SUNRPC: Track consumed rq_pages entries

The rq_pages array holds pages allocated for incoming RPC requests.
Two transport receive paths NULL entries in rq_pages to prevent
svc_rqst_release_pages() from freeing pages that the transport has
taken ownership of:

- svc_tcp_save_pages() moves partial request data pages to
  svsk->sk_pages during multi-fragment TCP reassembly.

- svc_rdma_clear_rqst_pages() moves request data pages to
  head->rc_pages because they are targets of active RDMA Read WRs.

A new rq_pages_nfree field in struct svc_rqst records how many
entries were NULLed. svc_alloc_arg() uses it to refill only those
entries rather than scanning the full rq_pages array. In steady
state, the transport NULLs a handful of entries per RPC, so the
allocator visits only those entries instead of the full ~259 slots
(for 1MB messages).

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

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 3b1a98ab5cba..c3399cf64524 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -143,6 +143,15 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
  * server thread needs to allocate more to replace those used in
  * sending.
  *
+ * rq_pages request page contract:
+ *
+ * Transport receive paths that move request data pages out of
+ * rq_pages -- TCP multi-fragment reassembly (svc_tcp_save_pages)
+ * and RDMA Read I/O (svc_rdma_clear_rqst_pages) -- NULL those
+ * entries to prevent svc_rqst_release_pages() from freeing pages
+ * still in transport use, and set rq_pages_nfree to the count.
+ * svc_alloc_arg() refills only that many rq_pages entries.
+ *
  * xdr_buf holds responses; the structure fits NFS read responses
  * (header, data pages, optional tail) and enables sharing of
  * client-side routines.
@@ -204,6 +213,7 @@ struct svc_rqst {
 	struct folio		*rq_scratch_folio;
 	struct xdr_buf		rq_res;
 	unsigned long		rq_maxpages;	/* entries per page array */
+	unsigned long		rq_pages_nfree;	/* rq_pages entries NULLed by transport */
 	struct page *		*rq_pages;	/* Call buffer pages */
 	struct page *		*rq_respages;	/* Reply buffer pages */
 	struct page *		*rq_next_page; /* next reply page to use */