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

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
>>>> _______________________________________________
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>>>>
>>> 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.

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?


Jakob

> 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: */
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