[PATCH v3 04/11] sunrpc: Replace the rq_vec 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 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 68f7d0094b06..ea0773bb7c05 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1096,7 +1096,7 @@ __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