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

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jul 03, 2024 at 03:04:05PM -0400, Mike Snitzer wrote:
> The answer to that is: someone(s) could try that, but there is no
> interest from me or my employer to resort to using block layout with
> centralized mapping of which client and DS are local so that the pNFS
> MDS could handout such pNFS block layouts.

Where did block layout suddenly come from?

> That added MDS complexity can be avoided if the client and server have
> autonomy to negotiate more performant access without a centralized
> arbiter (hence the "localio" handshake).

Doing a localio layout would actually be a lot simpler than the current
mess, so that argument goes the other way around.

> NFS can realize benefits from localio being completely decoupled from
> flexfiles and pNFS.

How about actually listing the benefits?

> There are clear benefits with container use-cases
> that don't use pNFS at all.

Well, the point would be to make them use pNFS, because pNFS is the
well known and proven way to bypass the main server in NFS.

> Just so happens that flexfiles ushers in the use of NFSv3.  Once the
> client gets a flexfiles layout that points to an NFSv3 DS: the client
> IO is issued in terms of NFSv3.  If the client happens to be on the
> same host as the server then using localio is a win.

I have no idea where flexfiles comes in here and why it matters.  The
Linux server does not even support flexfiles layouts.