netdev - [PATCH] SUNRPC: Refresh rq_pages using a bulk page allocator

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Date:   Fri, 12 Mar 2021 16:57:11 -0500
From:   Chuck Lever <chuck.lever@...cle.com>
To:     mgorman@...hsingularity.net
Cc:     akpm@...ux-foundation.org, brouer@...hat.com, hch@...radead.org,
        alexander.duyck@...il.com, willy@...radead.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, linux-nfs@...r.kernel.org
Subject: [PATCH] SUNRPC: Refresh rq_pages using a bulk page allocator

Reduce the rate at which nfsd threads hammer on the page allocator.
This improves throughput scalability by enabling the threads to run
more independently of each other.

Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
---
Hi Mel-

This patch replaces patch 5/7 in v4 of your alloc_pages_bulk()
series. It implements code clean-ups suggested by Alexander Duyck.
It builds and has seen some light testing.


 net/sunrpc/svc_xprt.c |   39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 4d58424db009..791ea24159b1 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -661,11 +661,13 @@ static void svc_check_conn_limits(struct svc_serv *serv)
 static int svc_alloc_arg(struct svc_rqst *rqstp)
 {
 	struct svc_serv *serv = rqstp->rq_server;
+	unsigned long needed;
 	struct xdr_buf *arg;
+	struct page *page;
+	LIST_HEAD(list);
 	int pages;
 	int i;
 
-	/* now allocate needed pages.  If we get a failure, sleep briefly */
 	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",
@@ -673,19 +675,32 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
 		/* use as many pages as possible */
 		pages = RPCSVC_MAXPAGES;
 	}
-	for (i = 0; i < pages ; i++)
-		while (rqstp->rq_pages[i] == NULL) {
-			struct page *p = alloc_page(GFP_KERNEL);
-			if (!p) {
-				set_current_state(TASK_INTERRUPTIBLE);
-				if (signalled() || kthread_should_stop()) {
-					set_current_state(TASK_RUNNING);
-					return -EINTR;
-				}
-				schedule_timeout(msecs_to_jiffies(500));
+
+	for (needed = 0, i = 0; i < pages ; i++) {
+		if (!rqstp->rq_pages[i])
+			needed++;
+	}
+	i = 0;
+	while (needed) {
+		needed -= alloc_pages_bulk(GFP_KERNEL, 0, needed, &list);
+		for (; i < pages; i++) {
+			if (rqstp->rq_pages[i])
+				continue;
+			page = list_first_entry_or_null(&list, struct page, lru);
+			if (likely(page)) {
+				list_del(&page->lru);
+				rqstp->rq_pages[i] = page;
+				continue;
 			}
-			rqstp->rq_pages[i] = p;
+			set_current_state(TASK_INTERRUPTIBLE);
+			if (signalled() || kthread_should_stop()) {
+				set_current_state(TASK_RUNNING);
+				return -EINTR;
+			}
+			schedule_timeout(msecs_to_jiffies(500));
+			break;
 		}
+	}
 	rqstp->rq_page_end = &rqstp->rq_pages[pages];
 	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */