8.1R ZFS almost locking up system
Dan Nelson
dnelson at allantgroup.com
Tue Aug 31 15:58:31 UTC 2010
In the last episode (Aug 31), Tim Bishop said:
> On Sat, Aug 21, 2010 at 05:24:29PM -0500, Dan Nelson wrote:
> > In the last episode (Aug 21), Tim Bishop said:
> > > A few items from top, including zfskern:
> > >
> > > PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
> > > 5 root 4 -8 - 0K 60K zio->i 0 54:38 3.47% zfskern
> > > 91775 70 1 44 0 53040K 31144K tx->tx 1 2:11 0.00% postgres
> > > 39661 tdb 1 44 0 55776K 32968K tx->tx 0 0:39 0.00% mutt
> > > 14828 root 1 47 0 14636K 1572K tx->tx 1 0:03 0.00% zfs
> > > 11188 root 1 51 0 14636K 1572K tx->tx 0 0:03 0.00% zfs
> > >
> > > At some point during this process my zfs snapshots have been failing to
> > > complete:
> > >
> > > root 5 0.8 0.0 0 60 ?? DL 7Aug10 54:43.83 [zfskern]
> > > root 8265 0.0 0.0 14636 1528 ?? D 10:00AM 0:03.12 zfs snapshot -r pool0 at 2010-08-21_10:00:01--1d
> > > root 11188 0.0 0.1 14636 1572 ?? D 11:00AM 0:02.93 zfs snapshot -r pool0 at 2010-08-21_11:00:01--1d
> > > root 14828 0.0 0.1 14636 1572 ?? D 12:00PM 0:03.04 zfs snapshot -r pool0 at 2010-08-21_12:00:00--1d
> > > root 17862 0.0 0.1 14636 1572 ?? D 1:00PM 0:01.96 zfs snapshot -r pool0 at 2010-08-21_13:00:01--1d
> > > root 20986 0.0 0.1 14636 1572 ?? D 2:00PM 0:02.07 zfs snapshot -r pool0 at 2010-08-21_14:00:01--1d
> >
> > procstat -k on some of these processes might help to pinpoint what part of
> > the zfs code they're all waiting in.
>
> It happened again this Saturday (clearly something in the weekly
> periodic run is triggering the issue). procstat -kk shows the following
> for processes doing something zfs related (where zfs related means the
> string 'zfs' in the procstat -kk output):
>
> 0 100084 kernel zfs_vn_rele_task mi_switch+0x16f sleepq_wait+0x42 _sleep+0x31c taskqueue_thread_loop+0xb7 fork_exit+0x118 fork_trampoline+0xe
> 5 100031 zfskern arc_reclaim_thre mi_switch+0x16f sleepq_timedwait+0x42 _cv_timedwait+0x129 arc_reclaim_thread+0x2d1 fork_exit+0x118 fork_trampoline+0xe
> 5 100032 zfskern l2arc_feed_threa mi_switch+0x16f sleepq_timedwait+0x42 _cv_timedwait+0x129 l2arc_feed_thread+0x1be fork_exit+0x118 fork_trampoline+0xe
> 5 100085 zfskern txg_thread_enter mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_thread_wait+0x79 txg_quiesce_thread+0xb5 fork_exit+0x118 fork_trampoline+0xe
> 5 100086 zfskern txg_thread_enter mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 zio_wait+0x61 dsl_pool_sync+0xea spa_sync+0x355 txg_sync_thread+0x195 fork_exit+0x118 fork_trampoline+0xe
> 17 100040 syncer - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_synced+0x7c zil_commit+0x416 zfs_sync+0xa6 sync_fsync+0x184 sync_vnode+0x16b sched_sync+0x1c9 fork_exit+0x118 fork_trampoline+0xe
> 2210 100156 syslogd - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 zfs_freebsd_write+0x378 VOP_WRITE_APV+0xb2 vn_write+0x2d7 dofilewrite+0x85 kern_writev+0x60 writev+0x41 syscall+0x1e7 Xfast_syscall+0xe1
> 3500 100177 syslogd - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 zfs_freebsd_write+0x378 VOP_WRITE_APV+0xb2 vn_write+0x2d7 dofilewrite+0x85 kern_writev+0x60 writev+0x41 syscall+0x1e7 Xfast_syscall+0xe1
> 3783 100056 syslogd - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 zfs_freebsd_write+0x378 VOP_WRITE_APV+0xb2 vn_write+0x2d7 dofilewrite+0x85 kern_writev+0x60 writev+0x41 syscall+0x1e7 Xfast_syscall+0xe1
> 4064 100165 mysqld initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23 closef+0x3b kern_close+0x14d syscall+0x1e7 Xfast_syscall+0xe1
> 4441 100224 python2.6 initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc null_reclaim+0xbc vgonel+0x12e vrecycle+0x7d null_inactive+0x1f vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23
> 4444 100227 python2.6 initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc null_reclaim+0xbc vgonel+0x12e vrecycle+0x7d null_inactive+0x1f vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23
> 4445 100228 python2.6 initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc null_reclaim+0xbc vgonel+0x12e vrecycle+0x7d null_inactive+0x1f vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23
> 4446 100229 python2.6 initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc null_reclaim+0xbc vgonel+0x12e vrecycle+0x7d null_inactive+0x1f vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23
> 4447 100089 python2.6 initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc null_reclaim+0xbc vgonel+0x12e vrecycle+0x7d null_inactive+0x1f vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23
> 5352 100270 mutt - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_synced+0x7c zil_commit+0x416 zfs_freebsd_fsync+0xd7 null_bypass+0xd3 fsync+0x161 syscall+0x1e7 Xfast_syscall+0xe1
> 52686 100200 tarsnap - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 dmu_tx_assign+0x16c zfs_inactive+0xd9 zfs_freebsd_inactive+0x1a vinactive+0x6a vputx+0x1cc vn_close+0xa1 vn_closefile+0x5a _fdrop+0x23 closef+0x3b kern_close+0x14d syscall+0x1e7 Xfast_syscall+0xe1
> 59049 100207 webalizer initial thread mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 zfs_freebsd_write+0x378 VOP_WRITE_APV+0xb2 null_bypass+0xd3 VOP_WRITE_APV+0x141 vn_write+0x2d7 dofilewrite+0x85 kern_pwritev+0x63 pwrite+0x59 syscall+0x1e7 Xfast_syscall+0xe1
> 77573 100479 perl - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_open+0x85 zfs_freebsd_write+0x378 VOP_WRITE_APV+0xb2 null_bypass+0xd3 VOP_WRITE_APV+0x141 vn_write+0x2d7 dofilewrite+0x85 kern_writev+0x60 write+0x55 syscall+0x1e7 Xfast_syscall+0xe1
> 78595 100275 zfs - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_synced+0x7c dsl_sync_task_group_wait+0x11c dmu_objset_snapshot+0x1b8 zfs_ioc_snapshot+0x7c zfsdev_ioctl+0x8d devfs_ioctl_f+0x77 kern_ioctl+0xf6 ioctl+0xfd syscall+0x1e7 Xfast_syscall+0xe1
> 81989 100596 zfs - mi_switch+0x16f sleepq_wait+0x42 _cv_wait+0x111 txg_wait_synced+0x7c dsl_sync_task_group_wait+0x11c dmu_objset_snapshot+0x1b8 zfs_ioc_snapshot+0x7c zfsdev_ioctl+0x8d devfs_ioctl_f+0x77 kern_ioctl+0xf6 ioctl+0xfd syscall+0x1e7 Xfast_syscall+0xe1
>
> I'm not sure if this shows anything useful?
All your userland processes are basically waiting for the kernel to finish
writing a ZFS transaction group to disk. mutt has called fsync, which may
have been the trigger. Usually writing a transaction group is fast, though,
because ZFS will batch up all the new data into one contiguous block and
write it at full speed to disk. That's why I asked about full filesystems
before, since if your FS has been near 99%, you may not have any large runs
of freespace left.
I noticed in your original post:
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
pool0 117G 16.7G 248 114 865K 269K
mirror 117G 16.7G 248 114 865K 269K
ad4s3 - - 43 56 2.47M 269K
ad6s3 - - 39 56 2.41M 269K
---------- ----- ----- ----- ----- ----- -----
# gstat
...
L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
1 48 48 3042 9.8 0 0 0.0 47.6| ad4
0 38 38 2406 10.5 0 0 0.0 39.5| ad6
You have a pair of mirrored disks, each doing around 40% I/O load, which is
80% load if a single-threaded task is driving all the I/O. I see the syncer
process is also trying to write to the ZIL. Are you running something that
does a lot of fsync calls (a database server for example)? Is this system
an NFS server maybe? Try setting the sysctl vfs.zfs.zil_disable=1 and see
if your performance improves.
--
Dan Nelson
dnelson at allantgroup.com
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