linux-kernel - Re: [PATCH 3/5] SUNRPC: Refresh rq_pages using a bulk page allocator

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Date:   Thu, 11 Mar 2021 14:23:53 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Net <netdev@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH 3/5] SUNRPC: Refresh rq_pages using a bulk page allocator



> On Mar 11, 2021, at 6:49 AM, Mel Gorman <mgorman@...hsingularity.net> wrote:
> 
> From: Chuck Lever <chuck.lever@...cle.com>
> 
> Reduce the rate at which nfsd threads hammer on the page allocator.
> This improve throughput scalability by enabling the threads to run
> more independently of each other.

Mel, if you should repost this series: ^improve^improves


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

--
Chuck Lever