On Sun, Aug 09, 2020 at 04:27:39PM -0400, Bruce Fields wrote:
> On Sun, Aug 09, 2020 at 01:11:36PM -0400, Chuck Lever wrote:
> > Hi Bruce-
> >
> > I noticed that one of my tests takes about 4x longer on NFSv4.0 than
> > it does on NFSv3 or NFSv4.[12]. As an initial stab at the cause, I'm
> > seeing lots of these:
>
> Oops, looks obvious in retrospect, but I didn't think of it.
>
> In the 4.1+ case, sessions mean that we know which client every
> operation comes from.
>
> In the 4.0 case that only works for operations that take a stateid or
> something else we can link back to a client.
>
> That means in the 4.0 case delegations are less useful, since they have
> to be broken on any (non-truncating) setattr, any link/unlink, etc.,
> even if the operation comes from the same client--the server doesn't
> have a way to know that.
>
> Maybe the change to give out read delegations even on write opens
> probably just isn't worth in the 4.0 case.
Untested, but maybe this?--b.
commit 2102ac0b68f3
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
Date: Sun Aug 9 17:11:59 2020 -0400
nfsd4: don't grant delegations on 4.0 create opens
Chuck reported a major slowdown running the git regression suite over
NFSv4.0.
In the 4.0 case, the server has no way to identify which client most
metadata-modifying operations come from. So, for example, the common
pattern of a a setattr is likely to result in an immediate break in the
4.0 case.
It's probably not worth giving out delegations on 4.0 creates.
Reported-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index fdba971d06c3..ce2d052b3f64 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -5096,6 +5096,16 @@ nfs4_open_delegation(struct svc_fh *fh, struct nfsd4_open *open,
goto out_no_deleg;
if (!cb_up || !(oo->oo_flags & NFS4_OO_CONFIRMED))
goto out_no_deleg;
+ /*
+ * In the absence of sessions, most operations
+ * that modify metadata (like setattr) can't
+ * be linked to the client sending them, so
+ * will result in a delegation break. That's
+ * especially likely for create opens:
+ */
+ if (clp->cl_minorversion == 0 &&
+ open->op_create == NFS4_OPEN_CREATE)
+ goto out_no_deleg;
break;
default:
goto out_no_deleg;
