[PATCH v4 05/14] sunrpc: Replace the rq_vec array with dynamically-allocated memory

cel
2025-04-28T19:37:11Z

From: Chuck Lever <chuck.lever@oracle.com>

As a step towards making NFSD's maximum rsize and wsize variable at
run-time, replace the fixed-size rq_vec[] array in struct svc_rqst
with a chunk of dynamically-allocated memory.

The rq_vec array is sized assuming request processing will need at
most one kvec per page in a maximum-sized RPC message.

On a system with 8-byte pointers and 4KB pages, pahole reports that
the rq_vec[] array is 4144 bytes. This patch replaces that array
with a single 8-byte pointer field.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
fs/nfsd/vfs.c | 2 +-
include/linux/sunrpc/svc.h | 2 +-
net/sunrpc/svc.c | 8 +++++++-
3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 9abdc4b75813..4eaac3aa7e15 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1094,7 +1094,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
++v;
base = 0;
}
- WARN_ON_ONCE(v > ARRAY_SIZE(rqstp->rq_vec));
+ WARN_ON_ONCE(v > rqstp->rq_maxpages);

trace_nfsd_read_vector(rqstp, fhp, offset, *count);
iov_iter_kvec(&iter, ITER_DEST, rqstp->rq_vec, v, *count);
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index ea3a33eec29b..f663d58abd7a 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -212,7 +212,7 @@ struct svc_rqst {
struct page * *rq_page_end; /* one past the last page */

struct folio_batch rq_fbatch;
- struct kvec rq_vec[RPCSVC_MAXPAGES]; /* generally useful.. */
+ struct kvec *rq_vec;
struct bio_vec rq_bvec[RPCSVC_MAXPAGES];

__be32 rq_xid; /* transmission id */
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 682e11c9be36..5808d4b97547 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -675,6 +675,7 @@ static void
svc_rqst_free(struct svc_rqst *rqstp)
{
folio_batch_release(&rqstp->rq_fbatch);
+ kfree(rqstp->rq_vec);
svc_release_buffer(rqstp);
if (rqstp->rq_scratch_page)
put_page(rqstp->rq_scratch_page);
@@ -713,6 +714,11 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
if (!svc_init_buffer(rqstp, serv, node))
goto out_enomem;

+ rqstp->rq_vec = kcalloc_node(rqstp->rq_maxpages, sizeof(struct kvec),
+ GFP_KERNEL, node);
+ if (!rqstp->rq_vec)
+ goto out_enomem;
+
rqstp->rq_err = -EAGAIN; /* No error yet */

serv->sv_nrthreads += 1;
@@ -1750,7 +1756,7 @@ unsigned int svc_fill_write_vector(struct svc_rqst *rqstp,
++pages;
}

- WARN_ON_ONCE(i > ARRAY_SIZE(rqstp->rq_vec));
+ WARN_ON_ONCE(i > rqstp->rq_maxpages);
return i;
}
EXPORT_SYMBOL_GPL(svc_fill_write_vector);
--
2.49.0