[PATCH] mm/page_alloc: call check_new_pages() while zone spinlock is not held

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

For high order pages not using pcp, rmqueue() is currently calling
the costly check_new_pages() while zone spinlock is held.

This is not needed, we can release the spinlock sooner to reduce
zone spinlock contention.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
---
 mm/page_alloc.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3589febc6d31928f850ebe5a4015ddc40e0469f3..0890a65f8cc2259e82bc1f5ba95a592fb30f9fb8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3685,7 +3685,6 @@ struct page *rmqueue(struct zone *preferred_zone,
 			gfp_t gfp_flags, unsigned int alloc_flags,
 			int migratetype)
 {
-	unsigned long flags;
 	struct page *page;
 
 	if (likely(pcp_allowed_order(order))) {
@@ -3706,10 +3705,12 @@ struct page *rmqueue(struct zone *preferred_zone,
 	 * allocate greater than order-1 page units with __GFP_NOFAIL.
 	 */
 	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
-	spin_lock_irqsave(&zone->lock, flags);
 
 	do {
+		unsigned long flags;
+
 		page = NULL;
+		spin_lock_irqsave(&zone->lock, flags);
 		/*
 		 * order-0 request can reach here when the pcplist is skipped
 		 * due to non-CMA allocation context. HIGHATOMIC area is
@@ -3723,13 +3724,13 @@ struct page *rmqueue(struct zone *preferred_zone,
 		}
 		if (!page)
 			page = __rmqueue(zone, order, migratetype, alloc_flags);
-	} while (page && check_new_pages(page, order));
-	if (!page)
-		goto failed;
+		spin_unlock_irqrestore(&zone->lock, flags);
+		if (!page)
+			return NULL;
+	} while (check_new_pages(page, order));
 
 	__mod_zone_freepage_state(zone, -(1 << order),
 				  get_pcppage_migratetype(page));
-	spin_unlock_irqrestore(&zone->lock, flags);
 
 	__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
 	zone_statistics(preferred_zone, zone, 1);
@@ -3743,10 +3744,6 @@ struct page *rmqueue(struct zone *preferred_zone,
 
 	VM_BUG_ON_PAGE(page && bad_range(zone, page), page);
 	return page;
-
-failed:
-	spin_unlock_irqrestore(&zone->lock, flags);
-	return NULL;
 }
 
 #ifdef CONFIG_FAIL_PAGE_ALLOC
-- 
2.35.1.616.g0bdcbb4464-goog