[PATCH] mm: vmscan: add tracepoints for node reclaim

[Yafang Shao <laoar.shao@gmail.com>]

In the page alloc fast path, it may do node reclaim, which may cause
latency spike.
We should add tracepoint for this event, and also mesure the latency
it causes.

So bellow two tracepoints are introduced,
	mm_vmscan_node_reclaim_begin
	mm_vmscan_node_reclaim_end

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/trace/events/vmscan.h | 48 +++++++++++++++++++++++++++++++++++++++++++
 mm/vmscan.c                   | 13 +++++++++++-
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index a1cb913..9310d5b 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -465,6 +465,54 @@
 		__entry->ratio,
 		show_reclaim_flags(__entry->reclaim_flags))
 );
+
+TRACE_EVENT(mm_vmscan_node_reclaim_begin,
+
+	TP_PROTO(int nid, int order, int may_writepage,
+		gfp_t gfp_flags, int zid),
+
+	TP_ARGS(nid, order, may_writepage, gfp_flags, zid),
+
+	TP_STRUCT__entry(
+		__field(int, nid)
+		__field(int, order)
+		__field(int, may_writepage)
+		__field(gfp_t, gfp_flags)
+		__field(int, zid)
+	),
+
+	TP_fast_assign(
+		__entry->nid = nid;
+		__entry->order = order;
+		__entry->may_writepage = may_writepage;
+		__entry->gfp_flags = gfp_flags;
+		__entry->zid = zid;
+	),
+
+	TP_printk("nid=%d zid=%d order=%d may_writepage=%d gfp_flags=%s",
+		__entry->nid,
+		__entry->zid,
+		__entry->order,
+		__entry->may_writepage,
+		show_gfp_flags(__entry->gfp_flags))
+);
+
+TRACE_EVENT(mm_vmscan_node_reclaim_end,
+
+	TP_PROTO(int result),
+
+	TP_ARGS(result),
+
+	TP_STRUCT__entry(
+		__field(int, result)
+	),
+
+	TP_fast_assign(
+		__entry->result = result;
+	),
+
+	TP_printk("result=%d", __entry->result)
+);
 #endif /* _TRACE_VMSCAN_H */
 
 /* This part must be outside protection */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ac4806f..01a0401 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4240,6 +4240,12 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 		.may_swap = 1,
 		.reclaim_idx = gfp_zone(gfp_mask),
 	};
+	int result;
+
+	trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
+					sc.may_writepage,
+					sc.gfp_mask,
+					sc.reclaim_idx);
 
 	cond_resched();
 	fs_reclaim_acquire(sc.gfp_mask);
@@ -4267,7 +4273,12 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 	current->flags &= ~PF_SWAPWRITE;
 	memalloc_noreclaim_restore(noreclaim_flag);
 	fs_reclaim_release(sc.gfp_mask);
-	return sc.nr_reclaimed >= nr_pages;
+
+	result = sc.nr_reclaimed >= nr_pages;
+
+	trace_mm_vmscan_node_reclaim_end(result);
+
+	return result;
 }
 
 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
-- 
1.8.3.1