Re: [PATCH v3 2/2] NFSD: enable support for write delegation

[dai.ngo@xxxxxxxxxx]

On 5/18/23 10:16 AM, Chuck Lever III wrote:
> > On May 18, 2023, at 1:11 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
> >
> >
> > On 5/18/23 6:23 AM, Chuck Lever III wrote:
> > > > On May 17, 2023, at 7:38 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
> > > >
> > > > This patch grants write delegation for OPEN with NFS4_SHARE_ACCESS_WRITE
> > > > if there is no conflict with other OPENs.
> > > >
> > > > Write delegation conflict with another OPEN, REMOVE, RENAME and SETATTR
> > > > are handled the same as read delegation using notify_change,
> > > > try_break_deleg.
> > > Very clean. A couple of suggestions, one is down below, and here is
> > > the other:
> > >
> > > I was thinking we should add one or two counters in fs/nfsd/stats.c
> > > to track how often read and write delegations are offered, and
> > > perhaps one to count the number of DELEGRETURN operations. What do
> > > you think makes sense?
> > I'm not sure what these counters will tell us, currently we already
> > has a counter for number of delegations handed out.
> I haven't found that, where is it? Certainly, if NFSD already
> has one, then no need to add more.

num_delegations in nfs4state.c

> It would be nice one day, perhaps, to have a metric of how many
> delegations a client holds. That's not for this series.

okay.

> > I think a counter
> > on how often nfsd has to recall the write delegation due to GETATTR can
> > be useful to know whether we should implement CB_GETATTR.
> I hesitated to mention that because I wonder if that's something
> that would be interesting only for defending a design choice,
> not for site-to-site tuning. In other words, after we plumb it
> into NFSD, it will never actually be used after CB_GETATTR
> support is added.
>
> Do you believe it's something that administrators can use to
> help balance or tune their workloads?

You're right. That is just for ourselves to determine if CB_GETATTR
is needed.

-Dai

> > > > Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> > > > ---
> > > > fs/nfsd/nfs4state.c | 24 ++++++++++++++++--------
> > > > 1 file changed, 16 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > > > index 6e61fa3acaf1..09a9e16407f9 100644
> > > > --- a/fs/nfsd/nfs4state.c
> > > > +++ b/fs/nfsd/nfs4state.c
> > > > @@ -1144,7 +1144,7 @@ static void block_delegations(struct knfsd_fh *fh)
> > > >
> > > > static struct nfs4_delegation *
> > > > alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
> > > > - struct nfs4_clnt_odstate *odstate)
> > > > + struct nfs4_clnt_odstate *odstate, u32 dl_type)
> > > > {
> > > > struct nfs4_delegation *dp;
> > > > long n;
> > > > @@ -1170,7 +1170,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
> > > > INIT_LIST_HEAD(&dp->dl_recall_lru);
> > > > dp->dl_clnt_odstate = odstate;
> > > > get_clnt_odstate(odstate);
> > > > - dp->dl_type = NFS4_OPEN_DELEGATE_READ;
> > > > + dp->dl_type = dl_type;
> > > > dp->dl_retries = 1;
> > > > dp->dl_recalled = false;
> > > > nfsd4_init_cb(&dp->dl_recall, dp->dl_stid.sc_client,
> > > > @@ -5451,6 +5451,7 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > > > struct nfs4_delegation *dp;
> > > > struct nfsd_file *nf;
> > > > struct file_lock *fl;
> > > > + u32 deleg;
> > > >
> > > > /*
> > > > * The fi_had_conflict and nfs_get_existing_delegation checks
> > > > @@ -5460,7 +5461,13 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > > > if (fp->fi_had_conflict)
> > > > return ERR_PTR(-EAGAIN);
> > > >
> > > > - nf = find_readable_file(fp);
> > > > + if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
> > > > + nf = find_writeable_file(fp);
> > > > + deleg = NFS4_OPEN_DELEGATE_WRITE;
> > > > + } else {
> > > > + nf = find_readable_file(fp);
> > > > + deleg = NFS4_OPEN_DELEGATE_READ;
> > > > + }
> > > > if (!nf) {
> > > > /*
> > > > * We probably could attempt another open and get a read
> > > > @@ -5491,11 +5498,11 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > > > return ERR_PTR(status);
> > > >
> > > > status = -ENOMEM;
> > > > - dp = alloc_init_deleg(clp, fp, odstate);
> > > > + dp = alloc_init_deleg(clp, fp, odstate, deleg);
> > > > if (!dp)
> > > > goto out_delegees;
> > > >
> > > > - fl = nfs4_alloc_init_lease(dp, NFS4_OPEN_DELEGATE_READ);
> > > > + fl = nfs4_alloc_init_lease(dp, deleg);
> > > > if (!fl)
> > > > goto out_clnt_odstate;
> > > >
> > > > @@ -5583,6 +5590,7 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > > > struct svc_fh *parent = NULL;
> > > > int cb_up;
> > > > int status = 0;
> > > > + u32 wdeleg = false;
> > > >
> > > > cb_up = nfsd4_cb_channel_good(oo->oo_owner.so_client);
> > > > open->op_recall = 0;
> > > > @@ -5590,8 +5598,6 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > > > case NFS4_OPEN_CLAIM_PREVIOUS:
> > > > if (!cb_up)
> > > > open->op_recall = 1;
> > > > - if (open->op_delegate_type != NFS4_OPEN_DELEGATE_READ)
> > > > - goto out_no_deleg;
> > > > break;
> > > > case NFS4_OPEN_CLAIM_NULL:
> > > > parent = currentfh;
> > > > @@ -5617,7 +5623,9 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> > > > memcpy(&open->op_delegate_stateid, &dp->dl_stid.sc_stateid, sizeof(dp->dl_stid.sc_stateid));
> > > >
> > > > trace_nfsd_deleg_read(&dp->dl_stid.sc_stateid);
> > > I'd like you to add a trace_nfsd_deleg_write(), and invoke
> > > it here instead of trace_nfsd_deleg_read when NFSD hands out
> > > a write delegation.
> > Fix in v4.
> >
> > -Dai
> >
> > > > - open->op_delegate_type = NFS4_OPEN_DELEGATE_READ;
> > > > + wdeleg = open->op_share_access & NFS4_SHARE_ACCESS_WRITE;
> > > > + open->op_delegate_type = wdeleg ?
> > > > + NFS4_OPEN_DELEGATE_WRITE : NFS4_OPEN_DELEGATE_READ;
> > > > nfs4_put_stid(&dp->dl_stid);
> > > > return;
> > > > out_no_deleg:
> > > > --
> > > > 2.9.5
> > > --
> > > Chuck Lever
>
> --
> Chuck Lever