Commit d7f3efd9 authored Feb 26, 2026 by Chuck Lever

SUNRPC: Optimize rq_respages allocation in svc_alloc_arg



svc_alloc_arg() invokes alloc_pages_bulk() with the full rq_maxpages
count (~259 for 1MB messages) for the rq_respages array, causing a
full-array scan despite most slots holding valid pages.

svc_rqst_release_pages() NULLs only the range

  [rq_respages, rq_next_page)

after each RPC, so only that range contains NULL entries. Limit the
rq_respages fill in svc_alloc_arg() to that range instead of
scanning the full array.

svc_init_buffer() initializes rq_next_page to span the entire
rq_respages array, so the first svc_alloc_arg() call fills all
slots.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

parent 7ed75042

include/linux/sunrpc/svc.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -152,6 +152,10 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
		* still in transport use, and set rq_pages_nfree to the count.
		* svc_alloc_arg() refills only that many rq_pages entries.
		*
		* For rq_respages, svc_rqst_release_pages() NULLs entries in
		* [rq_respages, rq_next_page) after each RPC. svc_alloc_arg()
		* refills only that range.
		*
		* xdr_buf holds responses; the structure fits NFS read responses
		* (header, data pages, optional tail) and enables sharing of
		* client-side routines.

net/sunrpc/svc.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -656,6 +656,7 @@ svc_init_buffer(struct svc_rqst rqstp, const struct svc_serv serv, int node)
		}

		rqstp->rq_pages_nfree = rqstp->rq_maxpages;
		rqstp->rq_next_page = rqstp->rq_respages + rqstp->rq_maxpages;
		return true;
		}

net/sunrpc/svc_xprt.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -686,8 +686,14 @@ static bool svc_alloc_arg(struct svc_rqst *rqstp)
		rqstp->rq_pages_nfree = 0;
		}

		if (!svc_fill_pages(rqstp, rqstp->rq_respages, pages))
		if (WARN_ON_ONCE(rqstp->rq_next_page < rqstp->rq_respages))
		return false;
		nfree = rqstp->rq_next_page - rqstp->rq_respages;
		if (nfree) {
		if (!svc_fill_pages(rqstp, rqstp->rq_respages, nfree))
		return false;
		}

		rqstp->rq_next_page = rqstp->rq_respages;
		rqstp->rq_page_end = &rqstp->rq_respages[pages];
		/* svc_rqst_replace_page() dereferences *rq_next_page even