linux-kernel - [60/70] [stable] [PATCH 3/3] mm: compaction: abort compaction if too many pages are isolated and caller is asynchronous V2

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Date:	Mon, 01 Aug 2011 16:19:15 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Sattler <tsattler@....de>, Mel Gorman <mgorman@...e.de>
Subject: [60/70] [stable] [PATCH 3/3] mm: compaction: abort compaction if too many pages are isolated and caller is asynchronous V2

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Mel Gorman <mgorman@...e.de>

commit: f9e35b3b41f47c4e17d8132edbcab305a6aaa4b0 upstream

Asynchronous compaction is used when promoting to huge pages.  This is all
very nice but if there are a number of processes in compacting memory, a
large number of pages can be isolated.  An "asynchronous" process can
stall for long periods of time as a result with a user reporting that
firefox can stall for 10s of seconds.  This patch aborts asynchronous
compaction if too many pages are isolated as it's better to fail a
hugepage promotion than stall a process.

[minchan.kim@...il.com: return COMPACT_PARTIAL for abort]
Reported-and-tested-by: Ury Stankevich <urykhy@...il.com>
Signed-off-by: Mel Gorman <mgorman@...e.de>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 mm/compaction.c |   29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -251,11 +251,18 @@ static bool too_many_isolated(struct zon
 	return isolated > (inactive + active) / 2;
 }
 
+/* possible outcome of isolate_migratepages */
+typedef enum {
+	ISOLATE_ABORT,		/* Abort compaction now */
+	ISOLATE_NONE,		/* No pages isolated, continue scanning */
+	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
+} isolate_migrate_t;
+
 /*
  * Isolate all pages that can be migrated from the block pointed to by
  * the migrate scanner within compact_control.
  */
-static unsigned long isolate_migratepages(struct zone *zone,
+static isolate_migrate_t isolate_migratepages(struct zone *zone,
 					struct compact_control *cc)
 {
 	unsigned long low_pfn, end_pfn;
@@ -272,7 +279,7 @@ static unsigned long isolate_migratepage
 	/* Do not cross the free scanner or scan within a memory hole */
 	if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
 		cc->migrate_pfn = end_pfn;
-		return 0;
+		return ISOLATE_NONE;
 	}
 
 	/*
@@ -281,10 +288,14 @@ static unsigned long isolate_migratepage
 	 * delay for some time until fewer pages are isolated
 	 */
 	while (unlikely(too_many_isolated(zone))) {
+		/* async migration should just abort */
+		if (!cc->sync)
+			return ISOLATE_ABORT;
+
 		congestion_wait(BLK_RW_ASYNC, HZ/10);
 
 		if (fatal_signal_pending(current))
-			return 0;
+			return ISOLATE_ABORT;
 	}
 
 	/* Time to isolate some pages for migration */
@@ -369,7 +380,7 @@ static unsigned long isolate_migratepage
 
 	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
 
-	return cc->nr_migratepages;
+	return ISOLATE_SUCCESS;
 }
 
 /*
@@ -533,8 +544,15 @@ static int compact_zone(struct zone *zon
 		unsigned long nr_migrate, nr_remaining;
 		int err;
 
-		if (!isolate_migratepages(zone, cc))
+		switch (isolate_migratepages(zone, cc)) {
+		case ISOLATE_ABORT:
+			ret = COMPACT_PARTIAL;
+			goto out;
+		case ISOLATE_NONE:
 			continue;
+		case ISOLATE_SUCCESS:
+			;
+		}
 
 		nr_migrate = cc->nr_migratepages;
 		err = migrate_pages(&cc->migratepages, compaction_alloc,
@@ -558,6 +576,7 @@ static int compact_zone(struct zone *zon
 
 	}
 
+out:
 	/* Release free pages and check accounting */
 	cc->nr_freepages -= release_freepages(&cc->freepages);
 	VM_BUG_ON(cc->nr_freepages != 0);


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