New function policycollectiontime estimates the time needed to collect the arena. mysterious constants are given names and moved to config.h.

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 Change: 188160
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mps/code/arena.c

@@ -1272,6 +1272,24 @@ Size ArenaAvail(Arena arena)
 }
 
 
+/* ArenaCollectable -- return estimate of collectable memory in arena */
+
+Size ArenaCollectable(Arena arena)
+{
+  /* Conservative estimate -- see job003929. */
+  return ArenaCommitted(arena) - ArenaSpareCommitted(arena);
+}
+
+
+/* ArenaScannable -- return estimate of scannable memory in arena */
+
+Size ArenaScannable(Arena arena)
+{
+  /* Conservative estimate -- see job003929. */
+  return ArenaCommitted(arena) - ArenaSpareCommitted(arena);
+}
+
+
 /* ArenaExtend -- Add a new chunk in the arena */
 
 Res ArenaExtend(Arena arena, Addr base, Size size)

mps/code/config.h

@@ -392,22 +392,45 @@
 #define MVT_FRAG_LIMIT_DEFAULT    30
 
 
-/* Arena Configuration -- see <code/arena.c>
- *
- * .client.seg-size: ARENA_CLIENT_GRAIN_SIZE is the minimum size, in
- * bytes, of a grain in the client arena. It's set at 8192 with no
- * particular justification.
- */
+/* Arena Configuration -- see <code/arena.c> */
 
 #define ArenaPollALLOCTIME (65536.0)
 
 #define ARENA_ZONESHIFT         ((Shift)20)
 
+/* .client.seg-size: ARENA_CLIENT_GRAIN_SIZE is the minimum size, in
+ * bytes, of a grain in the client arena. It's set at 8192 with no
+ * particular justification. */
+
 #define ARENA_CLIENT_GRAIN_SIZE          ((Size)8192)
 
 #define ARENA_DEFAULT_ZONED     TRUE
 
 #define ArenaDefaultZONESET (ZoneSetUNIV << (MPS_WORD_WIDTH / 2))
+
+/* ARENA_MINIMUM_COLLECTABLE_SIZE is the minimum size (in bytes) of
+ * collectable memory that might be considered worthwhile to run a
+ * full garbage collection. */
+
+#define ARENA_MINIMUM_COLLECTABLE_SIZE ((Size)1000000)
+
+/* ARENA_DEFAULT_COLLECTION_RATE is an estimate of the MPS's
+ * collection rate (in bytes per second), for use in the case where
+ * there isn't enough data to use a measured value. */
+
+#define ARENA_DEFAULT_COLLECTION_RATE (25000000.0)
+
+/* ARENA_DEFAULT_COLLECTION_OVERHEAD is an estimate of the MPS's
+ * collection overhead (in seconds), for use in the case where there
+ * isn't enough data to use a measured value. */
+
+#define ARENA_DEFAULT_COLLECTION_OVERHEAD (0.1)
+
+/* ARENA_MAX_COLLECT_FRACTION is the maximum fraction of runtime that
+ * ArenaStep is prepared to spend in collections. */
+
+#define ARENA_MAX_COLLECT_FRACTION (0.1)
+
 /* TODO: This is left over from before the branch/2014-01-29/mps-chain-zones
    and 2014-01-17/cbs-tract-alloc reformed allocation, and may now be doing
    more harm than good.  Experiment with setting to ZoneSetUNIV. */

mps/code/global.c

@@ -765,36 +765,24 @@ static Bool arenaShouldCollectWorld(Arena arena,
                                     Clock now,
                                     Clock clocks_per_sec)
 {
-  double scanRate;
-  Size arenaSize;
-  double arenaScanTime;
-  double sinceLastWorldCollect;
-
   /* don't collect the world if we're not given any time */
   if ((interval > 0.0) && (multiplier > 0.0)) {
     /* don't collect the world if we're already collecting. */
     if (arena->busyTraces == TraceSetEMPTY) {
       /* don't collect the world if it's very small */
-      arenaSize = ArenaCommitted(arena) - ArenaSpareCommitted(arena);
-      if (arenaSize > 1000000) {
+      Size collectableSize = ArenaCollectable(arena);
+      if (collectableSize > ARENA_MINIMUM_COLLECTABLE_SIZE) {
         /* how long would it take to collect the world? */
-        if ((arena->tracedSize > 1000000.0) &&
-            (arena->tracedTime > 1.0))
-          scanRate = arena->tracedSize / arena->tracedTime;
-        else
-          scanRate = 25000000.0; /* a reasonable default. */
-        arenaScanTime = arenaSize / scanRate;
-        arenaScanTime += 0.1;   /* for overheads. */
+        double collectionTime = PolicyCollectionTime(arena);
 
         /* how long since we last collected the world? */
-        sinceLastWorldCollect = ((now - arena->lastWorldCollect) /
-                                 (double) clocks_per_sec);
+        double sinceLastWorldCollect = ((now - arena->lastWorldCollect) /
+                                        (double) clocks_per_sec);
         /* have to be offered enough time, and it has to be a long time
          * since we last did it. */
-        if ((interval * multiplier > arenaScanTime) &&
-            sinceLastWorldCollect > arenaScanTime * 10.0) {
+        if ((interval * multiplier > collectionTime) &&
+            sinceLastWorldCollect > collectionTime / ARENA_MAX_COLLECT_FRACTION)
           return TRUE;
-        }
       }
     }
   }

mps/code/mpm.h

@@ -623,8 +623,9 @@ extern void ArenaSetSpareCommitLimit(Arena arena, Size limit);
 extern Size ArenaNoPurgeSpare(Arena arena, Size size);
 extern Res ArenaNoGrow(Arena arena, LocusPref pref, Size size);
 
-extern double ArenaMutatorAllocSize(Arena arena);
 extern Size ArenaAvail(Arena arena);
+extern Size ArenaCollectable(Arena arena);
+extern Size ArenaScannable(Arena arena);
 
 extern Res ArenaExtend(Arena, Addr base, Size size);
 
@@ -661,6 +662,7 @@ extern Res ArenaNoExtend(Arena arena, Addr base, Size size);
 extern Res PolicyAlloc(Tract *tractReturn, Arena arena, LocusPref pref,
                        Size size, Pool pool);
 extern Bool PolicyStartTrace(Trace *traceReturn, Arena arena);
+extern double PolicyCollectionTime(Arena arena);
 
 
 /* Locus interface */

mps/code/policy.c

@@ -258,6 +258,29 @@ failStart:
 }
 
 
+/* PolicyCollectionTime -- estimate time to collect the world, in seconds */
+
+double PolicyCollectionTime(Arena arena)
+{
+  Size collectableSize;
+  double collectionRate;
+  double collectionTime;
+  
+  AVERT(Arena, arena);
+
+  collectableSize = ArenaCollectable(arena);
+  if (arena->tracedSize >= ARENA_MINIMUM_COLLECTABLE_SIZE
+      && arena->tracedTime > 0)
+    collectionRate = arena->tracedSize / arena->tracedTime;
+  else
+    collectionRate = ARENA_DEFAULT_COLLECTION_RATE;
+  collectionTime = collectableSize / collectionRate;
+  collectionTime += ARENA_DEFAULT_COLLECTION_OVERHEAD;
+
+  return collectionTime;
+}
+
+
 /* C. COPYRIGHT AND LICENSE
  *
  * Copyright (C) 2001-2015 Ravenbrook Limited <http://www.ravenbrook.com/>.