Re: [Help-smalltalk] the garbage collector is not doing its job

[Derek Zhou]

On Monday 19 January 2009 12:34:02 am Paolo Bonzini wrote:
> I actually applied this patch instead, but you must be thanked anyway
> for the debugging.
While I was fooling around with the GC code, I found a few more minor issues:
* nearly all GCs trigger compaction, which sounds wasteful. 
* heap limit never shrink. So GC can be slow even if the real memory 
consumption has come down from a high peak. 
* the GC statistic is not right. 
Here is a patch I made to address them:

--- orig/libgst/oop.c
+++ mod/libgst/oop.c
@@ -1120,12 +1121,24 @@
     {
       old_limit = MAX (old_limit, _gst_mem.old->heap_total);
 
-      /* Check if it's time to compact the heap.  */
+      /* if memory is still low, go all the way on sweeping */
       if UNCOMMON ((next_allocation + _gst_mem.old->heap_total)
            * 100.0 / old_limit > _gst_mem.grow_threshold_percent)
         {
-          s = "done, heap compacted";
-          _gst_compact (0);
+          int target_limit;
+          _gst_finish_incremental_gc ();
+
+      /* Check if it's time to compact the heap. Compactions make the most 
+         sense if there were lots of garbage. And the heap limit is shrunk 
+         to avoid excessive garbage accumulation in the next round */
+          target_limit = (next_allocation + _gst_mem.old->heap_total) * 
+            (100.0 + _gst_mem.space_grow_rate) / 
_gst_mem.grow_threshold_percent;
+          if UNCOMMON ( target_limit < old_limit)
+            {
+              s = "done, heap compacted";
+              _gst_compact (0);
+              grow_memory_no_compact (target_limit);
+            }
         }
 
       /* Check if it's time to grow the heap.  */
@@ -1280,10 +1292,13 @@
   _gst_mem.live_flags &= ~F_REACHABLE;
   _gst_mem.live_flags |= F_OLD;
 
-  _gst_mem.reclaimedBytesPerGlobalGC =
-    _gst_mem.factor * stats.reclaimedOldSpaceBytesSinceLastGlobalGC +
-    (1 - _gst_mem.factor) * _gst_mem.reclaimedBytesPerScavenge;
-
+  if (stats.reclaimedOldSpaceBytesSinceLastGlobalGC) 
+    {
+      _gst_mem.reclaimedBytesPerGlobalGC =
+        _gst_mem.factor * stats.reclaimedOldSpaceBytesSinceLastGlobalGC +
+        (1 - _gst_mem.factor) * _gst_mem.reclaimedBytesPerGlobalGC;
+      stats.reclaimedOldSpaceBytesSinceLastGlobalGC = 0;
+    }
 #ifdef ENABLE_JIT_TRANSLATION
   /* Go and really free the blocks associated to garbage collected
      native code.  */