Re: Speed improvements in ZFS

On Sun, Aug 20, 2023 at 11:07:08PM +0200, Mateusz Guzik wrote:
> On 8/20/23, Alexander Leidinger <Alexander@leidinger.net> wrote:
> > Am 2023-08-20 22:02, schrieb Mateusz Guzik:
> >> On 8/20/23, Alexander Leidinger <Alexander@leidinger.net> wrote:
> >>> Am 2023-08-20 19:10, schrieb Mateusz Guzik:
> >>>> On 8/18/23, Alexander Leidinger <Alexander@leidinger.net> wrote:
> >>>
> >>>>> I have a 51MB text file, compressed to about 1MB. Are you interested
> >>>>> to
> >>>>> get it?
> >>>>>
> >>>>
> >>>> Your problem is not the vnode limit, but nullfs.
> >>>>
> >>>> https://people.freebsd.org/~mjg/netchild-periodic-find.svg
> >>>
> >>> 122 nullfs mounts on this system. And every jail I setup has several
> >>> null mounts. One basesystem mounted into every jail, and then shared
> >>> ports (packages/distfiles/ccache) across all of them.
> >>>
> >>>> First, some of the contention is notorious VI_LOCK in order to do
> >>>> anything.
> >>>>
> >>>> But more importantly the mind-boggling off-cpu time comes from
> >>>> exclusive locking which should not be there to begin with -- as in
> >>>> that xlock in stat should be a slock.
> >>>>
> >>>> Maybe I'm going to look into it later.
> >>>
> >>> That would be fantastic.
> >>>
> >>
> >> I did a quick test, things are shared locked as expected.
> >>
> >> However, I found the following:
> >>         if ((xmp->nullm_flags & NULLM_CACHE) != 0) {
> >>                 mp->mnt_kern_flag |=
> >> lowerrootvp->v_mount->mnt_kern_flag &
> >>                     (MNTK_SHARED_WRITES | MNTK_LOOKUP_SHARED |
> >>                     MNTK_EXTENDED_SHARED);
> >>         }
> >>
> >> are you using the "nocache" option? it has a side effect of xlocking
> >
> > I use noatime, noexec, nosuid, nfsv4acls. I do NOT use nocache.
> >
> 
> If you don't have "nocache" on null mounts, then I don't see how this
> could happen.

There is also MNTK_NULL_NOCACHE on lower fs, which is currently set for
fuse and nfs at least.