[PATCH -next 1/2] mm: shrinker: add new event to trace shrink count

[Bixuan Cui]

From: cuibixuan <cuibixuan@xxxxxxxx>

do_shrink_slab() calculates the freeable memory through shrinker->count_objects(),
and then reclaims the memory through shrinker->scan_objects(). When reclaiming
memory, shrinker->count_objects() takes a certain amount of time:

	Fun               spend(us)
	ext4_es_count     4302
	ext4_es_scan      12
	super_cache_count 4195
	super_cache_scan  2103

Therefore, adding the trace event to count_objects() can more accurately
obtain the time taken for slab memory recycling.

Example of output:
         kswapd0-103     [003] .....  1098.317942: mm_shrink_count_start: kfree_rcu_shrink_count.cfi_jt+0x0/0x8 00000000c540ff51: nid: 0
         kswapd0-103     [003] .....  1098.317951: mm_shrink_count_end: kfree_rcu_shrink_count.cfi_jt+0x0/0x8 00000000c540ff51: nid: 0 freeable:36

Signed-off-by: Bixuan Cui <cuibixuan@xxxxxxxx>
---
 include/trace/events/vmscan.h | 49 +++++++++++++++++++++++++++++++++++
 mm/shrinker.c                 |  4 +++
 2 files changed, 53 insertions(+)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 1a488c30afa5..406faa5591c1 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -196,6 +196,55 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_softlimit_re
 );
 #endif /* CONFIG_MEMCG */
 
+TRACE_EVENT(mm_shrink_count_start,
+	TP_PROTO(struct shrinker *shr, struct shrink_control *sc),
+
+	TP_ARGS(shr, sc),
+
+	TP_STRUCT__entry(
+		__field(struct shrinker *, shr)
+		__field(void *, shrink)
+		__field(int, nid)
+	),
+
+	TP_fast_assign(
+		__entry->shr = shr;
+		__entry->shrink = shr->count_objects;
+		__entry->nid = sc->nid;
+	),
+
+	TP_printk("%pS %p: nid: %d",
+		__entry->shrink,
+		__entry->shr,
+		__entry->nid)
+);
+
+TRACE_EVENT(mm_shrink_count_end,
+	TP_PROTO(struct shrinker *shr, struct shrink_control *sc, long freeable),
+
+	TP_ARGS(shr, sc, freeable),
+
+	TP_STRUCT__entry(
+		__field(struct shrinker *, shr)
+		__field(void *, shrink)
+		__field(int, nid)
+		__field(long, freeable)
+	),
+
+	TP_fast_assign(
+		__entry->shr = shr;
+		__entry->shrink = shr->count_objects;
+		__entry->nid = sc->nid;
+		__entry->freeable = freeable;
+	),
+
+	TP_printk("%pS %p: nid: %d freeable:%ld",
+		__entry->shrink,
+		__entry->shr,
+		__entry->nid,
+		__entry->freeable)
+);
+
 TRACE_EVENT(mm_shrink_slab_start,
 	TP_PROTO(struct shrinker *shr, struct shrink_control *sc,
 		long nr_objects_to_shrink, unsigned long cache_items,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index dd91eab43ed3..d0c7bf61db61 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -379,7 +379,11 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 					  : SHRINK_BATCH;
 	long scanned = 0, next_deferred;
 
+	trace_mm_shrink_count_start(shrinker, shrinkctl);
+
 	freeable = shrinker->count_objects(shrinker, shrinkctl);
+
+	trace_mm_shrink_count_end(shrinker, shrinkctl, freeable);
 	if (freeable == 0 || freeable == SHRINK_EMPTY)
 		return freeable;
 
-- 
2.39.0