Thanks for the test results:
On Mon, Aug 10, 2020 at 02:21:34PM -0400, Chuck Lever wrote:
> For these results I've switched to sec=sys so the test completes faster.
>
> NFSv3/sys: 953.37user 5101.96system 14:13.78elapsed 709%CPU (0avgtext+0avgdata 107160maxresident)k
>
> NFSv4.1/sys: 953.64user 5202.27system 17:54.51elapsed 572%CPU (0avgtext+0avgdata 107204maxresident)k
>
> NFSv4.0/sys unpatched: 965.44user 5406.75system 36:10.72elapsed 293%CPU (0avgtext+0avgdata 107252maxresident)k
>
> NFSv4.0/sys with fix: 968.38user 5359.18system 30:50.38elapsed 341%CPU (0avgtext+0avgdata 107140maxresident)k
Well, that didn't work!
So maybe it's write opens that are the problem in this case. The below
should mostly revert to pre-94415b06eb8a behavior in the 4.0 case, so if
this doesn't fix it then I was wrong about the cause....
--b.
commit 0e94ee0b6f11
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 an create or write open followed by 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 write or create
opens.
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..0d51d1751592 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -5096,6 +5096,19 @@ 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;
+ if (clp->cl_minorversion)
+ break;
+ /*
+ * 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 write and create opens:
+ */
+ if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE)
+ goto out_no_deleg;
+ if (open->op_create == NFS4_OPEN_CREATE)
+ goto out_no_deleg;
break;
default:
goto out_no_deleg;
