diff mbox series

[v13,15/19] pnfs/flexfiles: enable localio support

Message ID 20240823181423.20458-16-snitzer@kernel.org (mailing list archive)
State New
Headers show
Series nfs/nfsd: add support for localio | expand

Commit Message

Mike Snitzer Aug. 23, 2024, 6:14 p.m. UTC
From: Trond Myklebust <trond.myklebust@hammerspace.com>

If the DS is local to this client use localio to write the data.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 fs/nfs/flexfilelayout/flexfilelayout.c    | 136 +++++++++++++++++++++-
 fs/nfs/flexfilelayout/flexfilelayout.h    |   2 +
 fs/nfs/flexfilelayout/flexfilelayoutdev.c |   6 +
 3 files changed, 140 insertions(+), 4 deletions(-)

Comments

NeilBrown Aug. 26, 2024, 1:39 a.m. UTC | #1
On Sat, 24 Aug 2024, Mike Snitzer wrote:
> From: Trond Myklebust <trond.myklebust@hammerspace.com>
> 
> If the DS is local to this client use localio to write the data.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> ---
>  fs/nfs/flexfilelayout/flexfilelayout.c    | 136 +++++++++++++++++++++-
>  fs/nfs/flexfilelayout/flexfilelayout.h    |   2 +
>  fs/nfs/flexfilelayout/flexfilelayoutdev.c |   6 +
>  3 files changed, 140 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
> index 01ee52551a63..d91b640f6c05 100644
> --- a/fs/nfs/flexfilelayout/flexfilelayout.c
> +++ b/fs/nfs/flexfilelayout/flexfilelayout.c
> @@ -11,6 +11,7 @@
>  #include <linux/nfs_mount.h>
>  #include <linux/nfs_page.h>
>  #include <linux/module.h>
> +#include <linux/file.h>
>  #include <linux/sched/mm.h>
>  
>  #include <linux/sunrpc/metrics.h>
> @@ -162,6 +163,72 @@ decode_name(struct xdr_stream *xdr, u32 *id)
>  	return 0;
>  }
>  
> +/*
> + * A dummy definition to make RCU (and non-LOCALIO compilation) happy.
> + * struct nfsd_file should never be dereferenced in this file.
> + */
> +struct nfsd_file {
> +       int undefined__;
> +};

I removed this and tried building both with and without LOCALIO enabled
and the compiler didn't complain.
Could you tell me what to do to see the unhappiness you mention?


> diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
> index f84b3fb0dddd..562e7e27a8b5 100644
> --- a/fs/nfs/flexfilelayout/flexfilelayout.h
> +++ b/fs/nfs/flexfilelayout/flexfilelayout.h
> @@ -82,7 +82,9 @@ struct nfs4_ff_layout_mirror {
>  	struct nfs_fh			*fh_versions;
>  	nfs4_stateid			stateid;
>  	const struct cred __rcu		*ro_cred;
> +	struct nfsd_file __rcu		*ro_file;
>  	const struct cred __rcu		*rw_cred;
> +	struct nfsd_file __rcu		*rw_file;

What is the lifetime of a layout_mirror?  Does it live for longer than a
single IO request?  If so we have a problem as this will pin the
nfsd_file until the layout is returned.


Thanks,
NeilBrown
Mike Snitzer Aug. 26, 2024, 3:38 p.m. UTC | #2
On Mon, Aug 26, 2024 at 11:39:31AM +1000, NeilBrown wrote:
> On Sat, 24 Aug 2024, Mike Snitzer wrote:
> > From: Trond Myklebust <trond.myklebust@hammerspace.com>
> > 
> > If the DS is local to this client use localio to write the data.
> > 
> > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > ---
> >  fs/nfs/flexfilelayout/flexfilelayout.c    | 136 +++++++++++++++++++++-
> >  fs/nfs/flexfilelayout/flexfilelayout.h    |   2 +
> >  fs/nfs/flexfilelayout/flexfilelayoutdev.c |   6 +
> >  3 files changed, 140 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
> > index 01ee52551a63..d91b640f6c05 100644
> > --- a/fs/nfs/flexfilelayout/flexfilelayout.c
> > +++ b/fs/nfs/flexfilelayout/flexfilelayout.c
> > @@ -11,6 +11,7 @@
> >  #include <linux/nfs_mount.h>
> >  #include <linux/nfs_page.h>
> >  #include <linux/module.h>
> > +#include <linux/file.h>
> >  #include <linux/sched/mm.h>
> >  
> >  #include <linux/sunrpc/metrics.h>
> > @@ -162,6 +163,72 @@ decode_name(struct xdr_stream *xdr, u32 *id)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * A dummy definition to make RCU (and non-LOCALIO compilation) happy.
> > + * struct nfsd_file should never be dereferenced in this file.
> > + */
> > +struct nfsd_file {
> > +       int undefined__;
> > +};
> 
> I removed this and tried building both with and without LOCALIO enabled
> and the compiler didn't complain.
> Could you tell me what to do to see the unhappiness you mention?

Sorry, I can remove the dummy definition for upstream.  That was
leftover from the backport I did to 5.15.y stable@ kernel.  Older
kernels' RCU code dereferences what should just be an opaque pointer
and (ab)use typeof.  So without the dummy definition compiling against
5.15.y fails with:

  CC [M]  fs/nfs/flexfilelayout/flexfilelayout.o
In file included from ./include/linux/rbtree.h:24,
                 from ./include/linux/mm_types.h:10,
                 from ./include/linux/mmzone.h:21,
                 from ./include/linux/gfp.h:6,
                 from ./include/linux/mm.h:10,
                 from ./include/linux/nfs_fs.h:23,
                 from fs/nfs/flexfilelayout/flexfilelayout.c:10:
fs/nfs/flexfilelayout/flexfilelayout.c: In function `ff_local_open_fh´:
./include/linux/rcupdate.h:441:9: error: dereferencing pointer to incomplete type `struct nfsd_file´
  typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
         ^
./include/linux/rcupdate.h:580:2: note: in expansion of macro `__rcu_dereference_check´
  __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
  ^~~~~~~~~~~~~~~~~~~~~~~
./include/linux/rcupdate.h:648:28: note: in expansion of macro `rcu_dereference_check´
 #define rcu_dereference(p) rcu_dereference_check(p, 0)
                            ^~~~~~~~~~~~~~~~~~~~~
fs/nfs/flexfilelayout/flexfilelayout.c:193:7: note: in expansion of macro `rcu_dereference´
  nf = rcu_dereference(*pnf);
       ^~~~~~~~~~~~~~~

> > diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
> > index f84b3fb0dddd..562e7e27a8b5 100644
> > --- a/fs/nfs/flexfilelayout/flexfilelayout.h
> > +++ b/fs/nfs/flexfilelayout/flexfilelayout.h
> > @@ -82,7 +82,9 @@ struct nfs4_ff_layout_mirror {
> >  	struct nfs_fh			*fh_versions;
> >  	nfs4_stateid			stateid;
> >  	const struct cred __rcu		*ro_cred;
> > +	struct nfsd_file __rcu		*ro_file;
> >  	const struct cred __rcu		*rw_cred;
> > +	struct nfsd_file __rcu		*rw_file;
> 
> What is the lifetime of a layout_mirror?  Does it live for longer than a
> single IO request?  If so we have a problem as this will pin the
> nfsd_file until the layout is returned.

Ah, yeah lifetime is longer than an IO... so we have the issue of pnfs
(flexfileslayout) holding nfsd_files open in the client; which will
prevent backing filesystem from being unmounted.  I haven't done that
same unmount test (which you reported I fixed for normal NFS) against
pNFS with flexfiles.  Will sort it out.
NeilBrown Aug. 27, 2024, 9:27 p.m. UTC | #3
On Tue, 27 Aug 2024, Mike Snitzer wrote:
> On Mon, Aug 26, 2024 at 11:39:31AM +1000, NeilBrown wrote:
> > On Sat, 24 Aug 2024, Mike Snitzer wrote:
> > > From: Trond Myklebust <trond.myklebust@hammerspace.com>
> > > 
> > > If the DS is local to this client use localio to write the data.
> > > 
> > > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > > ---
> > >  fs/nfs/flexfilelayout/flexfilelayout.c    | 136 +++++++++++++++++++++-
> > >  fs/nfs/flexfilelayout/flexfilelayout.h    |   2 +
> > >  fs/nfs/flexfilelayout/flexfilelayoutdev.c |   6 +
> > >  3 files changed, 140 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
> > > index 01ee52551a63..d91b640f6c05 100644
> > > --- a/fs/nfs/flexfilelayout/flexfilelayout.c
> > > +++ b/fs/nfs/flexfilelayout/flexfilelayout.c
> > > @@ -11,6 +11,7 @@
> > >  #include <linux/nfs_mount.h>
> > >  #include <linux/nfs_page.h>
> > >  #include <linux/module.h>
> > > +#include <linux/file.h>
> > >  #include <linux/sched/mm.h>
> > >  
> > >  #include <linux/sunrpc/metrics.h>
> > > @@ -162,6 +163,72 @@ decode_name(struct xdr_stream *xdr, u32 *id)
> > >  	return 0;
> > >  }
> > >  
> > > +/*
> > > + * A dummy definition to make RCU (and non-LOCALIO compilation) happy.
> > > + * struct nfsd_file should never be dereferenced in this file.
> > > + */
> > > +struct nfsd_file {
> > > +       int undefined__;
> > > +};
> > 
> > I removed this and tried building both with and without LOCALIO enabled
> > and the compiler didn't complain.
> > Could you tell me what to do to see the unhappiness you mention?
> 
> Sorry, I can remove the dummy definition for upstream.  That was
> leftover from the backport I did to 5.15.y stable@ kernel.  Older
> kernels' RCU code dereferences what should just be an opaque pointer
> and (ab)use typeof.  So without the dummy definition compiling against
> 5.15.y fails with:
> 
>   CC [M]  fs/nfs/flexfilelayout/flexfilelayout.o
> In file included from ./include/linux/rbtree.h:24,
>                  from ./include/linux/mm_types.h:10,
>                  from ./include/linux/mmzone.h:21,
>                  from ./include/linux/gfp.h:6,
>                  from ./include/linux/mm.h:10,
>                  from ./include/linux/nfs_fs.h:23,
>                  from fs/nfs/flexfilelayout/flexfilelayout.c:10:
> fs/nfs/flexfilelayout/flexfilelayout.c: In function `ff_local_open_fh´:
> ./include/linux/rcupdate.h:441:9: error: dereferencing pointer to incomplete type `struct nfsd_file´
>   typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
>          ^
> ./include/linux/rcupdate.h:580:2: note: in expansion of macro `__rcu_dereference_check´
>   __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
>   ^~~~~~~~~~~~~~~~~~~~~~~
> ./include/linux/rcupdate.h:648:28: note: in expansion of macro `rcu_dereference_check´
>  #define rcu_dereference(p) rcu_dereference_check(p, 0)
>                             ^~~~~~~~~~~~~~~~~~~~~
> fs/nfs/flexfilelayout/flexfilelayout.c:193:7: note: in expansion of macro `rcu_dereference´
>   nf = rcu_dereference(*pnf);
>        ^~~~~~~~~~~~~~~

Ahhh - good to know.  Thanks!

NeilBrown
diff mbox series

Patch

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index 01ee52551a63..d91b640f6c05 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -11,6 +11,7 @@ 
 #include <linux/nfs_mount.h>
 #include <linux/nfs_page.h>
 #include <linux/module.h>
+#include <linux/file.h>
 #include <linux/sched/mm.h>
 
 #include <linux/sunrpc/metrics.h>
@@ -162,6 +163,72 @@  decode_name(struct xdr_stream *xdr, u32 *id)
 	return 0;
 }
 
+/*
+ * A dummy definition to make RCU (and non-LOCALIO compilation) happy.
+ * struct nfsd_file should never be dereferenced in this file.
+ */
+struct nfsd_file {
+       int undefined__;
+};
+
+#if IS_ENABLED(CONFIG_NFS_LOCALIO)
+
+static struct nfsd_file *
+ff_local_open_fh(struct pnfs_layout_segment *lseg,
+		 u32 ds_idx,
+		 struct nfs_client *clp,
+		 const struct cred *cred,
+		 struct nfs_fh *fh,
+		 fmode_t mode)
+{
+	struct nfs4_ff_layout_mirror *mirror = FF_LAYOUT_COMP(lseg, ds_idx);
+	struct nfsd_file *nf, *new, __rcu **pnf;
+
+	if (!nfs_server_is_local(clp))
+		return NULL;
+	if (mode & FMODE_WRITE) {
+		/*
+		 * Always request read and write access since this corresponds
+		 * to a rw layout.
+		 */
+		mode |= FMODE_READ;
+		pnf = &mirror->rw_file;
+	} else
+		pnf = &mirror->ro_file;
+
+	new = NULL;
+	rcu_read_lock();
+	nf = rcu_dereference(*pnf);
+	if (!nf) {
+		rcu_read_unlock();
+		new = nfs_local_open_fh(clp, cred, fh, mode);
+		if (IS_ERR(new))
+			return NULL;
+		rcu_read_lock();
+		/* try to swap in the pointer */
+		nf = cmpxchg(pnf, NULL, new);
+		if (!nf) {
+			nf = new;
+			new = NULL;
+		}
+	}
+	nf = nfs_to.nfsd_file_get(nf);
+	rcu_read_unlock();
+	if (new)
+		nfs_to.nfsd_file_put(new);
+	return nf;
+}
+
+#else
+static struct nfsd_file *
+ff_local_open_fh(struct pnfs_layout_segment *lseg, u32 ds_idx,
+		 struct nfs_client *clp, const struct cred *cred,
+		 struct nfs_fh *fh, fmode_t mode)
+{
+	return NULL;
+}
+#endif /* IS_ENABLED(CONFIG_NFS_LOCALIO) */
+
 static bool ff_mirror_match_fh(const struct nfs4_ff_layout_mirror *m1,
 		const struct nfs4_ff_layout_mirror *m2)
 {
@@ -237,8 +304,17 @@  static struct nfs4_ff_layout_mirror *ff_layout_alloc_mirror(gfp_t gfp_flags)
 
 static void ff_layout_free_mirror(struct nfs4_ff_layout_mirror *mirror)
 {
-	const struct cred	*cred;
+	struct nfsd_file * __maybe_unused nf;
+	const struct cred *cred;
 
+#if IS_ENABLED(CONFIG_NFS_LOCALIO)
+	nf = rcu_access_pointer(mirror->ro_file);
+	if (nf)
+		nfs_to.nfsd_file_put(nf);
+	nf = rcu_access_pointer(mirror->rw_file);
+	if (nf)
+		nfs_to.nfsd_file_put(nf);
+#endif
 	ff_layout_remove_mirror(mirror);
 	kfree(mirror->fh_versions);
 	cred = rcu_access_pointer(mirror->ro_cred);
@@ -514,6 +590,30 @@  ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh,
 		mirror = ff_layout_add_mirror(lh, fls->mirror_array[i]);
 		if (mirror != fls->mirror_array[i]) {
 			/* swap cred ptrs so free_mirror will clean up old */
+#if IS_ENABLED(CONFIG_NFS_LOCALIO)
+			if (lgr->range.iomode == IOMODE_READ) {
+				const struct cred __rcu *old =
+					xchg(&mirror->ro_cred, cred);
+				rcu_assign_pointer(fls->mirror_array[i]->ro_cred, old);
+				/* drop file if creds changed */
+				if (old != cred) {
+					struct nfsd_file *nf =
+						rcu_dereference_protected(xchg(&mirror->ro_file, NULL), 1);
+					if (nf)
+						nfs_to.nfsd_file_put(nf);
+				}
+			} else {
+				const struct cred __rcu *old =
+					xchg(&mirror->rw_cred, cred);
+				rcu_assign_pointer(fls->mirror_array[i]->rw_cred, old);
+				if (old != cred) {
+					struct nfsd_file *nf =
+						rcu_dereference_protected(xchg(&mirror->rw_file, NULL), 1);
+					if (nf)
+						nfs_to.nfsd_file_put(nf);
+				}
+			}
+#else
 			if (lgr->range.iomode == IOMODE_READ) {
 				cred = xchg(&mirror->ro_cred, cred);
 				rcu_assign_pointer(fls->mirror_array[i]->ro_cred, cred);
@@ -521,6 +621,7 @@  ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh,
 				cred = xchg(&mirror->rw_cred, cred);
 				rcu_assign_pointer(fls->mirror_array[i]->rw_cred, cred);
 			}
+#endif /* IS_ENABLED(CONFIG_NFS_LOCALIO) */
 			ff_layout_free_mirror(fls->mirror_array[i]);
 			fls->mirror_array[i] = mirror;
 		}
@@ -1756,6 +1857,7 @@  ff_layout_read_pagelist(struct nfs_pgio_header *hdr)
 	struct pnfs_layout_segment *lseg = hdr->lseg;
 	struct nfs4_pnfs_ds *ds;
 	struct rpc_clnt *ds_clnt;
+	struct nfsd_file *nf;
 	struct nfs4_ff_layout_mirror *mirror;
 	const struct cred *ds_cred;
 	loff_t offset = hdr->args.offset;
@@ -1802,11 +1904,19 @@  ff_layout_read_pagelist(struct nfs_pgio_header *hdr)
 	hdr->args.offset = offset;
 	hdr->mds_offset = offset;
 
+	/* Start IO accounting for local read */
+	nf = ff_local_open_fh(lseg, idx, ds->ds_clp, ds_cred, fh,
+			      FMODE_READ);
+	if (nf) {
+		hdr->task.tk_start = ktime_get();
+		ff_layout_read_record_layoutstats_start(&hdr->task, hdr);
+	}
+
 	/* Perform an asynchronous read to ds */
 	nfs_initiate_pgio(ds_clnt, hdr, ds_cred, ds->ds_clp->rpc_ops,
 			  vers == 3 ? &ff_layout_read_call_ops_v3 :
 				      &ff_layout_read_call_ops_v4,
-			  0, RPC_TASK_SOFTCONN, NULL);
+			  0, RPC_TASK_SOFTCONN, nf);
 	put_cred(ds_cred);
 	return PNFS_ATTEMPTED;
 
@@ -1826,6 +1936,7 @@  ff_layout_write_pagelist(struct nfs_pgio_header *hdr, int sync)
 	struct pnfs_layout_segment *lseg = hdr->lseg;
 	struct nfs4_pnfs_ds *ds;
 	struct rpc_clnt *ds_clnt;
+	struct nfsd_file *nf;
 	struct nfs4_ff_layout_mirror *mirror;
 	const struct cred *ds_cred;
 	loff_t offset = hdr->args.offset;
@@ -1870,11 +1981,19 @@  ff_layout_write_pagelist(struct nfs_pgio_header *hdr, int sync)
 	 */
 	hdr->args.offset = offset;
 
+	/* Start IO accounting for local write */
+	nf = ff_local_open_fh(lseg, idx, ds->ds_clp, ds_cred, fh,
+				FMODE_READ|FMODE_WRITE);
+	if (nf) {
+		hdr->task.tk_start = ktime_get();
+		ff_layout_write_record_layoutstats_start(&hdr->task, hdr);
+	}
+
 	/* Perform an asynchronous write */
 	nfs_initiate_pgio(ds_clnt, hdr, ds_cred, ds->ds_clp->rpc_ops,
 			  vers == 3 ? &ff_layout_write_call_ops_v3 :
 				      &ff_layout_write_call_ops_v4,
-			  sync, RPC_TASK_SOFTCONN, NULL);
+			  sync, RPC_TASK_SOFTCONN, nf);
 	put_cred(ds_cred);
 	return PNFS_ATTEMPTED;
 
@@ -1908,6 +2027,7 @@  static int ff_layout_initiate_commit(struct nfs_commit_data *data, int how)
 	struct pnfs_layout_segment *lseg = data->lseg;
 	struct nfs4_pnfs_ds *ds;
 	struct rpc_clnt *ds_clnt;
+	struct nfsd_file *nf;
 	struct nfs4_ff_layout_mirror *mirror;
 	const struct cred *ds_cred;
 	u32 idx;
@@ -1946,10 +2066,18 @@  static int ff_layout_initiate_commit(struct nfs_commit_data *data, int how)
 	if (fh)
 		data->args.fh = fh;
 
+	/* Start IO accounting for local commit */
+	nf = ff_local_open_fh(lseg, idx, ds->ds_clp, ds_cred, fh,
+			      FMODE_READ|FMODE_WRITE);
+	if (nf) {
+		data->task.tk_start = ktime_get();
+		ff_layout_commit_record_layoutstats_start(&data->task, data);
+	}
+
 	ret = nfs_initiate_commit(ds_clnt, data, ds->ds_clp->rpc_ops,
 				   vers == 3 ? &ff_layout_commit_call_ops_v3 :
 					       &ff_layout_commit_call_ops_v4,
-				   how, RPC_TASK_SOFTCONN, NULL);
+				   how, RPC_TASK_SOFTCONN, nf);
 	put_cred(ds_cred);
 	return ret;
 out_err:
diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index f84b3fb0dddd..562e7e27a8b5 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -82,7 +82,9 @@  struct nfs4_ff_layout_mirror {
 	struct nfs_fh			*fh_versions;
 	nfs4_stateid			stateid;
 	const struct cred __rcu		*ro_cred;
+	struct nfsd_file __rcu		*ro_file;
 	const struct cred __rcu		*rw_cred;
+	struct nfsd_file __rcu		*rw_file;
 	refcount_t			ref;
 	spinlock_t			lock;
 	unsigned long			flags;
diff --git a/fs/nfs/flexfilelayout/flexfilelayoutdev.c b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
index e028f5a0ef5f..e58bedfb1dcc 100644
--- a/fs/nfs/flexfilelayout/flexfilelayoutdev.c
+++ b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
@@ -395,6 +395,12 @@  nfs4_ff_layout_prepare_ds(struct pnfs_layout_segment *lseg,
 
 	/* connect success, check rsize/wsize limit */
 	if (!status) {
+		/*
+		 * ds_clp is put in destroy_ds().
+		 * keep ds_clp even if DS is local, so that if local IO cannot
+		 * proceed somehow, we can fall back to NFS whenever we want.
+		 */
+		nfs_local_probe(ds->ds_clp);
 		max_payload =
 			nfs_block_size(rpc_max_payload(ds->ds_clp->cl_rpcclient),
 				       NULL);