[RFC PATCH 6/6] sunrpc: Allocate svc request pages from large folios

[J Louis Kaplan <Louis.Kaplan@arm.com>]

Bulk allocation of base pages does not guarantee physical
contiguity, limiting opportunities to coalesce service buffers.

Allocate large folios opportunistically and populate the service
page arrays with their constituent pages. Cap folio size at
64 KiB and allocation order at PAGE_ALLOC_COSTLY_ORDER, falling
back through smaller orders to bulk base-page allocation.

Retain one reference per populated page-array slot so existing
page-based ownership and release paths remain valid.

Signed-off-by: J Louis Kaplan <Louis.Kaplan@arm.com>
Assisted-by: LLM
---
 net/sunrpc/svc_xprt.c | 44 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 9858dfcb846a8..90ec75a848da9 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -19,6 +19,7 @@
 #include <linux/sunrpc/bc_xprt.h>
 #include <linux/module.h>
 #include <linux/netdevice.h>
+#include <linux/sizes.h>
 #include <trace/events/sunrpc.h>
 
 #define RPCDBG_FACILITY	RPCDBG_SVCXPRT
@@ -708,20 +709,53 @@ static void svc_check_conn_limits(struct svc_serv *serv)
 static bool svc_fill_pages(struct svc_rqst *rqstp, struct page **pages,
 			   unsigned long npages)
 {
-	unsigned long filled, ret;
+	unsigned int order = min_t(unsigned int, PAGE_ALLOC_COSTLY_ORDER,
+				   get_order(SZ_64K));
+	unsigned long filled = 0;
 
-	for (filled = 0; filled < npages; filled = ret) {
-		ret = alloc_pages_bulk(GFP_KERNEL, npages, pages);
-		if (ret > filled)
+	/*
+	 * Prefer folios no larger than 64 KiB or the page allocator's
+	 * costly-order threshold. After a failure, use smaller orders for
+	 * the rest of this fill; order zero is handled by the bulk allocator.
+	 * All callers provide a range containing only NULL entries.
+	 */
+	while (filled < npages) {
+		struct folio *folio;
+		unsigned int nr_pages;
+		unsigned long ret;
+
+		while (order && (1UL << order) > npages - filled)
+			order--;
+
+		if (order) {
+			folio = folio_alloc(GFP_NOWAIT, order);
+			if (!folio) {
+				order--;
+				continue;
+			}
+
+			nr_pages = folio_nr_pages(folio);
+			folio_ref_add(folio, nr_pages - 1);
+			for (unsigned int i = 0; i < nr_pages; i++)
+				pages[filled + i] = folio_page(folio, i);
+			filled += nr_pages;
+			continue;
+		}
+
+		ret = alloc_pages_bulk(GFP_KERNEL, npages - filled,
+				       pages + filled);
+		if (ret) {
+			filled += ret;
 			/* Made progress, don't sleep yet */
 			continue;
+		}
 
 		set_current_state(TASK_IDLE);
 		if (svc_thread_should_stop(rqstp)) {
 			set_current_state(TASK_RUNNING);
 			return false;
 		}
-		trace_svc_alloc_arg_err(npages, ret);
+		trace_svc_alloc_arg_err(npages, filled);
 		memalloc_retry_wait(GFP_KERNEL);
 	}
 	return true;
-- 
2.43.0