Re: zfs pool behavior - is it ever freed?

[Greg Troxel <gdt%lexort.com@localhost>]

Hauke Fath <hf%spg.tu-darmstadt.de@localhost> writes:

> On Fri, 21 Jul 2023 08:31:46 -0400, Greg Troxel wrote:
> [zfs memory pressure]
>
>>   Are others having this problem?
>
> I have two machines, one at home (-10) and one at work (-9), in a 
> similar role as yours (fileserver and builds). While both have had 
> their moments, those have never been zfs related.
>
> They both have 32 GB RAM. The home machine, currently running a 
> netbsd-9 build natively and pkg_rr in a VM, is using 16 GB for pools as 
> we speak. 

Using half the ram for pools feels like perhaps a bug, depending -- even
if you are getting away with it.

I am curious:

  What VM approach?

  How much ram in the domU (generic term even if not xen)?

  Are you using NFS from the domU to dom0?  domU running zfs?  Something
  else?

  Is the 16G for pools the sum of the dom0 and domU pools?  Or ?

> My guess would be that your 8 GB are simply not enough for sustaining 
> both zfs and builds.

I think that's how it is, but it seems obviously buggy for that to be
the case.  It is dysfunctional to run the system to lockup caching
things that don't need to be cached.  The ffs vnode cache for example
does not do this.

The zfs howto currently talks about zfs taking 1G plus 1G per 1T of
disk.  For me that would be 1.8G, which would be ok.  But that's not
what happens.

Thanks for the data point; I'll probably edit the zfs HOWTO.  As it is
we should probably be recommending against zfs unless you have 64G of
RAM :-( as even your system doesn't seem healthy memory usage wise.