Dear Ted,
On 18.03.19 22:47, Theodore Ts'o wrote:
On Mon, Mar 18, 2019 at 12:24:55PM +0100, Paul Menzel wrote:
On Debian Sid/unstable, I noticed the new service `scrub/e2scrub_reap.service`
installed in the default target [1][2].
$ systemctl status -o short-precise e2scrub_reap.service
● e2scrub_reap.service - Remove Stale Online ext4 Metadata Check Snapshots
Loaded: loaded (/lib/systemd/system/e2scrub_reap.service; enabled; vendor preset: enabled)
Active: inactive (dead) since Mon 2019-03-18 12:17:13 CET; 1min 1s ago
Docs: man:e2scrub_all(8)
Process: 447 ExecStart=/sbin/e2scrub_all -A -r (code=exited, status=0/SUCCESS)
Main PID: 447 (code=exited, status=0/SUCCESS)
Mar 18 12:17:08.223560 plumpsklo systemd[1]: Starting Remove Stale Online ext4 Metadata Check Snapshots...
Mar 18 12:17:13.996465 plumpsklo systemd[1]: e2scrub_reap.service: Succeeded.
Mar 18 12:17:13.996808 plumpsklo systemd[1]: Started Remove Stale Online ext4 Metadata Check Snapshots.
Yeah, that's unfortunate. I'm seeing a similar time on my (fairly
high-end) laptop:
# time e2scrub_all -A -r
real 0m4.356s
user 0m0.677s
sys 0m1.285s
Thank you for your response and tests.
We should be able to fix this in general by avoiding the use of lsblk
at all, and in the case of e2scrub -r, just simply iterating over the
output of:
lvs --name-prefixes -o vg_name,lv_name,lv_path,origin -S lv_role=snapshot
(which takes about a fifth of a second on my laptop and it should be
even faster if there are no LVM volumes on the system)
And without the -r option, we should just be able to do this:
lvs --name-prefixes -o vg_name,lv_name,lv_path -S lv_active=active,lv_role=public
Right now we're calling lvs for every single block device emitted by
lsblk, and from what I can tell, we can do a much better job
optimizing e2scrub_all.
Indeed. That sounds like a way to improve the situation.
Reading the manual, the switch `-r` “removes e2scrub snapshots but do not
check anything”.
Does this have to be done during boot-up, or could it be done after the
default target was reached, or even during shutting down?
This shouldn't be blocking any other targets, I think there should be
a way to configure the unit file so that it runs in parallel with the
other systemd units. My systemd-fu is not super strong, so I'll have
to do some investigating to see how we can fix this.
Sorry about my wording. It’s not about blocking targets, but an
additional program which fights for the resources. Until the graphical
target (or graphical login manager) is reached on my system, a lot of
process already wait for CPU resources. That is the bottleneck during
the boot-up of my system.
So it’d be great, if services, which actually do not have to run during
boot-up would only be started after the default target has been reached.
Something like the ordering dependency
After=default.target
which does not work though to my knowledge. I’ll ask the systemd folks
again.
Kind regards,
Paul
