[PATCH v2 3/3] mm, compaction: disginguish contended status in tracepoints

[Vlastimil Babka]

Compaction returns prematurely with COMPACT_PARTIAL when contended or has fatal
signal pending. This is ok for the callers, but might be misleading in the
traces, as the usual reason to return COMPACT_PARTIAL is that we think the
allocation should succeed. After this patch we distinguish the premature ending
condition in the mm_compaction_finished and mm_compaction_end tracepoints.

The contended status covers the following reasons:
- lock contention or need_resched() detected in async compaction
- fatal signal pending
- too many pages isolated in the zone (only for async compaction)
Further distinguishing the exact reason seems unnecessary for now.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
---
v2: extend to mm_compaction_end (pointed out by Joonsoo)

 include/linux/compaction.h        | 1 +
 include/trace/events/compaction.h | 3 ++-
 mm/compaction.c                   | 9 ++++++---
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index f14ba98..4cd4ddf 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -15,6 +15,7 @@
 /* For more detailed tracepoint output */
 #define COMPACT_NO_SUITABLE_PAGE	5
 #define COMPACT_NOT_SUITABLE_ZONE	6
+#define COMPACT_CONTENDED		7
 /* When adding new states, please adjust include/trace/events/compaction.h */
 
 /* Used to signal whether compaction detected need_sched() or lock contention */
diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
index 8daa8fa..5604994 100644
--- a/include/trace/events/compaction.h
+++ b/include/trace/events/compaction.h
@@ -16,7 +16,8 @@
 	EM( COMPACT_PARTIAL,		"partial")		\
 	EM( COMPACT_COMPLETE,		"complete")		\
 	EM( COMPACT_NO_SUITABLE_PAGE,	"no_suitable_page")	\
-	EMe(COMPACT_NOT_SUITABLE_ZONE,	"not_suitable_zone")
+	EM( COMPACT_NOT_SUITABLE_ZONE,	"not_suitable_zone")	\
+	EMe(COMPACT_CONTENDED,		"contended")
 
 #ifdef CONFIG_ZONE_DMA
 #define IFDEF_ZONE_DMA(X) X
diff --git a/mm/compaction.c b/mm/compaction.c
index a5849c4..de3e1e7 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1202,7 +1202,7 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc,
 	unsigned long watermark;
 
 	if (cc->contended || fatal_signal_pending(current))
-		return COMPACT_PARTIAL;
+		return COMPACT_CONTENDED;
 
 	/* Compaction run completes if the migrate and free scanner meet */
 	if (compact_scanners_met(cc)) {
@@ -1393,7 +1393,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 
 		switch (isolate_migratepages(zone, cc)) {
 		case ISOLATE_ABORT:
-			ret = COMPACT_PARTIAL;
+			ret = COMPACT_CONTENDED;
 			putback_movable_pages(&cc->migratepages);
 			cc->nr_migratepages = 0;
 			goto out;
@@ -1424,7 +1424,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 			 * and we want compact_finished() to detect it
 			 */
 			if (err == -ENOMEM && !compact_scanners_met(cc)) {
-				ret = COMPACT_PARTIAL;
+				ret = COMPACT_CONTENDED;
 				goto out;
 			}
 		}
@@ -1477,6 +1477,9 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 	trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
 				cc->free_pfn, end_pfn, sync, ret);
 
+	if (ret == COMPACT_CONTENDED)
+		ret = COMPACT_PARTIAL;
+
 	return ret;
 }
 
-- 
2.5.1

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