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

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+

Could you please retest with the patch below applied, instead of
reverting r338416?

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
index 2bc065e12509..9b039b7d4a96 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
_at__at_ -538,7 +538,7 _at__at_ typedef struct arc_state {
  */
 int zfs_arc_meta_prune = 10000;
 unsigned long zfs_arc_dnode_limit_percent = 10;
-int zfs_arc_meta_strategy = ARC_STRATEGY_META_BALANCED;
+int zfs_arc_meta_strategy = ARC_STRATEGY_META_ONLY;
 int zfs_arc_meta_adjust_restarts = 4096;
 
 /* The 6 states: */