3 files changed, 5 insertions, 1 deletions

diff --git a/mps/code/arenavm.c b/mps/code/arenavm.c
index 399145f3629..f29d860dfae 100644
--- a/mps/code/arenavm.c
+++ b/mps/code/arenavm.c
@@ -1675,6 +1675,7 @@ static void VMCompact(Arena arena, Trace trace)
   }
 
   DIAG(
+    Size vmem0 = trace->preTraceArenaReserved;
     Size vmem2 = VMArenaReserved(arena);
     Size vmemD = vmem1 - vmem2;
     Size live = trace->forwardedSize + trace->preservedInPlaceSize;
@@ -1684,7 +1685,8 @@ static void VMCompact(Arena arena, Trace trace)
        || trace->why == TraceStartWhyCLIENTFULL_INCREMENTAL
        || trace->why == TraceStartWhyCLIENTFULL_BLOCK) {
       DIAG_SINGLEF(( "VMCompact",
-        "vmem was $Um$3, ", M_whole(vmem1), M_frac(vmem1),
+        "pre-collection vmem was $Um$3, ", M_whole(vmem0), M_frac(vmem0),
+        "peaked at $Um$3, ", M_whole(vmem1), M_frac(vmem1),
         "released $Um$3, ", M_whole(vmemD), M_frac(vmemD),
         "now $Um$3", M_whole(vmem2), M_frac(vmem2),
         " (why $U", trace->why,
diff --git a/mps/code/mpmst.h b/mps/code/mpmst.h
index c5a4fe0e3f3..488a6d1b54b 100644
--- a/mps/code/mpmst.h
+++ b/mps/code/mpmst.h
@@ -506,6 +506,7 @@ typedef struct TraceStruct {
   Bool firstStretch;            /* in first stretch of band (see accessor) */
   Bool emergency;               /* ran out of memory during trace */
   Chain chain;                  /* chain being incrementally collected */
+  STATISTIC_DECL(Size preTraceArenaReserved); /* ArenaReserved before this trace */
   Size condemned;               /* condemned bytes */
   Size notCondemned;            /* collectable but not condemned */
   Size foundation;              /* initial grey set size */
diff --git a/mps/code/trace.c b/mps/code/trace.c
index 5cffa818009..e553d160318 100644
--- a/mps/code/trace.c
+++ b/mps/code/trace.c
@@ -663,6 +663,7 @@ found:
   trace->band = RankAMBIG;      /* Required to be the earliest rank. */
   trace->emergency = FALSE;
   trace->chain = NULL;
+  STATISTIC(trace->preTraceArenaReserved = ArenaReserved(arena));
   trace->condemned = (Size)0;   /* nothing condemned yet */
   trace->notCondemned = (Size)0;
   trace->foundation = (Size)0;  /* nothing grey yet */