On Mon, Mar 18, 2019 at 12:24:55PM +0100, Paul Menzel wrote: > Dear Ted, dear Darrick, > > 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 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. > 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. Regards, - Ted
