--- old/src/share/vm/gc/g1/g1CollectedHeap.cpp	2015-11-24 10:09:18.609590666 +0100
+++ new/src/share/vm/gc/g1/g1CollectedHeap.cpp	2015-11-24 10:09:18.497586332 +0100
@@ -2250,15 +2250,21 @@
   return blk.result();
 }
 
+bool  G1CollectedHeap::is_user_requested_concurrent_full_gc(GCCause::Cause cause) {
+  switch (cause) {
+    case GCCause::_java_lang_system_gc:                 return ExplicitGCInvokesConcurrent;
+    case GCCause::_dcmd_gc_run:                         return ExplicitGCInvokesConcurrent;
+    case GCCause::_update_allocation_context_stats_inc: return true;
+    case GCCause::_wb_conc_mark:                        return true;
+    default :                                           return false;
+  }
+}
+
 bool G1CollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
   switch (cause) {
     case GCCause::_gc_locker:               return GCLockerInvokesConcurrent;
-    case GCCause::_java_lang_system_gc:     return ExplicitGCInvokesConcurrent;
-    case GCCause::_dcmd_gc_run:             return ExplicitGCInvokesConcurrent;
     case GCCause::_g1_humongous_allocation: return true;
-    case GCCause::_update_allocation_context_stats_inc: return true;
-    case GCCause::_wb_conc_mark:            return true;
-    default:                                return false;
+    default:                                return is_user_requested_concurrent_full_gc(cause);
   }
 }
 
--- old/src/share/vm/gc/g1/g1CollectedHeap.hpp	2015-11-24 10:09:19.317618064 +0100
+++ new/src/share/vm/gc/g1/g1CollectedHeap.hpp	2015-11-24 10:09:19.213614039 +0100
@@ -244,9 +244,11 @@
   // instead of doing a STW GC. Currently, a concurrent cycle is
   // explicitly started if:
   // (a) cause == _gc_locker and +GCLockerInvokesConcurrent, or
-  // (b) cause == _java_lang_system_gc and +ExplicitGCInvokesConcurrent.
-  // (c) cause == _dcmd_gc_run and +ExplicitGCInvokesConcurrent.
-  // (d) cause == _g1_humongous_allocation
+  // (b) cause == _g1_humongous_allocation
+  // (c) cause == _java_lang_system_gc and +ExplicitGCInvokesConcurrent.
+  // (d) cause == _dcmd_gc_run and +ExplicitGCInvokesConcurrent.
+  // (e) cause == _update_allocation_context_stats_inc
+  // (f) cause == _wb_conc_mark
   bool should_do_concurrent_full_gc(GCCause::Cause cause);
 
   // indicates whether we are in young or mixed GC mode
@@ -576,6 +578,8 @@
     _in_cset_fast_test.clear();
   }
 
+  bool is_user_requested_concurrent_full_gc(GCCause::Cause cause);
+
   // This is called at the start of either a concurrent cycle or a Full
   // GC to update the number of old marking cycles started.
   void increment_old_marking_cycles_started();
--- old/src/share/vm/gc/g1/g1CollectorPolicy.cpp	2015-11-24 10:09:19.925641592 +0100
+++ new/src/share/vm/gc/g1/g1CollectorPolicy.cpp	2015-11-24 10:09:19.809637103 +0100
@@ -1621,6 +1621,11 @@
   }
 }
 
+void G1CollectorPolicy::initiate_conc_mark() {
+  collector_state()->set_during_initial_mark_pause(true);
+  collector_state()->set_initiate_conc_mark_if_possible(false);
+}
+
 void G1CollectorPolicy::decide_on_conc_mark_initiation() {
   // We are about to decide on whether this pause will be an
   // initial-mark pause.
@@ -1637,17 +1642,21 @@
     // concurrent marking cycle. So we might initiate one.
 
     if (!about_to_start_mixed_phase() && collector_state()->gcs_are_young()) {
-      // Initiate a new initial mark only if there is no marking or reclamation going
-      // on.
-
-      collector_state()->set_during_initial_mark_pause(true);
-      // And we can now clear initiate_conc_mark_if_possible() as
-      // we've already acted on it.
-      collector_state()->set_initiate_conc_mark_if_possible(false);
+      // Initiate a new initial mark if there is no marking or reclamation going on.
+      initiate_conc_mark();
+      ergo_verbose0(ErgoConcCycles,
+                    "initiate concurrent cycle",
+                    ergo_format_reason("concurrent cycle initiation requested"));
+    } else if (_g1->is_user_requested_concurrent_full_gc(_g1->gc_cause())) {
+      // Initiate a user requested initial mark. An initial mark must be young only
+      // GC, so the collector state must be updated to reflect this.
+      collector_state()->set_gcs_are_young(true);
+      collector_state()->set_last_young_gc(false);
 
+      initiate_conc_mark();
       ergo_verbose0(ErgoConcCycles,
-                  "initiate concurrent cycle",
-                  ergo_format_reason("concurrent cycle initiation requested"));
+                    "initiate concurrent cycle",
+                    ergo_format_reason("user requested concurrent cycle"));
     } else {
       // The concurrent marking thread is still finishing up the
       // previous cycle. If we start one right now the two cycles
--- old/src/share/vm/gc/g1/g1CollectorPolicy.hpp	2015-11-24 10:09:20.657669919 +0100
+++ new/src/share/vm/gc/g1/g1CollectorPolicy.hpp	2015-11-24 10:09:20.557666049 +0100
@@ -681,6 +681,11 @@
   // (should not be called directly).
   void add_region_to_incremental_cset_common(HeapRegion* hr);
 
+  // Set the state to start a concurrent marking cycle and clear
+  // _initiate_conc_mark_if_possible because it has now been
+  // acted on.
+  void initiate_conc_mark();
+
 public:
   // Add hr to the LHS of the incremental collection set.
   void add_region_to_incremental_cset_lhs(HeapRegion* hr);