay..."
> and the originally proposed "ExecStartPost=/bin/touch /run/lvm2/boot-
> finished",
> but I think still better than missing important uevents completely in
> this window.

That sounds reasonable. I was thinking along similar lines. Note that
in the case where we had problems lately, all actual activation (and
slowness) happened in lvm2-activation-early.service.

Regards,
Martin