Add memory fields (sometimes) available from getrusage()

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index f99dd0a..7f57a84 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -4467,6 +4467,21 @@ ShowUsage(const char *title)
 					 r.ru_nvcsw - Save_r.ru_nvcsw,
 					 r.ru_nivcsw - Save_r.ru_nivcsw,
 					 r.ru_nvcsw, r.ru_nivcsw);
+
+#if defined(__linux__)
+	appendStringInfo(&str,
+			 "!\t%ld max resident (kB)\n",
+					 r.ru_maxrss);
+#elif defined(BSD)
+	appendStringInfo(&str,
+			 "!\t%ld max resident, %ld shared, %ld unshared data, %ld unshared stack (kB)\n",
+					 r.ru_maxrss, r.ru_ixrss, r.ru_idrss, r.ru_isrss);
+#elif defined(__darwin__)
+	appendStringInfo(&str,
+			 "!\t%ld max resident, %ld shared, %ld unshared data, %ld unshared stack (kB)\n",
+					 r.ru_maxrss/1024, r.ru_ixrss/1024, r.ru_idrss/1024, r.ru_isrss/1024);
+#endif /* __linux__ */
+
 #endif   /* HAVE_GETRUSAGE */
 
 	/* remove trailing newline */