Date: Wed, 5 Sep 2018 23:15:03 +0300 From: Subbsd <subbsd@gmail.com> To: allanjude@freebsd.org Cc: freebsd-current Current <freebsd-current@freebsd.org> Subject: Re: ZFS perfomance regression in FreeBSD 12 APLHA3->ALPHA4 Message-ID: <CAFt_eMozS6_9VWBu%2B3LZ9n12bFdykZkz9HTi-zb0kgSKS2Riag@mail.gmail.com> In-Reply-To: <e26c530e-88e4-0481-9012-f814dd8ed569@freebsd.org> References: <CAFt_eMrhFiV0OJQ2w05-pFj4EkYr9dbYf4APLuJdBykwkOjRsQ@mail.gmail.com> <e26c530e-88e4-0481-9012-f814dd8ed569@freebsd.org>
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On Wed, Sep 5, 2018 at 5:58 PM Allan Jude <allanjude@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@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/freebsd-current > > To unsubscribe, send any mail to "freebsd-current-unsubscribe@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. > > -- > Allan Jude > Hi, 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+
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