linux-kernel - [PATCH 17/28] mm, page_alloc: Check once if a zone has isolated pageblocks

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Message-Id: <1460711275-1130-5-git-send-email-mgorman@techsingularity.net>
Date:	Fri, 15 Apr 2016 10:07:44 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 17/28] mm, page_alloc: Check once if a zone has isolated pageblocks

When bulk freeing pages from the per-cpu lists the zone is checked
for isolated pageblocks on every release. This patch checks it once
per drain. Technically this is race-prone but so is the existing
code.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 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 4a364e318873..835a1c434832 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -831,6 +831,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 	int batch_free = 0;
 	int to_free = count;
 	unsigned long nr_scanned;
+	bool isolated_pageblocks = has_isolate_pageblock(zone);
 
 	spin_lock(&zone->lock);
 	nr_scanned = zone_page_state(zone, NR_PAGES_SCANNED);
@@ -870,7 +871,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 			/* MIGRATE_ISOLATE page should not go to pcplists */
 			VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
 			/* Pageblock could have been isolated meanwhile */
-			if (unlikely(has_isolate_pageblock(zone)))
+			if (unlikely(isolated_pageblocks))
 				mt = get_pageblock_migratetype(page);
 
 			__free_one_page(page, page_to_pfn(page), zone, 0, mt);
-- 
2.6.4