[PATCH v2 09/19] sunrpc: Allocate one more page per svc_rqst

Chuck Lever
2017-06-16T15:21:34Z

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)

Let's remove the "-1" to get 260 pages maximum.

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-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
---
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 9463102..682cd7c 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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