Re: [PATCH 2/2] SUNRPC: Refresh rq_pages using a bulk page allocator

[Chuck Lever III <chuck.lever@oracle.com>]

> On Mar 23, 2021, at 3:56 PM, Mel Gorman <mgorman@techsingularity.net> wrote:
> 
> On Tue, Mar 23, 2021 at 11:10:05AM -0400, Chuck Lever wrote:
>> 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@oracle.com>
> 
> I've picked up the series and merged the leader with the first patch
> because I think the array vs list data is interesting but I did change
> the patch.
> 
>> +	for (;;) {
>> +		filled = alloc_pages_bulk_array(GFP_KERNEL, pages,
>> +						rqstp->rq_pages);
>> +		/* We assume that if the next array element is populated,
>> +		 * all the following elements are as well, thus we're done. */
>> +		if (filled == pages || rqstp->rq_pages[filled])
>> +			break;
>> +
> 
> I altered this check because the implementation now returns a useful
> index. I know I had concerns about this but while the implementation
> cost is higher, the caller needs less knowledge of alloc_bulk_pages
> implementation. It might be unfortunate if new users all had to have
> their own optimisations around hole management so lets keep it simpler
> to start with.

Agreed! Your version below looks like what I'm testing now --
the "rq_pages[filled]" test and the comment have been removed.


> Version current in my tree is below but also available in 
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git mm-bulk-rebase-v6r5
> 
> ---8<---
> SUNRPC: Refresh rq_pages using a bulk page allocator
> 
> From: Chuck Lever <chuck.lever@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.
> 
> [mgorman: Update interpretation of alloc_pages_bulk return value]
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
> net/sunrpc/svc_xprt.c | 31 +++++++++++++++----------------
> 1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 609bda97d4ae..0c27c3291ca1 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -643,30 +643,29 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
> {
> 	struct svc_serv *serv = rqstp->rq_server;
> 	struct xdr_buf *arg = &rqstp->rq_arg;
> -	int pages;
> -	int i;
> +	unsigned long pages, filled;
> 
> -	/* 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",
> +		pr_warn_once("svc: warning: pages=%lu > RPCSVC_MAXPAGES=%lu\n",
> 			     pages, RPCSVC_MAXPAGES);
> 		/* 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));
> -			}
> -			rqstp->rq_pages[i] = p;
> +
> +	for (;;) {
> +		filled = alloc_pages_bulk_array(GFP_KERNEL, pages,
> +						rqstp->rq_pages);
> +		if (filled == pages)
> +			break;
> +
> +		set_current_state(TASK_INTERRUPTIBLE);
> +		if (signalled() || kthread_should_stop()) {
> +			set_current_state(TASK_RUNNING);
> +			return -EINTR;
> 		}
> +		schedule_timeout(msecs_to_jiffies(500));
> +	}
> 	rqstp->rq_page_end = &rqstp->rq_pages[pages];
> 	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
> 

--
Chuck Lever