Re: ZFS perfomance regression in FreeBSD 12 APLHA3->ALPHA4

On Fri, Sep 07, 2018 at 03:40:52PM +0200, Jakob Alvermark wrote:
> On 9/6/18 2:28 AM, Mark Johnston wrote:
> > On Wed, Sep 05, 2018 at 11:15:03PM +0300, Subbsd wrote:
> >> On Wed, Sep 5, 2018 at 5:58 PM Allan Jude <allanjude_at_freebsd.org> wrote:
> >>> On 2018-09-05 10:04, Subbsd wrote:
> >>>> Hi,
> >>>>
> >>>> I'm seeing a huge loss in performance ZFS after upgrading FreeBSD 12
> >>>> to latest revision (r338466 the moment) and related to ARC.
> >>>>
> >>>> I can not say which revision was before except that the newver.sh
> >>>> pointed to ALPHA3.
> >>>>
> >>>> Problems are observed if you try to limit ARC. In my case:
> >>>>
> >>>> vfs.zfs.arc_max="128M"
> >>>>
> >>>> I know that this is very small. However, for two years with this there
> >>>> were no problems.
> >>>>
> >>>> When i send SIGINFO to process which is currently working with ZFS, i
> >>>> see "arc_reclaim_waiters_cv":
> >>>>
> >>>> e.g when i type:
> >>>>
> >>>> /bin/csh
> >>>>
> >>>> I have time (~5 seconds) to press several times 'ctrl+t' before csh is executed:
> >>>>
> >>>> load: 0.70  cmd: csh 5935 [arc_reclaim_waiters_cv] 1.41r 0.00u 0.00s 0% 3512k
> >>>> load: 0.70  cmd: csh 5935 [zio->io_cv] 1.69r 0.00u 0.00s 0% 3512k
> >>>> load: 0.70  cmd: csh 5935 [arc_reclaim_waiters_cv] 1.98r 0.00u 0.01s 0% 3512k
> >>>> load: 0.73  cmd: csh 5935 [arc_reclaim_waiters_cv] 2.19r 0.00u 0.01s 0% 4156k
> >>>>
> >>>> same story with find or any other commans:
> >>>>
> >>>> load: 0.34  cmd: find 5993 [zio->io_cv] 0.99r 0.00u 0.00s 0% 2676k
> >>>> load: 0.34  cmd: find 5993 [arc_reclaim_waiters_cv] 1.13r 0.00u 0.00s 0% 2676k
> >>>> load: 0.34  cmd: find 5993 [arc_reclaim_waiters_cv] 1.25r 0.00u 0.00s 0% 2680k
> >>>> load: 0.34  cmd: find 5993 [arc_reclaim_waiters_cv] 1.38r 0.00u 0.00s 0% 2684k
> >>>> load: 0.34  cmd: find 5993 [arc_reclaim_waiters_cv] 1.51r 0.00u 0.00s 0% 2704k
> >>>> load: 0.34  cmd: find 5993 [arc_reclaim_waiters_cv] 1.64r 0.00u 0.00s 0% 2716k
> >>>> load: 0.34  cmd: find 5993 [arc_reclaim_waiters_cv] 1.78r 0.00u 0.00s 0% 2760k
> >>>>
> >>>> this problem goes away after increasing vfs.zfs.arc_max
> >>>> _______________________________________________
> >>>> freebsd-current_at_freebsd.org mailing list
> >>>> https://lists.freebsd.org/mailman/listinfo/freebsd-current
> >>>> To unsubscribe, send any mail to "freebsd-current-unsubscribe_at_freebsd.org"
> >>>>
> >>> Previously, ZFS was not actually able to evict enough dnodes to keep
> >>> your arc_max under 128MB, it would have been much higher based on the
> >>> number of open files you had. A recent improvement from upstream ZFS
> >>> (r337653 and r337660) was pulled in that fixed this, so setting an
> >>> arc_max of 128MB is much more effective now, and that is causing the
> >>> side effect of "actually doing what you asked it to do", in this case,
> >>> what you are asking is a bit silly. If you have a working set that is
> >>> greater than 128MB, and you ask ZFS to use less than that, it'll have to
> >>> constantly try to reclaim memory to keep under that very low bar.
> >>>
> >> Thanks for comments. Mark was right when he pointed to r338416 (
> >> https://svnweb.freebsd.org/base/head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c?r1=338416&r2=338415&pathrev=338416
> >> ). Commenting aggsum_value returns normal speed regardless of the rest
> >> of the new code from upstream.
> >> I would like to repeat that the speed with these two lines is not just
> >> slow, but _INCREDIBLY_ slow! Probably, this should be written in the
> >> relevant documentation for FreeBSD 12+
> 
> Hi,
> 
> I am experiencing the same slowness when there is a bit of load on the 
> system (buildworld for example) which I haven't seen before.

Is it a regression following a recent kernel update?

> I have vfs.zfs.arc_max=2G.
> 
> Top is reporting
> 
> ARC: 607M Total, 140M MFU, 245M MRU, 1060K Anon, 4592K Header, 217M Other
>       105M Compressed, 281M Uncompressed, 2.67:1 Ratio
> 
> Should I test the patch?

I would be interested in the results, assuming it is indeed a
regression.