I'm confused by this one:
On Fri, Jun 23, 2017 at 05:18:16PM -0400, Chuck Lever wrote:
> svcrdma needs 259 pages for 1MB NFSv4.0 READ requests:
>
> - 1 page for the transport header and head iovec
> - 256 pages for the data payload
> - 1 page for the trailing GETATTR request (since NFSD XDR decoding
> does not look for a tail iovec, the GETATTR is stuck at the end
> of the rqstp->rq_arg.pages list)
> - 1 page for building the reply xdr_buf
>
> Note that RPCSVC_MAXPAGES is defined as:
>
> ((RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE + 2 + 1)
>
> I don't understand why the "+PAGE_SIZE-1" is in there, because
> division will always round the result down to
>
> (RPCSVC_MAXPAYLOAD / PAGE_SIZE + 2 + 1)
I think you're assuming that RPCSVC_MAXPAYLOAD is a multiple of
PAGE_SIZE. Maybe that's true in all cases (I haven't checked), but it
seems harmless to handle the case where it's not.
> Let's remove the "-1" to get 260 pages maximum.
Why? (I'm not necessarily opposed, I just missed the explanation.)
--b.
> Then svc_alloc_args() needs to ask for pages according to this
> same formula, otherwise it will never allocate enough.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> include/linux/sunrpc/svc.h | 3 +--
> net/sunrpc/svc_xprt.c | 8 +++++---
> 2 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 11cef5a..35c274f 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -176,8 +176,7 @@ static inline void svc_get(struct svc_serv *serv)
> * We using ->sendfile to return read data, we might need one extra page
> * if the request is not page-aligned. So add another '1'.
> */
> -#define RPCSVC_MAXPAGES ((RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE \
> - + 2 + 1)
> +#define RPCSVC_MAXPAGES ((RPCSVC_MAXPAYLOAD + PAGE_SIZE) / PAGE_SIZE + 2 + 1)
>
> static inline u32 svc_getnl(struct kvec *iov)
> {
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 7bfe1fb..9bd484d 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -659,11 +659,13 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
> int i;
>
> /* now allocate needed pages. If we get a failure, sleep briefly */
> - pages = (serv->sv_max_mesg + PAGE_SIZE) / PAGE_SIZE;
> - WARN_ON_ONCE(pages >= RPCSVC_MAXPAGES);
> - if (pages >= RPCSVC_MAXPAGES)
> + pages = (serv->sv_max_mesg + (2 * PAGE_SIZE)) >> PAGE_SHIFT;
> + if (pages >= RPCSVC_MAXPAGES) {
> + pr_warn_once("svc: warning: pages=%u >= RPCSVC_MAXPAGES=%lu\n",
> + pages, RPCSVC_MAXPAGES);
> /* use as many pages as possible */
> pages = RPCSVC_MAXPAGES - 1;
> + }
> for (i = 0; i < pages ; i++)
> while (rqstp->rq_pages[i] == NULL) {
> struct page *p = alloc_page(GFP_KERNEL);
--
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