--- old/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	2019-11-06 19:09:40.499602945 -0500
+++ new/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	2019-11-06 19:09:40.231588572 -0500
@@ -1990,7 +1990,7 @@
 }
 
 bool G1CollectedHeap::should_upgrade_to_full_gc(GCCause::Cause cause) {
-  if(policy()->force_upgrade_to_full()) {
+  if (policy()->force_upgrade_to_full()) {
     return true;
   } else if (should_do_concurrent_full_gc(_gc_cause)) {
     return false;
@@ -2086,6 +2086,7 @@
   try_collect(cause);
 }
 
+// Return true if (x < y) with allowance for wraparound.
 static bool gc_counter_less_than(uint x, uint y) {
   return (x - y) > (UINT_MAX/2);
 }
@@ -2094,13 +2095,13 @@
 // Macro so msg printing is format-checked.
 #define LOG_COLLECT_CONCURRENTLY(cause, ...)                            \
   do {                                                                  \
-    LogTarget(Debug, gc) LOG_COLLECT_CONCURRENTLY_lt;                   \
+    LogTarget(Trace, gc) LOG_COLLECT_CONCURRENTLY_lt;                   \
     if (LOG_COLLECT_CONCURRENTLY_lt.is_enabled()) {                     \
       ResourceMark rm; /* For thread name. */                           \
       LogStream LOG_COLLECT_CONCURRENTLY_s(&LOG_COLLECT_CONCURRENTLY_lt); \
-      LOG_COLLECT_CONCURRENTLY_s.print("Try Collect Concurrently (%s) for %s: ", \
-                                       GCCause::to_string(cause),       \
-                                       Thread::current()->name());      \
+      LOG_COLLECT_CONCURRENTLY_s.print("%s: Try Collect Concurrently (%s): ", \
+                                       Thread::current()->name(),       \
+                                       GCCause::to_string(cause));      \
       LOG_COLLECT_CONCURRENTLY_s.print(__VA_ARGS__);                    \
     }                                                                   \
   } while (0)
--- old/src/hotspot/share/gc/g1/g1VMOperations.cpp	2019-11-06 19:09:41.531658289 -0500
+++ new/src/hotspot/share/gc/g1/g1VMOperations.cpp	2019-11-06 19:09:41.283644989 -0500
@@ -72,8 +72,13 @@
     // to notify the caller and return immediately.
     _cycle_already_in_progress = true;
   } else if (!g1h->do_collection_pause_at_safepoint(_target_pause_time_ms)) {
+    // Failure to perform the collection at all occurs because GCLocker is
+    // active, and we have the bad luck to be the collection request that
+    // makes a later _gc_locker collection needed.  (Else we would have hit
+    // the GCLocker check in the prologue.)
     _transient_failure = true;
   } else if (g1h->should_upgrade_to_full_gc(_gc_cause)) {
+    // GC ran, but we're still in trouble and need a full GC.
     log_info(gc, ergo)("Attempting maximally compacting collection");
     _gc_succeeded = g1h->do_full_collection(false, /* explicit gc */
                                             true /* clear_all_soft_refs */);
@@ -121,17 +126,13 @@
       // An allocation had been requested. Do it, eventually trying a stronger
       // kind of GC.
       _result = g1h->satisfy_failed_allocation(_word_size, &_gc_succeeded);
-    } else {
-      bool should_upgrade_to_full = g1h->should_upgrade_to_full_gc(_gc_cause);
-
-      if (should_upgrade_to_full) {
-        // There has been a request to perform a GC to free some space. We have no
-        // information on how much memory has been asked for. In case there are
-        // absolutely no regions left to allocate into, do a maximally compacting full GC.
-        log_info(gc, ergo)("Attempting maximally compacting collection");
-        _gc_succeeded = g1h->do_full_collection(false, /* explicit gc */
-                                                   true   /* clear_all_soft_refs */);
-      }
+    } else if (g1h->should_upgrade_to_full_gc(_gc_cause)) {
+      // There has been a request to perform a GC to free some space. We have no
+      // information on how much memory has been asked for. In case there are
+      // absolutely no regions left to allocate into, do a maximally compacting full GC.
+      log_info(gc, ergo)("Attempting maximally compacting collection");
+      _gc_succeeded = g1h->do_full_collection(false, /* explicit gc */
+                                              true   /* clear_all_soft_refs */);
     }
     guarantee(_gc_succeeded, "Elevated collections during the safepoint must always succeed.");
   }