On Thu, May 22, 2014 at 08:52:34PM +0000, Duncan wrote:
> > It's been running for at least 15mn in 'cancel mode'. Is that normal?
>
> I'd guess so. It's probably in the middle of operations for a single
> chunk, and only checks for cancel between chunks. Given the possible
> complexity of those operations with snapshotting and quotas factored in
> as well as COW fragmentation, 15 minutes on a single chunk isn't
> /entirely/ out there.
That's probably what I saw indeed.
> That being symptomatic of the whole performance problem they're battling
> ATM. They've turned off snapshot-aware-defrag for the time being, and
> there's the quota handling rework in the pipeline, but...
Right. I'm just surprised that sync would hang too. That feels pretty
bad.
> I've seen patches for at least one related race-related problem (where
> snapshot deletion could collide with balance or send) go by, and don't
> believe it's in Linus-mainline yet, tho I haven't closely tracked status
> beyond that.
That's indeed what I've been seeing and since I have snapshots and btrfs
send both from cron, I'm hitting this too often :(
If god forbid scrub kicks in from cron too, then I'm toast.
> Basically, at this point running only one such "major" btrfs operation at
> a time should drastically reduce the possibility of problems, because
> there /are/ known races. Even after the known races are fixed, it's
> probably a good idea anyway where possible, since just one such operation
> is complex enough and running more than one at a time is only going to
> slow them all down as well as requiring more CPU/IO/memory bandwidth, but
> there /is/ recognition of the very real likelihood that people /will/ end
> up doing it, especially since one or more of the operations may be cron
The thing is that scrub takes hours to run.
I run btrfs send and snapshots once an hour for backups.
I'm not took keen on stopping backups for hours while scrub runs.
I understand it's a workaround for now though.
I've just stopped scrub altogether now and will see if I still have
problems.
Thanks,
Marc
--
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
.... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/ | PGP 1024R/763BE901
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