On 9/9/25 7:33 PM, Mike Snitzer wrote:
> nfsd_iter_read() might need two extra pages when a READ payload is not
> DIO-aligned -- but nfsd_iter_read() and nfsd_splice_actor() are
> mutually exclusive (so reuse page reserved for nfsd_splice_actor).
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> include/linux/sunrpc/svc.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index e64ab444e0a7f..190c2667500e2 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -163,10 +163,13 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
> * pages, one for the request, and one for the reply.
> * nfsd_splice_actor() might need an extra page when a READ payload
> * is not page-aligned.
> + * nfsd_iter_read() might need two extra pages when a READ payload
> + * is not DIO-aligned -- but nfsd_iter_read() and nfsd_splice_actor()
> + * are mutually exclusive (so reuse page reserved for nfsd_splice_actor).
> */
> static inline unsigned long svc_serv_maxpages(const struct svc_serv *serv)
> {
> - return DIV_ROUND_UP(serv->sv_max_mesg, PAGE_SIZE) + 2 + 1;
> + return DIV_ROUND_UP(serv->sv_max_mesg, PAGE_SIZE) + 2 + 1 + 1;
> }
>
> /*
I'm not convinced an additional page is necessary. The most the direct
I/O range can be is rsize + 1 page, AFAICT, and that seems to be covered
already.
If we want NFSD to support file systems / block devices with alignment
requirements large than a page, then perhaps additional buffer space
will be needed... or NFSD can return a short read.
--
Chuck Lever
