Questions abou nfsd file cache and open files

Questions abou nfsd file cache and open files

[Charles 'Boyo]

Hello all.

Please guide me into to find out the impact a busy nfsd is having on
the Linux page cache. Is it possible to determine which files have
portions in the page cache?

Secondly, files opened by nfs clients do not show up in lsof (or ftop)
on the nfs server? Is there any way to list these open files and more
importantly, observe the i/o to them?

Charles

Re: Questions abou nfsd file cache and open files

[Chuck Lever]

Hi-

Questions about NFSD should go to Bruce Fields (copied), the Linux NFS server maintainer.


On Nov 29, 2013, at 6:21 AM, Charles 'Boyo <charlesboyo@gmail.com> wrote:

> Hello all.
> 
> Please guide me into to find out the impact a busy nfsd is having on
> the Linux page cache. Is it possible to determine which files have
> portions in the page cache?

That is not possible even for local files, AFAIK.  (/me prepares to eat his words).

> Secondly, files opened by nfs clients do not show up in lsof (or ftop)
> on the nfs server? Is there any way to list these open files and more
> importantly, observe the i/o to them?


NFSv3 does not have an OPEN operation.  It would be difficult to tell, accurately, what an NFSv3 client was up to by looking for open files on an NFS server.

NFSv4 does perform file OPENs on the wire, but our I/O metrics are per-NFS operation, not per-file.  So you can see how many READs and WRITEs are done in aggregate, but not by which client, and not for a particular file.

NFSv4 also has delegation, which allows clients to operate on files without contacting the NFS server.  I/O activity that is cached by a client would not be visible to the storage server in any way.

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com

Re: Questions abou nfsd file cache and open files

[J. Bruce Fields]

On Mon, Dec 02, 2013 at 11:46:32AM -0500, Chuck Lever wrote:
> Hi-
> 
> Questions about NFSD should go to Bruce Fields (copied), the Linux NFS server maintainer.
> 
> 
> On Nov 29, 2013, at 6:21 AM, Charles 'Boyo <charlesboyo@gmail.com> wrote:
> 
> > Hello all.
> > 
> > Please guide me into to find out the impact a busy nfsd is having on
> > the Linux page cache. Is it possible to determine which files have
> > portions in the page cache?
> 
> That is not possible even for local files, AFAIK.  (/me prepares to eat his words).

Right.  Sounds like an interesting research project....

> > Secondly, files opened by nfs clients do not show up in lsof (or ftop)
> > on the nfs server? Is there any way to list these open files and more
> > importantly, observe the i/o to them?
> 
> 
> NFSv3 does not have an OPEN operation.  It would be difficult to tell, accurately, what an NFSv3 client was up to by looking for open files on an NFS server.
> 
> NFSv4 does perform file OPENs on the wire, but our I/O metrics are per-NFS operation, not per-file.  So you can see how many READs and WRITEs are done in aggregate, but not by which client, and not for a particular file.
> 
> NFSv4 also has delegation, which allows clients to operate on files without contacting the NFS server.  I/O activity that is cached by a client would not be visible to the storage server in any way.

Yes.  We could (and really should) have some statistics/debugging
interfaces to expose information like which clients currently hold NFSv4
opens, but we don't currently.

--b.