mm/vmscan: add tracepoints for node reclaim

The page alloc fast path it may perform node reclaim, which may cause a
latency spike.  We should add tracepoint for this event, and also measure
the latency it causes.

So bellow two tracepoints are introduced,
	mm_vmscan_node_reclaim_begin
	mm_vmscan_node_reclaim_end

Link: http://lkml.kernel.org/r/1551421452-5385-1-git-send-email-laoar.shao@gmail.comSigned-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: <shaoyafang@didiglobal.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/trace/events/vmscan.h

@@ -469,6 +469,38 @@ TRACE_EVENT(mm_vmscan_inactive_list_is_low,
 		__entry->ratio,
 		show_reclaim_flags(__entry->reclaim_flags))
 );
+
+TRACE_EVENT(mm_vmscan_node_reclaim_begin,
+
+	TP_PROTO(int nid, int order, gfp_t gfp_flags),
+
+	TP_ARGS(nid, order, gfp_flags),
+
+	TP_STRUCT__entry(
+		__field(int, nid)
+		__field(int, order)
+		__field(gfp_t, gfp_flags)
+	),
+
+	TP_fast_assign(
+		__entry->nid = nid;
+		__entry->order = order;
+		__entry->gfp_flags = gfp_flags;
+	),
+
+	TP_printk("nid=%d order=%d gfp_flags=%s",
+		__entry->nid,
+		__entry->order,
+		show_gfp_flags(__entry->gfp_flags))
+);
+
+DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_node_reclaim_end,
+
+	TP_PROTO(unsigned long nr_reclaimed),
+
+	TP_ARGS(nr_reclaimed)
+);
+
 #endif /* _TRACE_VMSCAN_H */
 
 /* This part must be outside protection */

mm/vmscan.c

@@ -4111,6 +4111,9 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 		.reclaim_idx = gfp_zone(gfp_mask),
 	};
 
+	trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
+					   sc.gfp_mask);
+
 	cond_resched();
 	fs_reclaim_acquire(sc.gfp_mask);
 	/*
@@ -4137,6 +4140,9 @@ 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);
+
+	trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
+
 	return sc.nr_reclaimed >= nr_pages;
 }