Re: Networked filesystems vs backing_dev_info

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Sat, 2007-10-27 at 11:22 -0400, Jan Harkes wrote:
> On Sat, Oct 27, 2007 at 11:34:26AM +0200, Peter Zijlstra wrote:
> > I had me a little look at bdi usage in networked filesystems.
> > 
> >  NFS, CIFS, (smbfs), AFS, CODA and NCP
> > 
> > And of those, NFS is the only one that I could find that creates
> > backing_dev_info structures. The rest seems to fall back to
> > default_backing_dev_info.
> 
> While a file is opened in Coda we associate the open file handle with a
> local cache file. All read and write operations are redirected to this
> local file and we even redirect inode->i_mapping. Actual reads and
> writes are completely handled by the underlying file system. We send the
> new file contents back to the servers only after all local references
> have been released (last-close semantics).
> 
> As a result, there is no need for backing_dev_info structures in Coda,
> if any congestion control is needed it will be handled by the underlying
> file system where our locally cached copies are stored.

Ok, that works. Thanks for this explanation!