On Sat, 2025-04-19 at 13:28 -0400, cel@xxxxxxxxxx wrote:
> From: Chuck Lever <chuck.lever@xxxxxxxxxx>
>
> 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. Replacing it with a single
> pointer reduces the size of struct svc_rqst to about 5400 bytes.
nit: so I guess the current struct is ~9k or so? If you're going to
post numbers here, they should probably refer to the same thing.
I'm lazy -- don't make me do math.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4proc.c | 1 -
> fs/nfsd/vfs.c | 2 +-
> include/linux/sunrpc/svc.h | 2 +-
> net/sunrpc/svc.c | 8 +++++++-
> 4 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index b397246dae7b..d1be58b557d1 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1228,7 +1228,6 @@ 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));
>
> 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..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 96ac12dbb04d..72d016772711 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -207,7 +207,7 @@ 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);
--
Jeff Layton <jlayton@xxxxxxxxxx>
