Re: zfs questions

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Takashi YAMAMOTO <yamt9999%gmail.com@localhost> writes:

> On Sat, Feb 21, 2026 at 9:34 AM Brad Spencer <brad%anduin.eldar.org@localhost> wrote:
>>
>> Greg Troxel <gdt%lexort.com@localhost> writes:
>>
>> > Takashi YAMAMOTO <yamt9999%gmail.com@localhost> writes:
>> >
>> >> * is anyone using zfs in netbsd seriously? :-)
>> >
>> > I am using it on my desktop, and a on a dom0 hosting pkg builders.
>> >
>> > It mostly works, except that one must be careful not to simultaneously
>> >
>> >   run low on memory
>> >   run programs that dirty mmap'd pages (syncthing!)
>> >
>> > and probably also not
>> >
>> >   run really low on memory such that there is a lot of paging
>> >
>>
>> This is a reaonsably summary of the quirks.
>
> what's the symptom of the issues? do you have PRs?

The system will hang up, either very hard or just decay into a unusable
state.  I reduced the maxvnodes is a very low value and that made it
sometimes possible to use ps and one will notice one or more processes
that are claiming that some form of memory isn't available, flt_noram5
is pretty common, but not the only state I have seen.  These processes
will not be killable.

I don't think I created a PR specifically about what I see.  kern/57558
likely covers it, however.

I trigger the situation by doing 3 or 4 parallel builds of the OS,
"build.sh -someargs -j2", one a DOMU with 2 vcpus and 16GB (it is
assumed that the system will page hard at times, which is fine).
However, even if I do only 1 build over and over (actually only 3 or 4
times), the system will eventually put itself into the same state.
Something builds up over time or memory fragments in a manor that makes
it unusable, I suspect.  The system is backed up using zfs snapshots and
even if I am not doing builds the system will decay into the same state,
but that tends to take a very long time (many months).  The daily cron
jobs are mostly disabled as the ones that use find (hunting down core
files, etc) can hang up the system when they cross into the zfs
filesets, especially if they happen to run when a build it going on.

Fairly easy to trigger, it just takes a while for everything to grind to
a halt so one has to be patience about it all.


Currently on a Xen DOMU PVH guest you can't get a kernel crash dump. so
that is a frustration point to figuring out what is happening.


(Been dealing with this for a long time, and a number of others know
about it)





-- 
Brad Spencer - brad%anduin.eldar.org@localhost