[RFC PATCH 3/3] mm: compaction: Fix the migration stats in trace_mm_compaction_migratepages()

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Now the migrate_pages() has changed to return the number of {normal page,
THP, hugetlb} instead, thus we should not use the return value to calculate
the number of pages migrated successfully. Instead we can just use the
'nr_succeeded' which indicates the number of normal pages migrated successfully
to calculate the non-migrated pages in trace_mm_compaction_migratepages().

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 include/trace/events/compaction.h | 24 ++++--------------------
 mm/compaction.c                   |  7 ++++---
 2 files changed, 8 insertions(+), 23 deletions(-)

diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
index 54e5bf0..7d48e70 100644
--- a/include/trace/events/compaction.h
+++ b/include/trace/events/compaction.h
@@ -68,10 +68,9 @@
 TRACE_EVENT(mm_compaction_migratepages,
 
 	TP_PROTO(unsigned long nr_all,
-		int migrate_rc,
-		struct list_head *migratepages),
+		unsigned int nr_succeeded),
 
-	TP_ARGS(nr_all, migrate_rc, migratepages),
+	TP_ARGS(nr_all, nr_succeeded),
 
 	TP_STRUCT__entry(
 		__field(unsigned long, nr_migrated)
@@ -79,23 +78,8 @@
 	),
 
 	TP_fast_assign(
-		unsigned long nr_failed = 0;
-		struct list_head *page_lru;
-
-		/*
-		 * migrate_pages() returns either a non-negative number
-		 * with the number of pages that failed migration, or an
-		 * error code, in which case we need to count the remaining
-		 * pages manually
-		 */
-		if (migrate_rc >= 0)
-			nr_failed = migrate_rc;
-		else
-			list_for_each(page_lru, migratepages)
-				nr_failed++;
-
-		__entry->nr_migrated = nr_all - nr_failed;
-		__entry->nr_failed = nr_failed;
+		__entry->nr_migrated = nr_succeeded;
+		__entry->nr_failed = nr_all - nr_succeeded;
 	),
 
 	TP_printk("nr_migrated=%lu nr_failed=%lu",
diff --git a/mm/compaction.c b/mm/compaction.c
index 6e44609..b4e94cd 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2280,6 +2280,7 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 	unsigned long last_migrated_pfn;
 	const bool sync = cc->mode != MIGRATE_ASYNC;
 	bool update_cached;
+	unsigned int nr_succeeded = 0;
 
 	/*
 	 * These counters track activities during zone compaction.  Initialize
@@ -2398,10 +2399,10 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 
 		err = migrate_pages(&cc->migratepages, compaction_alloc,
 				compaction_free, (unsigned long)cc, cc->mode,
-				MR_COMPACTION, NULL);
+				MR_COMPACTION, &nr_succeeded);
 
-		trace_mm_compaction_migratepages(cc->nr_migratepages, err,
-							&cc->migratepages);
+		trace_mm_compaction_migratepages(cc->nr_migratepages,
+						 nr_succeeded);
 
 		/* All pages were either migrated or will be released */
 		cc->nr_migratepages = 0;
-- 
1.8.3.1