On Mon, May 6, 2024 at 2:04 PM <cel@xxxxxxxxxx> wrote:
>
> From: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> We've discovered that delivering a CB_OFFLOAD operation can be
> unreliable in some pretty unremarkable situations, and the Linux
> NFS client does not yet support sending an OFFLOAD_STATUS
> operation to probe whether an asynchronous COPY operation has
> finished. On Linux NFS clients, COPY can hang until manually
> interrupted.
>
> I've tried a couple of remedies, but so far the side-effects are
> worse than the disease. For now, force COPY operations to be
> synchronous so that the use of CB_OFFLOAD is avoided entirely.
Just a yellow warning light from my experience with the FreeBSD server
(which always does synchronous Copy's).
A large synchronous Copy can take a long time, resulting in a slow RPC
response time. A user reported 25sec.
The 25sec case turned out to be a ZFS specific issue that could be avoided
via a ZFS tunable.
I do not have a good generic solution, but I do have a tunable that can
be used to clip the Copy len, which is a rather blunt and ugly workaround.
(The generic copy routine internal to FreeBSD can accept a flag that indicates
"return after 1sec with a partial copy done", but that is not implemented for
file systems like ZFS.)
Although there is no hard limit in the RFCs for RPC response times,
I've typically
assumed a max of 1-2sec is desirable.
rick
>
> I have some patches that add an OFFLOAD_STATUS implementation to the
> Linux NFS client, but that is not likely to fix older clients.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4proc.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index ea3cc3e870a7..12722c709cc6 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1807,6 +1807,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> __be32 status;
> struct nfsd4_copy *async_copy = NULL;
>
> + /*
> + * Currently, async COPY is not reliable. Force all COPY
> + * requests to be synchronous to avoid client application
> + * hangs waiting for completion.
> + */
> + nfsd4_copy_set_sync(copy, true);
> +
> copy->cp_clp = cstate->clp;
> if (nfsd4_ssc_is_inter(copy)) {
> trace_nfsd_copy_inter(copy);
>
> base-commit: 939cb14d51a150e3c12ef7a8ce0ba04ce6131bd2
> --
> 2.44.0
>
>
