Re: [nfsv4] Current-stateid/special-stateid for Layoutget

[Trond Myklebust <[e-mail]>]

Hi Rick,

Please see: https://tools.ietf.org/html/rfc5661#section-8.2.3
The '"other" is zero and "seqid" is 1' option should be what you are
looking for.

Cheers
  Trond

On 6 March 2017 at 15:59, Rick Macklem <[e-mail]> wrote:

> Boring background...
> I created a pNFS server using Flex File layout and GlusterFS. It was
> a dud. Basically worked, but was very slow.
> I came up with Plan B, which is a simple, single MDS server using
> File layout and FreeBSD's nfsd. It seems to work pretty well, which
> brings me to...
>
> When I have a client mounted with pNFS enabled, I see better I/O
> performance for tests on fairly big files, however for software builds
> (lots of I/O on small files), the performance is about the same for pNFS
> as when pNFS is disabled and all I/O is being done through the MDS.
>
> I am not 100% sure, but when pNFS is enabled, the client does two RPCs
> when a file is opened:
> - one that does the Open
> - one that does the LayoutGet
> and I think the extra RPC round trip time slows the pNFS case down.
>
> The obvious fix is to do the Open and LayoutGet in the same compound RPC.
> If the client already has a layout for the file, the LayoutGet can use the
> Current-FH set by the Open operation and the layout_stateid and life is
> good.
> However, if the client is getting the first layout for the file (this is
> usually the
> case for the File Layout), then it doesn`t work, because LayoutGet needs
> an open_stateid argument.
>
> So, here`s what I am thinking of:
> - Define a Current-OpenStateID, which is unset at the start of a compound.
> - A successful Open op. sets the Current-OpenStateID to the one in its
> reply,
>   so that it is set along with the Current-FH.
> - Any other operation that sets the Current-FH unsets Current-OpenStateID.
> - Redefine the case of LayoutGet with a special stateid as...
>   If the stateid in LayoutGet`s argument is a special stateid, replace it
> with
>   the Current-OpenStateID if one is set.
> --> Then, do everything else just as RFC-5661 states.
>
> I don't know about other implementations, but this would be easy to do in
> the FreeBSD NFSv4.1 server and would allow LayoutGet to follow Open in
> the same RPC, I think? (I haven't actually coded this yet.)
>
> For server's that don't support this, I don't think it would be a problem,
> since the compound would fail at the LayoutGet with NFS4ERR_BAD_STATEID.
> At that point, the client would have the Open reply and could just do the
> additional compound RPC with LayoutGet, using the OpenStateID in the Open
> reply.
>
> So, what do others think?
>
> Also, I haven't followed the versioning discussion, so I have no idea if
> this
> can be done without having a new minor version?
>
> Thanks, rick
> ps: I will probably code this up in FreeBSD experimentally, to see how it
> works.
>
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