Re: "failed to reclaim memory" with much free physmem

On Fri, Sep 12, 2025 at 5:46 PM Rick Macklem <rick.macklem@gmail.com> wrote:
>
> On Fri, Sep 12, 2025 at 8:58 AM Garrett Wollman <wollman@bimajority.org> wrote:
> >
> > <<On Fri, 12 Sep 2025 08:50:10 -0700, Rick Macklem <rick.macklem@gmail.com> said:
> >
> > > Ok, but don't we want something that prevents the arc from taking all
> > > the memory? (It seems like 932Gbytes should be close to a hard
> > > upper bound for a system with 1Tbyte of ram?)
> >
> > Presently it says:
> >
> > kstat.zfs.misc.arcstats.c_max: 1098065367040
> >
> > That's 1 TiB less 1379 MiB.  Which in all honesty *ought to be enough*
> > for munin-node, nrpe, ntpd, sendmail, inetd, lldpd, nslcd, sshd, syslogd,
> > mountd, and nfsuserd.
> If you look at arc_default_max() in
> sys/contrib/openzfs/module/os/freebsd/arc_os.c
> you'll see it returns "allmem - 1Gbyte".
> This may make sense for a machine with a few Gbytes of ram, but I'd bump it
> up for machines like you have. (As I noted, a system that boots with
> 128Gbyte->1Tbyte
> of ram is going to size things a lot larger and "allmem" looks like
> the total ram in the
> system. They haven't even subtracted out what the kernel uses.)
> (Disclaimer: I know nothing about ZFS, so the above may be crap!!)
>
> It's a trivial function to patch, rick
Here's another simple one..look at..
# sysctl -a | fgrep maxmbufmem
It appears to be set to 1/2 of the physical memory for me.

Lets see, 50% of memory allocated to mbufs and 99.9%
of physical memory allowed for the arc.
- This reminds me of the stats CNN puts up, where the
  percentages never add up to 100.

rick

>
> >
> > -GAWollman
> >