Commit 8c6ae498 authored Jun 30, 2017 by Chuck Lever Committed by J. Bruce Fields Jul 12, 2017

sunrpc: Allocate up to RPCSVC_MAXPAGES per svc_rqst



svcrdma needs 259 pages allocated to receive 1MB NFSv4.0 WRITE 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

But RPCSVC_MAXPAGES is already 259 (on x86_64). The problem is that
svc_alloc_arg never allocates that many pages. To address this:

1. The final element of rq_pages always points to NULL. To
   accommodate up to 259 pages in rq_pages, add an extra element
   to rq_pages for the array termination sentinel.

2. Adjust the calculation of "pages" to match how RPCSVC_MAXPAGES
   is calculated, so it can go up to 259. Bruce noted that the
   calculation assumes sv_max_mesg is a multiple of PAGE_SIZE,
   which might not always be true. I didn't change this assumption.

3. Change the loop boundaries to allow 259 pages to be allocated.

Additional clean-up: WARN_ON_ONCE adds an extra conditional branch,
which is basically never taken. And there's no need to dump the
stack here because svc_alloc_arg has only one caller.

Keeping that NULL "array termination sentinel"; there doesn't appear to
be any code that depends on it, only code in nfsd_splice_actor() which
needs the 259th element to be initialized to *something*.  So it's
possible we could just keep the array at 259 elements and drop that
final NULL, but we're being conservative for now.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

parent 2d6491a5

include/linux/sunrpc/svc.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -246,7 +246,7 @@ struct svc_rqst {
		size_t rq_xprt_hlen; /* xprt header len */
		struct xdr_buf rq_arg;
		struct xdr_buf rq_res;
		struct page * rq_pages[RPCSVC_MAXPAGES];
		struct page *rq_pages[RPCSVC_MAXPAGES + 1];
		struct page * rq_respages; / points into rq_pages */
		struct page * rq_next_page; / next reply page to use */
		struct page * rq_page_end; / one past the last page */

net/sunrpc/svc_xprt.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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;
		pages = RPCSVC_MAXPAGES;
		}
		for (i = 0; i < pages ; i++)
		while (rqstp->rq_pages[i] == NULL) {
		struct page *p = alloc_page(GFP_KERNEL);