Introduced the "keepalive_time" directive. Similar to lingering_time, it limits total connection lifetime before keepalive is switched off. The default is 1 hour, which is close to the total maximum connection lifetime possible with default keepalive_requests and keepalive_timeout.

--- a/src/core/ngx_connection.h
+++ b/src/core/ngx_connection.h
@@ -162,6 +162,7 @@ struct ngx_connection_s {
 
     ngx_atomic_uint_t   number;
 
+    ngx_msec_t          start_time;
     ngx_uint_t          requests;
 
     unsigned            buffered:8;