Swap on ZFS Volume still panics?

App Deb appdebgr at gmail.com
Sun Sep 12 21:14:16 UTC 2010


I just tried your settings (setting primary and secondary cache to none).

 (also tried it with checksum=off and volblocksize=4k, all together)

It somewhat helped. In the beginning I though it would deadlock. The system
was inaccessible for ~10 minutes, but after that it managed to allocate the
required swap, and the system resumed.

I measured the speed that it allocated swap and it was only around ~0.4MB/s
max. With the native freebsd-swap partition the speed using my "selfmade
memory filling program" it almost reaches native disk speeds (~80MB/s).

I still see a problem here.

Thanks.


On Sat, Sep 11, 2010 at 10:05 AM, jhell <jhell at dataix.net> wrote:

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> On 09/10/2010 03:39, Pawel Jakub Dawidek wrote:
> > On Wed, Sep 08, 2010 at 07:19:40PM +0300, App Deb wrote:
> >> Reading the wiki guides they mention the official way to add swap
> volumes on
> >> ZFS (set org.freebsd:swap=on etc..),
> >>
> >> So I thought that it should work now, But I just got a panic in
> 8.1-RELEASE
> >> after a heavy memory situation that touched swap for the first time.
> >
> > Swap on ZVOL is still not recommended. Where did you find information
> > that it now recommended? I can't find anything about swap on
> > http://wiki.freebsd.org/ZFS and on
> > http://wiki.freebsd.org/ZFSQuickStartGuide there is a note that it is
> > not recommended. Let me know where it is advised and I'll remove it or
> > add a note (if the documentation is mine).
> >
> >> It is a hassle to add gmirror volumes for swap on full zfs systems, is
> there
> >> any workaround for this, or any news when a fix is coming or if it is
> >> coming?
> >
> > I've no plans to fix it, maybe with ZFSv28 it will be easier to fix, but
> > this is really low priority. If you use full ZFS system the recommended
> > layout is described here:
> >
> >
> http://blogs.freebsdish.org/pjd/2010/08/06/from-sysinstall-to-zfs-only-configuration/
> >
> >> If the current code procudes guaranteed panics with zfs swap, I think
> that
> >> every mention of swap on zfs should be removed from the semi-official
> wiki
> >> guides.
> >
> > BTW. If this issue will be worked on in the future, it will be useful to
> > actually see your panic, backtrace and other debug info. To be honest, I
> > didn't expect it to panic, rather deadlock. Maybe panic is from deadlock
> > resolver? Hard to say without any debug info.
> >
>
> For reference I have been using swap on ZFS for a while. I recieve no
> panics when doing so and have the following properties set.
>
> exports/swap  refreservation        2G                     local
> exports/swap  primarycache          none                   local
> exports/swap  secondarycache        none                   local
> exports/swap  org.freebsd:swap      on                     local
>
> As someone already mentioned, it might help to also change volblocksize
> property to 4k but I have never had to do that as changing the primary
> and secondary caches were enough to keep it from panic here.
>
> I would be interested to hear if this helped anyone else.
>
>
> Regards,
>
> - --
>
>  jhell,v
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