4 files changed, 27 insertions, 18 deletions

diff --git a/mps/code/config.h b/mps/code/config.h
index c25b6c443c0..f88c6d867b3 100644
--- a/mps/code/config.h
+++ b/mps/code/config.h
@@ -212,7 +212,7 @@
 /* Length (in chars) of a char buffer used to store the reason why a
    collection started in the TraceStartMessageStruct (used by
    mps_message_type_gc_start). */
-#define TRACE_START_MESSAGE_WHY_LEN 64
+#define TRACE_START_MESSAGE_WHY_LEN 128
 
 
 
diff --git a/mps/code/mpmtypes.h b/mps/code/mpmtypes.h
index 7686ba26e16..ba49f280350 100644
--- a/mps/code/mpmtypes.h
+++ b/mps/code/mpmtypes.h
@@ -404,14 +404,17 @@ enum {
   TraceFINISHED
 };
 
-/* TraceStart reasons.  Reasons for why a trace is started. */
+/* TraceStart reasons: the trigger that caused a trace to start. */
+/* Make these specific trigger names, not broad categories; */
+/* and if a new trigger is added, add a new reason. */
 
 enum {
   TraceStartWhyBASE = 1, /* not a reason, the base of the enum. */
-  TraceStartWhyNURSERY = TraceStartWhyBASE,
-  TraceStartWhyGLOBAL,
-  TraceStartWhyOPPORTUNISM,
-  TraceStartWhyCLIENT,
+  TraceStartWhyCHAIN_GEN0CAP = TraceStartWhyBASE,  /* start minor */
+  TraceStartWhyDYNAMICCRITERION, /* start full */
+  TraceStartWhyOPPORTUNISM,      /* start full */
+  TraceStartWhyCLIENTFULL_INCREMENTAL,   /* start full */
+  TraceStartWhyCLIENTFULL_BLOCK, /* do full */
   TraceStartWhyWALK,
   TraceStartWhyLIMIT /* not a reason, the limit of the enum. */
 };
diff --git a/mps/code/mpsi.c b/mps/code/mpsi.c
index 5f224f56c40..29b9be40a56 100644
--- a/mps/code/mpsi.c
+++ b/mps/code/mpsi.c
@@ -346,7 +346,7 @@ mps_res_t mps_arena_start_collect(mps_space_t mps_space)
   Res res;
   Arena arena = (Arena)mps_space;
   ArenaEnter(arena);
-  res = ArenaStartCollect(ArenaGlobals(arena), TraceStartWhyCLIENT);
+  res = ArenaStartCollect(ArenaGlobals(arena), TraceStartWhyCLIENTFULL_INCREMENTAL);
   ArenaLeave(arena);
   return res;
 }
@@ -356,7 +356,7 @@ mps_res_t mps_arena_collect(mps_space_t mps_space)
   Res res;
   Arena arena = (Arena)mps_space;
   ArenaEnter(arena);
-  res = ArenaCollect(ArenaGlobals(arena), TraceStartWhyCLIENT);
+  res = ArenaCollect(ArenaGlobals(arena), TraceStartWhyCLIENTFULL_BLOCK);
   ArenaLeave(arena);
   return res;
 }
diff --git a/mps/code/trace.c b/mps/code/trace.c
index 757aee17db4..c9c36c0a0f5 100644
--- a/mps/code/trace.c
+++ b/mps/code/trace.c
@@ -223,20 +223,26 @@ static void traceStartWhyToString(char *s, size_t len, int why)
   AVER(why < TraceStartWhyLIMIT);
 
   switch(why) {
-  case TraceStartWhyNURSERY:
-    r = "Nursery generation is full.";
+  case TraceStartWhyCHAIN_GEN0CAP:
+    r = "Generation 0 of a chain has reached capacity:"
+        " start a minor collection.";
     break;
-  case TraceStartWhyGLOBAL:
-    r = "Preventing global exhaustion of memory.";
+  case TraceStartWhyDYNAMICCRITERION:
+    r = "Need to start full collection now, or there won't be enough"
+        " memory (ArenaAvail) to complete it.";
     break;
   case TraceStartWhyOPPORTUNISM:
-    r = "Opportunism.";
+    r = "Opportunism: client predicts plenty of idle time,"
+        " so start full collection.";
     break;
-  case TraceStartWhyCLIENT:
-    r = "Client request.";
+  case TraceStartWhyCLIENTFULL_INCREMENTAL:
+    r = "Client requests: start incremental full collection now.";
+    break;
+  case TraceStartWhyCLIENTFULL_BLOCK:
+    r = "Client requests: immediate full collection.";
     break;
   case TraceStartWhyWALK:
-    r = "Walking.";
+    r = "Walking all live objects.";
     break;
   default:
     NOTREACHED;
@@ -1730,7 +1736,7 @@ Size TracePoll(Globals globals)
     dynamicDeferral = (double)ArenaAvail(arena) - (double)sConsTrace;
 
     if (dynamicDeferral < 0.0) { /* start full GC */
-      res = traceStartCollectAll(&trace, arena, TraceStartWhyGLOBAL);
+      res = traceStartCollectAll(&trace, arena, TraceStartWhyDYNAMICCRITERION);
       if (res != ResOK)
         goto failStart;
       scannedSize = traceWorkClock(trace);
@@ -1754,7 +1760,7 @@ Size TracePoll(Globals globals)
       if (firstTime < 0) {
         double mortality;
 
-        res = TraceCreate(&trace, arena, TraceStartWhyNURSERY);
+        res = TraceCreate(&trace, arena, TraceStartWhyCHAIN_GEN0CAP);
         AVER(res == ResOK);
         res = ChainCondemnAuto(&mortality, firstChain, trace);
         if (res != ResOK) /* should try some other trace, really @@@@ */