tracing, memcg, vmscan: Hide trace events when not in use

When trace events are defined but not used they still create data
structures and functions for their use, even though nothing may be
using them.

The trace events mm_vmscan_memcg_reclaim_begin,
mm_vmscan_memcg_softlimit_reclaim_begin, mm_vmscan_memcg_reclaim_end,
and mm_vmscan_memcg_softlimit_reclaim_end are not used if CONFIG_MEMCG
is not defined. Do not create these trace events unless CONFIG_MEMCG is
defined.

Link: http://lkml.kernel.org/r/20171012184632.2bd247cd@gandalf.local.home

Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/trace/events/vmscan.h

@@ -133,6 +133,7 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_direct_reclaim_b
 	TP_ARGS(order, may_writepage, gfp_flags, classzone_idx)
 );
 
+#ifdef CONFIG_MEMCG
 DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_memcg_reclaim_begin,
 
 	TP_PROTO(int order, int may_writepage, gfp_t gfp_flags, int classzone_idx),
@@ -146,6 +147,7 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_memcg_softlimit_
 
 	TP_ARGS(order, may_writepage, gfp_flags, classzone_idx)
 );
+#endif /* CONFIG_MEMCG */
 
 DECLARE_EVENT_CLASS(mm_vmscan_direct_reclaim_end_template,
 
@@ -171,6 +173,7 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_direct_reclaim_end
 	TP_ARGS(nr_reclaimed)
 );
 
+#ifdef CONFIG_MEMCG
 DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_reclaim_end,
 
 	TP_PROTO(unsigned long nr_reclaimed),
@@ -184,6 +187,7 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_softlimit_re
 
 	TP_ARGS(nr_reclaimed)
 );
+#endif /* CONFIG_MEMCG */
 
 TRACE_EVENT(mm_shrink_slab_start,
 	TP_PROTO(struct shrinker *shr, struct shrink_control *sc,