[RFC PATCH 2/2] 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,
replace the fixed-size rq_vec[] 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_vec[] array is 4144 bytes. Replacing it with a single
pointer reduces the size of struct svc_rqst to about 3300 bytes.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4proc.c         | 2 +-
 fs/nfsd/vfs.c              | 2 +-
 include/linux/sunrpc/svc.h | 2 +-
 net/sunrpc/svc.c           | 8 +++++++-
 4 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index b397246dae7b..79ee58202396 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1228,7 +1228,7 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	write->wr_how_written = write->wr_stable_how;
 
 	nvecs = svc_fill_write_vector(rqstp, &write->wr_payload);
-	WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec));
+	/* WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec)); */
 
 	status = nfsd_vfs_write(rqstp, &cstate->current_fh, nf,
 				write->wr_offset, rqstp->rq_vec, nvecs, &cnt,
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 9abdc4b75813..ae0901d6db1a 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 > RPCSVC_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 225c385085c3..13b6d0753bc0 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -194,7 +194,7 @@ 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;
 
 	__be32			rq_xid;		/* transmission id */
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index db29819716b8..8d28aeb74e1b 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -674,6 +674,7 @@ svc_rqst_free(struct svc_rqst *rqstp)
 {
 	folio_batch_release(&rqstp->rq_fbatch);
 	kfree(rqstp->rq_bvec);
+	kfree(rqstp->rq_vec);
 	svc_release_buffer(rqstp);
 	if (rqstp->rq_scratch_page)
 		put_page(rqstp->rq_scratch_page);
@@ -712,6 +713,11 @@ 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_vec = kcalloc_node(RPCSVC_MAXPAGES, sizeof(struct kvec),
+				      GFP_KERNEL, node);
+	if (!rqstp->rq_vec)
+		goto out_enomem;
+
 	rqstp->rq_bvec = kcalloc_node(RPCSVC_MAXPAGES, sizeof(struct bio_vec),
 				      GFP_KERNEL, node);
 	if (!rqstp->rq_bvec)
@@ -1754,7 +1760,7 @@ unsigned int svc_fill_write_vector(struct svc_rqst *rqstp,
 		++pages;
 	}
 
-	WARN_ON_ONCE(i > ARRAY_SIZE(rqstp->rq_vec));
+	WARN_ON_ONCE(i > RPCSVC_MAXPAGES);
 	return i;
 }
 EXPORT_SYMBOL_GPL(svc_fill_write_vector);
-- 
2.49.0