Hi all !
I got a UniProcessor AMD64 box, with 512 MB ram with 2 ZFS pools as a home-NAS.

I got some IO issues since I moved from 7.2 to 8.0.
With a GENERIC kernel (or a stripped down one), during high IO activity (as a make buildword can cause), I encounter random hangs or deadlocks. top show system CPU usage at 99%, the most CPU using process being [zfskern] ( {txg_thread_enter} if I switch to thread view). The box still respond to ping. Current processes can still run, but I can't run new ones. Sometimes, I can return to normal by Ctrl-C-ing the buildworld (or other operation), sometimes I can't, I got to reboot the box.

The Issue seemed to become less frequent with 8.0-stable instead of 8.0-RELEASE, but still present (I get approximately 75% chance of hang with a buildworld).
I got the hang with Prefetch enabled or disabled. Idem for ZIL.

I tried to enable kernel dumps, but the box hangs saving the dump (root is on ZFS) or when starting kdbg on it. I recompiled kernel with SCHED_4BSD, and it seems I can't reproduce the hang.

What do you think ?
Did I misconfigured something ?


cat /boot/loader.conf
zfs_load="YES"
vfs.root.mountfrom="zfs:unsafe/root"
vm.kmem_size="512M"
vm.kmem_size_max="512M"
vfs.zfs.arc_max="100M"
vfs.zfs.vdev.cache.size="10M"
vfs.zfs.prefetch_disable="0"
vfs.zfs.zil_disable="1"


[carenath] ~> zpool status
 pool: tank
state: ONLINE
scrub: none requested
config:

       NAME        STATE     READ WRITE CKSUM
       tank        ONLINE       0     0     0
         raidz1    ONLINE       0     0     0
           ad6p1   ONLINE       0     0     0
           ad10p1  ONLINE       0     0     0
           ad8p1   ONLINE       0     0     0
           ad4p1   ONLINE       0     0     0

errors: No known data errors

 pool: unsafe
state: ONLINE
scrub: none requested
config:

       NAME        STATE     READ WRITE CKSUM
       unsafe      ONLINE       0     0     0
         ad0p3     ONLINE       0     0     0

errors: No known data errors




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