Date:   Tue, 14 Dec 2021 11:45:07 -0500
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     "suy.fnst@fujitsu.com" <suy.fnst@fujitsu.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "jlayton@kernel.org" <jlayton@kernel.org>,
        "trond.myklebust@hammerspace.com" <trond.myklebust@hammerspace.com>,
        "bfields@redhat.com" <bfields@redhat.com>
Subject: Re: [bug report] nfs clients fail to get read delegations after file
 open with O_RDWR
Message-ID: <20211214164507.GC12078@fieldses.org>
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 <20211213215550.GA2230@fieldses.org>
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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.