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

On Wed, 13 May 2026 at 01:02, Rick Macklem <[email protected]> wrote:
>
> On Tue, May 12, 2026 at 6:18 AM Cedric Blancher
> <[email protected]> wrote:
> >
> > 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?
> The default is 128K. (You can see what it is via "sysctl vfs.nfsd.srvmaxio".)
>
> With "main",

Which FreeBSD version is "main" exactly, i.e. which 16.0 snapshot
date? Is this supported for 15.0?

> you can increase that up to 4M by putting
> nfs_server_maxio=N (where N can be up to 4194304 for "main" and 1048576 for 15)

What line do I have to put into /etc/sysctl.conf and /etc/rc.conf?

> - adding an entry in /etc/sysctl.conf for a larger value for kern.ipc.maxsockbuf
>   (It will tell you the recommended minimum setting if you boot after
>    putting nfs_server_maxio=N in /etc/rc.conf.)

How can I verify that the settings work, on the NFS server side? Can
we programmatically probe which values are supported?

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