Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.1\))
Subject: Re: [PATCH v1] NFS: Zero-stateid SETATTR should first return
 delegation
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20200829161718.GC20499@fieldses.org>
Date:   Sat, 29 Aug 2020 12:37:12 -0400
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Content-Transfer-Encoding: 7bit
Message-Id: <B3A78318-5404-4A71-8FE9-B7E7053E891B@oracle.com>
References: <159864470513.1031951.14868951913532221090.stgit@manet.1015granger.net>
 <f5827110d3627096bdd4c07060876e69089a8d87.camel@hammerspace.com>
 <20200829161718.GC20499@fieldses.org>
To:     Bruce Fields <bfields@fieldses.org>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Aug 29, 2020, at 12:17 PM, bfields@fieldses.org wrote:
> 
> On Fri, Aug 28, 2020 at 09:13:07PM +0000, Trond Myklebust wrote:
>> On Fri, 2020-08-28 at 15:58 -0400, Chuck Lever wrote:
>>> If a write delegation isn't available, the Linux NFS client uses
>>> a zero-stateid when performing a SETATTR.
>>> 
>>> If that client happens to hold a read delegation, the server will
>>> recall it immediately, resulting in a short delay while the
>>> CB_RECALL operation is done. Optimize out this delay by having the
>>> client return any delegation it may hold on a file before issuing a
>>> SETATTR(zero-stateid) on that file.
>>> 
>>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>>> ---
>>> fs/nfs/nfs4proc.c |    1 +
>>> 1 file changed, 1 insertion(+)
>>> 
>>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>>> index dbd01548335b..53a56250cf4b 100644
>>> --- a/fs/nfs/nfs4proc.c
>>> +++ b/fs/nfs/nfs4proc.c
>>> @@ -3314,6 +3314,7 @@ static int _nfs4_do_setattr(struct inode
>>> *inode,
>>> 			goto zero_stateid;
>>> 	} else {
>>> zero_stateid:
>>> +		nfs4_inode_return_delegation(inode);
>>> 		nfs4_stateid_copy(&arg->stateid, &zero_stateid);
>>> 	}
>>> 	if (delegation_cred)
>>> 
>> 
>> This should not be needed for NFSv4.1 or greater. Only NFSv4.0 is
>> incapable of identifying the caller and recognising that it is the
>> holder of the delegation.
> 
> And the server should be getting this right now in the >=4.1 case, so
> let me know if you see otherwise.

The v5.9-rc1 server appears to be getting this right for v4.1.

Your earlier patch to avoid offering a delegation on OPEN(CREATE) helps
reduce the extra CB_RECALLs for v4.0, but the above patch is needed to
address the non-open-create cases.


--
Chuck Lever