Date: Tue, 22 Aug 2023 18:59:36 +0200 From: Mateusz Guzik <mjguzik@gmail.com> To: Alexander Leidinger <Alexander@leidinger.net> Cc: Konstantin Belousov <kostikbel@gmail.com>, current@freebsd.org Subject: Re: Speed improvements in ZFS Message-ID: <CAGudoHF20EVPcrdRixfhktp-==8=CuYLY6wpPkXLRRizQLCsKA@mail.gmail.com> In-Reply-To: <444770b977b02b98985928bea450e4ce@Leidinger.net> References: <CAGudoHEP8TrSzz0TL-PsOx0WNc7z3042wJk-jhhVwhTyJ0VEQQ@mail.gmail.com> <88e837aeb5a65c1f001de2077fb7bcbd@Leidinger.net> <4d60bd12b482e020fd4b186a9ec1a250@Leidinger.net> <CAGudoHE7RPcHpQEqKbzRM8cJcYKue17=iPVv8iOfZq03h22tTA@mail.gmail.com> <73f7c9d3db8f117deb077fb17b1e352a@Leidinger.net> <CAGudoHGPw0Dmnv6ont8JGyLsT7qv%2BQqAFZO3tKOpNo3eN%2BJgLQ@mail.gmail.com> <58493b568dbe9fb52cc55de86e01f5e2@Leidinger.net> <CAGudoHEyZh1DU=j_6mOfB3tSKhC-pNokPgONDbf4oF3D3A5=jg@mail.gmail.com> <ZOKC3-6uyPUO8qNY@kib.kiev.ua> <58ac6211235c52d744666e8ae2ec7568@Leidinger.net> <ZOMmHF0RiVyroUk8@kib.kiev.ua> <444770b977b02b98985928bea450e4ce@Leidinger.net>
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On 8/22/23, Alexander Leidinger <Alexander@leidinger.net> wrote: > Am 2023-08-21 10:53, schrieb Konstantin Belousov: >> On Mon, Aug 21, 2023 at 08:19:28AM +0200, Alexander Leidinger wrote: >>> Am 2023-08-20 23:17, schrieb Konstantin Belousov: >>> > 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. >>> >>> 11 of those 122 nullfs mounts are ZFS datasets which are also NFS >>> exported. >>> 6 of those nullfs mounts are also exported via Samba. The NFS exports >>> shouldn't be needed anymore, I will remove them. >> By nfs I meant nfs client, not nfs exports. > > No NFS client mounts anywhere on this system. So where is this exclusive > lock coming from then... > This is a ZFS system. 2 pools: one for the root, one for anything I need > space for. Both pools reside on the same disks. The root pool is a 3-way > mirror, the "space-pool" is a 5-disk raidz2. All jails are on the > space-pool. The jails are all basejail-style jails. > While I don't see why xlocking happens, you should be able to dtrace or printf your way into finding out. -- Mateusz Guzik <mjguzik gmail.com>
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