[PATCH 06/22] mm, page_alloc: Use __dec_zone_state for order-0 page allocation

[Mel Gorman]

__dec_zone_state is cheaper to use for removing an order-0 page as it
has fewer conditions to check.

The performance difference on a page allocator microbenchmark is;

                                           4.6.0-rc2                  4.6.0-rc2
                                       optiter-v1r11              decstat-v1r11
Min      alloc-odr0-1               382.00 (  0.00%)           382.00 (  0.00%)
Min      alloc-odr0-2               283.00 (  0.00%)           275.00 (  2.83%)
Min      alloc-odr0-4               232.00 (  0.00%)           228.00 (  1.72%)
Min      alloc-odr0-8               203.00 (  0.00%)           199.00 (  1.97%)
Min      alloc-odr0-16              188.00 (  0.00%)           186.00 (  1.06%)
Min      alloc-odr0-32              181.00 (  0.00%)           178.00 (  1.66%)
Min      alloc-odr0-64              177.00 (  0.00%)           174.00 (  1.69%)
Min      alloc-odr0-128             175.00 (  0.00%)           172.00 (  1.71%)
Min      alloc-odr0-256             189.00 (  0.00%)           181.00 (  4.23%)
Min      alloc-odr0-512             198.00 (  0.00%)           193.00 (  2.53%)
Min      alloc-odr0-1024            203.00 (  0.00%)           200.00 (  1.48%)
Min      alloc-odr0-2048            209.00 (  0.00%)           206.00 (  1.44%)
Min      alloc-odr0-4096            214.00 (  0.00%)           212.00 (  0.93%)
Min      alloc-odr0-8192            218.00 (  0.00%)           215.00 (  1.38%)
Min      alloc-odr0-16384           219.00 (  0.00%)           215.00 (  1.83%)

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e9acc0b0f787..ab16560b76e6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2414,6 +2414,7 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
 		else
 			page = list_first_entry(list, struct page, lru);
 
+		__dec_zone_state(zone, NR_ALLOC_BATCH);
 		list_del(&page->lru);
 		pcp->count--;
 	} else {
@@ -2435,11 +2436,11 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
 		spin_unlock(&zone->lock);
 		if (!page)
 			goto failed;
+		__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
 		__mod_zone_freepage_state(zone, -(1 << order),
 					  get_pcppage_migratetype(page));
 	}
 
-	__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
 	if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0 &&
 	    !test_bit(ZONE_FAIR_DEPLETED, &zone->flags))
 		set_bit(ZONE_FAIR_DEPLETED, &zone->flags);
-- 
2.6.4