SUNRPC: Add svc_rqst_page_release() helper

svc_rqst_replace_page() releases displaced pages through a
per-rqst folio batch, but exposes the add-or-flush sequence
directly. svc_tcp_restore_pages() releases displaced pages
individually with put_page().

Introduce svc_rqst_page_release() to encapsulate the
batched release mechanism. Convert svc_rqst_replace_page()
and svc_tcp_restore_pages() to use it. The latter now
benefits from the same batched release that
svc_rqst_replace_page() already uses.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: chucklever

include/linux/sunrpc/svc.h

@@ -498,6 +498,21 @@ int		   svc_generic_rpcbind_set(struct net *net,
 
 #define	RPC_MAX_ADDRBUFLEN	(63U)
 
+/**
+ * svc_rqst_page_release - release a page associated with an RPC transaction
+ * @rqstp: RPC transaction context
+ * @page: page to release
+ *
+ * Released pages are batched and freed together, reducing
+ * allocator pressure under heavy RPC workloads.
+ */
+static inline void svc_rqst_page_release(struct svc_rqst *rqstp,
+					 struct page *page)
+{
+	if (!folio_batch_add(&rqstp->rq_fbatch, page_folio(page)))
+		__folio_batch_release(&rqstp->rq_fbatch);
+}
+
 /*
  * When we want to reduce the size of the reserved space in the response
  * buffer, we need to take into account the size of any checksum data that

net/sunrpc/svc.c

@@ -976,11 +976,8 @@ bool svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
 		return false;
 	}
 
-	if (*rqstp->rq_next_page) {
-		if (!folio_batch_add(&rqstp->rq_fbatch,
-				page_folio(*rqstp->rq_next_page)))
-			__folio_batch_release(&rqstp->rq_fbatch);
-	}
+	if (*rqstp->rq_next_page)
+		svc_rqst_page_release(rqstp, *rqstp->rq_next_page);
 
 	get_page(page);
 	*(rqstp->rq_next_page++) = page;

net/sunrpc/svcsock.c

@@ -988,7 +988,7 @@ static size_t svc_tcp_restore_pages(struct svc_sock *svsk,
 	npages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	for (i = 0; i < npages; i++) {
 		if (rqstp->rq_pages[i] != NULL)
-			put_page(rqstp->rq_pages[i]);
+			svc_rqst_page_release(rqstp, rqstp->rq_pages[i]);
 		BUG_ON(svsk->sk_pages[i] == NULL);
 		rqstp->rq_pages[i] = svsk->sk_pages[i];
 		svsk->sk_pages[i] = NULL;