[PATCH] mm/compaction: fix isolated page counting bug in compaction

[Joonsoo Kim]

acct_isolated() is the function to adjust isolated page count. It
iterates cc->migratepages list and add
NR_ISOLATED_ANON/NR_ISOLATED_FILE count according to number of anon,
file pages in migratepages list, respectively. Before commit (mm,
compaction: move pageblock checks up from isolate_migratepages_range()),
it is called just once in isolate_migratepages_range(), but, after commit,
it is called in newly introduced isolate_migratepages_block() and this
isolate_migratepages_block() could be called many times in
isolate_migratepages_range() so that some page could be counted more
than once. This duplicate counting bug results in hang in cma_alloc(),
because too_many_isolated() returns true continually.

This patch fixes this bug by moving acct_isolated() into upper layer
function, isolate_migratepages_range() and isolate_migratepages().
After this change, isolated page would be counted only once so
problem would be gone.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/compaction.c |   19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 7d9d92e..48129b6 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -514,22 +514,19 @@ isolate_freepages_range(struct compact_control *cc,
 }
 
 /* Update the number of anon and file isolated pages in the zone */
-static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
+static void acct_isolated(struct zone *zone, struct compact_control *cc)
 {
 	struct page *page;
 	unsigned int count[2] = { 0, };
 
+	if (list_empty(&cc->migratepages))
+		return;
+
 	list_for_each_entry(page, &cc->migratepages, lru)
 		count[!!page_is_file_cache(page)]++;
 
-	/* If locked we can use the interrupt unsafe versions */
-	if (locked) {
-		__mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
-		__mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
-	} else {
-		mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
-		mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
-	}
+	mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
+	mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
 }
 
 /* Similar to reclaim, but different enough that they don't share logic */
@@ -726,8 +723,6 @@ isolate_success:
 	if (unlikely(low_pfn > end_pfn))
 		low_pfn = end_pfn;
 
-	acct_isolated(zone, locked, cc);
-
 	if (locked)
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 
@@ -789,6 +784,7 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 			break;
 		}
 	}
+	acct_isolated(cc->zone, cc);
 
 	return pfn;
 }
@@ -1028,6 +1024,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		break;
 	}
 
+	acct_isolated(zone, cc);
 	/* Record where migration scanner will be restarted */
 	cc->migrate_pfn = low_pfn;
 
-- 
1.7.9.5

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/