Re: [bug report] nfs clients fail to get read delegations after file open with O_RDWR

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Dec 14, 2021 at 12:50:53AM +0000, suy.fnst@fujitsu.com wrote:
> Thanks for your quick reply!
> 
> >>Without looking at this case in detail:
> 
> >>Delegations are granted at the server's discretion, so this certainly
> >>isn't a bug.
> 
> Got it.
> 
> >>It might be suboptimal behavior.  If there's evidence that this causes
> >>significant regressions on some important workload, then we'd want to
> >>look into fixing it.
> 
> If I understand the case correctly, the most common workload it influences like:
> 
> One nfs client opens a file with flag O_WRONLY/O_RDWR, close it.
> Then some nfs clients open the file with O_RDONLY right now then it will prevent
> server to give any delegation to other clients.  It may cause many unnecessary
> requests from clients because lack of delegations.

Right.

For the moment, this is something I'd accept patches for, but I'm not
actively working on.

I think it's been suggested that we could even turn off the file cache
completely in the v4 case, since in that case we don't have to re-open
on every IO.

--b.