Re: [PATCH v1] NFS: Zero-stateid SETATTR should first return delegation

From: bfields@fieldses.org (J. Bruce Fields)
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: "anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
	"chuck.lever@oracle.com" <chuck.lever@oracle.com>,
	"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v1] NFS: Zero-stateid SETATTR should first return delegation
Date: Sat, 29 Aug 2020 12:17:18 -0400	[thread overview]
Message-ID: <20200829161718.GC20499@fieldses.org> (raw)
In-Reply-To: <f5827110d3627096bdd4c07060876e69089a8d87.camel@hammerspace.com>

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.

--b.