2018-08-13 21:48, Volodymyr Kostyrko wrote:
I've been in the same situation. ZFS, only pool, no ZFS errors.
I think the problem is rather between swapping and ZFS ARC. This host
has different load, sometimes it needs more active memory, somtimes
less... This means that active zone can expand and shrink like +-2G os
mem (I have 16Gb installed there). The problem is, when huge task is
idle it doesn't use much active memory and other activity is pushing
it's memory to the swap. When active runs low and ARC runs >50% of
memory it becomes very hard to make ARC give some memory back. My host
even was broght to the point when it couldn't get tasks back into
memory from swap, because while some pages were restored from swap the
time passes by and the other pages are instead stored to swap due to
zome ARC activity. Finally active zone shrinks so bad that the host
becomes unresponsive.
Like 6 month ago I tried tweaking kernel and swap to make things go
other way. Currently I have `vm.swap_idle_enabled=1` in
/etc/loader.conf and looks like this solves my problem. The other
interesting things to look at are `vfs.zfs.arc_free_target`,
`vfs.zfs.arc_shrink_shift`, `vfs.zfs.arc_grow_retry`.
Or you can take another route and plain limit current ARC size with
`vfs.zfs.arc_max`.
What you describe is not the same problem as the one I described
in this thread. In my case the ZFS malloc'ed memory ("solaris" zone)
is growing, while the size of the ARC remains capped to a reasonably
low value, and the ARC even shrinks as the "solaris" zone approaches
the memory size.
I too have been bitten previously by the ARC size being reluctant to
shrink. Ths problem is described here, but only partially mitigated
now in the 11.? version:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=187594
The usually suggested workaround is to limit the size of the ARC,
although it would be nice to find a solution to handle ARC UMA
shrinking automatically, like it worked well in FreeBSD 9 but
broke in FreeBSD 10.
Like I said, the problem I described in this thread is different.
Mark
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