Increase FreeBSD NFSv4 nfsd buffer size? Re: Increase default NFSv4 server size "max_block_size" to 4MB

On Tue, 17 Mar 2026 at 00:35, Rick Macklem <[email protected]> wrote:
>
> On Mon, Mar 16, 2026 at 5:41 AM Chuck Lever <[email protected]> wrote:
> >
> >
> > On Mon, Mar 16, 2026, at 3:51 AM, Cedric Blancher wrote:
> > > As debated a while ago, can the default NFSv4 server size for
> > > "max_block_size" be increased to 4MB, please?
> >
> > There is an administrative setting to raise this limit for
> > recent versions of the kernel. Can you report your experience
> > when you raise the limit? Hiccups, performance issues, etc? I
> > would kind of like this exercise to be data-driven.
> >
> > What is still unknown to me is which NFS client implementations
> > can support 4MB or 8MB. Without client support, an increase in
> > the default in NFSD doesn't mean anything. Rick, Anna, Roland?
> Although it has not seen much testing, it is possible to do a > 1Mbyte NFSv4
> mount in FreeBSD.
> For a 2Mbyte mount, (the only size > 1Mbyte I've tried) the settings would be..
> In /boot/loader.conf
> kern.maxphys=2097152
> vfs.maxbcachebuf=2097152
>
> and in /etc/sysctl.conf
> kern.ipc.maxsockbuf=9455616
>
> Then a mount will use 2Mbytes if the server supports it.

How can I verify that the FreeBSD NFSv4 nfsd now uses 2M for NFS buffers?

Ced
-- 
Cedric Blancher <[email protected]>
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur