Re: [PATCH 2/3] mm/page_alloc: Add a bulk page allocator

On Tue, Mar 23, 2021 at 05:00:08PM +0100, Jesper Dangaard Brouer wrote:

quoted

+	/*
+	 * If there are no allowed local zones that meets the watermarks then
+	 * try to allocate a single page and reclaim if necessary.
+	 */
+	if (!zone)
+		goto failed;
+
+	/* Attempt the batch allocation */
+	local_irq_save(flags);
+	pcp = &this_cpu_ptr(zone->pageset)->pcp;
+	pcp_list = &pcp->lists[ac.migratetype];
+
+	while (allocated < nr_pages) {
+		page = __rmqueue_pcplist(zone, ac.migratetype, alloc_flags,
+								pcp, pcp_list);

The function __rmqueue_pcplist() is now used two places, this cause the
compiler to uninline the static function.

This was expected. It was not something I was particularly happy with
but avoiding it was problematic without major refactoring.

My tests show you should inline __rmqueue_pcplist().  See patch I'm
using below signature, which also have some benchmark notes. (Please
squash it into your patch and drop these notes).

The cycle savings per element is very marginal at just 4 cycles. I
expect just the silly stat updates are way more costly but the series
that addresses that is likely to be controversial. As I know the cycle
budget for processing a packet is tight, I've applied the patch but am
keeping it separate to preserve the data in case someone points out that
is a big function to inline and "fixes" it.

-- 
Mel Gorman
SUSE Labs