[PATCH 5/7] SUNRPC: Refresh rq_pages using a bulk page allocator

[Mel Gorman]

From: Chuck Lever <chuck.le...@oracle.com>

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.le...@oracle.com>
Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
---
 net/sunrpc/svc_xprt.c | 43 +++++++++++++++++++++++++++++++------------
 1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index cfa7e4776d0e..38a8d6283801 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -642,11 +642,12 @@ 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;
        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",
@@ -654,19 +655,28 @@ 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, needed, &list);
+               for (i = 0; i < pages; i++) {
+                       if (!rqstp->rq_pages[i]) {
+                               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() */
 
@@ -681,6 +691,15 @@ 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:
+       set_current_state(TASK_INTERRUPTIBLE);
+       if (signalled() || kthread_should_stop()) {
+               set_current_state(TASK_RUNNING);
+               return -EINTR;
+       }
+       schedule_timeout(msecs_to_jiffies(500));
+       goto retry;
 }
 
 static bool
-- 
2.26.2