On 4/21/25 8:22 AM, Jeff Layton wrote:
> 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?
11K plus, on my test system.
> 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.
Well it's a running total. Each patch in this part of the series reduces
the size of struct svc_rqst.
But I can update the descriptions. What math were you attempting to do?
>> 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);
>
--
Chuck Lever
