[patch 1/2 v2]compaction: abort compaction loop if lock is contended or run too long

[Shaohua Li <shli@kernel.org>]

isolate_migratepages_range() might isolate none pages, for example, when
zone->lru_lock is contended and compaction is async. In this case, we should
abort compaction, otherwise, compact_zone will run a useless loop and make
zone->lru_lock is even contended.

V2:
only abort the compaction if lock is contended or run too long
Rearranged the code by Andrea Arcangeli.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Shaohua Li <shli@fusionio.com>
---
 mm/compaction.c |   12 +++++++-----
 mm/internal.h   |    2 +-
 2 files changed, 8 insertions(+), 6 deletions(-)

Index: linux/mm/compaction.c
===================================================================
--- linux.orig/mm/compaction.c	2012-09-06 18:37:52.636413761 +0800
+++ linux/mm/compaction.c	2012-09-10 08:49:40.377869710 +0800
@@ -70,8 +70,7 @@ static bool compact_checklock_irqsave(sp
 
 		/* async aborts if taking too long or contended */
 		if (!cc->sync) {
-			if (cc->contended)
-				*cc->contended = true;
+			cc->contended = true;
 			return false;
 		}
 
@@ -634,7 +633,7 @@ static isolate_migrate_t isolate_migrate
 
 	/* Perform the isolation */
 	low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
-	if (!low_pfn)
+	if (!low_pfn || cc->contended)
 		return ISOLATE_ABORT;
 
 	cc->migrate_pfn = low_pfn;
@@ -831,6 +830,7 @@ static unsigned long compact_zone_order(
 				 int order, gfp_t gfp_mask,
 				 bool sync, bool *contended)
 {
+	unsigned long ret;
 	struct compact_control cc = {
 		.nr_freepages = 0,
 		.nr_migratepages = 0,
@@ -838,12 +838,14 @@ static unsigned long compact_zone_order(
 		.migratetype = allocflags_to_migratetype(gfp_mask),
 		.zone = zone,
 		.sync = sync,
-		.contended = contended,
 	};
 	INIT_LIST_HEAD(&cc.freepages);
 	INIT_LIST_HEAD(&cc.migratepages);
 
-	return compact_zone(zone, &cc);
+	ret = compact_zone(zone, &cc);
+	if (contended)
+		*contended = cc.contended;
+	return ret;
 }
 
 int sysctl_extfrag_threshold = 500;
Index: linux/mm/internal.h
===================================================================
--- linux.orig/mm/internal.h	2012-09-03 15:16:30.566299444 +0800
+++ linux/mm/internal.h	2012-09-10 08:45:41.980866645 +0800
@@ -131,7 +131,7 @@ struct compact_control {
 	int order;			/* order a direct compactor needs */
 	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
 	struct zone *zone;
-	bool *contended;		/* True if a lock was contended */
+	bool contended;			/* True if a lock was contended */
 };
 
 unsigned long

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