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Subject: [PATCH RFC] SUNRPC: Refresh rq_pages using a bulk page allocator
From:   Chuck Lever <chuck.lever@oracle.com>
To:     mgorman@techsingularity.net
Cc:     linux-nfs@vger.kernel.org, linux-mm@kvack.org, kuba@kernel.org
Date:   Mon, 15 Feb 2021 11:06:07 -0500
Message-ID: <161340498400.7780.962495219428962117.stgit@klimt.1015granger.net>
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Precedence: bulk

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

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/svc_xprt.c |   44 ++++++++++++++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 12 deletions(-)

Note: I haven't actually tried the "min_t(needed, 13)" bit yet.


diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 4730bac409b5..8f398179d818 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -647,11 +647,11 @@ 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;
 	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",
@@ -659,19 +659,33 @@ 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++;
+	if (needed) {
+		LIST_HEAD(list);
+
+retry:
+		alloc_pages_bulk(GFP_KERNEL, 0,
+				 /* to test the retry logic: */
+				 min_t(unsigned long, needed, 13),
+				 &list);
+		for (i = 0; i < pages; i++) {
+			if (!rqstp->rq_pages[i]) {
+				struct page *page;
+
+				page = list_first_entry_or_null(&list,
+								struct page,
+								lru);
+				if (unlikely(!page))
+					goto empty_list;
+				list_del(&page->lru);
+				rqstp->rq_pages[i] = page;
+				needed--;
 			}
-			rqstp->rq_pages[i] = p;
 		}
+	}
 	rqstp->rq_page_end = &rqstp->rq_pages[pages];
 	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
 
@@ -686,6 +700,12 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
 	arg->len = (pages-1)*PAGE_SIZE;
 	arg->tail[0].iov_len = 0;
 	return 0;
+
+empty_list:
+	if (signalled() || kthread_should_stop())
+		return -EINTR;
+	cond_resched();
+	goto retry;
 }
 
 static bool