Re: Write delegation

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Wed, 2010-08-04 at 14:11 -0700, Yudong Gao wrote:
> Thanks for the reply, Andy!
> 
> So the write delegation can only reduce the unnecessary open/close and
> lock/locku. But if a client modify the same page for multiple times,
> e.g. editing the file in a editor, is there any optimization to
> prevent the client from sending the half-updated pages? Ideally only
> the final update need to be put on the wire.
> 

Yes. However that optimisation is not linked to whether or not we hold a
write delegation. The NFS client assumes close-to-open cache
consistency, and so will cache writes until either the VM tries to
reclaim memory by writing out dirty page, or the application calls one
of fcntl(F_UNLCK), fsync() or close().

Trond

> Thanks!
> 
> best,
> 
> Yudong
> 
> On Wed, Aug 4, 2010 at 1:59 PM, Andy Adamson <andros@netapp.com> wrote:
> >
> > On Aug 4, 2010, at 3:21 PM, Yudong Gao wrote:
> >
> >> Hi,
> >>
> >> I am not able to find the implementation of directory delegation,
> >> either. Similarly, the callback functions CB_NOTIFY is not
> >> implemented, either. I find that in preprocss_nfs41_op() in
> >> callback_xdr.c, whenever a CB_NOTIFY is encountered, an
> >> NFS4ERR_NOTSUPP is returned directly.
> >
> > CB_NOTIFY is not currently supported on the Linux NFS client.
> >
> >>
> >> Am I missing something? Or they are just not supported in the current version?
> >>
> >> Thanks a lot!
> >>
> >> best,
> >>
> >> Yudong
> >>
> >> On Mon, Aug 2, 2010 at 5:17 PM, Yudong Gao <stgyd@umich.edu> wrote:
> >>> Hi,
> >>>
> >>> I am looking at the delegation implementation in the source code of
> >>> NFS 4.1 in kernel 2.6.32.15. I can find the code for read delegation,
> >>> which is working and can serve the read requests locally. But I can
> >>> never find the code about write delegation, which is supposed to cache
> >>> the write update locally. I try to look at the functions including
> >>> nfs_writepage(s), nfs_file_flush() but none of them checks or uses the
> >>> write delegation.
> >>>
> >>> Is write delegation currently implemented in NFS 4.1?
> >
> > Write delegation is supported but I don't think write behavior changes - writes are still cached and flushed as without a write delegation. The write delegation does prevent open/close and lock/locku from being put on the wire.
> >
> > -->Andy
> >
> >>>
> >>> Thanks!
> >>>
> >>> best,
> >>>
> >>> Yudong
> >>>
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> >> the body of a message to majordomo@vger.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >
> >
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html