perf tools: Release thread resources on PERF_RECORD_EXIT

For long running sessions with many threads with short lifetimes the
amount of memory that the buildid process takes is too much.

Since we don't have hist_entries that may be pointing to them, we can
just release the resources associated with each thread when the exit
(PERF_RECORD_EXIT) event is received.

For normal processing we need to annotate maps with hits, and thus
hist_entries pointing to it and drop the ones that had none. Will be
done in a followup patch.

Cc: David S. Miller <davem@davemloft.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
index 3b2f706..20eba42 100644
--- a/tools/perf/util/map.h
+++ b/tools/perf/util/map.h
@@ -127,6 +127,7 @@
 void maps__insert(struct rb_root *maps, struct map *map);
 struct map *maps__find(struct rb_root *maps, u64 addr);
 void map_groups__init(struct map_groups *self);
+void map_groups__exit(struct map_groups *self);
 int map_groups__clone(struct map_groups *self,
 		      struct map_groups *parent, enum map_type type);
 size_t map_groups__fprintf(struct map_groups *self, int verbose, FILE *fp);