Re: [PATCH v11 00/20] nfs/nfsd: add support for localio

Christoph Hellwig
2024-07-06T06:42:30Z

On Sat, Jul 06, 2024 at 04:37:22PM +1000, NeilBrown wrote:
> > a different scheme for bypassing the server for I/O. Maybe there is
> > a really good killer argument for doing that, but it needs to be clearly
> > stated and defended instead of assumed.
>
> Could you provide a reference to the text book - or RFC - that describes
> a pNFS DS protocol that completely bypasses the network, allowing the
> client and MDS to determine if they are the same host and to potentially
> do zero-copy IO.

I did not say that we have the exact same functionality available and
there is no work to do at all, just that it is the standard way to bypass
the server.

RFC 5662, RFC 5663 and RFC 8154 specify layouts that completely bypass
the network and require the client and server to find out that they talk
to the same storage devuce, and directly perform zero copy I/O.
They do not require to be on the same host, though.

> If not, I will find it hard to understand your claim that it is "the
> text book example".

pNFS is all about handing out grants to bypass the server for I/O.
That is exactly what localio is doing.