[RFC PATCH 1/2] sunrpc: Replace the rq_bvec array with dynamically-allocated memory

[cel@kernel.org]

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

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

On a system with 8-byte pointers and 4KB pages, pahole reports that
the rq_bvec[] array is 4144 bytes. Replacing it with a single
pointer reduces the size of struct svc_rqst to about 7500 bytes.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/linux/sunrpc/svc.h | 2 +-
 net/sunrpc/svc.c           | 6 ++++++
 net/sunrpc/svcsock.c       | 7 +++----
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 74658cca0f38..225c385085c3 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -195,7 +195,7 @@ struct svc_rqst {
 
 	struct folio_batch	rq_fbatch;
 	struct kvec		rq_vec[RPCSVC_MAXPAGES]; /* generally useful.. */
-	struct bio_vec		rq_bvec[RPCSVC_MAXPAGES];
+	struct bio_vec		*rq_bvec;
 
 	__be32			rq_xid;		/* transmission id */
 	u32			rq_prog;	/* program number */
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index e7f9c295d13c..db29819716b8 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -673,6 +673,7 @@ static void
 svc_rqst_free(struct svc_rqst *rqstp)
 {
 	folio_batch_release(&rqstp->rq_fbatch);
+	kfree(rqstp->rq_bvec);
 	svc_release_buffer(rqstp);
 	if (rqstp->rq_scratch_page)
 		put_page(rqstp->rq_scratch_page);
@@ -711,6 +712,11 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
 	if (!svc_init_buffer(rqstp, serv->sv_max_mesg, node))
 		goto out_enomem;
 
+	rqstp->rq_bvec = kcalloc_node(RPCSVC_MAXPAGES, sizeof(struct bio_vec),
+				      GFP_KERNEL, node);
+	if (!rqstp->rq_bvec)
+		goto out_enomem;
+
 	rqstp->rq_err = -EAGAIN; /* No error yet */
 
 	serv->sv_nrthreads += 1;
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 72e5a01df3d3..671640933f18 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -713,8 +713,7 @@ static int svc_udp_sendto(struct svc_rqst *rqstp)
 	if (svc_xprt_is_dead(xprt))
 		goto out_notconn;
 
-	count = xdr_buf_to_bvec(rqstp->rq_bvec,
-				ARRAY_SIZE(rqstp->rq_bvec), xdr);
+	count = xdr_buf_to_bvec(rqstp->rq_bvec, RPCSVC_MAXPAGES, xdr);
 
 	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,
 		      count, rqstp->rq_res.len);
@@ -1219,8 +1218,8 @@ static int svc_tcp_sendmsg(struct svc_sock *svsk, struct svc_rqst *rqstp,
 	memcpy(buf, &marker, sizeof(marker));
 	bvec_set_virt(rqstp->rq_bvec, buf, sizeof(marker));
 
-	count = xdr_buf_to_bvec(rqstp->rq_bvec + 1,
-				ARRAY_SIZE(rqstp->rq_bvec) - 1, &rqstp->rq_res);
+	count = xdr_buf_to_bvec(rqstp->rq_bvec + 1, RPCSVC_MAXPAGES,
+				&rqstp->rq_res);
 
 	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec,
 		      1 + count, sizeof(marker) + rqstp->rq_res.len);
-- 
2.49.0