linux-kernel - [PATCH 13/14] Do not compact within a preferred zone after a compaction failure

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Message-Id: <1270224168-14775-14-git-send-email-mel@csn.ul.ie>
Date:	Fri,  2 Apr 2010 17:02:47 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 13/14] Do not compact within a preferred zone after a compaction failure

The fragmentation index may indicate that a failure is due to external
fragmentation but after a compaction run completes, it is still possible
for an allocation to fail. There are two obvious reasons as to why

  o Page migration cannot move all pages so fragmentation remains
  o A suitable page may exist but watermarks are not met

In the event of compaction followed by an allocation failure, this patch
defers further compaction in the zone for a period of time. The zone that
is deferred is the first zone in the zonelist - i.e. the preferred zone.
To defer compaction in the other zones, the information would need to be
stored in the zonelist or implemented similar to the zonelist_cache.
This would impact the fast-paths and is not justified at this time.

Signed-off-by: Mel Gorman <mel@....ul.ie>
Acked-by: Rik van Riel <riel@...hat.com>
---
 include/linux/compaction.h |   35 +++++++++++++++++++++++++++++++++++
 include/linux/mmzone.h     |    7 +++++++
 mm/page_alloc.c            |    5 ++++-
 3 files changed, 46 insertions(+), 1 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index ae98afc..2a02719 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -18,6 +18,32 @@ extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
 extern int fragmentation_index(struct zone *zone, unsigned int order);
 extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
 			int order, gfp_t gfp_mask, nodemask_t *mask);
+
+/* defer_compaction - Do not compact within a zone until a given time */
+static inline void defer_compaction(struct zone *zone, unsigned long resume)
+{
+	/*
+	 * This function is called when compaction fails to result in a page
+	 * allocation success. This is somewhat unsatisfactory as the failure
+	 * to compact has nothing to do with time and everything to do with
+	 * the requested order, the number of free pages and watermarks. How
+	 * to wait on that is more unclear, but the answer would apply to
+	 * other areas where the VM waits based on time.
+	 */
+	zone->compact_resume = resume;
+}
+
+static inline int compaction_deferred(struct zone *zone)
+{
+	/* init once if necessary */
+	if (unlikely(!zone->compact_resume)) {
+		zone->compact_resume = jiffies;
+		return 0;
+	}
+
+	return time_before(jiffies, zone->compact_resume);
+}
+
 #else
 static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
 			int order, gfp_t gfp_mask, nodemask_t *nodemask)
@@ -25,6 +51,15 @@ static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
 	return COMPACT_INCOMPLETE;
 }
 
+static inline void defer_compaction(struct zone *zone, unsigned long resume)
+{
+}
+
+static inline int compaction_deferred(struct zone *zone)
+{
+	return 1;
+}
+
 #endif /* CONFIG_COMPACTION */
 
 #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index cf9e458..bde879b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -321,6 +321,13 @@ struct zone {
 	unsigned long		*pageblock_flags;
 #endif /* CONFIG_SPARSEMEM */
 
+#ifdef CONFIG_COMPACTION
+	/*
+	 * If a compaction fails, do not try compaction again until
+	 * jiffies is after the value of compact_resume
+	 */
+	unsigned long		compact_resume;
+#endif
 
 	ZONE_PADDING(_pad1_)
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7a2e4a2..66823bd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1770,7 +1770,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
 	cond_resched();
 
 	/* Try memory compaction for high-order allocations before reclaim */
-	if (order) {
+	if (order && !compaction_deferred(preferred_zone)) {
 		*did_some_progress = try_to_compact_pages(zonelist,
 						order, gfp_mask, nodemask);
 		if (*did_some_progress != COMPACT_SKIPPED) {
@@ -1795,6 +1795,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
 			 */
 			count_vm_event(COMPACTFAIL);
 
+			/* On failure, avoid compaction for a short time. */
+			defer_compaction(preferred_zone, jiffies + HZ/50);
+
 			cond_resched();
 		}
 	}
-- 
1.6.5

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